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ORNL/TM~6474
Dist. Categories UC-79b,-c

Contract No. W-7405-eng-26

METALS AND CERAMICS DIVISION
CHEMICAL TECHNOLOGY DIVISION
HEALTH AND ENVIRONMENTAL SAFETY DIVISION

ENVIRONMENTAL ASSESSMENT OF ALTERNATE FBR FUELS: RADIOLOGICAL
ASSESSMENT OF AIRBORNE RELEASES FROM
THORIUM MINING AND MILLING

V. J. Tennery ™ H. R. Meyer »%
E. S. Bomar \ J. E. Till #¢

W. D. Bond ~7 M. G. Yalcintas ¢
L. E. Morse ¢ *

Date Published: October 1978

NOTICE This document contains information of a preliminary nature.
1t is subject to revision or correction and therefore does not represent a
final report.

OAK RIDGE HATTONAL LABORATORY
Dak Ridge, Tennessee 37830
cperated by
UNION CARBIDE CORFORATION
for the
DEPARTMENT OF ENERGY
CONTENTS

LIST OF FIGURES . . & ¢ v ¢ o o 4 o o o s s o « s =

LIST OF TABLES » - - - * . * - - . . - - > . -

ABSTRACT & v v v ¢ o & o o « o o & o « o o o =

1.

2.

INTRODUCTION + & ¢ o & @ o o o o o o 2 o o o o

FACILITY SITING, METEOROLOGY, AND POPULATION

CHARACTERISTICS PERTAINING TO THORIUM ORE DEPOSITS

2.1 U.S. Thorium Deposits . . « . « ¢« « « + &
2.2 GSites Selected for Analysis . . . . . . .
2.3 Characteristics of Deposits in the Lemhi
Pass District o o« o « ¢ & ¢ o o o o « «
Population Distribution . . . . . . . . .
Meteorological Data . . . . . « . . « . .
References . ¢« ¢ o o o « o o o &+ o o« o &

-

NN
Ch U b~

DESCRIPTION OF MODEL MINE AND MILL . . . .
3.1 Facility Description . . . « ¢« « ¢« ¢ + &
3.2 Thorium Mining . . +« + & o ¢ ¢ o « o 4 &
3.3 Thorium Milling and Refining . . . . .
3.3.1 Introduction . . . . « . . . . .
The ore storage pile . . . . . .
Ore preparation « . « « +« + « .
Sulfuric acid leaching . . . . .
Countercurrent decantation . . .
Amine solvent extraction . . . .
Stripping « « ¢« o o 4o ¢ 6o e 4 s
Steam distillation . . . . . . .
Filtrationm . . . . . . . . . . .
0 Thorium refining . . . . . . . .
3.3.11 The tailings pond . . . . . . .
3.4 References .« o« o« o o 2 o o o o 4 o o o

» . . - - £
- . . »

w L wwiwiwwww
*

W W wwWwiwwww

H WO~V P WD

GENERATION OF SOURCE TERMS . . . .« + « & + .« .
4.1 Mining .« ¢ o« o ¢« ¢ 4 s e e s e a4 e e .
4,1.1 Radon-220 . . + . &« ¢« v s 4+ & o
4.1.2 Fugitive dust . . . . + + . . . .
4.2 MI1lIng . & ¢ 4 4 v e e e e e e e e e e s

4.2.1 Introduction . « + ¢ v 4 4 ¢ v 4 . . .
4.2.2 The ore stockpile . . . . . . . . . .
4.2.3 Dry crushing and sizing . . . . . . . .
4.2.4 Acid leaching of ore . . . . . . . .
4,2.5 Other mill operations . . . . . . . . .
4.2.6 Thorium refining . . . . . ¢« « + « . .
4.2.7 Source terms for the tailings impoundment
4,3 References .« v v 4 ¢ v v 4 e v 4w e 4 .

iii

*

Page

vi

oo~

10
11
11
16

20
20
23
23
23
26
26
26
27
27
27
28
28
28
29
31

32
32
32
32
34
34
36
38
38
39
39
40
47
5. RADIOLOGTCAL ASSESSMENT METHODOLOGY . . + « o« o « o & & «

5.1
5.2

Additional Assumplbions . + ¢« + + o ¢ « o 4 ¢ 4 0 0
References « v o« o o o o o o o o o s s « s s o o & o

6. ANALYSIS OF RADIOLOGICAL IMPACT . . . « +« + « « + & &

6.1

oo
0N

6.
6.

oy i

Maximum Individual Doses . . .« .« « « ¢ « ¢« ¢ « o & + &
Population DosSes .+ « + ¢« ¢ o ¢ ¢ o « o o o o+ 0 s e .
Dose Commitments Following Plant Shutdown . . . . . .

Impact of Mine~and Mill-Generated 220Rp on
Populations Outside the 50-mile Radius . . . . . . . .

DiSCUSSiOD - - - - . . - - . * - . - . . » - . . - . -

RefeTenCes v o o » o o o o o s o o s o o o o o &«

RECOMMENDATIONS FOR FUTURE WORK . . . . .+ « ¢ « « ¢« & o« « « &

ACKNOWLEDGMENTS . & v 4 ¢« o o o o o o &+ o s s o o o « o s s o &
Appendix 1. SUMMARIES OF METEOROLOGICAL DATA . . . . . . . .
Appendix 2. DIFFUSION EQUATION USED FOR THE ESTIMATION OF

Appendix

Appendix

Appendix

Appendix

Appendix

Appendix

Appendix

RADON"'Z 20 EMISSIONS . . . . . . . . . . . . . . .

3. RADON-220 RELEASE FROM THE OPEN-PIT THORIUM
MINE . & ¢ & o o « o o o o o o o o o o s o o« o o

4, RADIOACTIVITY CONTAINED IN DUST GENERATED BY
MINING OPERATIONS . . . . « « o ¢« o v « o 4 .

5. ORIGIN CODE CALCULATIONS OF RADIONUCLIDES iIN
EQUILIBRIUM WITH THORIUM IN THE ORE AND IN THE
MILL TAILINGS . . .+ &« o ¢« ¢ o &+ o o o o+ &

6. MODEL TAILINGS IMPOUNDMENT . . . . + « +« « o« « + &

7. CALCULATION OF AREAS FOR DRY TATILINGS BEACH AND
POND DURING THE 20-YEAR OPERATION OF THE MILL .

8., EVAPORATION OF THE TAILING POND AFTER MILL CLOSING
AND EXPOSURE OF DRY TATILINGS SURFACE . . . . . . .

9. RADON-220 FLUX FROM THE DRY TAILINGS AND FROM THE
POND SURFACE . . v & ¢ v 4« 6 v & o 4 o o o o « o &

iv

53
54
56
56
58
60
64
66
68
69
70

Al-1
A2-1
A3-1
Ab4-1
A5-1
Ab-1

A7-1
Figure

2.1

2.2

3.1

3.3

3.4

3.5

5.1

6.1

A.6.1

LIST OF FIGURES

Thorium resources in the United States . .

Topographical map of Lemhi Pass district of
Idaho and Montana . . . o « + « o o o & + &

Identified vein deposits of thorium ore in the

vicinity of the Lemhi Pass . . . . . . . . .

Typical features of open-pit mine . . . . .
Artist's rendition of ore-treatment mill . .
Conceptual thorium milling. Flow diagram
Conceptual thorium milling. Flow diagram
Exposure pathways toman . . . . +« . . . . .

Thorium—232 decay chain . . . « . « + « .« .

Cross section of the natural wedge-shaped basin

22

22

23

24

25

50

63

A6-3
Table
2.1(a)
2.1(b)

2.2

2.3

3.1

4.1

b,2

4.3

b.b

4.5

4.6

4.7

4.8

4.9

LIST OF TABLES

Page
Vein thorium deposits — United States . . . . . « + « « . 6
Other thorium deposits -~ United States . . . . . « . . . 7
Population data for Lemhi Pass thorium resource site
region — 1970 census informatiomn . . . « . . . « .+ o . . 12
Population data for Wet Mountains thorium resource
site region — 1970 census information . . . . . . . . . . 12
Characteristics of the open-pit thorium mine and the
model thorium mill and refinery . . . . « « « ¢ « « + + & 21
Mass and volume flow rates for principal process streams
of the model mill and refinery . « ¢« ¢ o ¢ + « o« & « o . 25
Radioactivity contained in dust generated by wmining
OpPerations .+ « ¢ 4 ¢ ¢ e e 0 4 e e 4 e s e e e e e e e e 33
Estimated source terms for operation and closing of
the model nlill - . . . . - . - . - * - * . - * * - . - . 35
Values of concentrations of radionuclides in thorite
ore and in dry mill tailings that were employed in
calculation for 20-year mill operation . . . . . . . . . 35
Estimation of areas of the dry tailings beach and pond
during mill operation for the hypothetical Montana and
Colorado 1locations « « v v o o ¢ o « o« o o o & 0 e . e s 41
Estimation of areas of dry beach and pond as a function
of time after closing down mill operations at the
hypothetical Montana and Colorado locations . . . . . . . 42
Source terms for 220gg during will operating life and
during final evaporation of the pond and covering of
the dry tailings after the mill is closed . . . . . . . . 43
Wind velocities and particle size distribution used in
saltation model calculation . « . « « « ¢« o ¢ « + « « . 45
Calculated suspension rates as a function of wind
velocity, using the saltation model . . . . . . . . . . . 45
Suspension rates weighted for wind velocity
distribution - . . - . - . - * - . - . . - . - - - - . - 46

vi
Table Page

5.1 Dose conversion factors for total body, bone, and
lungs for radionuclides in the 232Th decay chain . . . . 52
6.1 Maximum individual 50-year dose commitment to total

body and various organs from radiocactivity released
to the atmosphere during one year of facility
operatiom . 4 v 4 i e h i s s e e e e e e e e e e e e 56

6.2 Radionuclide contributors to the dose commitment to
various organs for maximally exposed individual . . . . 57

6.3 Contribution of exposure pathways to dose commitment
to total body, bone, and lungs for maximally exposed
individual . . ¢ v L e e e s e s e e e e e s e e e e e s 58

6.4 Population dose commitment to total body and various
organs from radioactivity released to the atmosphere
during one year of facility operation . . . . . . . . . 39

6.5 Radionuclide contributions to the population dose
commitment to VATious OYELANS + « o ¢ » o o o s o s o s+ 59

6.6 Contribution of exposure pathways to population dose
commitment to total body, bone, and lungs . . . . . . . 60

6.7 Maximum individual 50-vyear dose commitments to total
body and various organs from radioactivity released
to the atmosphere during the first vear after facility

Shutdowll L ] » . - . ® o & - 3 o * > . . - » - a * . - a » 61
6.8 Radionuclide contributors to the dose commitments

to various organs for individuals exposed during the

first year after facility shutdown . . . . « « ¢« ¢« + « . 61
6.9 Contribution of exposure pathways to the dose

commitment to total body, bone, and lungs for
individuals exposed during the first year after
facility shutdown - . . * » * - - . » - - . . L - . . - 62

6.10 Population dose commitments to total body and wvarious
organs from radicactivity released to the atmosphere
during the first year after facility shutdown . . . . . 62

6.11 Radionuclide contributors to the population dose
commitment to various organs for exposures during
the first year after facility shutdown . . . . . . . . . 63

A.5.1 Calculated values of radionuclide activities and

masses in equilibrium with 1 g of thorium (by
ORIGEN COAE) v « v v o v v v v o o 4 & o v e e v v v o . A5-3

vii
Table Page

A.5.1 Calculated values of radionuclide activities and
masses in equilibrium with 1 g of thorium (by
ORIGEN code) v v ¢« o o o o « o o o o o o o o o o o o « = AS5-3

A.5.2 Activity of tailings left from the extraction of
1 g of thorium: 917% extraction {(from ORIGEN
code calculations) -+ « « + « s e o 4 4 e e e e 4 e s e e AS5-4

A.6.1 Relationship of triangular areas and sides to the
dam height (d.h) . . . . . . . . . . . . . . . . * . . . A6""4

A.6.2 Characteristics of model tailings pile . . + + + « + .+ . Ab~5

A.7.1 Constants used in Bond-Godbee equation and the
calculated steady-state volume cf the tailings
pOfld - . . . . . - . . . - . . . . . . . . . . » . . - . A7—5

A.7.2 Calculated values of the minimum water addition rate
required to keep tailings under water over the
20-year life of mill . . .« « ¢ &« v & & ¢ ¢« ¢ o 4 o . . A7-5

A.7.3 Change in volume of pond (V_) with time as a result
of evaporation . . . . . . . A7-6

A.7.4 Evaporation surface area of tailings pond (A.) and
values of AC used to calculate area of tailings
underneath the pond . ¢« ¢ v ¢ v « ¢ ¢ e« t e s e 0 . A7-6

A.7.5 Calculated values for the area of tailings covered
by water and of the dry tailings beach . . . . . . . . . A7-7

A.8.1 Volume of liquid in the tailings pond (V.) as a

function of elapsed time after closing the thorium
mill - . . . . . . . . - . . - . . - . . - . . - . . . . A8—3

viii
ENVIRONMENTAL ASSESSMENT OF ALTERNATE FBR FUELS: RADIOCLOGICAL
ASSESSMENT OF AIRBORNE RELEASES FROM THORIUM MINING AND MILLING*

V. J. Tennery't H., R. Meyer®
E. S. Bomar® J. E. Ti118/
W. D. Bond¥ , M. G. Yalcintas?
L. E. Morse
ABSTRACT

A radiological environmental assessment was performed for
airborne releases from a thorium mining and milling facility
based on site-specific analyses for known vein-type U.S. thorium
ore deposits, using proximate meterological data for the geo-
graphical region where these deposits are located. The assess-
ment was done for a conceptual open-pit thorium mine plus a mill
having a throughput rate of 1.5 Gg (1600 metric tons/day). The
thorium ore was assumed to have an average ThO, equivalent content
of 0.5%4. The mill facility consisted of a mill and refinery
whose product was reactor—-grade thorium nitrate tetrahydrate.
Several assumptions were necessary in order to conduct this
analysis due to scarcity of data specific to erosion and dusting
of thorium ore storage piles and a thorium mill-derived tailings
beach.

Radiological dose commitments were calculated for airborne
effluents from the mine and mill facility, using the AIRDOS-II
code. The 50-year dose commitment to the maximally exposed
individual and to the population, as shown by the 1970 census,
living within 50 miles of the operation site was estimated for
both Lemhi Pass, Idaho, and Wet Mountains, Colorado, sites.
Principal airborne radionuclides which contribute to the popu-
lation dose commitment for either site are 228Ra and 220Rrn plus
the daughters of 2ZPRrp. Total-body dose commitments to the
maximally exposed individual for one year of facility operation
for the Lemhi Pass and Wet Mountains sites are V2.4 and 3.5
millirems respectively. Population dose commitments to total
body for the Lemhi Pasz and Wet Mountains sites are 0.05 and 0.3
man-rem respectively. Tor both sites and both types of dose
commitment, inhalation and ingestion are the largest pathway con-
tributors to the dose. Several operations for thorium ore mining
and milling were identified during this assessment for which the
data base required for radionuclide source term generation was

 

%
Work performed under DOE/RRT 189a OH107/1488, "Environmental
Assessment of Advanced FBR Fuels."

+Metals and Ceramics Division.
&

Chemical Technology Division.
§Health and Safety Research Division.

Consultant.
either small or nonexistent. For operations where the data
base was judged insufficient for generation of at least a
first-approximation source term, data appropriate to the
similar operation for uranium mining or milling were used as
the basis for the source term. Areas where data needs are
greatest include (1) quantitative wvalues of emanation factors
and diffusion coefficients for %20Rn for thorium ore materials,
(2) fugitive dust generation rates from mine activities and
thorium ore piles, (3) release rates of 220Rpn from thorium
ores under various storage conditions, (4) release rates of
220Rn from thorium ores for various milling process treat-
ments, (5) properties of soils in mountainous locations of
vein-type thorium deposits to determine their suitability for
construction of tailings ponds and retention of radioactive
species contained in the mill tailings, and (6) site-specific
meteorvlogy appropriate to prime candidate sites for thorium
mines and mills.

 

1. INTRODUCTION

The thorium-—uranium nuclear fuel cycle is being studied in several
programs in the United States in order to better identify the nuclear
weapons proliferation resistance of this cycle compared with that of
the uranium-plutonium cycle. Another important feature of any fuel
cycle considered for commercialization is the radiological impact of the
cycle on the population. The impact derives from several sources,
including contributions from ore mining and milling, fuel fabricatioua,
reactor operation, transportation, fuel reprocessing, and fuel refabri-
cation,

This report describes the results of a radiological analysis of the
impact of thorium ore mining and milling from vein deposits at two
specific sites, one in the Lemhi Pass district of Idaho and Montana and
the other in the Wet Mouantains of Colorado. Mining of vein-type deposits
was analyzed because they are of the highest grade, and it is estimated
that as much as 407 of United States thorium reserves reside in such
deposits.

Compositional data for the known vein-type thorium ore deposits plus

the local topography of the region were employed in establishing details
of a model mine capable of providing 1.6 Gg (1600 metric tons) of ore
per day plus a mill of equivalent throughput capacity. This plant is
considered to be of reasonable size for such a mining endeavor.

This analysis differs in certain respects from a related and recently
published study of thorium mining and milling reported in ERDA 1541 con~
cerning the Light-~Water Breeder Reactor Program. In the current work,
recently improved assessment codes were employed and two site-specific
cases were analyzed. The entire mining operation was considered to be
open-pit type based on the geology of the known ore deposits at the sites.
Source terms are included based on dust from the mining, movement of ore
at the mine and mill, and ore crushing, plus the release of 220y from
the mine, ore pile, mill, and tailings pond.

The appropriate source terms‘were used along with population
density and meteorological data for the sites to estimate the population
dose commitment associated with the extraction and processing of the

thorium ore.
2, FACTLITY SITING, METEOROLOGY, AND POPULATION CHARACTERISTICS
PERTAINING TO THORIUM ORE DEPOSITS

2,1 U.S. Thorium Deposits

For the purposes of this report, it is assumed that the sources of
thorium to be considered are within the continental United States.

Thorium is found in several types of deposits in this country, including
(1) veins, (2) stream and beach placer deposits or placer deposits
incorporated in sedimentary rock, and (3) concentrations in igneous or
metamorphic rocks. The largest recoverable thorium reserves are in the
form of vein or placer deposits. Thorium dioxide resources in the
United States available at a cost of $11 to $22 per kg ($4 to $10 per
pound, 1969 dollars) are placed at approximately 600 Gg (600,000 metric
tons).?!

Monazite sands, which are primarily phosphates of the rare-earth
elements, are formed as a result of the weathering of rocks such as
granites. Running water carries the sands to locations remote from the
original rock formations to places where conditions permit the heavier
minerals to settle; this may occur in a river, or the sands may be
carried to the ocean and coastal locations. Wave action has resulted in
placer deposits of heavy minerals, such as ilmenite and wmonazite, along
some beaches on the Atlantic Coast of the United States. A few of these
deposits have been worked commercially to recover titanium-bearing
minerals with monazite as a secondary product. Large-scale working of
beach deposits in the future is unlikely, however, because of the high
populdtion density of the coastal region.

Figure 2.1 and Tables 2.1(a) and 2.1(b) present available information
concerning significant thorium resource sites in the contiguous United
States., Table 2.1(a) gives the locations, extent of sampling and observed
thorium content, physical dimension, and nearby populations for vein-
type deposits of thorium in the United States.' 1?2 Table 2.1(b)
identifies deposits of other types but which are predominately monazite
ores.13717,31-3%  Ttrems A and B give the locations of placer deposits

of monazite sands: the thorium content of these deposits at Jacksonville,
ORNL-DWG 78-19R

 

 

   
 
 

 

 

KILOMETERS
; 0 500
} i
/ i i {
0 200 400
T~ MILES
+—_ !
i I

 

 

Fig. 2.1. Thorium resources in the United States.
Table 2.1{a}.

Vein thorium deposits — United States

 

 

Max
Max vein Thorium Population
Location County, state Latitude Longitude Num?er of vein length thickness content within 80 km Ref
(see map) (°N) (°W) samples (m) {m) (%) {1979)
i. Lemhi Pass Lemhi, iID 44,93 113.5 200+ 1.2 x 103 9 0.001-16.3 14,242 2-5
Beaver, MT
2. Diamond Lemhi, ID 45 114 9 1.7 x 102 7.5 0.02-1.71 7,364 3
Creek
3. Hall Mt. Boundary, 1D 48.99 116. 38 14 1 x 102 0.01-21 15,359 6
4, Powderhorn Gunnison, CO 38.25 107 200+ 1.1 x 103 5.5 0.01-4.3 32,192 7
5. Wet Mts. Custer, CO 38.25 105.35 400+ 1.5 x 163 i5 0.02-12.5 252,144 8,9
6. Laughlin Colfax, NM 36.75 104.25 16 2.4 x 102 5.1 0.05-0.82 27,615 2
Pk,
7. Capitan Lincoln, NM 33.5 105.78 12 46 2.4 0.01-1.12 47,668 10
Mts.
8. Gold Hill Grant, NM 33 109 2 12 0.05-0.72 39,900 2
9. Quartzite Yuma, AZ 33.75 114.25 2 15 2.4 0.027-0.27 22,613 2
10. Cotronwood Yavapai, AZ 34,75 112 1 30 i8 0.013-0.91 64,769 2
11. Monroe Seiver, UT 38. 58 112 1 7.6 15 0.18-0.29 19,868 2
Canyon
12. Mountain San Bernardino 35. 4% 115.5 18 4.9 x 102 3 0.02-4.9 30,321 11
Pass CA
13. Wausau Marathon, WI 45 89.5 20 4.6 x 102 0.5 338,408 12

 
Table 2.1(b).

Other thorium deposits — United States

 

 

Population
Location County, state Latitude Longitude Thorium content within 80 km Ref.
(see map) (°N) (°W) {ppm) (1970)
14. Conway Conway, NH 44,00 71.16 b4 29
15, Mineville Essex, NY 44,16 73.58 100-3800 30
16. Palmer Marquette, MI 46,5 87.5 50,000 31
17. Owl Creek Hot Spring, WY 43.48 165.50 134 30,292 13,14
18. Rowlins uplift Carbon, WY 41,78 107.13 146 13,201 13,14
19. Wind River Fremont, WY 43.5 109.5 366 31,648 13,14
20, Wind River Fremont, WY 43,5 109.6 66 31,648 13,14
21. Seminoe Natrona, WY 42,47 106.75 194-273 51,995 13,14
22, Deer Creek MT 45.2 112.5 30
23. Blue Mt. Greenlee, AZ 32.55 109.20 40 30,481 13,15
24, Dos Cabesas Cochise, AZ 32.2 109.42 19 30,098 13,15
25. Mineral Hill Lemhi, IB 45.6 114.9 13,15
26. Diamond Rim Gila, AZ 34,25 111.08 24 10,416 13,15
27. Little Big Horn Big Horn, WY 44,66 106.95
28. Bear Lodge Crook, WY 44,5 104.33 4002500 30
29. Idaho Idaho, ID 46 115 200 32
30. McCullough Mt. Clark, NV 36 116 55-283 145,059 13,15
31. Black Mts, Mohave, AZ 35.5 114.5 180-253 137,958 13,15
32. S. Peacock Mts. Mohave, AZ 35 114 37-153 137,958 13,15
33. Big Maria Mts. Riverside, CA 33.5 116 29-146 136,470 13,15
34, Marble Mts. San Bernardino, CA 35 116 75-148 136,470 13,15
35. 8t. Ffrancois Mts. St. Francois, MO 37.5 90 47 320,378 13,17
36, Idaho Batholith Boise, ID 44.0 115.90 100 32
37. Gallinas Lincoln, NM 34.15 105.63 33
3B. HWorcester Worcester, MA 42,25 71.75 300 30
A, Georgla Charlton, GA 32 81.6 <1000 34
. Florida Nassau, FL 30.2 81.3 <1000 34
C. California San Bernardino, CA 36 117 200-5000 30
D. Piedmont District VA, NC, SC, AL 32-38 78-87 [5.67%] 30

 
Florida; Folkston, Georgia; and on Hilton Head Island, South Carolina;3°
was estimated at 14 Gg (15,600 tons). The Folkston deposit has been
reported more recently, however, to have been exhausted.3® Basnaesite
deposits are being mined at Mountain Pass, California (item C). Two
extensive deposits are identified as item D, The western belt extends

for 1 Mu (600 miles) from eastern Virginia southwest to Alabama. It
ranges from 0.02 to 0.8 Mm (10 to 50 miles) wide with an average width

of about 0.03 Mm (20 miles). The eastern belt originates near Fredericks-
burg, Virginia, and continues for about 200 miles into North Carolina

with an average width of about 0.01 Mm (5 miles).

2.2 Sites Selected for Analysis

The most promising thorium deposits for large—scale exploitation
are thorite-bearing veins such as those located in Colorado, Idaho,
and Montana. As much as 407 of U.S. thorium reserves occur as vein

deposits.18

Reserves equal to about 100 Gg (100,000 metric tons) of
ThO, at $22 per kg ($10 per pound) or less (1969 dollars) are estimated
to be available in the Lemhi Pass district of Idaho and Montana,1 which
lies astride the Continental Divide about 16 km (10 miles) east of Tendoy,
Idaho. The Lemhi Pass is shown on the relief map19 in Fig. 2.2 between
the vertical coordinates UEO~-UEl and the horizontal coordinates 8-9.
The thorium resources of the Lemhi Pass district could supply the
requirements of a very large number of FBRs fueled with (Th, U)C and
ThC, since calculations by Caspersson et al.?0 show a core blanket
requirement of 83 to 117 Mg (83 to 117 metric tons) of thorium carbide
equivalent per 1200-MW(e) core, depending on the core and blanket
configuration. Additional vein deposits have been found in the Powder-
horn and Wet Mountains districts of Colorado.

The winters in the Lemhi Pass district are described as moderate,
and some of the deposits at the lower elevations can be worked vyear
round. In severe winters, operations may, however, be shut down for

several months.
 

 

——— =
-DWG 78-15182
: T T

 

. ORNL

“a

 

 

B! ‘flllifl;" T ’ A Y 'k /

Fig. 2.2. Topographical map of Lemhi Pass district of Idaho and
Montana. (Photograph of selected portions of relief maps titled Dillonm,
Montana, NL12-7, and Dubois, Idaho, NL12-10; Hubbard Co., Northbrook,
Illinois 60062.)
10

2.3 Characteristics of Deposits in the Lemhi Pass District

Information on the topography, general geology, and the nature
of the thorium-bearing deposits in the Lemhi Pass area is given in
Atomic Energy Commission reports by Sharp and Hetland and by Austin

issued in 1968,21,22

Over 200 samples were taken from about 100 pros-
pects along a 110-km (70-mile) trend paralleling the Idaho-Montana
border from Leadore, Idaho, to North Fork, Idaho. Elevations in this
region range from 1.5 km (5000 feet) above sea level along the Lemhi
River up to 2.7 km (9000 feet) at the Continental Divide. The ore
minerals include phosphatic thorite, monazite, and rare—earth concen-
trations. Rare-earth phosphates such as xenotime (YPO,) form an isomor-
phous series with thorite (ThSiO,) to yield the mineral aueralite. The
ratio of rare earth to thorium in these deposits varies from 10:1 to

23 on

1:5. Additional information was reported by Ross and George
metallurgical amenability tests and compositions of Idaho-Montana
thorium ores. Spectrographic analyses show that these ores contain
undetectable amounts of uranium (<0.0001 to 0.001%).

The thorium-bearing veins are, in general, not exposed but are
covered by a thick layer of soil. The presence of the veins can often
be detected by surveying the soil cover for radiocactivity with sensitive
instruments., Detection is possible due to a degree of mixing of minerals
from the veins with the soil. Bulldozing is necessary to expose the
veins. The vein deposits show a northwesterly trend paralleling the
Continental Divide from the vicinity of Leadore, Idaho, at the southern
end, and all are found in an area about 110 km (70 miles) long and 13 km
(8 miles) wide. The inclination of the veins varies, particularly near
major faults. It is estimated that 60% of the veins dip at angles of 45
to 60° and 40% dip at >60°. The flatter-dipping veins are from 0.9 to
4,6 m (3 to 15 ft) wide, while the steeper veins measure 0.15 to 1.5 m
(0.5 to 5 ft) wide. Flat-dipping veins paralleling canyon walls can be
mined by open-cut methods, possibly to 91 to 122 m (300 to 400 ft) below
the outcrop. Underground methods would eventually have to be used to
recover a major portion of the thorium. This study does not, however,

consider the radiological hazards of underground thorium mines.
11

Borrowman and Rosenbaum?" demonstrated the recovery of the thorium
content of thorite samples by acid dissolution. These samples were
taken from vein deposits in the Lemhi Pass district of Tdaho~Montana and
the Powderhorn and Wet Mountains districts of Colorado. The samples

ranged in content from 0.2 to 3.9 wt % thorium dioxide equivalent.

2.4 Population Distribution

Population data specific to the thorium resource sites under study
in this report were obtained via the "Reactor Site Population Analysis"
computer code available at ORNL. Output from this code is based on
U.S. 1970 census information. Approximation of future population data
was not deemed necessary for the purposes of this report, since thorium
mining and milling population doses were found to be low, and population
centers with the potential for significant growth are located at dis-
tances in excess of 32 km (20 miles) from either the Lemhi Pass or Wet
Mountains sites, a condition which renders the dose estimation procedure
relatively insensitive to moderate vpopulation increases., Tables 2.2 and
2.3 present population data breakdowns as input to the AIRDOS-~II dose

estimation code.

2.5 Meteorological Data

Since variations in meteorology have the potential for significantly
modifying both individual and population doses calculated via methodologies
using wind and stability category-dependent radionuclide dispersal models,
use of local rather than generic meteorological data was deemed necessary
in this study. Best available meteorological data for both the Lemhi
Pass and the Wet Mountains resource sites were obtalned from first-order
weather stations located near each site. Two sets of data were obtained
for each resource site, since no first-order weather station is located
in the immediate wvicinity of either Lemhi Pass or Wet Mountains. These
data were obtained through the courtesy of the National Oceanic and
Atmospheric Administration offices located at the National Climatic

Center (NCC) in Asheville, North Carolina, and were provided in the form
12

Table 2.2, Population data for Lemhi Pass thorium resource
site region — 1970 census Information

 

Population distribution?

 

Compass direction
0-8.0Y  8.0-16 16~32 12-48 48~64 64-80

 

 

N 0 0 /8 211 0

NNE 0 0 0 0 0

NE 0 0 0 557 0

ENE 0 0 245 0 0 5,897

E 0 0 0 129 0

ESE 0 0 0 0 589

SE 0 0 0 0 0

SSE 0 0 111 0 70

s 0 0 0 0 0

SSW 0 412 0 0 4

SW 0 0 0 0 277 784

WSW 0 0 0 181 0 0

W 0 0 0 0 0 0

WNW 0 0 0 825 0 0

NW 0 0 337 2,910 534 168

NNW 0 0 0 0 0 0
0 412 693 3,916 1,782 7,438

 

aTotal population = 14,241,
Distance x 10~3 m {(applicable to each heading).

Tahle 2.3. Population data for Wet Mountains thorium resource
site region — 1970 census information

 

Population distribution?
Compass direction

 

 

 

 

0-8.0F  8,0-16 16-32 32-48 48-64 64—80

N 0 0 0 0 0 835
NNE 0 264 12,264 70 791 18,910
NE 0 6,662 1,246 0 93,790
ENE 0 713 0 753 0
E 0 0 884 65,014 46,808
ESE 0 0 0 0 106
SE 0 318 0 0 1,563 404
SSE 0 0 0 0 170 0
S 0 0 164 0 363 0
SSW 0 126 0 0 20 741
SW 0 0 512 34 0 859
WSW 0 0 0 0 98 642
W 0 0 0 350 0 10
WNW 0 0 377 0 2,164 3,567
NW 0 0 0 0 0 0
NNW 0 0 0 346 24 182
0 708 20,692 2,930 70,960 166,854

 

aTotal population = 262,144,
bDistance x 10=3 m (applicable to each heading) .
13

of monthly or seasonal summaries of wind speed and Pasquill stability
category data based on extended observation periods. The data were
condensed into AIRDOS-II format via ORNL IBM-360/91 computer manipulation
and are presented in this condensed format in Appendix 1 of this report.

As noted in Sect. 2.2, it is anticipated that severe weather in the
Lemhi Pass region may shut down mining (but not milling) operations for
the winter months, since temperature, wind, and snowfall hinder outdoor
operations. This report therefore assumes the establishment of an ore
pile adjacent to the mill of a size sufficient to continue milling
operations uninterrupted during the period December through February. It
is concurrently assumed that mine-generated source terms are reduced to
near zero during the winter season at the Lemhi Pass site. For this
reason the appended AIRDOS-II meteorological summaries (Butte and Mullan
Pass meteorologies) utilized in thorium mining AIRDOS-IT dose estimations
were composed from data excluding the winter season., Dose calculations
for the Lemhi mill, ore pile, and tailings beach utilize four—season
meteorological summaries, as do all calculations for the Wet Mountains
site, where the winter climate is less severe,

The original STAR program meteorological summaries are on file at

ORNL. and at NCC-Asheville and are accessible under NCC I1.D. as follows:

 

Thorium resource site  Best available meteorology  Station No. STAR run

Wet Mountains Alamosa, Colorado 23061 12/13/77
Wet Mountains Pueblo, Colorado 93058 1/23/75
Lemhi Pass Mullan Pass, Idaho 24154 11/21/77
Lemhi Pass Butte, Montana 24135 3/22/72

Because no reliable method is available to determine which of the
substitute meteorologies best represents exact conditions at the thorium
resource site under consideration, dose estimates in this study were
calculated for all four sets of meteorological data, and discussion
emphasizes those meteorologies found to maximize radiological dose, a

conservative procedure.
14

Detailed long-term study of wind speed and stability class wvaria-
tions at representative thorium resource sites is necessary before less
conservative radiological studies can be performed for these sites,

To assist the reader in visualization of climatological conditions
at the two resource sites, narrative climatological summaries have been
abstracted from the STAR program data as obtained from NCC, and from
25-27

other sources and are presented in the following pages.

NARRATIVE CLIMATOLOGICAIL SUMMARY

Lemhi Pass Area

The thorium deposits in the Lemhi Pass area are centered approxi-
mately 16 km (10 miles) east of Tendoy, Idaho, over an area of about
260 km? (100 square miles), astride the Continental Divide, which forms
the Idaho-Montana border. The area 1s mountainous but not rugged and is
characterized by rounded ridges rising steeply from the valley floors,
providing sharp relief of as much as 0.91 km (3000 ft). The altitiude
ranges from 1.5 km (4800 ft) above mean sea level in the Temhi Valley
to 2.4 km (9000 ft) at the Pass. North~facing slopes in the higher
elevations are well timbered with pine, fir, and hemlock. Nontimbered
areas are covered primarily with bunchgrass and sagebrush.

Predominant wind direction in the area is from the west with little
seasonal variation in direction. Wind velocities average between 3.1
and 4.0 m/sec (7 to 9 mph) throughout the year.Z5,26

January is the coldest month, with an average temperature of -12°C
(10°F). July and August both record approximately 16°C (60°F) mean
temperatures as the warmest months of the year. Mean temperatures in
spring through fall progress in an orderly fashion from cool to warm to
cool, without secondary maxima or minima. The period between the last
freeze of spring (late June) and the first freeze of fall (late August)
averages about 60 days. The mean annual number of days for which the
daily wminimum tewmperature is below freezing is 240, An average of two
days each year exceed a temperature of 32°C (90°F). The average daily
temperature range is 18 C° (32.5 F°), with the greatest range (22 C°,

40 ¥°) occurring in July, August, and September.
15

Total annual precipitation for the Lemhi area averages 0.6 m
(24 in.), evenly distributed throughout the year. The mean annual
number of days with measurable precipitation is 120. Mean annual snow-~

fall is 2.5 m (100 in.).28

NARRATIVE CLIMATOLOGICAL SUMMARY

Wet Mountains Area

The Wet Mountains are located about 80 km (50 miles) southwest of
Colorado Springs and about 60 km (35 miles) west-southwest of Pueblo on
the east side of the Sangre de Cristo Mountains and the San Isabel
National TForest. These mountains are oriented northwest-southeast with
peak altitudes of about 4 km (13,000 ft), and the terrain slopes down-
ward to the east and northeast along the valley of the Arkansas River.

The vegetation around Pueblo is sparse, and the region is largely tree-
less. Along the skirts of the Sangre de Cristo Mountains the San Luis
Valley lies from northwest to southeast, with the Great Sand Dunes
National Monument located at the southwest extremity of the Sangre de
Cristos. The town of Alamosa is located about 40 km (25 miles) south-
west of the Great Sand Dunes National Monument within the San Luis Valley.

The wind directions in Alamosa are usually from south-~southwest,
southwest, and west-southwest with 8.5 te 11 m/sec (19 to 24 mph)
maximum and 5.4 to 5.8 m/sec (12 to 13 wph) mean velocities. 1In Pueblo
the wind is usually from the northwest or west, except in May and June,
when it blows from the west or southwest. Seasonal mean wind velocities
range from 3.1 to 5.4 m/sec (7 to 12 mph). Maximum wind velocities during
December through July occur during the afternoon hours and reach 8.5 to 11
m/sec (19 to 24 mph). Between August and November, maximum velocities
reach 5.8 to 8.0 m/sec (13 to 18'mph).29’30

The coldest month is normally December (-7°C, 20°F mean temperature),
but differences between the mean temperatures of December, January, and
February are small. August 1Is usually the warmest month, but differences
between the mean temperature of June, July, and August are also relatively
small. Mean temperatures of the spring and fall months progress in an

orderly fashion from cool to warm to cool without secondary maxima or
16

minima. The average period between the last freeze of spring (May 30) and
the first freeze of fall (August 15 to August 30) is 82 days. Annual
occurrence of daily minimum temperature 0°C (32°F) or below is 210 days.
Temperatures of 32°C (90°F) or above occur an average of 11 days annually.
The average daily temperature range is about 18 C° (32.5 F°).

Normal annual total precipitation is between 0.4 and 0.6 m (16 and
24 in.). Summer is the season of heaviest precipitation, with the
monthly maximum normally occurring in July (0.08 m, 3 in.) or August
(0.05 to 0.10 m, 2 to 4 in.). A mean of 92 days annually receives
measurable (0.25 mm, 0.01 in. or more) precipitation. Annual snowfall

is 1.5 to 2.5 m (60 to 100 in.).?%7

2.6 References

1. U.S. Bureau of Mines, 1970 Edition Mineral Facts and Problems, U.S.

Department of the Interior, Bureau of the Mines Bulletin 650,

2. H. H. Staatz, "Thorium Veins in the United States," Feon. Geol.
69: 494 (1974).

3. S. R. Austin, Thoriwn, Yttrium and Rare Farth Analyses, Lemhi
Pass — Idaho and Montana, USAEC Technical Memorandum AEC-RID-2,
p. 12 (1968).

4, W, N, Sharp and W. S. Cavender, Geology and Thorium-Bearing Deposits
of the Lewmhi Pass Area, Lemhi County, Tdaho and Beaverhead County,

Montana, U,S. Geol. Survey Bulletin 1126, 76 (1962).

5. A. F. Triters and E. W. Tooker, Uranium and Thorium Deposits in
East—-Central Idaho and Southwestern Montana, U.S. Geol. Survey

Bulletin 933-H, 157 (1953).

6. M. H. Staatz, "Thorium Rich Veins of Hall Mountain in Northern-Most

Idaho," Eeon. Geol. 67: 240 (1972).

7. J. C. Olson and S. R. Wallace, Thorium and Rare Farth Minerals in
Powderhorn District, Gunnison County, Colorado, U.S. Geol. Survey

Bulletin 1027-0, 693 (1956).

8. R. A, Christman et al., Geology and Thorium Deposits of the Wet
Mountains, Colorado, U.S. Geol. Survey Bulletin 1072-H, 491 (1960).
10.

11.

12,

13.

14.

15.

16.

17.

18.

19.

17

M. R. Brock and Q. D. Singewald, Geologic Map of the Mount Tyndal
Quadrangle, Custer County, Colorado, U.S. Geol. Survey Geol. Quad.
Map GQ-596.

G. B. Griswold, Mineral Deposits of Lincoln County, New Mexico,

N. M. Bur. Mines Minerals Res. Bulletin 67, 117 (1959).

J. C. Olson et al., Rare-Earth Mineral Deposits of the Mountain Pass
District, San Bernardino, California, U.S. Geo. Survey Prof. Paper

261, 75 (1954).

S. R. Vickers, Airborn and Ground Reconnaissance of Part of the
Syenite Complex Near Wausau, Wisconsin, U.S. Geol. Survey Prof.

Paper 300, 587 (1956).

R. C. Malan, Swmmary Report — Distribution of Uranium and Thoriwn
in the Precambrian of the Westerwn United States, USAEC AEC-RID-12
(1972).

C. R. Anhaeusser et al., "A Reappraisal of Some Aspects of

Precambrian Shield Geology,'" Geol. Soe. Am. Bull. 80: 2175 (1969).

R, C. Malan and D. A. Sterling, An Introduction to the Distribution
of Uranium and Thoriwnm in Precambrian Rocks Including the Results
of Preliminary Studies in the Southwesterm United States, USAEC
AEC-RID-9.54 (1969).

R. C. Malan and D. A. Sterling, Distribution of Uranium and Thorium
in Precambrian Rocks of the Western Great Lakes Region, USAEC
AEC~-RID-10 (1969).

R. C. Malan and D. A. Sterling, Distribution of Uranium and Thorium
in the Precambrian of the West-Central and Northwest, USAEC AEC-
RID-11 (1970).

Fugene N. Cameron, Ed., The Mineral Position of the United States,
1975-2000, Society of Economic Geologists Foundation, Inc., Univer-

sity of Wisconsin Press, 1973.

Hubbard Co., Northbrook, Illinois 60062, Relief Maps Titled Dillion,
Montana, NL 12-7 and Dubois, Idaho, NL 12~10.
20.

21.

22.

23.

24.

25.

26.

28.

29.

31.

18

J. A. Caspersson et al., CE~-FBR-77-370 (C00-2426-108), Initial
Assessment of (Th,U) Alternate Fuels Performance in LMFBRs (August
1977).

Byron J. Sharp and Domnald L. Hetland, Thorium and Rare Earth Resources
of the Lemhi Pass Area, Idaho and Mowntana, USAEC AEC-RID-3 (July 1968).

S. R. Austin, Thorium, Yttrium, and Rare Earth Analyses, Lemhi
Pass — Idaho and Montana, USAEC Technical Memorandum AEC-RID-2
(August 1968).

J. Richard Ross and D'Arcy R. George, Metallurgical Amenability Tests
on Idaho/Montana Thorium Ores, Research Report 62.1, U.S. Department
of Interior, Bureau of Mines, Salt Lake City Metallurgy Research

Center (November 1966).

S. R. Borrowman and J. B. Rosenbaum, Recovery of Thorium from Ores
in Colorado, Idaho, and Montana, U.S. Bureau of Mines Report of

Investigations RI-5916 (1962).

Seasonal and Annual Wind Distribution for Butte, Montana, 1956-60,
U.S. Department of Commerce, National Oceanic and Atmospheric

Administration, Environmental Data Service, Asheville, N.C., 1972,

Monthly and Annual Wind Distribution for Mullah Pass, Idaho, 1950-54,
U.S. Department of Commerce, National Oceanic and Atmospheric

Administration, Environmental Data Service, Asheville, N.C., 1977,

Climatic Atlas of the United States, U.S. Department of Commerce,

Environmental Data Service, Asheville, N.C., 1974,

Revised Uniform Summary of Surface Water Hourly Observations for
Alamosa, Colorado, from 1948 to 1972, Data Processing Braach

USAFETAC, Air Weather Service, 1973.

Summary of Hourly Observations for Pueblo, Colorado, from 1950 to

1955, U.S. Department of Commerce, Weather Bureau, 1956.

J. A. Adams, "The Conway Granite of NH as a Major Low Grade Thorium

Resource," Natl., Acad. Sei. Proc. 48: 1898 (1962).

W. S. Twenhofel and K. L. Buck, "The Geology of Thorium Deposits in
the U.S.," Peaceful Use of Atomic Energy, p. 562, Geneva, 1955.
32.

33.

34.

35.

36.

19

R. A. Vickers, '"'Geology and Monazite Content of the Gandrich Quart-
zite, Palmer Area, Marquette County, Michigan," Peaceful Use of
Atomie Energy, p. 597, Geneva, 1955.

J. H. Mackin apnd D. L. Schmidt, "Uranium and Thorium-Bearing Minerals

in Placer Deposits, Idaho," Peaceful Use of Atomic Energy, p. 587,

Geneva, 1955,

J. J. Glass, '"Basnaesite," Am. Mineral. 30: 601 (1945).

C. K. McCauley, "Exploration for Heavy Minerals on Hilton Head Island,

South Carolina," South Carolima Board Div., Geo. Bulletin, Vol. 26,
p. 13, 1960.

R. V. Sondermayor, "Thorium,'" Mineral Yearbook 1974, Dept. of Interior,

U.S. Bureau of Mines, Vol. 1, p. 1269, 1974,
20

3. DESCRIPTION OF MODEL MINE AND MILL

3.1 Facility Description

The characteristics of the mine and mill considered here are similar
to those described in the environmental statement for the Light-Water

1 Mine and mill characteristics are listed in

Breeder Reactor Program.
Table 3.1. Actually, the ore may originate from concurrent mining of
several veins at different locations. In a study of possible mining
methods and costs applicable to the Lemhi Pass area, Peck and Birch
reported2 selection of a mill site where power, water, and an area
suitable for a tailings pond can be provided. This site wcould locate
the mill at an average distance of 7 miles from the majority of the
deposits. The distribution of Chese deposits in the viecinity of the
Lemhi Pass and the towns of Tendoy and Lemhi, Idaho, is shown in
Fig. 3.1. Location of the veins was identified from a reconnaissance
map obtained from the Grand Junction Office of the Department of Energy,3
Locations of the veins are indicated on the relief map copy, Fig. 2.2,

Flat or mildly dipping veins near the surface would be mined first
using open—cut methods since this is least costly. The radiological
effects on the environment of open pit vs underground mining should be
similar. Figure 3.2 shows the principal features of an open-pit mine,
which include overburden storage, surface-drainage diversion, and haul-
road access. The actual appearance of the mine would depend on the local
terrain and the characteristics of the particular vein being mined. The
location of some veins will allow natural drainage rather than pumping
from a sump. Not shown but required is a holding pond for mine drainage
water to provide for removal of suspended solids by settling. 1If close
enocugh to the mill, this water can be used as part of the mill-process
requirements. Otherwise, it will be disposed of by evaporation or
natural seepage to groundwater.

The mill complex will be composed of an ore storage area, a tailings
pond, and buildings to enclose ore processing and thorium nitrate tetra-

hydrate (ThNT) product refining equipment. While it is possible that
21

Table 3.1. Characteristics of the open-pit thorium mine

and the model thorium mill and refinery

 

Mine

Approximate total area (m?)

Exposed thorium-bearing vein(s) (m?)

Ore production (Mg/day)

Average thorium content (% ThO, equivalent)
Water drainage (m3 /day)

Average depth (m)

MLl and Refinery

Ore capacity (Mg/day)
Days of operation annually
Thorium recovery efficiency (%)
Mill
Refinery
Th(NOg),+4H,0 production (Gg/year)
Water required (m3/day)
Ore pile (m)

(Gg)
Tailings impoundment
Montana
Average area during 20-vear mill
life (m®)
Dry beach 4E3
Pond 57E4
Average area exposed durlng post-mill
life (m?)
Dry beach ' 4E3
Pond 38E4

Air discharge from complex (m3/sec)

Filter losses (%)

Crusher dust
Th(NO3)y*4Ho0 product line

(bags plus HEPA)

4,944
1.2E4
1600
0.5
6.8E2
23

1600
300

917%

99.5%

4.5

2.4E3

100 x 32 x 15
96

Colorado

36E3
 49E4

4E3
27E4

11.3

0.7

 

4,984 = 4.9 x 10“.

a thorium refinery may be located elsewhere, perhaps central to several

thorium mine and mill operations in several states, the purposes of this

study are best served by analyzing the impact of a local refinery, as

well as mine and mill impacts. The thorium ore pile will contain a

60~-day reserve to allow operation of the mill during periods when winter
22

 

 

 

 

Fig. 3.1. Identified vein deposits of thorium ore in the vicinity
of the Lemhi Pass. (Photograph of selected portion of relief map titled
Dubois, Idaho, NL12-10, Hubbard Co., Northbrook, Illinois 60062.) Deposit
locations identified by (e-e-e).
23

ORNL-DWG 78-15184

s

 
 
 

OVERBURDEN
SPOIL PILE

 
    
   
 
    

 

TGP OF
ORE BOLY

 
  
 

BOTTOM OF
QRE BOOY

 

 

 

=ZE S L i _x\\

Fig. 3.2. Typical features of open-pit mine. (Taken from Tennessee
Valley Authority Final Environmental Statement, Morton Ranch Uranium Mine.)
24

weather stops mining activities at the higher elevations. An artist's
rendition of a typical mill complex is shown in Fig. 3.3. The ore will
probably be stored in two or more piles based on thorium content.

Selective blending will provide a more consistent thorium content of

feed to the acid leaching step in the mill process.

ORNL-DWG 78-12804

 

  
 

  

S
= -»

  

Fig. 3.3. Artist's rendition of ore-treatment mill. (Taken from

U.S. Nuclear Regulatory Commission, Final Environmental Statement Bear
Creek Project, NUREG-0129, Docket No. 40-8452, June 1977.)

3.2 Thorium Mining

The overburden is first removed by bulldozers or other earth-moving
equipment and transferred to a storage pile. The exposed vein(s) of
thorium-bearing ore is broken up by bulldozers, dozer-rippers, or
selective blasting as required. Spot analyses are made of the thorium
content of the ore, and the results are used to classify the ore for
subsequent blending. Front-end loaders of about 5.4 Mg (5.4 metric tons)
capacity transfer the ore to 35-Mg-capacity (35-metric ton) trucks to
haul the ore to the mill. Generation of dust at the mine will be mini-

mized by frequent sprinkling of the surface with water.

3.3 Thorium Milling and Refining

3.3.1 Introduction

The model plant chosen for identification of airborne effluents

produces reactor-grade ThNT. The ore processing rate was 1.6 Gg of
25

thorite ore per day containing 0.5% ThO; and 300-day annual operations.
A 91% recovery of thorium was assumed. This is the same processing rate
as reported in a previous study.1 The nitrate salt was chosen as the
end product since it is a convenient starting point for the denitration,
sol-gel, or coprecipitation routes to preparation of metal oxides.

Because there is at present no industry in the United States which
produces thorium as a primary product, the model plant for the milling
and refining of thorium ore was patterned after those reported for

uranium ore.”

The model plant selected for thorium ore consists of a
milling and a refining operation (Figs. 3.4 and 3.5). The conceptual
flowsheet for the mill was derived from chemical flowsheets reported

by the U.S. Bureau of Mines,”»® whereas the conceptual flowsheet for

the refinery was derived from a flowsheet developed for the reprocessing
of irradiated Th02.7 Mass and the volumetric flow rates are given for

key process streams in the conceptual flowsheets in Table 3.2.

QRNL~-DWG TB-196

TO ATMOSPHERE {Taj}—@——-»m STACK

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

   

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3 WATER
ORE DRY GROUND WET
SROM___ ol sTOCK (D sizE ORE - SIZE
MINE PILE REDUCTION ST%fAGE REDUCTION
IN
H2504 WATER AMINE, KEROSENE  (NH4)2C03
SCRUBBER e
STACK [ FLOCCULANT ALCOHOL SOL'N.
1 1 y
ACID COUNTER AMINE
LEAGHERS »| CURRENT » SOLVENT STRIPPING
DECANTATION EXTRACTION
AQUEQUS RAFFINATE ORGANIC
SANDS, SLIME, TO RECYCLE RAFFINATE
LIQUID WASTES TO RECYCLE
TO TAILINGS POND
NM3£0,
| RECYCLE ;"“*Hao
STEAM
OISTILLATION > FILTRATION »--w(:)-—--»Tn(co.s)z-tzo ~———=TO REFINERY

 

 

 

 

 

 

l—*AQ. (NH4)2 S04 FOR NHM3 RECOVERY

Fig. 3.4. Conceptual thorium milling. Flow diagram.
26

ORNL-DWG 78-195

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

TO RECYCLE
ORGANIC ORGANIC
EXTRACT CLEAN UP | AQUEOQUS
WASHES
M0 Q DILUTE HNOsx
3 " WASH RAFFINATES
2 ~ TO STORAGE
o D
O 3 o
FEED °2 z
AQ. Tnmc@p z o TO STORAGE
HNOs SOL'N, zz o DILUTE HNO4
O
[l
2 c
2 z
ORGANIC @
30% TBP IN

NPH DILUENT

 

 

 

AQ. RAFFINATE
TO ACID RECOVERY
AND WASTE CONC'N.

Fig. 3.5.

Table 3.2,

Conceptual thorium refining.

 

 

 

CONCEN-
TRATOR

 

CONC. Th(NQO3l4
HNO, SOU'N

DILUTE
AQ. PRODUCT

 

 

 

 

 

 

 

Th(NQ:;)q . 4H20

RYSTALLIZER f=-
PRODUCT 4 CRYSTALLIZE

 

 

 

 

MOTHER LIQUOR
TO RECYCLE &+

 

Flow diagram.

Mass and volume flow rates for principal process streams
of the model mill and refinery

 

 

 

 

Mill Refinery
Feed? Product Tailings Feed ThNT Aqueous
product wastes
Thorium
kg/sec 8.14E-20 7.41E-2 7.33E-3 7.41E-2 7.37E-2 3.70E-3
(kg/day) (7.03E+3) {6.40E4+3) (6.33E+2) (6.40E4+3) (6.37E+3) (3.20E+2)
Volume®
m3/sec 3,47E-2 d 3.47E-2 4.06E~4 d 3.11E-3
(ft3/day) (1.06E+5) d (1.06E+5) (1.24E+3) d (9.50E+3)

 

%Feed rate of ore is 18.5 kg/sec (1.6 Gg/day).
bread as 8.14 x 10-2.

“Includes both process liquids and solids.

dNot determined.
The mill employs sulfuric acid leaching of the ground ore to solu-
bilize the thorium, which is then purified and concentrated by an amine
extraction process to produce a crude thorium product. The crude product
is subsequently refined by TBP (tributyl phosphate) solvent extraction
to yield reactor-grade ThNT.

It should be emphasized here that the chemical flowsheets utilized
are conceptual in nature and have not been demonstrated on a pilot scale
with all of the process steps operating in tandem. We assumed that the
mill and refinery would be colocated for the purposes of this study. It
is realized that the refinery could be geographically separated from the
mill if overall economics, availability of skilled labor, or material
resources dictate it. It was not the aim of this study to determine the

best overall process and equipment configurations.

3.3.2 The ore storage pile

 

An outdoor storage pile containing a 60-day supply (96 Gg) of ore
is assumed to be located about 60 m from the mill (Fig. IX.G.3-2, ref. 1).
The stockpile will have the form of a rectangular parallelepiped with a
base 100 x 32 m and a height of 15 m. The ore will be transported from
the stockpile to the ore crusher by front-end loaders. Due to thorium
decay, 220Rn will escape from the stockpile. Ore dusts will be generated

by the transportation associated with the stockpile.

3.3.3 Ore preparation

 

Ore conditioning consists of a series of dry crushing and wet grinding
operations preparatory to acid leaching. A gaseous radioactive effluent
(stream 3, Fig. 3.4) results from the release of all the 220Rp inventory

v and

in the ore, which is assumed to occur in the dry crushing operation
during its residence in the ore bins. Air from the dry crushing and the
ore storage bins is assumed to contain entrained radioactive particulate
matter which is removed by bag filters (stream 4, Fig. 3.4) before being

released to the stack.l»"

 

3.3.4 Sulfuric acid leaching

The wet ground ore is leached with sulfuric acid in order to solu-

bilize the thorium values.”»® Radon-220 is released from the leachers
28

as a consequence of the decay chain ??"Ra (3.14 x 10° sec) ~ 220gp

(55.6 sec). The leacher off-gases are scrubbed before being released
to the stack. Mechanical stirring rather than air sparging is assumed
to be employed in the leachers to minimize entrainment of liquid droplets

which contain soluble radionuclides.

3.3.5 Countercurrent decantation

The slurry from the leachers is passed through a liquid-solid
separation to recover the solubilized thorium values. The solubilized
thorium is transferred to the solvent extraction unit. The washed
residual solids are pumped to a tailings pond for storage. The tailings
pond, which contains 2327h daughters from the residual solids as well
as a small amount of unrecovered thorium, is a source of radicactive

effluents and is discussed in Sect. 3.3.11.

3.3.6 Amine solvent extraction

 

The leached thorium values are purified and concentrated by solvent
extraction, This is done utilizing a primary amine in a hydrocarbon
diluent with an alcohol additive to obtain desirable physical properties
for the extractant.%»2»6 Recycling the aqueous raffinate is employed
to reduce the process requirements for water and mitigate the problem
of disposing of a radioactive liquid effluent from the mill. About
5.7 x 1072 m3/sec (1.7 x 10° ft3/day) of aqueous raffinate is produced
by the amine extraction (Fig. 3.4). In our conceptual flowsheet, about
95% of the flow of this stream is assumed to be recycled to the counter-
current leaching and washing operations. Assumption of 95% recycle of
this stream may be optimistic and requires experimental verification.
There is not enough information available to determine whether recycle

is severely hampered by buildup of deleterious impurities.

3.3.7 Stripping
Thorium is stripped from the loaded organic extractant by an aqueous
(NHy )2 COg solution.® Other aqueous salt solutions may be used for

stripping;S’8 however, the potential advantages of (NH,),CO03 will become
29

apparent in the discussion of subsequent operations. The stripped

organic is recycled after washing.

3.3.8 Steam distillation

 

The aqueous strip solution is decomposed by steam distillation to
yield a crude thorium solid product, and NH3 and CO, are recovered and
recycled.® Experimental work is needed to determine the percentages

of the NH; and CO, that may be recycled and to demonstrate feasibility.

3.3.9 Filtration

The crude Th(CO3)> product of the milling operation is filtered and
washed to remove the (NHL)»S0y, which is treated with Ca(OH), and steam-
distilled to recover the NH3.6 Thorium carbonate undergoes further
purification in the refinery to produce reactor-grade Th(NOj3),*4H,0. Over-
all recovery of thorium through the milling process is estimated at
91%.°3

3.3.10 Thorium refining

 

The Th(CO3)2 mill product (stream 7, Fig. 3.4) is dissolved in HNOjg
and subjected to a solvent extraction cycle using 30%Z TBP in normal paraf-
fin hydrocarbon diluent as the extractant (Fig. 3.5). Thorium is obtained
from a stripping column as a dilute HNO3 solution which is concentrated
and crystallized to obtain reactor-grade Th(NO3),;*4H,0. The organic
extractant phase will be recycled in this operation. Packaging of the
ThNT would generate airborne radioactive particulate matter. Before air
from this operation is released to the stack, it 1s passed through a bag
filter and then through an HEPA filter. Thorium recovery for the refining
cycle is estimated to be 99.5%.7

Aqueous solutions of nitrate wastes (streams 2 and 3, Fig. 3.5)
are produced in the refinery and are impounded separately from the mill
tailings. The best method for impoundment has not yet been determined;
but an example ;f an acceptable method? may be a neutralization of the
combined waste streams to immobilize any soluble radionuclides and sub-
sequent impoundment of the wastes in a barrier-lined evaporation pond.

Although the present study does not deal with liquid wastes, those future
30

investigations which do should take cognizance that experimental infor-
mation is needed in regard to (1) the radionuclide and chemical composi-
tion of the aqueous nitrate wastes and (2) the possible process options
for recycle of nitric acid and water, and the percentages of recycle of
these waste components that are likely to be attained using these options.
In the conceptual flowsheet for the refinery (Fig. 3.4), it was assumed
that significant amounts of the nitric acid and water could be evaporated
or distilled and recycled. However, it is not known whether deleterious

impurities might be introduced into process streams by this recycle method.

3.3.11 The tailings pond

 

Large quantities of liquid and solid wastes are produced in the
milling of thorium ores. About 1 kg of solids and 1.5 kg of liquids will
be produced per 1 kg of thorium ore processed. This waste is impounded
in a tailings pond within the restricted mill area where the solids separate
out and are eventually allowed to dry. The residual dry solids are per-
manently impounded on this site. Since approximately 1.6 Gg/day of solids
contains about 0.23 TBq (6.3 Ci) of radicactivity from the decay of
232Th, at the time of discharge the amount of activity available over the
assumed 20-year life of the mill operation is appreciable. The tailings
pond is a potential source of airborne radiocactive effluents due to
(1) the release of 220Rn and (2) wind-generated radiocactive dusts from
the dry solids. There is also a possibility of other types of radio-
nuclide source terms because of the potential for seepage of liquids
containing soluble radionuclides from the tailings pond into the sur-
rounding terrain. Soluble radionuclides may also be present in the
liquid phase of the mill wastes. If the solubilities of 2327h, 226Ra,
and 210pp in liquid wastes from uranium mills" are assumed to be repre--
sentative of the solubilities of the corresponding radionuclides in the
thorium mill waste liquids, the appropriate values for this case are:

4.11 MBq/m3 for ?32Th, 41 Bq/m? for 2?28Th, 70 MBq/m® for 22"%Ra, 5.14

MBq/m3 for 228Ra, and 290 MBq/m3 for 212Pb. Experimental data are needed
to determine whether the analogy with the pond liquor for uranium mills

is correct. The absence of certain elements such as barium in thorium ores

could apptreciably increase the solubility of radium. Recommended practices
31

in the siting, construction, and management of tailings ponds to minimize
release of radiocactive effleunts have been described previously,1=”’9’10
and these have been utilized in designing the pond described here. It
was outside the scope of this study to determine radionuclide source terms
resulting from seepage of liquids.

The impoundment is formed by constructing a dam on terrain with
favorable topographical and geological features to minimize the potential
for seepage. At normal liquid discharge rates of mills in the early stages
of the operation, the tailings solids will be covered by liquid. The
combined effect of increasing tailings volume and water evaporation will
eventually expose the tailings solids. During mill life, measures are
taken to prevent the solids from completely drying and becoming subject
to wind erosion. During the time liquid waste is present in the tailings
pond, a potential exists for the seepage of soluble radionuclides into
the surrounding terrain. 1If this seepage reaches the local aquifers, it
becomes a radiocactive liquid effluent., Careful siting and construction
of the tailings pond will minimize seepage. Monitoring for radiocactive
seepage with provision for its collection and return to the tailings
pond is employed in the design and is used as a control measure. Again
it is emphasized that this study does not deal with the potential for
liquid waste releases and its site-specific aspects, particularly the
potential for seepage through the bottom of the tailings pile and for
horizontal movements that might reach surface streams.

At the end of the mill operation, the tailings pond is permitted to
dry in a controlled manner so that only a relatively small area of dry
tailings is exposed to the atmosphere at any time and is thus subject
to wind erosion. After drying is completed, the active residue is
covered with a layer of protective material sufficient to substantially
reduce the escape of 229Rn to the atmosphere and to immobilize the dry
tailings with respect to wind erosion. Because of the relatively short
half-1life of 220Rn (55.6 sec), only about 0.30 m (v1 ft) of earth cover
is required to reduce its emission by a factor of ~OE/. The stability
of the dry tailings pile and its covering with respect to geological

and climatological factors is beyond the scope of this study.
4

10,

32

3.4 References

Energy Research and Development Administration, Final Environmental
Statement, Light-Water Breeder Reactor Program, ERDA-1541, Vol. 4,
Appendix 1X-G, June 1976.

G. B. Peck and L. B. Birch, Mining Methods and Production Costs,
USAEC AEC-RA-12, Grand Junction, Colorado (1968).

Reconnaissance Geologic Map Showing Distribution of Thorium Veins,
Lemhi County, Idaho, and Beaverhead County, Montana (south half).
Provided by Eugene W. Grutt, Jr., Manager, Grand Junction Office,

Department of Energy.

M. B. Sears, R. E. Blanco, R. G. Dahlman, G. S. Hill, A. D. Ryon,
and J, P. Witherspoon, Correlation of Radiocactive Waste Treatment
Costs and the Envirommental Impact of Waste Effluents in the
Nuclear Fuel Cycle for Use in Establishing "as Low as FPracticable"
Guides — Milling of Uranium Ores, ORNL/TM-4903, Vol. 1 (May 1975).

S. R. Borrowman and J. B. Rosenbaum, Recovery of Thorium from Ores
in Colorado, Idaho, and Montana, Bureau of Mines Report of Investi-

gation RI 5916 (1962).

J. R. Ross and D. R. George, Metallurgical Amenability Tests on
Idaho-Montana Thorium Ores, Bureau of Mines Research Report 62.1
(November 1966).

G. F. Smith, Purex Plant Chemical Flowsheet for the 1970 Thorium
Campaign, ARH-1748 (July 10, 1970).

D. J. Crouse, Jr., and K. B. Brown, '"The Amex Process for Extracting

Thorium Ores with Alkyl Amines," Ind. Eng. Chem. 51: 1461-64 (1959).

U.S. Envirommental Protection Agency, Office of Radiation Programs,
Envivonmental Analysis of the Uranium Fuel Cycle, Part I — Fuel

Supply, EPA-520/9~73-003-B (October 1973).

U.S. Environmental Protection Agency, Office of Radiation Programs,
Environmental Analysis of the Uranium Fuel Cycle, Part IV -~ Supple~-
mentary Analysis 1976, EPA 520/4-76-~017 (July 1978).
33

4, GENERATION OF SOURCE TERMS

4.1 Mining
4,1.1 Radon-220

Release of 220Rn from a thorium mine will depend on several physical
and chemical characteristics of the ore plus the amount of exposed ore
in the mine. It is assumed here, as in ERDA~1541,1 that 3 acres of
thorium-bearing ore containing the equivalent of 0.5% ThO;, are exposed
in one or more pits being worked to supply 1.6 Gg/day (1600 metric
tons/day) of ore to the mill. There appears to be no information in
the technical literature relating to the measurement of 220Rn release
from vein-type ore deposits. Radon-220 release as reported in ERDA-1541
was calculated by assuming that the characteristics which control the
release from thorium ore are the same as those of a sandstone uranium
ore from Ambrose Lake, New Mexico.! Radon-222 release from this sand-
stone was reported at 2.16 mBq/cm?+sec (0.0583 pCi/cm?+sec) by Schroeder
and Evans. Using an expression developed by Culot and Schaigerl’2
and correcting for differences of 2%22Rn and 229Rn half-lives and of the
concentration of their radium parents in the ores, a flux rate was cal-
culated for 220Rn of 1.32 kBq/m%-sec (3.56 x 10" pCi/m?-sec), or a
total of 16 MBg/sec (4.32 x 108 pCi/sec) from 3 acres of exposed ore in
the open-pit mine. Additional details of the calculation of 220pn flux

from the mine are shown in Appendixes 2 and 3.

4.1.2 Fugitive dust

A number of activities at the mine site will contribute to entrain-~
ment of dust in the air. In most envirommental statements, dust formation
and control is treated only in a qualitative manner by stating that
appropriate measures will be taken to meet federal and state air quality
standards with the expectation that the off-site effects will be negli-
gible. Information upon which to make a quantitative determination of
the amount of fugitive dust which will be generated is limited, and at
best a number of assumptions must be employed. However, in spite of

the required assumptions, a source term for fugitive dust generation at
34

the mine site is calculated as part of this analysis. Movement of heavy
equipment, drilling, and blasting will contribute to generation of
fugitive dust at the mine. A major portion of dust from vehicles will
come from movement of front—-end loaders and ore haulers. Front-end
loaders of 3 m® (4 yd3) capacity would make 296 "trips" per day, amounting
to about 18 km (11 miles) to move 1.6 Gg (1600 metric tons) of ore.
Concurrently, 35 Mg-capacity (35-metric ton) ore trucks would make 46
trips amounting to 27 km (17 miles). As shown in Appendix 4, the amount
of dust raised by vehicular traffic can be estimated from the speed and
distance traveled.® At an estimated average speed of 8.9 m/sec (20 mph),
about 450 g (1 1b) of dust will be injected into the air for each mile
traveled if the surface is dry, resulting in generation of about 13 kg
(29 1b) of dust per day. Other activities at the mine will double this
to about 26 kg/day (58 1lb/day). The expected dampness of the ore plus
routine sprinkling of the mine area with water should reduce the rate of
dust generation by about 50%.3 The concentration of thorium in the air-
borne dust will be further reduced to about half that of the ore by
dilution with rock containing no thorium. An estimate of the contribution
of the mine dust to airborne activity is given in Table 4.1. For lack
of the necessary information, no attempt was made to estimate wind-blown
loss of ore dust from trucks in tramsit to the mill.

Table 4.1. Radioactivity contained in dust generated

by mining operations

Radicactivity, Bg (pCi)

 

Isotope 00—

 

Per g of ore Per 13 kg (29 1b) dusta/day
2320, 1 (s.eEnt 1.2E5 (3.2E6)
128p, 18 (4.8E2) 1.2E5 (3.2E8)
228, 18 (4.8E2) 1,2E5 (3.2E6)
2287y, 18 (4.8E2) 1.2E5 (3.2E6)
224pa 18 (4.8E2) 1.2E5 (3.2E6)
220, 18 (4.8E2) 1.2E5 (3.2E6)
2l6pg 18 (4.8E2) 1.2E5 (3.2E6)
212py, 18 (4.8E2) 1.2E5 (3.2E6)
2124 18 (4.8E2) 1.2E5 (3.2E6)
212p, 11 (3.1E2) 7.5E4 (2.0E6)
2087q 6 (1.7E2) 4. 2E4 (1.1E6)

a . . s
Concentration of Th in fugitive dust is diluted by dust
containing no Th to about half that of the ore.

Dy 8E2 = 4.8 x 102,
35
4,2 Milling

4.2.1 Introduction

Methods of calculations and calculated values of the airborne radio-
active source terms from the model mill and refinery are presented in
this section. Because there were no experimental data available for
making source term calculations on thorium milling and refining, we
made the assumption that the distribution of radionuclides throughout
the liquid or solid process streams was essentially identical with
that of a uranium wmill and refinery.L+ In the case of the gaseous
radionuclide 22%Rn, we assumed it had the same escape potential from
the ore and tailings as does 22ZRn (after correcting for half-1life
difference) in the processing of sandstone ores of uranium. This assump-
tion regarding 220Rn emission may lead to an overly conservative estima-
tion of the source term, since the escape factors from different types of
minerals vary greatly.?> Clearly, experimental data are needed for many
of the operations in the thorium milling and refining flowsheet. Areas
requiring experimental data will be pointed out in the subsequent
discussions.

Even with the uncertainties of the assumptions used in estimating
source terms for thorium milling and mining, we believe our study shows
that the airborne radionuclide releases for a thorium mill and refinery
are comparable to that of a uranium mill and refinery of equivalent ore
capacity and design. In order to determine the values of source terms
with a reasonable degree of confidence, experimental data are needed
regarding the escape of 220Rn and the distribution of all members of the
thorium decay chain throughout the process streams.

Source terms estimated for the ore storage pile, the mill and
refinery, the tailings beach and pond during 20-year operation of the
mill, and the covering of the dry tailings at the end of mill life are
shown in Table 4.2. Concentration of the radionuclides in the ore and
tailings as used in source term estimations were calculated by the ORIGEN
code® and are given in Appendix 4. A summary of these concentrations is

given in Table 4. 3.
36

Table 4.2, Estimated source terms for operation
and closing of the model mill

 

Source term” (Bq/sec)

 

 

 

 

Tailings beach Covering dry
and pond tallings
Mill
Ore +

Nuclide handling refinery Montana Colorado Montana Colorado
2321y 0.52 0.18 0.037 0.33 0.37 0.37
228, 0.52 0.18 0.33 3.0 3.3 3.3
228p0 0.52 0.18 0.33 3.0 3.3 3.3
228t1p 0.52 0.18 0.26 2,2 2.4 2.4
224Ra 0.52 0.18 0.26 2.2 2.4 2.4
216pg 0.52 0.18 0.26 2.2 2.4 2.4
212p5 0.52 0.18 0.26 2.2 2.4 2.4
212py, 0.52 0.18 0.26 2.2 2.4 2.4
20873 0.18 0.07 0.09 0.8 0.8 0.8
212p 0.33 0.11 0.18 1.4 1.6 1.6
220g, 1.57° 3. 6E7 1.2E7 1.6E7 1.1E7 9.3E6

 

2} Bg/sec = 27 pCi/sec.
b 587 = 1.5 x 107,

Table 4.3. Values of concentrations of radionuclides in thorite
ore and in dry mill tailings that were employed in
calculation for 20-year mill operation

 

Concentration (kBq/kg)

 

 

Nuclide ore Bulk Tailings (<80 um
tailings particle size)?
232yp 17.7 1.6 4.0
2281y 17.7 10,57 26. 87
2285, 17.7 17.7 45.1
228pg 17.7 17.7 45.1
224ga 17.7 17.7 45.1
220pq 17.7 17.7 45.1
216pg 17.7 17.7 45.1
212p, 17.7 17.7 45.1
21l2pj 17.7 17.7 45.1
212p, 11. 4 11.4 29.0
20871 6.3 6.3 16.1

 

%pssumes nuclides are of a concentration that is 2.55 times
greater than the average in the bulk tailings (ref. 4).

P raximum 228Th concentration in aged tailings (10.5 kBq/k%)
occurs approximately three years after discharge because of 232Th
decay. In calculating source terms, a correction factor allowing
for the age of the tailings was utilized. Maximum concentration
of other nuclides 1s at discharge.
37

4.,2.2 The ore stockpile

 

The ore stockpile is assumed to contain 96 Gg of ore, which is
equivalent to a 60-day supply for the model mill and is assumed to be
in the form of a rectangular parallelepiped with a base 100 x 32 m and
a height of 15 m. Its surface area is 7160 m?. The ore stockpile is
a source of airborne effluents due to radioactive ore dusts and the
emission of 22%Rn. WNo model was available for calculation of a source
term resulting from the action of winds on the ore pile. The only
source terms calculated were those of 2?0Rn emission and particulates

resulting from the movement of ore to and from the site.

4,2.2.1 Radon-220 emission. The 220Rn emission from the ore

 

stockpile was calculated in the following manner, using Eq. (5) developed
in Appendix 2. The 220Rn flux from the surface of the ore stockpile is
given by

3, = 4550 (kp~ 1y 1/2 | (1)
where

(xp~ 1) = 5E-6 m?/sec

(a term related to the diffusion of 42%Rn in the porous medium; we

assumed the wvalue for coarse sand“),

0 = bulk density of the ore stockpile, 2E3 kg/m?> .
Substitution of these values into Eq. (1) gives

Jo = 2.04 kBq/m?%ssec .
The emission of 229Rn from the 7160-m? surface is

220pn = 7160 x 2.04 = 14.6 MBq/sec (3.94E8 pCi/sec) .
38

4,2,2.2 Ore movements at the mill site. Ore is transported from

 

the stockpile to the mill by front-end loaders, and it is reasonable
to assume that some spillage will occur. The spilled ore will be further
pulverized by the road traffic and impacted into the unpaved road. Dust
subsequently raised by traffic on this road will constitute a source
of airborne radioactivity. The calculation of this source term is made
in a similar manner to that for movement of ore at the mine site.

A front-end loader transporting 5.4 Mg of ore per load will require
296 "trips" to move 1.6 Gg of ore per day from the stockpile to the mill,
an assumed distance of 60 m one way or a round trip of 120 m. This is
equivalent to an average speed of 0.41 m/sec. The road speed of the
transporter is assumed to be 8.9 m/sec.

The dust generated by this traffic3 as a function of vehicle speed

is given by expression (2):

76(1.158)° (2)

=2
I

where

vehicle speed in m/sec

w
it

Substitution for s gives E = 280 mg/m of traffic, and the mass of dust W

generated per day is given by

E>
I

E(d) , (3)

where

o
I

total distance traveled per day.

Substitution into (3) gives 115 mg/sec (22 1b/day) for a dry surface.
Wetting the unpaved road is assumed to reduce dusting by 50%, that is,
to 58 mg/sec. The rvoad dust generated in this manner is assumed to have

a thorium content approximately 507% of that of the ore. The source term
39

for 232Th is calculated to be 520 mBq/sec. Source terms for the release

of the other radionuclides from ore movements are shown in Table 4.2.

4.2.3 Dry crushing and sizing

 

All of the 22%Rn inventory is assumed to be released during the

crushing operation.l

Ore particulate releases were calculated assuming
that 0.008% of the ore was released as a dust! to bag filters which
operate at 99.3% efficiency.1 This assumption implies that 0.77% of the
dust entering the filters was released to the atmosphere; thus the
fraction of ore that is airborme is 5.6 x 10~7., The source term was

calculated to be

220g,

17.7 kBq/kg ore x 18.5 kg/sec

328 kBq/sec (8.9E6 pCi/sec) .

An example calculation of the particulate source terms is as follows:

232TH = 328 kBq/sec x 5.6E~7 = 0.18 Bq/sec (5.0 pCi/sec) .

The filter burden of ore dust for this operation is about 1.5 g/sec.

4.2.4 Acid leaching of ore

 

Radon~220 produced by the decay of 22%Ra during the 12~hr leaching
period is considered to be the only radiocactive emission from this opera-
tion. It requires only about 10 min for the %2%Rn (t1/2 = 55.6 sec)
to reattain secular equilibrium after it is released. Therefore, it was
assumed that process holdup in bin storage allowed sufficient time for
220Rn to reattain secular equilibrium. For purposes of contrast, <22Rn
present in uranium ore requires about 40 days to reattain secular
equilibrium.

The source term for 220Rn was calculated by the following equation:

220 = . . . .
Rn = Cp = Agpg = E = w - £, (4)
40

where

CRn = gecular equilibrium concentration of 220Rn, 17.7 kBq/kg ore,

Aosg = decay constant for 229Rm, 0.0125/sec,

t = leaching time, 4.32 x 10" sec,
w = mass of ore processed per day, 1.6 Gg, (18.5 kg/sec),
f =0.2.

The factor f corrects for the decay of 220Rn in the time period between
its generation and release.! Using Eq. (4), the calculated value of the
220Rn source term is 35.3 MBq/sec. Technology is available for increasing
the holdup (factor f) so that the 2?ORn release is negligible, provided
detailed cost~benefit analyses justify it. However, it was outside the

scope of the present study to make this assessment.

4.2.5 Other mill operations

 

The remaining mill operations, including amine solvent extraction,
stripping, steam distillation, and filtration are not regarded as sources

of airborne radioactive emissions.

4,2.6 Thorium refining

 

The fraction of Th(NO3),+4H,0 dispersed as dust is assumed to be
the same as the fraction of yellow cake dispersed as dust in a uranium
milling operation. This quantity, 1.25% of the product, becomes airborne
to the filters.'' The bag filters operate at 99.3% efficiency, which is
equivalent to a product loss of 0.7%Z. An efficiency of 99.95% was
assumed for the HEPA filter located downstream of the bag filter.
Thorium recovery through refining but not including packaging is assumed

to be 99.5%. The source term for 232Th was calculated using Eq. (5):

232Th = (W) (R) (D) (L) (?32Th) (w) , (5)

where

weight of Th in refinery feed, 7.4 x 1072 kg/sec,

=]
I

=
i

Th recovery in refining, 99.57%,
41

D = suspended fraction of Th~bearing dusts, which is 1.257% of the

refined product,
L, = Th loss through bag filters, 0.77%,

H = fraction of particulates passing through the HEPA filter,
5 x 107",

(232Th) = thorium activity = 4.03 MBq/kg.

The resulting source term for 232Th or 228Th 1g 13.0 mBq
(35.0E~2 pCi/sec).
Due to lack of data on dusting characteristics of Th(NOj3),*4H,0,
it was assumed that they are similar to those of uranium yvellow cake
powder. If this assumption is not supported by later experimental data,

the calculation of a more realistic source term can be made easily.

4,2.7 Source terms for the tailings impoundment

 

4,2.7.1 Introduction. The tailings impoundment is a source of
220Rn and airborne particulates during both mill operation and final
covering of the dry tailings after the mill operations have ceased.
A 220Rn source term results from a flux generated at the surface of
both the exposed dry tailings and the pond. Soluble 22%Ra in the pond
liquor is responsible for the flux at the surface of the pond. We
assumed there would be a negligible 220Rn flux resulting from wet tailings
underneath the pond. The relaxation length for diffusion of 220Rp
(tl/z = 55.6 sec) in water is about 300 ym. The flux resulting from
this source would be negligible in comparison to those from the dry
tailings beach and from the pond surface due to the “2%“Ra dissolved in
the pond liquid. The particulate source terms resulted from a flux term
generated by the prevailing winds at the specific site. The flux term
for 220Rn was calculated by the diffusion model previously described
(Sect. 4.1 and Appendix 2), wherecas the particulate flux term was cal-
culated from the saltation model.’ Since the source terms are a product
of a flux term and an area term, it was necessary to develop a model for
determination of the average surface area of the dry tailings beach and
of the pond during mill operations and during final covering of the

tailings pile.
42

The general features of the tailings impoundment basin were previously
described in Sect. 3.3.11. Details of the development of the calculational
models for the estimation of the average surface area of dry tailings
beach and the pond are given in Appendixes 6, 7, and 8. The rate of
exposure of dry tailings and the growth of the surface area of the pond

are a function of the evaporation rate and the geometric configuration

8 at the Montana and

of the tailings impoundment. Evaporation rates
Colorado sites were estimated to be 19 and 29 nm/sec respectively.

The combined effects of increasing tailings volume and water evaporation
eventually expose the tailings (Table 4.4) during mill operations. After
mill operations have ceased, natural evaporation is utilized to dry up

the pond so that covering of the residual tailings can be accomplished
(Table 4.5). Covering may begin before the end of mill life or after mill

operations have ceased. Note that the model tailings pond employed in

this study never reaches a ''steady-state' surface area during mill

 

 

 

operations.9
Table 4.4. Estimation of areas of the dry tailings
beach and pond during mill operation for the
hypothetical Montana and Colorado locations
Dry beach area (w2 x E3) Pond area (m? x E4)
Time (years) Montana Colaorado Montana Colorado

1 0 0 23% 22

2 0 0 31 29

3 0 0 37 34

4 0 0 42 38

5 o ¢ 46 41

6 0 0 49 44

7 0 Sb 52 46

8 Q 7 55 48

9 o 18 57 50

10 0 25 59 51

11 ¢ 32 62 53

12 0 39 64 54

13 0 47 65 55

14 0 54 67 56

15 4 61 68 57

16 8 68 70 57

17 12 76 71 58

18 16 83 72 59

19 21 91 73 59

20 26 98 74 60
Average 4 36 57 49

 

%Read as 230,000 m2.
bRead as 5000 m?.
43

Table 4.5, Estimation of areas of dry beach and pond as a function
of time after closing down mill coperaticns at the hypothetical
Montana and Colorado locations

 

 

 

 

Dry beach area (m? x E&4) Pond area (w2 x E4)
Time (years) Montana Colorado Montana Colorado
1 9@ 24 62 31
2 16 33 50 13
3 23 40 38 0
4 30 40 25 Q
5 36 40 i3 Q
6 40 40 0 0

 

Read as 90,000 m2.

During mill operating life, it was assumed that chemical sprays and/or
wetting were utilized to reduce the amount of airborne particulates and
that covering would commence near the end of mill life. This procedure
was assumed to reduce the average effective dry tailings area by about
90%. For the Montana and Colorado sites the reduced areas were 4.0E2 and
36E2 m? respectively. After the end of mill life, it was assumed that,
on the average, about 4.0E3 m? of dry beach surface was exposed per year
during the tailings covering process at each site. We assumed that
whenever 4.0E3 m? of dry beach (9 x 440 m) was exposed by evaporation,
covering of the tailings pile commenced and was carried out at a rate
commensurate with the rate of generation of an additional 4.0 x 103 m?

of fresh tailings surface.

4.2.7.2 Source terms for the emmission of 220Rn. The flux terms
for 220Rn for the surface of the dry tailings and the pond were calculated
using the diffusion equation previously described. The calculated flux

terms were

Jo (tailings) = 1.67 kBq/mz-sec .

J, (pond) = 19.3 Bq/mZ-sec .
Details of the flux calculations are given in Appendix 9. The calculated
source terms for the 20~year mill operation and covering of the tailings

pile at the end of mill life for the hypothetical Montana and Colorado

mills are given in Table 4.6,
b

Table 4.6. Source terms for 2%0Rn during mill operating life and during final
evaporation of the pond and covering of the dry tailings after the mill 1s closed

 

 

 

Area of Area of Source term (Bq/sec x E5)
Hypothetical location dry tailings pond
(m?2 x E2) (m? x E4) Dry tailings Pond Total
Montana
Mill operating life 44 57 7 110 117
Evaporation of pond and 40 38 40b 73 113
covering of tailings
Colorado
Mill operating life 36 49 60 95 155
Evaporation of pond and 40 27 40b 52 92

covering of tailings

 

aRead as 4 x 102 n?,

A factor of 0.6 was used to correct for decay of 22%Ra parent.

It is possible to contour the surface of the tailings pile near the
end of mill 1life, so that the time required to dry out the pond is
decreased. However, this would not decrease the source terms significantly.
The equivalent area of dry tailings would have to be exposed during mill
life to accomplish it. There may be economic advantages to shortening
the on—-site activities as quickly as possible after mill operatiomns
cease. Again, it is pointed out that it was not the object of this study
to determine the optimum operational methods, processes, and equipment

for the thorium mill and vefinery.

4.2.7.3 Source terms for airborne particulate emissions. The

 

source terms for radiocactive emissions from the milling waste solids

are due to wind-borme dusts from the dry tailings beach. During mill
operations the tailings deposit is either kept wet or treated chemically
to prevent dusting. These procedures may not be completely effective,
and it may be expected that a small dry beach will be subject to wind
erosion. At the close of mill operations, the taillings impoundment

is permitted to dry in a controlled fashion and at this time wmay be
subject to wind erosion.

It was assumed that the principal mechanism for the generation of
dusts is saltation, a process whereby the larger wind-drivem particles
with diameters >80 um impact on the smaller particles and cause their
suspension in the air. The application of saltation theory permits the

calculation of the amount of wind-borne dust generated and consequently
45

the amount of wind-borne radioactivity.7 The working equations for

galtation calculations are

d_ = 36.22V2 (6)

v, = 0.166(ds)0-5 , (7)

q = 9.318 x 10“3(ds)0-5 (V’-V£)3; v>v), (8)

Q, = Kqg , (9)
where

dt = threshold diameter of the largest particle moved by the wind,

um,

V = wind velocity at 1 m above ground, m/sec,

dS = gverage diameter for saltation for wind velocity V, um,
Vt = threshold wind velocity for ds’ m/sec,

q = saltation rate (q = 0 for V < Vt)’ kg/m-sec,

QS = particulate suspension rate, kg/mz-sec,
K =

1 x 10>, m ',

The numerical values used in these equations result from various
experimental values and estimates. The calculations are based on
knowledge of the applicable wind velocities and the particle size dis-
tribution for the tailings (Table 4.7). Saltation cannot be caused by
particles <80 um in diameter, and since the tailings have a negligible
concentration of particles >600 um in diameter, the particle size range
leading to saltation of the tailings is established. First, the
threshold diameter, dt, for each wind velocity is determined [Eq. (6)],
and then the saltation diameter, dg, is calculated from the weighted
average of particle diameters between 80 um and d¢ (Table 4.8). The
threshold wind velocity, Vi, for each dg is then calculated by use of

Eq. (7). These values along with corresponding wind velocities are used
46

 

 

 

 

 

 

Table 4.7, Wind velocities and particle size distribution
used in saltation model calculation
Wind velocities
Wind
velocities 1.85 3.14 4.98 7.02 9.23 11.08 12.93
{m/zec)
Frequency 22 36 18 5 1.4 0.51 0.18
(%)
Tailings particle size distribution (ref. 4, p. 230)
Diameter 44 61 125 250 500 840 <10 10-80%
(um)
% less than
stated size 26.6 27.6 38.1 65.4 96.8 99.5 10. 23.2

 

aCalculated from
d = particle diameter

linear regression equation for particle size distribution.
(ym); ¥ = wt. % less than d.

Table 4.8. Calculated suspension rates as a function of
wind velocity, using the saltation model

d = 0.1711x1-753;

 

 

 

Threshold
Wind Threshold Saltation wind Saltation Suspension
veloclty (v) diam (dt) diam (ds) velocity (Vt) rate {q) rate (Qs)
(m/sec) (um) (pm) {m/sec) (kg/m°sec) (kg/m-~=ec)
1.85 124 102 1.68 4.62E~7% 4.628-12
3.14 357 197 2.33 6.95E-5 6.95E~-10
4,98 898 270 2.73 1.74E-3 1.74E-8
7.02 1784 270 2.73 1.21E-2 1.21E-7
9.23 3086 270 2.73 4.20E~-2 4 ,20E-7
11.08 4447 270 2.73 8.91E-2 8.91E-7
12.93 6055 270 2.73 1.62E-1 1.62E-6
%Read as 4.62 x 1077,
to calculate the saltation rate, q, with Eq. (8). Finally, the suspen-

sion rate, Qg, is obtained
according to wind velocity

to obtain an average (Qgy)

(9).

frequencies appropriate to the specific site

using Eq. These Qg values are weighted

used in the source term calculations (Table

4.9).

was 22.8 ug/m®-sec.

The average value of Qg weighted for wind velocity distribution
Source terms are calculated by multiplying the
value of Quw by the radionuclide concentration times the area available
for saltation, according to the following equation:

source term = {(2,28E-8) Cr'AS , (10)
47

Table 4.9. Suspension rates weighted for wind
velocity distribution

 

Wind Wind Suspension Weighted
velocity (v) frequency rate (QS) suspension
(m/sec) (%) (kg/mZ-sec) rate (Q

)
(kg/m2°se§y

 

b

i.85 22 4.52E-12 1,02E~12
3.14 36 6.95E~-10 2.50E~10
4,98 18 1.74E-8 3.13E-9

7.02 5 1.21E-7 6.05E~09

9.23 1.4 4. 20E-7 5.88E~9

11.908 0.51 8.91E~7 4 .54E-9
12,93 0.18 1.62E-6 2.92E-9

 

The average of the values in this column is 22.8 ug/m?-sec.
bRead as 4.52 x 10712,

2
it

radionuclide concentration, Bq/kg,

>
0
H

area available for saltation, m?.

Source terms estimated from this equation are shown in Table 4.2. Values
of C, listed in Table 4.3 for the <80 um particle size fraction were used
in calculating the source terms during the 20-year operation of the mill.
All of the particulate radionuclide concentrations except 232Th were
reduced because of radioactive decay. The reduction factors utilized

to correct the concentration for decay were as follows:

Nuclides Factor
228pa, 22Bpc 0.8
Remaining nuclides 0.6

(except 432Th, 228Th)

The reduction factors and the Cy values for 228Th were estimated from
graphical plots of the data in Table A.5.2, Appendix 5. Values of Ag

utilized in the calculations were the following:

Montana Colorado

20-year mill life 4.0E2 m? 3.6E3 m?
Post-mill life 4.0E3 m? 4.0E3 m?
48

4.2.7.4 Long-term stabilization of the dry tailings pile. A

 

source term for the covered dry tailings pile after the mill operations
have ceased and the residual pond liquid has been evaporated was not
calculated. As pointed out in Sect. 3.3.11, in principle the 220Ryp
(172 = 55.6 sec) source term can be reduced by a factor of about 5E7
with the use of about 0.3 m (1 ft) of earth cover. Also, the covering
would reduce the airborne particulate source term to near zero. Such
source terms would be negligible in relation to those calculated for our
model plant during mill operation and final impoundment operations.

The stabilized thorium mill tailings would not present the potential
long-term radionuclide source terms as do the uranium mill tailings,
which contain 22°Ra (t1/p = 1622 years) and its secular equilibrium
daughter 222Rn (t1/2 = 3,82 days). The longest—-lived daughter in the
232y decay chain is 228Rg (t1/2 = 5.75 years). After a decay period
of about ten half-lives, the tailings pile will be equivalent to a thorium

ore body containing about 0.057% thorium oxide.

4.3 References

1. Energy Research and Development Administration, Final Environmental
Statement, Light-Water Breeder Reactor Program, ERDA-1541, Vol. 4,
Appendix IX-G, June 1976.

2. M, V. J. Culot and K. J, Schaiger, "Radon Progeny Control in
Buildings,'" Colorado State University, Fort Collins, C00-2273-1
(May 1973).

3. PEDCO-Environmental Specialists, Inc., "Investigation of Fugitive
Dust — Sources, Emissions, and Control," PB 226 693, Cincinnati,

Ohio, May 1973.

4., M., B. Sears, R. E. Blanco, R. G. Dahlwan, G. S. Hill, A. D. Ryon,
and J. P. Witherspoon, Correlation of Radiocactive Waste Treatment
Costs and the Fnvirommental Impact of Waste Effluents in the
Nuclear Fuel Cycle for Use in Establishing "as Low as Practicable”

Guides — Mi1lling of Uraniwn Ores, ORNL/TM-4903, Vol. 1 (May 1975).

5. P. M, C. Barretto, R. B, Clark, and J. A, S. Adams, Physical

Characteristics of Radon-282 Emanation from Rocks, Soils, and
49

Minerals: Its Relation to Temperature ond Alpha Dose, the Natural
Radiation Envirowment II, Proceedings of the Second International

Symposium on the Natural Radiation Environment, August 7-11, 1972,
Houston, Texas, CONF~720805~-Ps, ed. J. A. S. Adams, W. M. Lowdeo,

and T. F. Gesell.

M. J. Bell, ORIGEN — The ORNL Isotope Generation and Depletion
Code, ORNL-4628 (May 1973).

M. T. Mills, R. C. Dahlmann, and J. S. Olson, Ground Level Air
Concentrations of Dust Particles from a Tailings Area During a
Typieal Windstorm, ORNL/TM-4375 (September 1974).

Climatic Atlas of the United States, U.S. Department of Commerce
(C. R. Smith, Secretary), Environmental Science Services Division,
(Robert M. White, Administrator), Environmental Data Service,
(Woodrow C. Jacobs, Director), June 1968, reprinted by the National

Oceanic and Atmospheric Administration, p. 63, 1974.

Humble 0il and Refining Company, Minerals Dept., Applicant's
Environmental Report, Highland Uranium Mill, Converse County,

Wyoming, Docket 40-8102 (July 1971).
50

5. RADIOLOGICAL ASSESSMENT METHODOLOGY

The radiological impact to man resulting from the operation of the
model thorium mining and milling complex is assessed by calculating
the dose to the maximally exposed individual and the total dose to the
population living within a 50-mile radius. There are several potential
pathways of exposure to man from radioactive effluents released to the
environment. These are illustrated schematically in Fig. 5.1. Radio~
nuclides enter the environment from a facility via either liquid or
atmospheric transport modes. They reach man through one or more col-
lectors (air, soil, or water) with possible reconcentration by animals,
crops, or aquatic biota. Pathways of human exposure include inhalation,
ingestion, immersion, land surface contamination, and submersion. Ulti-
mately, energy is deposited in human tissue by the radionuclides via
internal or external exposure.

Radiological impact is calculated as the 50-~year dose commitment,
to individuals or populations, in units of millirems or man-rems per
year of facility operation. The dose commitment is calculated for a
specific intake of radionuclide and is defined as the total dose to
a reference organ, resulting from a one-year exposure, which will accrue
during the remaining lifetime of an individual. For radionuclides
that have short biological or physical half-lives, the 50-year dose
commitment would be approximately the same as the annual dose rate.

For example, all of the dose commitment for %29Rn exposure (including
radon daughters) is received during the first year.

On the other hand, 232Th is eliminated from the body very slowly
and has a long half~life (1.4 x 10!0 years), so that an individual will
continue to receive a dose from the ingested material for many years
after exposure., Under these conditions, the approximate dose received
in the year that the radionuclide enters the body is obtained by
dividing the dose commitment by 50. Thus the average annual dose rate
is only 1/50 of the dose commitment. Tf an individual is exposed to
mill effluents for the 20-year operating life of the plant, his annual
dose rate during the twentieth vear 1s about 20 times the annual dose

rate for one year of exposure, and his total dose commitment is the
 

 

 

ATMOSPHERIC
RELEASE

51

      
       
  

NUCLEAR
FACILITY

IRRIGATION

 

FiSH

ORNL-DWG 78-15181

 

AGUATIC
RELEASE

 

 

 

 

 

1

 

INTERNAL

 

 

 

LAND
SURFACE

CONTAMINATION

(Y

-

 

SUBMERSION

 

v

 

 

EXTERNAL

 

 

SOURCE

mMoo£

COLLESTORS

ACCUMULATORS

PATHWAYS

TYPE OF EXPOSURE

T )

Fig. 5.1.

Exposure pathways to man.

summation of the 50-year dose commitments for each of the 20 years.

These generalized dose estimates are approximately correct for the con-

ditions cited. However,

a4 detailed calculation must be made to determine

a more precise value for the actual dose received in a given year.l
52

The exposed person is assumed to be an adult, 20 years of age,
having physiological parameters defined by the Intermational Commission
on Radiological Protection (ICRP).? In our report the terms "dose
commitment" and "dose'" are used interchangeably; each implies a 50-year
dose commitment. Doses to specific organs can vary comnsiderably for
internal exposure from ingested or inhaled radionuclides concentrated
in certain organs of the body. Estimates of radiation dose to the total
body and to major organs are, therefore, considered for all pathways
of internal exposure and are based on parameters applicable to the
average adult. Radiation dose to the intermal organs of children in
the population may vary from those received by an adult because of
differences in radionuclide metabolism, organ size, and diet.3

Population total~body dose estimates are the sums of the total-body
doses to individuals within 50 miles of the mine-mill complex. It is
assumed for the purposes of this report that radiation dose to the total
body is relatively independent of age;"“ therefore, man-rem estimates
are based on the total-body doses calculated for adults. Similarly, the
population dose estimates for the various organs are the sum of specific
adult organ doses for the individuals within 50 miles of the plant. The
man-organ—-rem estimates are also based on adult organ doses.

The AIRDOS-II computer code® was used to estimate 50-year dose
commitments from effluents released to the atmosphere. The AIRDOS-II
code is a FORTRAN-IV computer code that calculates the dose commitment
to individuals and populations for up to 36 radionuclides released from
one to six stacks. Site-specific annual average meteorological, popula-
tion, beef cattle, milk cattle, and crop data are supplied as input to
the computer code. OQutput data include ground-level radionuclide
concentrations in air and rate of deposition on ground and water surfaces
for each radionuclide at specified distances and directions from the
release point. From these values, doses to man at each distance and
direction specified are estimated for total body, GI tract, bone,
thyroid, lungs, muscle, kidneys, liver, spleen, testes, and ovaries,
via each of the five significant pathways illustrated in Fig. 5.1.

Dose calculations are made with the use of dose conversion factors

supplied as input data for each radionuclide and exposure mode. Dose
53

conversion factors for submersion in the gas-borne effluent, exposure

to contaminated ground surface, and intake of radionuclides through
inhalation and ingestion are calculated by the use of dosimetric criteria
of the TICRP and other recognized authorities. These factors are computed
and summarized in twe computer codes, one for external exposure,
EXREM~III,® and one for intermal exposure, INREM-II.’ Because recent
revisions have been made in the INREM-II data base, a number of dose
conversion factors used in this study are listed in Table 5.1 and
supercede those listed in ref. 7.

Radiocactive particulates are removed from the atmosphere and
deposited on the ground through mechanisms of dry deposition and
scavenging. Dry deposition, as used in this analyvsis, represents an
integrated deposition of radicactive materials by processes of gravi-
tational settling, adsorption, particle interception, diffusion, chemical,
and electrostatic effects. Deposition velocity values for particulates

range from 0.1 to 6.0 cm/sec.®

Based on an analysis of the effect of
deposition velocities on estimates of radiological impact, a value of

1 cm/sec is used for calculation of ground concentrations of radioactive
particles for this facility. Scavenging of radionuclides in a plume is
a process through which rain or snow washes out particles or dissolves
gases and deposits them on the ground or water surfaces. Methods for

estimating the scavenging coefficient can be found in Meteorology and

Atomic @nergz.B

 

Table 5.1. Dose conversion factors for total body, bone, and
lungs for radionuclides in the 2327h decay chain

 

Conversion factors (rems/uCi)

 

 

 

 

 

Total body Bone Lungs
Radionuclide Inhalation Ingestion Inhalation Ingestion Inhalation Ingestion
2321y 7.9 x 10! 1.4 8.7 x 10% 1.8 x 10! 2.3 x 102 1.1 x 107%
228pa 5.0 3.8 1.3 x 1pl 9.8 2.6 2.4 x 1073
228p¢ 5.1 x 10-% 2.7 x 2,6 x 1077 1.2 x 107% 1.3 x 1071 2.6 x 1073
2287y 1.4 x 10! 2.8 x 1071 6.9 x 101 3.3 3.7 x 102 1.0 x 107"
224pa 1.4 x 107! 1.0 x 107} 1.2 x 107} 1.6 x 107! 4.5 1.3 x 107

220pn 1.6 x 1077 0 0 0 1.1 x 1073 0
212py, 1.2 x 1072 4.2 x 103 6.5 x 1077 4.6 x 102 9.2 x 10~1 5.3 x 107%
2124 2.2 x 1077 9.0 » 107° 8.0 x 107 1.3 x 10™% 1.4 x 1071 1.3 x 1075
2081 2.3 x 1076 3.2 x 1076 1.0 x 1076 1.0 x 1076 7.2 x 1075 2.6 x 107

 
54

5.1 Additional Assumptions

Many of the basic incremental parameters used in AIRDOS-II indi-
vidual and population dose estimates atre conservative; that is, values
are chosen to maximize hypothesized intake by man. Many factors that
would reduce the radiation dose, such as shielding provided by dwellings
and time spent away from the reference location, are not considered.

It is assumed that persons remain unghielded at the reference location
100% of the time. Moreover, in estimating the doses to maximally
exposed individuals via the ingestion of vegetables, beef, and milk,
all the food consumed by this individual is assumed Lo be produced at
the reference location specified. Thus the dose estimated for the
maximally exposed individual in this and other studies using AIRDOS-II
is likely to be higher than doses that would occur in a real-world
situation.

A special case exists in the methodology for the calculation of
dose from 22%Rn which deserves further elaboration. For purposes of
this report, 220gn gas is released from four locations within the
mine-mil]l complex: the mine proper, the ore storage pile, the mill-
refinery, and the tailings beach. It was further assumed that the
nearest residence is located no closer than 1 wile from these facilities,
in the direction of the prevailing wind. Given the short half-life of
220gn (55.6 sec), we conservatively assumed in this study that all
220gp decays to airborne 212py particulates prior to crossing the
l-mile facility boundary. Doses listed in the results as due to
"220pn + D" (?20Rn + daughters) are therefore actually the result of
ingestion and inhalation of 212pp, for both the maximally exposed
individuals and the general populations. As confirmation of the accu-
racy of this approximation, doses were independently calculated both
for 220Rn gas alone and for 2!2pp suspended as dust (rather than created
by decay of airborne 220Rn) from the four site operations. Doses calcu-
lated for these cases were insignificant in comparison to %1%PL doses
generated from airborne 220Rn and were excluded from the tabulated
results.

Additionally, dose commitment to the lung, as computed for this

report via the INREM-II code7, is calculated as dose to the entire
55

lung, commonly identified as the "smeared lung' dose. Dose to the

bronchial epithelium region of the lung from ?2ORn daughters may be

higher than that to the entire lung. A discussion of this relationship

is available in Dunning et al., Vol. II.?

5.2 References

M. F. Sears, R. E. Blanco, R. G. Dahlman, G. S. Hill, A. D. Ryan,
and J. P. Witherspoon, Correlation of Radicactive Waste Treatment
Costa and the Environmmental Impact of Waste Effleunts in the
Nuclear Fuel Cycle for Use in Establishing "As Low As Practicable'
Guides — Milling of Uranium Ores, ORNL/TM-4903, Vol. 1 (May 1975).

International Commission on Radiological Protection, Report of

the Task Group on Reference Man, ICRP 23, Pergamon, New York, 1975.

G. R. Hoenes and J. K. Soldat, Age~Specific Radiation Dose Commit-
ment Factors for a One-Year Chronic Intake, NUREG-0172 (Novem-
ber 1977).

Federal Radiation Council, Fstimates and Evaluation of Fallout in
the United States from Nuclear Weapons Testing Conducted through

1968, Report No. 4, Government Printing Office, Washington, D.C.

(1963).

R. E. Moore, The AIRDOS-II Computer Code for Estimating Radiation
Dose to Man from Airborme Radionuclides in Areas Surrounding

Nuclear Facilities, ORNL-5245 (April 1977).

D. K. Truby and S. V. Kaye, The EXREM-III Computer Code for Esti-
mating External Radiation Doses to FPopulations from Envivonmental
Releases, ORNL/TM=-4322 (December 1973).

G. G. Killough, D. E. Dunning, Jr., and J. C. Pleasant, INREM-IT:
A Computer Implementation of Recent Models for Estimating the Dose

Equivalent to Organs of Man from an Inmhaled or Ingested Radionuclide,
ORNL/NUREG/TM-84 (in press).

D. H. Slade, Meteorology and Atomic Energy, Atomic Energy Commission,
TID~24190, Oak Ridge, Tennessee, 1968.
56
G. G. Killough et al., Fstimates of Internal Dose Equivalent to 22
Target Organs for Radionuclides Occurring in Routine Releases From

Nuclear Fuel-Cycle Facilities, wol. 2, ORNL/NUREG/TM-190, in press

(1978).
57

6. ANALYSIS OF RADIOLOGICAL IMPACT

6.1 Maximum Individual Doses

The maximum individual doses at 1 one mile from the point of release
of radionuclides are shown in Table 6.1. Data are listed for both the
Lemhi Pass site and the Wet Mountains site; meteorologies for each site

are also indicated.

Table 6.1. Maximum individual 50-year dose commitment to total body and
various organs from radiocactivity released to the atmosphere
during one year of facility operation

Dose commitment (millirems)

 

 

1
Meteorology Total body Gl tract Bone Thyreid Lungs Kidneys Liver
Lemhi Pase site
Butte 2.4 4.1 9.5 2.4 35.3 4.3 2.9
Mullan Pass 2.4 3.7 9.4 2.4 32.0 3.9 2.7
Wet Mountaine site
Pueblo 3.7 3.8 13.1 3.7 33.4 4.2 3.3
Alamosa 3.2 3.3 11.2 3.2 28.7 3.7 2.8

 

For lemhi Pass, the Butte, Montana, meteorology gives doses that are
slightly higher than those for the Mullan Pass meteorology. Therefore,
the Butte meteorology will be considered in greater depth in this
analysis. Lung is the critical organ, receiving a dose commitment of
35.3 millirems, while 9.5 and 2.4 millirems are delivered to bone and
total body respectively. At the Colorado site, the Pueblo meteorology
gives the highest doses. Again, lungs and bone are the organs receiving
the highest doses, 33.4 and 13.1 millirems respectively, while dose to
total body is 3.7 millirems.

A breakdown of the dose by radionuclides to various organs is shown
in Table 6.2. For the Lemhi Pass site, 229Rn and daughters are the
primary contributors to all organs. The second most important radio-
nuclide is 22BRa, delivering 367 of the dose to total body and thyroid.
The relative distribution of the dose from radionuclides at the Wet
Mountains site is similar to that for Lemhi Pass, with the exception

that 22B8Ra is the major contributor to total body (59%) and thyroid (59%).
58

Table 6.2. Radionuclide contributors to the dose commitment
to various organs for maximally exposed individual

 

Contribution to dose commitment (%)

 

 

Radionuclide Total body GI tract Bone Thyroid Lungs Kidneys Liver
Lelmi Pass site (Butte meteorclogy)
2327h 3 <1 10 4 <1 1 13
228ga 36 2 23 36 <1 4 6
2285, <1 <1 <1 <1 <1 <1l <1l
2287y 1 <1 2 2 <1 <l 3
224p, <1 <1 <1 <1 <1 <1 <1
220 + p“ 59 98 65 58 98 95 78
Wet Mountains site (Peublo meteorology)
2320 4 <1 12 4 <1 2 18
228pa 59 4 42 59 <1 9 13
228p¢ <1 <1 <1 <1 <1 <1 <1
2281y 2 1 3 2 2 1 5
224p, <1 <1 <1 <1 <1 <1 <1
220gy + D% 35 94 43 35 96 87 63

 

a
Contribution of 220Rn and daughters of 220Rpp,

The contribution of various exposure pathways to the dose commit-
ment to the total body, bone, and lungs is shown in Table 6.3. For
Lemhi Pass, ingestion is the primary mode of exposure for total body
(47%) and bone (61%), while inhalation contributes 99% of the cose to
the lungs. A similar distribution exists for the Wet Mountains site.

Additional AIRDOS-1) computer runs were made to determine the
increase in dose commitment if the site boundary were located at 0.5
mile from the point of release of radionuclides, instead of 1.0 mile
as assumed in this assessment. It was determined that the maximum
individual dose would increase by a factor of approximately 2.3 when
the distance to the maximally exposed individual is reduced by one-half.
Maximally exposed individual dose commitments calculated in this report
could be reduced by imposing more stringent controls on the handling of
ore and tailings and/or more effective treatment of airborne radio-
nuclides prior to release at the mill site.

Maximum individual doses from thorium mining and milling appear to
be comparable to those reported in assessments on uranium mining and
1

milling operations. However, it is emphasized that many of the assump~

tions made in this study are based on extrapolations from current practices
59

Tahle 6.3. Contribution of exposure pathways to dose
commitment to total body, bone, and lungs
for maximally exposed individual

 

 

Contribution to dose commitment (%)

 

 

Pathway Total body Bone Lungs
Lemni Pass site (Butte meteorology)
Inhalation 32 31 99
Submersion <1 <1 <1
Surface 21 8 1
Ingestion 47 61 <1
Swimming <1 <l <1
Wet Mountains site (Pueblo meteorology)
Inhalation 20 24 98
Submersion <1 <1 <1
Surface 15 6 2
Ingestion 64 69 <1
Swimming <1 <1 <1

 

 

in the uranium mining and milling industry. These assumptions may not

be exactly correct for thorium mining and milling. Therefore, as the
thorium industry expands to accommodate the demand for thorium as a fertile
material in nonproliferative fuel cycles, this assessment should be
extended to include on-~site measurements of source terms and meteorological

and environmental parameters.

6.2. Population Doses

Population dose commitments in man-rems for each site and meteorology
considered are listed in Table 6.4. Bone, lungs, and kidneys receive
the highest doses at each site. The dose commitments for the Wet
Mountains site (Alamosa meteorology) range from five to seven times higher
than those for the Lemhi Pass site (Butte meteorology). This difference
1s primarily due to the greater population of the Wet Mountains area.
Table 6.5 lists the contribution of radionuclides to the population-
organ-dose commitments. The most important radionuclides are 220Rrn
and its daughters, which deliver 64 to 987 of the dose to the organs
shown. Radium=-228 is the second most important contributor, with the

remainder of the dose being given by 2327h and 428Th,
60

Table 6.4. Population dose commitment to total body and various
organs from radicactivity released to the atmeosphere
during one year of facility operation

 

Dose commitment {(man-~rems)

 

 

 

 

 

 

 

 

Metecorology Total body GI tract Bone Thyroid Lungs Kidneys Liver
Lemhi Pass site
Butte 0.05 0.03 0.1 0.05 Q.7 0.07 0.06
Mullan Pass 0.05 0.03 0.1 0.05 0.8 0.08 0.06
Wet Mpuntaing site
Pueblo 0.3 0.1 0.7 0.2 2.8 0.3 0.3
Alamosa 0.3 0.2 0.9 0.3 3.7 0.4 0.3
Table 6.5. Radionuclide contributions to the population dose
commitment to various organs
Contribution to the dose commitment (%)
Radionuclide Total body GI tract Bone Thyroid Lungs Kidneys
Lemhi Pass site (Butte meteorclogyl
237th 3 <1 12 3 <1 1
228Ra 28 7 22 28 <1 4
228p¢ <1 <1 <1 <1 <1 <l
2287 2 2 2 2 <1 <1
22hpa <1 <1 <1 <1 <1 <1
220p, + p 67 91 64 67 98 94
Wet Mountains site (Alomosa meteorology)
232t 3 <1 13 3 <1 1
228pa 48 16 40 48 <1 10
228p¢ <1 <1 <1 <1 <1 <1
2281y 3 3 3 3 2 1
ZZBRa <1 <1 <1 <1 <1 <1

220p, + p“ 46 81 45 46 97 87

 

 

%Contribution of 220Rn and daughters of 220Rn.

The contribution of various exposure pathways O the population
dose for each site (Butte and Alamosa meteorology) is shown in Table
6.6. The dose to total body is rather uniformly divided between inha-
lation (39%), surface exposure (36%), and ingestion (25%). Dose to
bone is primarily by inhalation (53%), while surface exposure and
ingestion contribute 18 and 247% respectively. Exposure to lungs is

almost entirely from inhalation of particulate matter (98%).
61

Table 6.6. Contribution of exposure pathways to population dose
commitment to total body, bone, and lungs

 

Contribution to population dose commitment (%)

 

 

Pathway Total body Bone Lungs
Lemhi Pass site (Butte meteorology)
Inhalation 39 53 98
Submersion <} <1 <1
Surface 36 18 2
Ingestion 25 29 <1
Swimming <1 <1 <1

Wwet Mountains site {Alamosa meteorology)

Inhalation 27 41 98
Submersion <1 <1 <1
Surface 31 15 2
Ingestion 41 43 <1
Swimming <1 <1 <1

 

Population dose commitments appear to be acceptable in terms of risk
to the public when compared with those reported for mining and milling of

uranium ores.1

One factor leading to relatively low population exposures
from thorium mining and wmilling is the rapid decay of 220gn (55.6 sec)
compared with that of #?ZRn (3.8 days). This property implies that the
mean distance of 220Rn transport from the site will not be great before
decay to particulate daughters. Since the probability of deposition
through washout, rainout, or gravitational settling is greater for
particulates than gases, daughters of 220Rn are less likely to reach

populated areas.

Again, however, it must be emphasized that these calculations are

based on source terms that have primarily been developed {from assumptions

and extrapolations from mining and milling of uranium ore., Effort should
be made to incorporate actual data from a large-scale thorium operation

as it becomes available.

6.3 Dose Commitments Following Plant Shutdown

An analysis of maximum individual doses during the first year

following plant shutdown indicates that dose commitments are significantly
62

lower than during facility operation and would continue to decrease with
time. Typical postshutdown dose commitments are shown in Table 6.7.
The lungs receive the highest dose (6.8 millirems), bone second
(6.1 millirems), and total body and thyroid third (2.1 millirems).
Primary contributors to the dose {(Table 6.8) are 228Ra for bone, total
body, and thyroid; and 42%Rn + D for GI tract, lungs, liver, and kidneys.
The only other important contributors are 228Th, which delivers 12% of
the dose to liver and a smaller percentage to other organs, and 232rh,
which delivers 11% of the dose to liver and 5% of the dose to bone.

Table 6.9 shows postoperational exposure via the different path-
ways. Ingestion is the dominant pathway for all organs with the excep-
tion of luags, where inhalation contributes 97% of the dose due primarily

to airborne 212Pb, a daughter of 220Rpn.

Table 6.7. Maximum individual 50-year dose commitments to total body and various
organs from radiocactivity released to the atmosphere
during the first vear after facility shutdown

 

Dose commitment (millirems)

 

Site (meteorology)

 

Total body GI tract Bone Thyroid Lungs Kidneys Liver
Lemhi Pass (Butte) 2.1 0.9 6.1 2.1 6.8 1.1 1.0
Wet Mountains (Pueblo) 1.5 0.6 4.4 1.5 4.3 0.7 0.7

 

Table 6.8. Radionuclide contributeors to the dese commitments to various organs for
individuals exposed during the first vear after facility shutdown
(Lemhi Pass site, Butte meteorology?)

 

Contribution to the dose commitwment (%)

 

 

Radionuclide Total body GI tract Bone Thyroid Lungs Kidneys Liver
2321p 1 <1 5 1 <1 1 11
228ga 85 15 73 85 2 30 35
2285¢ <1 <1 <1 <1 <1 <1 <1
2287y 2 3 4 2 6 3 12
2Z%Ra <1 2 <1 <1 <1 <1 <1
220gn + D 12 80 18 12 91 66 41

 

a . -. . . : . e -
Radionuclide contributions for the Wet Mountains site were similar to those listed here.
63

Table 6.%. Contribution of exposure pathways to the dose
commitment to total body, bone, and lungs for individuals
exposed during the first year after facilit& shutdown
(Lemhi Pass site, Butte meteorology )

 

Contribution of exposure pathway to dose commitment (%)

 

 

Pathway Total body Bone Lungs
Inhalation 8 11 97
Submersion in air <1 <1 <1
Surface 10 4 3
Ingestion 82 85 <1
Swimming <1 <1 <1

 

a . . ;
Contributions of exposure pathways for the Wet Mountains site
were similar to those listed here.

Population dose commitments for the first year after shutdown are
shown in Table 6.10, It is evident from these data that population
dose commitments would drop significantly after the facility ceases
operation and would continue to drecp with the decay of 232Th daughters
present in the tailings. The highest postshutdown doses occur at the
Wet Mountains site (Alamosa meteorology). Radionuclide contributors
to the population dose commitment are listed in Table 6.11. As with
the postoperational individual doses, the primary contributors are 228Ra
for bone, total body, GI tract, thyroid, and liver; and 220pn + D for
Jungs and kidneys.

Figure 6.1 illustrates that 232Th-chain daughter activities are
controlled by the 1.39 X 101 0—year half-life of 232Th in fresh ore. Since

91% of this 2327h is assumed to be removed during the milling process,

Table 6.10. Population dose commitments to total body and various organs
from radicactivity released to the atmosphere during
the first year after facility shutdeown

Doge commitment (man-rems)
Liver

Site (meteocrology) Total body GIL tract Bone Thyroid Lungs Kidaoeys

Lemhi Pass (Butte) 0.02 0.007 0.06 0.02 0.11 0,01 0.01
Wet Mountains (Alamosa) 0.11 0.03 0.28 0.11 0.43 0.06 0.06
64

Table 6.11. Radionuclide contributors to the population dose commitment to various
organs for exposures during the first year after facility shutdown
(Wet Mountains site, Alamosa population)

 

Contribution to the dese commitment (%)

 

Radionuclide

 

Total body CI tract Bone Thyroid Tungs Kidneys Liver
23271h 1 <1 5 <1 <1 <l 9
228Ra 81 48 76 82 4 38 41
2284¢ <1 <l <1 <1 <1 <1 <1
2287y 4 8 4 4 8 b4 10
224Rpa <1 1 <1 <1 <1l <1 <1
220pn + D 14 43 15 14 87 57 40

 

ORNL OWG, 78-5i11i

 

232Th 228Th
QL39!§0my 86,13k
228 Ac al.9y
PETy
22BRa 224 Re
83.644

220 Rn 212 Po

154.55 86 4% a304x10 s
216 Po 21281 208Pb

60.6m {atgble)
*
201588 %/ 83Im
208T7I

212 Pb

Fig. 6.1. Thorium—232 decay chain.
65

the tailings beach radionuclide chain activity would then be controlled
largely by the 5.75-year half-life of 228Ra, Thorium-228, also removed
in the milling process, is assumed to again approach equilibrium with
228Ra activity in the tailings during the 20-year plant lifetime.
(Calculation of postshutdown radionuclide releases takes into account
the layering of material in the tailings beach, correcting for reduced
228Th activity in recently released tailings materials.) Extraction of
232Th from thorium ore therefore effectively reduces the long-term
toxicity of the tailings by approximately an order of magnitude and
causes the short-term toxicity of the tailings (controlled by 228Ra) to
be maximized during the period immediately following shutdown, decaying

with a 5.75-year half-life toward recontrol by the reduced 232Th content.

6.4 Impact of Mine-and Mill-Generated 220Rn on Populations
Qutside the 50~mile radius

To illustrate the relative radiological impact of mine- and mill-
generated 220Rn, calculation of the total U.S. population dose due to
crustal 232Th content follows. The average crustal abundance of 232Th
is estimated to be 10.33 ppm,% or 1.03 x 107> g Th/g crust. Using an
average soil density of 2 g/cm® and a decay rate A for 229Rn of
0.693/55.6 sec = 1.27 x 107%/sec, an exhalation rate from soil for 2?ORn
of 0.336 pCi/cm?-sec has been calculated.? Multiplying this rate times
the area of the contiguous U.S., 8 X 1016 cmz, gives the total 220Rp
exhalation rate for the contiguous U.S., 2.69 x 10'® pCi/sec. Eichholz"
has estimated that the human lung receives an annual alpha dose of
0.6 millirad from daughters of naturally emanating 220Rn; other organs
receive lesser doses.

The 229Rn activity leaving the 50-mile~radius circle surrounding
the hypothetical mine and mill site may be calculated as follows: The
average sum of the estimated 220Rn activities generated at the mine and
mill site (from Sect. 4.1) is 2.2 x 10° pCi/sec. Allow a l-sec increment
of 220rp gas (2.2 x 10° pCi) to travel downwind to the 50-mile radiums
boundary at 15 mph (an arbitrarily chosen wind speed). During the
3.33 hr required for transit to the boundary, the 220Rn activity (A)

At

is reduced to A = A e , where A = 2.2 x 109 pCi, A = 1.27 x 107?%/sec
66

and t = 1.2 x 10" sec. Therefore, the 220Rp activity per second leaving
the 50-mile diameter under these assumptions is 2.2 X 109 pCi x

(7.6 x 10787y = 1.7 x 107°7 pCi, an insignificant activity when compared
with the 2?9Rn exhalation rate calculated in the preceding paragraph.

To complete the analysis, it is necessary to consider the impact of
212ph, daughter of 220Rn. Since one atom of ?12Ph is created per decay
of an atom of 220Rn, 212py activity is calculated by multiplying the
activity of 220pn released by the ratio of the radionuclide half-lives
(see Fig. 6.1). Thus, release of 2.2 x 107 pCi/sec of 220Rn at the

facility results in the effective release of

- :212
g pCi _ 55 sec 1 hr _ g pCi“ " “Pb .
2.2 x 10 ec © 10.6 hr ~ 3.6 X 10° sec 3.2 x 10 sec

The AIRDOS~II computer code was used to estimate air concentrations
of this 212Pb particulate both at the l-mile facility boundary (locatiom
of the hypothetical maximally exposed individual) and at the 50-mile
study area boundary. Meteorology specific to Butte, Montana, was used
(see Appendix 1), and parameters including radionuclide decay, dilution
in the atmosphere, dry deposition, and scavenging (see Sect. 5) were
incorporated. Under these conditions, maximum air concentrations occur
in the northeasterly direction from the facility. The concentration in
air for “12Pb particulates at 50 miles vs 1 mile is reduced by a factor
of about 3 x 103.

Table 6.1 lists doses to the maximally exposed individual at 1 mile
under these conditions, and Table 6.2 lists the percent contribution
of 220Rn + D (essentially 212pp) to these doses. Doses from 2'?Pb to a
maximally exposed individual at 50 miles from the facility would be
roughly proportional to the 212ph air concentration (above) and would
therefore be reduced with respect to the tabulated doses by approxi-
mately 2.9 x 103, Under the conservative conditions used for maximal
exposure {(see Sect. 5), doses due to 220Rn + D (212pb) release would
approximate 5 x 107" millirem to total body, 2 x 1073 millirem to bone,
and 1 x 1072 millirem to lungs at 50 miles from the facility. Doses
to individuals residing outside this boundary, and not subject to maxi~
mal exposure conditions, would be further reduced and are judged insignif-

icant when compared with natural background 220gn + D exposures.
o7
6.5 Discussion

Effect on estimated doses of variation in population size

One of the goals of this study was the radiological assessment of a
range of thorium resource sites to estimate a range for the radiological
hazards associated with the mining and milling of thorium. Analysis
of available literature indicated the likelihood that, in the event of
wide-spread implementation of a thorium~uranium~233 fuel cycle, extraction
of large quantities of thorium would occur primarily in the vein deposits
of the western United States. Ifispection of data estimating thorium
reserves at the various western resource sites led to identification
of the Lemhi Pass and the Wet Mountains areas as likely to be worked.
These sites were chosen for further analysis based on data indicating
nearly 20 times the population residing within a 50-mile radius of the
Wet Mountains site as compared with the Lemhi Pass site. This size
range in potentially impacted populations provides the primary basis for
the study's range of a factor of 4 to 5 (Tables 6.4 and 6.10} in

estimated radiological doses for the two populations.

Effect on estimated doses of substitution of meteorological data sets

As noted in Sect. 2.5, choices of meteorological assumptions have
the potential for significantly modifying doses calculated for fuel
cycle facilities. Table 6.1 indicates that, for the meteorological
data sets used in this study (and described in Sect. 2 and Appendix 1),
lung doses to maximally exposed individuals may vary by as much as 10%
in the case of the Lemhi Pass site and 16%Z in the Wet Mountains case,
depending upon choice of meteorological data. Presumably, choice of
less site-specific meteorological data, including generic or average
U.S. meteorological summaries, could lead to further uncertainty in
maximum individual dose estimates.

Population dose estimates (Table 6.4) are also found to be sensitive
to choice of meteorological data, with lung doses to the general popula-
tion varying by 147 in the Lemhi cases and by 32% in the Wet Mountains
results. _

In general, given the likelihood of complex local ajr flow patterns

over mountainous terrains such as are encountered at these study sites,
68

actual doses to individuals residing near operating facilities may be

greatly affected by local topography, orientation, and specific diurnal
wind regimes. Doses in this report are necessarily calculated without
access to such information and should be recalculated when data become

available.

Conclusions

This analysis of radiological impact suggests that maximum individual
dose commitmeats at 1 mile from the point of release should be similar
to those encountered in uranium operaiions. It was not possible to
make a direct comparison of this assessment of thorium mining and milling
with previous published assessments dealing with uranium ore. The
primary reason for this difficulty is that this analysis incorporated
different sets of meteorological data, site-specific population data,
and assumed a l-mile (vs 0.5 mile) distance to the facility boundary.
Also, no operational experience existed on which to base the development
of source terms. Therefore, use of conservative assumptions was required.

Doses to the maximally exposed individual at both sites were similar,
between 2 and 4 millirems to the total body, 9 to 13 millirems to bomne,
and 29 to 35 millirems to lungs. General population doses were estimated
to be highest for the Wet Mountains site, at 0.3 man-rem (total body),

0.9 man-rem (bone), and 3.7 man-rems (lungs). Doses calculated were
largely the result of ingestion and inhalation of 220Rn daughters for
both the maximum individual and general population cases. Significant
contributions to dose were also found for 228Ra, 232Th, and 228Th in order
of decreasing importance. Radon-220 and daughter doses to individuals
outside the 50-mile-radius study area were determined to be insignificant
when compared with natural background.

A distinct advantage of thorium mining and milling compared with
uranium mining and milling may be that the radiological hazard encountered
following plant shutdown is significantly lower and decreases rapidly
after shutdown. Because radioactivity residual in the thorium tailings
pile will be controlled primarily by the half-life of 2?8Ra (5.75 years),
the need for extensive maintenance (compared to uranium facilities) of mill

tailings for long periods after shutdown will be greatly reduced. In the
69

ALARA uranium mining and milling study,l it was concliuded that at the

New Mexico site, maximum doses to bone and total body at 0.5 mile from

an interim-treated (via chemical dust-reducing spray) tailings area

could be as high as 933 and 92 millirems respectively, using conservative
assumptions. The magnitude of these doses suggests that extensive final
treatment and long~term maintenance of a uranium tailings area might be
necessary. In comparison, in this study of thorium mining and milling,
the tailings pile (assumed treated by chemical spray) results in maximum
individual doses estimated at 6.8 millirems to lungs and 2.1 millirems

to total body for the Lemhi Pass site immediately after shutdown. Doses
are also estimated to be reduced with time fdllowing shutdown. Therefore,
it is concluded that postoperational handling of a thorium mine and mill
facility may be significantly less complex than for a uranium facility,
and that the radiological doses associated with the post-operational
thorium facility might be significantly less for a given level of tailings
pile treatment. It should be emphasized, however, that no difficulties
in meeting current or proposed radiological standards are anticipated |
for either type of facility, given application of appropriate, available

technologies.

6.6 References

1. M. F. Sears, R. E. Blanco, R. G. Dahlman, G. S. Hill, A. D. Ryan,
and J. P. Witherspoon, Correlation of Radiocactive Waste Treatment
Costs and the Envirommental Impact of Waste Effluente in the Nuclear
Fuel Cycle for Use in Establishing "As Low As Practicable” Guides —

Milling of Uranium Ores, ORNL/TM-4903, Vol. 1 (May 1975).

2. R. C. Malan, Summary Report — Distribution of Uranium and Thorium

in the Precambrian of the Western United States, AEC-RID-12 (1975).
3. C. E. Junge, Air Chemistry and Radiocactivity, A.P., 1963.

4. G. G. Eichholz, "Environmental Aspects of Nuclear Power,'" Ann Arbor

Science Publishers, Ann Arbor, Michigan, 1976.
70

RECOMMENDATIONS FOR FUTURE WORK

During the conduct of this analysis, it became apparent that some
of the technical data required for detailed radiological environmental
assessments of thorium wmining and milling were not available. In these
cases, appropriate data pertinent to uranium mining and milling were
often substituted and used in this work. 1In order for more refined
assessments of thorium mining and milling to be performed in the future,
data pertaining to the following areas are needed:

1. Quantitative measurement of emanation factors and diffusion
coefficients for 220Rn in thorium ore materials such as those found in
vein deposits.

2. Determination of fugitive dust generation rates and the dust
properties characteristic of mine activities and from exposed thorium
ore deposits and ore piles. The latter should include studies of wind~
blown dust from ore piles and involve quantitative descriptions of the
saltation behavior of the thorium ores, when appropriate.

3. Rates of release of 2?0Rn from thorium ore under various storage
conditions are required. Effects of water sprays and/or other treatments
in reducing dust and 220Rn releases from thorium ore storage piles should
also be determined.

4. Determination of the release rate of 220Rn from thorium ores is
required for such typical mill treatments as crushing, grinding, and
dissolution.

5. The concentrations and compositions of thorium decay products
in thorium mill waste liquors are required.

6. Specific properties of soils from the mountainous locations
where vein-type thorium ore deposits are located should be determined
to assess the soils' suitability for construction of tailings ponds,
controlling leakage of waste liquor from the pond, and reduction of

migration of radionuclides from the tailings waste liquor.
71

ACKNOWLEDGMENTS

The authors wish to extend their thanks and acknowledge the contri-
butions which several individuals made in the preparation of this report.
K. H. Vogel and S. K. Beal* provided supplemental information on
the assessment of thorium mining and milling as presented in the Light-

Water Breeder Reactor Program envirommental statement. Eugene W.

Grutt, Jr., and Donald L. Hetland™ provided copies of several reports
containing information about thorium deposits in the Lemhi Pass region.
R. E. Moore* performed AIRDOS-II radiological dose calculations, and

Don E. Dunning and George G. Killougfi1C provided current dose conversion
factors for the radionuclides of concern in this report. Mildred B.
Searsi provided many helpful suggestions and discussions throughout

the course of this study. Hershel W. Godsbee* contributed to the
determination of the applicability of various diffusion models for
estimation of ?20Rn releases and assisted in the development of the
equations for estimating the change in area of the tailings pond during
the operation and closing down of the mill. The support and encourage-
ment of George L. Sherwood, RRT/DOE, during the conduct of this work were
also appreciated. Typing assistance was given by Susan Masingo, Beverly

Varnadore, and Rebecca Hamley.

 

*
Bettis Atomic Power Laboratory.

+Grand Junction Office, DOE.

%
Oak Ridge National Laboratory.
Appendix 1

SUMMARIES OF METEOROLOGICAL DATA
OF ATMOSPHERIC STABILITY CLASSES FOR FACH DIRECTION

FREAUENCY

Pueblo, Colorado

FRACYION OF TIME IN EACH STABILITY CLASS

SECTOR

a

Al-3

DM D ar O 0N DY e
PO M IO P = A D OO -
DM et O S o P DO
vt o] e el DO Ot DN OY MY (MY (DY
* % 8 & 5 & & & & g % s 8 00
QODOOOOOOODOO OO

PmINEFIO MO R e Dt e OO0
D d ATV MDD M DN S D D
Voot g NN DAY O
Y DO ok pod wot ik vd (Lo iyt wod i [
* » & & 5 8 4% & " g e B s s g
COOOOOOOOOOORDOO0O
IO Med 29O 2 0 P PN 2 OO
MO e DM NN AN N
Y ey e e A0S Y O O D I O
ANNMM g NN
. 2 & & B B & g o BB e e P
DO2OOOOOCODOOLOD0

RO R U e S 20 P e 1Y o PG O N
DM oUheoomm e Ny
— g Y R OGO A D T QT e
NGO st et QLTI O D i e
* 4 % g o ® P o @ B 4" a2 g

OOOOOOOOOOOOOLOD

MO D) el GO P0G et e PR D
Wit o PP (N2 vt ot P NN
Moo NN S O WO M N
U e OO DS )
" 3 5 2 & P B 9 B 9 e B & bHm
DO OOOOOOOOO o

ML o F NN O T e
MY S G O A P O MY R S e
YOG O e O e D Y e (D O O et £y
CHEBEn OO QIDOAOCD G
* .8 5 & P A 8 s B 5 g * K 8 oA
OO OOLEC OO OQOM OO

w OIS D O N S OO
wof gk o o ok e
Pueblo, Colorado - fFurguenNCTIFS 0OF #IND DIRECTIONS AND TRUCE=-AVERAGE WIND SPEEDS

#IND TOWA®D FREQUENCY WIND SPEEDS FOR FACH STABILITY CLASS
{METERSZSECH
A £ C D F F
1 C.086 1470 2.22 381 4496 3,48 1e38
< CeaDBE 178 2.73 Ao 3D Sel2 1.75 1leh4
3 CeU8A8 1674 2.54 4,18 5,02 3.72 1.41
4 CeDT7E 1.81 2+54 4,25 5+28 372 1«55
5 CQGGQ 155 2elbd 1. 656 4,85 3,77 1«60
o Coelaf 123 2e04 3.648 5. 45 3.92 1.568
7 D.0548 155 1,70 3,656 £e20 3.956 153
8 0032 1415 1.85 4.1% 7«45 4,02 162
3 Ce64 1203 1,990 3,449 8,00 3493 1.63
1e D047 158 195 3.13 681 3.88 1476
11 Nel 86 107 1.84 3. 37 Hs29 3.75 1.54
1(2 3.5’}3 1053 1;9# 3-68 7.&1 3.71 1-71
13 0e107 1432 1.58 3,52 6451 3.84 1.62
14 DeU67 1e81 1.98 370 6. 34 3e.81 1,68
15 DeD489 1467 1.74% 1,67 6.18 3.57 a4
i 04029 1.756 2.08 3,65 6.01 3 .49 133
HIND DIRFCTYTIONS ARE NUMIBFRFD COUNTERCLOCK®WISE STARTINS AT 1 FOR DUE NORTH

y=1Y
FREQUENCY OF ATMOSPHERIC STABILITY CLASSES FOR EACH DIRECTION

Alamosa, Colorado

FRACTION OF TIME IN EACH STABILETY CLASS

SECYOR

Al-5

M DIONO QO DMNO OO
DO OMNANOM NN S DN
Nt AWM O D vl wt i MY i MOV N
wd 0 e d O SN OO O ol O # VY O el v
. h B 9 b & F 4 & H 2 s e
COOAOOOOOROQLOOO

=HOMNIONDZ O SNONONIOM
MY P 10 A LY v o e Y MY O e SO YO
MmN MNMNMsEMOIN M S
* % % 0 & 0 A 0 "t 0P g

COOOOOOOQOoOOQOODOO

Th e sl 2150 O 0 V0
O o}

0
¢
0
0
G
G
0
0
0
0
0
De

BT el I el PIED O e 23000 @ O e D
PO MNF "N OO
U COOQ=IIRNCO A o0
L2 vt el ek g (0 O e L0 e O D €O KD D
O 8 % » a8 8 s e 0 g e s

AN N AN T e
W DeAMNG I e NI O
AL OO D
*a B & A 5 & ® » ® 9 2 ¥ s p
QOO MO0 OO0

vt DU N0 M DT D vl (PR O
Alamosa, Colorado - ¥FwYGUFACIES OF WIND DIRFCTIONS AND TRUE-AVERAGE WIND SPEEDS

HITND THwARD FREQUENCY WIND SPEFDS FNOR FALH STABILITY CLASS
{ METERSZSECH
A 5 C D £ F
1 0e135 1664 2418 3,68 6e56 3.87 1480
2 NDe(HE 1.68 205 3+ 56 Sel 3 3.79 190
3 Ne053 152 2.13 3.33 S.11 3.86 1491
& 0,058 1.59 2450 3,11 5453 3,85 1e77
5 0073 1.46 2.05 1,02 624 3.569 170
5 O+ a2 1.74 2.06 2.76 4495 3,38 1.84
7 CeD 34 152 1,96 3.01 4,82 3,30 1e71%1
3 Ce033 1452 2.18 3,07 5.06 3,70 1.80
9 3005% 1058 2.‘43 3-21 6-@'3 3076 1085
14 Le0tbH 1.35 2441 3.77 H+13 3.70 1.89
11 T e(54 1 59 2.13 3,94 65615 3.66 175
12 7,051 ledl 197 2457 5 o0 3653 1.91
£3 CeN 72 1e¢ 35 2,21 3.30C Se 85 3.55 1.89
in CeD74 137 1.91 3.80 He7l 3.85 194
E De0 79 L1e37 2410 3,23 7e26 3.82 1-.82
lfi 603?1 1053 2.24 4.84 5.7; 3.93 108‘
ATND DINTCTINNS ARD MNUMRBRFRID CUOUNTERCLOCKWISE STARTING AT 1 FOR DUE NORTH

9~1V
OF ATHMDSPHERIC STABILITY CLASSES FUR EACH DIRECTION

FREGUENCY

Mullan Pass, Idaho

CLASS

0F TIME IN FACH STABILTITY

FRACYION

SECTOR

0

Al~7

C ot g g TR0 T T e O e
P 2 o wed 7120V AT SOV 0 O OO I T
N N DI SN e D MO D
O et ot 0w 10 et ) et () ot 233w () vk
*® % 4 @ ® R R P R e e
IOl OOCo OO oo

A E A O T Y S e 0 PO N
MO N SN O DD e
S NTIOO LMD - D
ore et el ek gt T 0 O el et 0 (T 0
. 0 " 2 " 8 & P a2 s PR AN
DOQOCOCOCTOoOOOmC

.

63

De 0206
Qe OHBH
008

™~

A P DN e P 00N 0 T O
ST S e e T 0 A O O e B
TN e U e LD DT 2 e O PN
O N WD e O G A Y e T
® ® B % & & w 2 s & B 8 e * B
QOQoOLOQOQOOQOLOOD

MO O ONNO- DTN
M NNNeORNC M2 Oy
A D e e OO e LD D e M O Y
ol ool e kg ot £ S LTS OO Y el et
S 8 R & 0 O k& & & 5 s 28
COOOoOOC Qo OCODO00

e M e O T Nk N M
AT L RNV OO PN
SRR MO I O
At OO OOCOOCOTOTO m
* & % & » & O 4 & . p s 6 r 8

COQQUCODOTOoROOCCO

NP OO T h MR A
F e e D TR YNNI IO D O
D et MDD OO OO w O owd O
O CoOGOOOOOoOC OO
4 R ¥ P & 0 & & P BT B R B

OO OOCOQ OOl OO

e O P RS L e GO CR LD ek (N F D
ol el et gl o ot g
Mulian Pass, Idah0o -~ FREQUINMCIFS OF WIND DIRFCTIONS AND TRUF—-AVTRAGE #IND SPLYDS

WIND T0OnRARD FRFEGUENCY #IND SPEEDRS FOH FACH STASILIYY CELASS
v TURSASEL
A & i i3 r &
A De020 1e12 1.7% Ta04 Lef5 403 1«85
5 G026 1. 05 157 .12 e 2H LR 1268
5 0.030 D77 167 o &3 e 39 12 175
7 De5H1 103 1aD4 307 5«19 3.9%8 1.H68
8 0059 Oe498 2a0% 3228 L ah3 4402 1e5HB
¥ Gal24 1.10 1773 el G5« 85 Je71 153
10 Oe007 125 Ze18 Te 873 Hald 383 1,756
11 Cel59 102 2alt JeT01 SRR 377 Lo 88
12 Q.Ufif» io’afl ?'12 3-?3 %350 ‘g.fi? 1'?5
3 Ca 0813 101 {78 2 e B 49 36 383 1656
14 De376 1a0}4 2ali 350 S e23 4 e(8 172
15 D.,106 1.4 185 1420 5414 F 90 1553
15h CeTit 7 120 2623 Te 2% 4415 3287 1e0:4

HIND DIRCCYLIONS ART WNUMBERQUD COUNTERCLIOK @IS STARYING AT 1 508 UUT NIRRT

81V
DIRECTION

EACH

OF ATMOSPHERIC STASILITY CLASSES FOR

FREQUENCY

Mullan Pass, Idaho -

March through November average

SECTOR

L
b

~
As

CLASS

STASTLIYY

FACH

N

gF TIME

FRACT N

2

X

Al-9

;JH.\}!; VAT NN e TN
wfin)«ficll.:))_a‘.?.i.«\)
A:.n?:r P U7 O A e S0
ek 7 d et (7 ek e e e T e (O
® & 8 % 3 8 5 &% ¢ 8 2
OO OoCOOOOGCDO0

D.1382
U« 1358
D.11190
0.0868

2D A I P 2 T e TN eed e e
A e e e PO SE R P TR DD D e O O
e NP T O e AT D T et 5T e TR T
vl el ol ot v oo I LT el O D el g e (T
* & & @ 2 2 ¢ F 2 b a2 % 2 *P»

CoRUOoCCODTQoLQUooQo

WD A ALy P Y b TN N e e
T CRITO D A R G T
YA P T T ed LT Y e T i g o
Wit o NI Oy
2 % & & % g ¢ * » & 4 ® n

CoOOOOOOOO0LOon

+

P
=
=

.
o

0."3(‘4

MRS et O O
O D P DD e YOG D TN O N
D P et e it g ] 0 OO N D
W wed ok ot ol gl gt wod md o 3 (YD
® R 2 8 & 5 8 R 2R R S 2P
o OO OoOOOCOoOoOoC

WM OIS G e OO O e

_H\,_nvnfivl.flqifflnbg.fln,i?r)nu)
Rl s 0D T D e W S GO LD I Y e
QOCAQQOQO SO OO0 0O D
4 " 2 8% 2 B 8 8 F e s 8 89
OCOOOOCOoOCOCOCooOC

AL AL O D e 0 e MY 0 D
SR LQ U O e NOT  MO D
SO COOoOToooool o
e ® 2 & ® 2 F ® & 8 4 P A a®
DPOCCOoOOLOODOOQOC

vl AP D P DT Y el A e iy
it rd et el pad et gt
Mullan Pass, Idaho - FRUQUINCIFS
March through November average

AIND Tiw ARD

1 D085
? O.i)qfw
4 NaD33
3 031
£3 Ceae024
7 D,011
B 0013
3 G018
i0 e85
11 I B
12 0 a7
i3 D079
14 010806
15 Galsh
15 DeORBY

#IND DIRECTINONS AGF NUMKERYD

FRUODITNCY

OF WIND DIRFCTEONS AND TRUL -BYERAGE

YIND SRR

4 - C
L1 2 137 a7
e i3h 1,594 Te 28
e 38 1475 T.131
Gae?7 1RG0 Te 56
1.06 14873 1«07
DeBe 2e U4 tenn?
faléd 1«28 1401
1,901 1491 2s98
1e 34 ] ettt ER
1.19 192 e it
14313 1232 3e 1)
1.{}) v“}-’)g 1. 2h
105 1.8 I.13
a8 2720 T 52
14086 2a2 0 3674
1.1% 14704 .72

COUNTENCLOCK®1SE STARTING Al

r

i

=
24

4or A

3

e

-
b

WAl S h

o
% B 5 & % Bt & b 8 8 e

UTLY b e N O e B
e D e W B ke g O

Lt a

Fun

Wl

CH

g

LA

a0
P s

DL

D OSPEIDS

STARTLEYTY LLASS
{MoTeRRSIS5ECH

Soed B ol ket ol G B B

P

Wl &L St o B de & LI
B E 6 e RS 5N s s e

~ WD ONE Or N LD

o} bbb LN

N2 T

F
ie51
171
177
170
155
1«50
ieb64
1e 48
1«56
163
ie5e
157
1«74
1e 556
1.55
1268

OT-1IV
EACH DIRECTION

CLASSES FUR

FREPGUEMCY OF ATMIOSOHERLIC STABILITY

Butte, Montana

STABILETY CLASS

aF TIME IN £ACH

FRACT LN

SECT xR

L

Al-11

e BTN UL el B MO O e o O D
O0 30 e (7 A |72 0 O A M et MO
AT e P OO T e O P e A
4 9 2 8 & 8 B W 28" s a0

CCoOoOOoOOoOCooooOC

o P ALY e N DU R O B MY
ot Y OF T et (M O O e o L) e Y
P WM SO OO
AR Re® R e E RN R LN
COOoOOoOCOoCCOOOQOo0

R A D N AN O S e
TP e P D I N RN D A T el O
N A e T YA PT e O et i T
Aok O D M e m P A P D 00 )
 ®* n s " 5 @& % 2 ¥y e P p e gpn
DOOCCOODOODoOODooC

WD M T O N O N D Ty
G Pt i e o e Y0 OO
MG W TN e SN AN O
o w] el {0 et i C3 DO YD -t
PR s & # v oBR AR e e .
COOoOUOOoOQOoToooood

3

U O e R0 e B U
MY P B MY et 10 G0 T
O me WM O B YN
et PO TN e e OO D
. 2 ® & B T s ® a =

O OoOQOODOOO

746

13 10

-

24

0400

3
Dal
G»0501

0. 0769

FaY
[

Co e Ot ) =T WO M DY 0
e OO v E DU PTG DU T N e U0 P D
DD NN O et e KO DD
QO QT OGO Ooe
® R ®* % # & 9 ¢ F & 3 ¥ B &P~
OO oo Om

v O AT P S0 O e O3 o
Butte, Montana - ¢erauirvC1sy 0% aInD {1070

10D T ARD FREIENTY

A
i fio%){;fi 1+05
2 D081 Tal5
: Dal 24 Na?7
h NaN14 1215
6 fl.fiiR 1-13
% G329 Qw35
7 Q0R7 lal5
£ 0118 DeT7
4 e 108 D477
in e 081 30
11 Ne D57 1.02
12 Ne 171 I«15
i e N4y 1) Yoi7
146 Qe y D e 46
i5 G100 1«15
15 0.089 1al1%

ATHD DIHCCTINNS AVFE NUMETFD COUNTE PCLOCK 0] SE

MSOAND TRUT-&VEIRPAGT

VIR
Te 35
1373
t 238
1o 2
fe31
o1
1437
14210
1a21
a2l
154
1.87%
174
{57
165
149

STARTING

TLENS

[

Dad el i kb R e e PN T TN s N O R RO D
& & & a ¥ ® 0 8 @ B B B W s G

DWW WO S Do NS N

}.."

S B

TN e

N AN

-~

T b

030

ifed

NI SPLINS

D e

FACH
Mo T-RSISECH

U P TN N e e e B

a " 8 & & P 4 & & 8 g T @

¥
£

W
»

WO e O L mow b (0D =y (5 30D
WA G De e QD P O e s N D W

1

4e 3)

DL

NIRRT

3 & 9 3 8 & & ¥ & & 5 8B
= D VNN O B N
Wl DN Y e WD O o DN

Lid G (o L LA L L) Sl Rl g L G IO G L

o
48]

Jett7

STABILITY CLASS

& % 8 5§ 6 % 56 s s e W
i L L e N L B NS R e D
i BHEerAND AN ® e

ek o ok ik b gk Pl pak Pt o Bk et ek o b

¢1-1V
Butte, Montana

- FREGUENCY

3F OATHMOSPHERIC STARILITY CLASSES

March through November average

SECTQO?

A
00021
G.0019
Da00332
D«0139
et 393
D.0154
D+0719
D055
J0.0327
D052
C=0343
D.013%1
00055
00078
Je0128
DaN24813

FRACIION

® & & ¥ @ & & ¥
rJ Wk Lk B e 3O O
N LD E D

O R e DN b
N LT L R P

to U

DB OODDODSO

.
n
=

0. 1069
0. 0870
C.0523
0. 3893
Gae{)4RY
008428
N+0494

C

004859

0.0603

01225
J.0895
0N,1908
0«+1513
018732
Os 1565
0s-1313
01000
0208986
0.0877
00015
00366
J:0565

OF TIME

0

COoARDLI2ODToDOOQ

0 % 5 ¥ &N g b ®s w6 now
NP IOME BN WL
T e O W D e (OO NS B O N
WO R &0 &0 5 U0 5 SO0
ON RN BRGNE AN DD

IN FACH STABILITY CLASS

FIOIR EACH DIRECTION

rt

PO ODOLOCODDOODDTOo0
& % % & 0N u o0 @ U B 5 e
g D e e o S DO N
WMy kT g e e B ek T L e LS
b OB D B D N

G P om0 ot o pomt pot e vk o ek (U O 1M

¢ET-TV
Butte, Montana - ¢fRe@ITHCIFS OF ®IND DIRFCTIANS AND TRUF-AVERAGE AIND SPLEODS
March through November average

A IND TawAxD FROQJQUENCY W IND SPEEDS £ FACH STARILITY CLASS
[METERS/ZSECH
A i C 2 € ¥
1 0.108 D277 Yo aH 207 72 .73 155
2 0ai19 D77 {712 Tad 2 541 22060 1. 36
3 {} o 3 A7 1450 14457 3427 5oae 5 3447 1.356
4 D032 1i.13 1,39 1.9 Se 37 3.05 1435
5 e 1H 150 14373 F2072 433 3222 1.44%
% Qe 14 150 tall g Te 27 hel? 3. 29 1.17
7 3024 Da77 167 2¢e57 2ebB2 289 130
4 0080 150 iae882 2s 41 3. 50 3.438 1,15
9 DeDB3 1.01 1446 de 60 4 47 3. 39 1.33
() TaBG 170 f1aH28 1a 32 4 .83 3.H3 le22
i1 G104 150 T1e33 Ta ) 5:H0 3276 1+433
12 0100 Oa.R2 1.80 3, 8% 5895 3.82 130
13 a4 1.50 1835 1.127 Hal7 3.60 lal17
i3 P?-.G‘:)f! 1-:-'{) 1.’_311 4;21‘1‘:! f}tifi 3-59 1.21
10 De}&2 is6 1,30 1enH S5 44 3«37 1«30
149 707D Da-““f) 1401 Ta630 E)ofj’_’ 30“37 1.#6

SIND DIRECYIOND ARL NUMPAIRED COUNTERCLOCK R ISL STARTINMG AT 1 FUR DUF NITH

i

71-1v
Appendix 2

DIFFUSION EQUATION USED FOR THE ESTIMATION OF RADON-220 EMISSIONS
AZ-3

An equation developed by Culot and Schaiger (ref. 2, Sect. 4.3) was
used to estimate the “20Rn release from the open-pit mine, the ore pile,
and the tailings pile. This equation was also used in the ERDA-1541
(ref. 1, Sect. 4.3) study. This equation, which describes the steady-
state diffusion of radon from porous, uniform solids containing the

radium parent, is

- g fE _L
Jg = D tanh( - ) . (1)

where

Jo, = radon flux at the surface of the solids, Bq/m?-sec,

S = production rate of radon in a unit volume of the solid,
Bq/m3.sec,

k = effective diffusion coefficient of radon in the interparticle
void space, m?/sec,

p = void fraction: the fraction of total volume which is not
occupied by solid particles (this is often called porosity
and should not be confused with the porosity of an individual
particle),

A = radon decay constant, sec‘l,

L. = depth of the solids medium, m.

The term vk/Ap is called the relaxation length. If the depth, L, of the
so0lids is 22 or 3 relaxation legnths, then tanh L ') approaches 1,
i/ Ap

and radon flux from the solid surface is described by

J =8 vk/Ap . : (2)

O

In the present study the depth of the ore body, the ore storage pile, and
the tailings pile was sufficient to use Eq. (2).
A2-4

The production rate of radon, S, is calculated by the following

equation:

8§ = Cp Eo) , (3)
where

CRa = concentration of radium parent, Bq/kg,

E = emanation factor, dimensionless (this factor represents the
fraction of radon which escapes from the solids particles

and reaches interparticle void space),

o = bulk density of solids, kg/m3,

A = radon decay constant, sec” !l.

By combining Egqs. (2) and (3), Egq. (4) is obtained:

Jo = Cp Eor/2 (pmh)1/2 (4)

In all our estimates of “20Rrn release, we assumed that the emanation
factor, E, was the same for 220Rn (t1/2 = 55.6 sec) as it is for 222Rn
(3.30 x 10° sec). Values of E have not been measured for 220Rn. 1If the
release mechanism of 220Rn is primarily a vesult of recoil energy of
decay, this may be a good assumption. However, if the rate-controlling
process is governed by gaseous diffusion through the solid, along grain
boundaries, or from intraparticle porosity, the assumption would make our
estimates of 22URn release much too high. Reported values of E for *?ZRn
range from about 0.01 to 0.23. We used a value of 0.23 in all of our
calculations so that a conservative estimate was obtained. Clearly,
measurements of E values for 220Rn from thorium—-containing solids are
needed.

In calculating the radon flux from the mine, ore pile, and tailings,
the only wvalues which change for the different media are (kp"l)l/2 and p.

Therefore, we substituted £ = 0.23, Cry = 17.7 x 103 Bq/kg, and the value
AZ2-5

for A of 220Rn (0.0125/sec) in Eq. (4) and obtained Eq. (3), which was
utilized as the general equation for an estimation of 220Rn release from

thorium~containing solids:

3, = 4550 (k/p)1/2 (5)
Appendix 3

RADON-220 RELEASE FROM THE OPEN-PIT THORIUM MINE

A3-1
A3-3

The “?0Rn flux was estimated using Eq. (5) (Appendix 2) after
making the assumption that the in-place ore density was 2.25 x 103 kg/m3
and the value of k/p was identical with that of 2??Rn from the Ambrosia
Lake deposit (1.65 x 107°% m?/sec):

J, = 455 x 2,25 x 103+(1.65 x 1076)1/2 = 1,32 kBq/m?-sec .

Therefore, for the 1.21 x 10%m? (3-acre) mine surface the source

term ST is
ST = 1.32 x 1.21 x 10% = 16 MBq/sec .

The value of k/p of 222Rn from the Ambrosia Lake deposit was cal-
culated using Eq. (4) (Appendix 2) and the following values for the
constants in Eq. (5):

Jq 19.9 Bq/m?-sec ,

il

2,25 x 103 kg/m3

o
i

Aopp = 2.097 x 107% |

]
i

Ra 20.7 kBq/kg ,

E=0.23.
Appendix 4

RADIOACTIVITY CONTAINED IN DUST GENERATED BY MINING OPERATIONS

A4-1
A4-3

The principal traffic in the mine area will be due to front-end

loaders and the ore trucks plus activity of rippers and bulldozers,
Front-End Loaders [3 m3 (4 yda) capacity]

The fractured ore will have an apparent density of about 80% of

theoretical or 1.8 Mg/m3 (1.8 metric tons/m3).

3m3 x 1.8 mg/m3

Capacity of loaders

= 5,4 Mg/load

Moo+ " i = 1.6 G /d&
Trips"/day for 1.6 Gg (1600 metric tons) of ore gtzffi§7IE§g

= 296 loads/day

Round—-trip distance of front~end loader = 30 m x 2

= 60 m

Distance traveled/day by front-end loaders = 296 trips x 60 m
= 18 km

= 11 miles/day

Ore Trucks [35 Mg (35 metric tons) capacity]

1.6 Gg
35 Mg capacity

it

"Trips'"/day for 1.6 Gg (1600 metric tons) of ore

i

46 loads/day

Round trip out of pit and return = 300 m x 2

600 m

i

(Assumes 10% grade out of pit of average depth of 23 m plus 75 m travel

in pit. Does not include travel distance from mine to mill.)
Ab—4

ii

Distance traveled/day by ore haulers = 600 m x 46 trips

ii

28 km/day

17.4 miles/day

Observations made by PEDCO-Enviroomental Specialists, Inc.,* show the

rate of dust generation relates to vehicle speed as follows:

E = (76)(1.158)° ,

where
E = dust emission in mg/vehicle-meter from dry rvoad,
s = vehicle speed, m/sec.

An equivalent vehicle speed of 8.9 m/sec (20 mph) was selected for the
mine vehicles, This is probably too high but is justified on the basis
that heavy equipment is operated at high engine speeds with an attendant

increase in dust from air blown by the engine cooling fan. Therefore,

E = 0.285 g/vehicle~meter (1.01 1b/vehicle-mile)

Dust generated by loaders and ore trucks = (17.7 km/day +
28 km/day) (103)

(0.285 g/vehicle-
meter)

il

13 kg dust/day

i

29 1b dust/day

Other mine activities such as ripping, bulldozing, drilling, and selective
blasting will double this value. However, routine wetting with water

should reduce dust generation by 50%,* resulting in an estimate of

 

%

PEDCO-Environmental Specialists, Inc., "Investigation of Fugitive
Dust — Sources, Emissions, and Control," PB 226 693, Cincinnati, Ohio,
May 1973.
A4~5

13 kg/day (29 1b/day) of fugitive dust from mine operations. Although
thorium-bearing rock will become spread around the pit, it is assumed
that dust containing no thorium will dilute the fugitive ore dust to a
concentration of about 0.25% ThO,., The isotopic content of the fugitive

dust is given in Table 4.1 of the report text.
Appendix 5

ORIGEN CODE CALCULATIONS OF RADIONUCLIDES IN EQUILIBRIUM WITH
THORIUM IN THE ORE AND IN THE MILL TAILINGS

A5~1
A5-3

Thorium Ore

The radionuclide concentrations of the ore were computed from
ORIGEN code calculations of the quaatities of a daughter in equilibrium
with 1 g of thorium (Table A.5.1). The wvalues listed in Table 4.3
(Sect. 4.2) were computed by multiplying the values in Table A.5.1 by
the factor 4.39 x 10”3, which is the weight fraction of Th in a thorium

ore of 0.5%Z ThO, content. For example, 228Th concentration is

228Th = 4,39 x 10~3 x 4.03 x 103 = 17.7 Bq/kg .

Table A.5.1. Calculated values of radionuclide
activities and masses in equilibrium with 1 g
of thorium (by ORIGEN code)

 

 

Buclide Activity (kBq) Mass (g)
2327h 4.03 1.00E0%
2287y 4.03 1.33E-10
228p¢ 4.03 4. 8BE-14
2283q 4,03 4.67E~10
224p4 4.03 6.83E-13
220gn 4.03 1.19E-16
216pg 4.03 3.14E~19
212pg 2.59 3.95E~25
212py 4.03 7.47E~15
217pg 4.03 7.84E~14
20871 1.46 1.35E-16

 

Read as 1.00 x 100,

Dry Tailings

The radionculide concentrations of the tailings were computed from
ORIGEN code calculations of the quantity of thorium daughters remaining
after extraction of 1 g of thorium from an ore with a 91% extraction
efficiency (Table A.5.2). Removal of 1 g of thorium with an extraction
efficiency of 91% from the thorium ore (0.5% ThO,; 0.4397 Th) produces
about 250 g of tailings. This quantity is calculated as follows:

mass of tailings per g of Th = 1 + (0.91 X 4.39 x 1073) = 250 g .
A5-4

Tahle A.5.2. Adtivity of tailings left from the extraction of 1 g
of thorium: 91% extraction (from ORIGEN code calculations)

 

Activity (Bq)

 

Nuclide

 

Discharge 1yr 3 yr 10 yr 100 yr 300 yr 30,000 yr
2327 4.00E24 4.00E2 4.00E2 4.00E2 4, 00E2 4.00E2 4 ,00E2
2281p 4.00E2 1.56E3 2.64E3 2.26E3 5.85E2 4,00E2 4 .00E2
2284¢ 4.44E3 4.03E3 3.36E3 1.84E3 5.81E2 4.00E2 4.00E2
22Bpg 4,44E3 4.03E3 3.36E3 1.84E3 5.81E2 4 .00E2 4.00E2
224pa 4. 44E3 1.57E3 2.64E3 2.26E3 5.85E2 4.00E2 4.00E2
229Rn 4.4L4E3 1.57E3 2.64E3 2.26E3 5.85E2 4.00E2 4.00E2
216pq 4. 44E3 1.57E3 2.64E3 2.26E3 5.85E2 4.00E2 4.00E2
212p, 2.84E3 1.C00E3 1.69E3 1.44E3 3.74E2 2.56E2 2.56E2
212p4 4.44E3 1.57E3 2.64E3 2.26E3 5.85E2 4.00E2 4 .00F2
212pp 4, 44E3 1.57E3 2.64E3 2.26E3 5.85E2 4.00E2 4.00E2
2087y 1.60E3 5.62E2 9.51E2 8.14E2 2.10E2 1.44E2 1.464E2

 

aRead as 4.00 x 102.

The values for tailings listed in Table 4.3 (Sect. 4.2) were obtained by
multiplying the appropriate values listed in Table A.5.2 by the factor 4.
At discharge, of course, the daughter concentrations in the tailings are
equal to those of the original ore.

Note from Table A.5.2 that after about 100 years, the daughter
activity, originally associated with the separated thorium, has about
completely decayed. In comparison with uranium mill tailings, which
contain an 226Ra daughter (t1/p = 1622 years), this is a relatively short

time.
Appendix 6

MODEL TAILINGS IMPOUNDMENT

Ab-1
A6-3

The model used for impoundment of the tailings is a natural wedge-
shaped basin (Fig. A.6.1). The upstream face of the dam slopes 27°
(about 2:1) with the horizontal. The walls of the basin are assumed to
be perpendicular to triangle ABD in Fig. A.6.1. The tailings surface
slopes downward 1° with the horizontal along line AC, and the bottom of
the basin slopes upward 1° from the upstream face of the dam along line

BD. The length of dam, d_ , necessary to contain a given volume of

>
tailings at a fixed dam hiight, dy, can readily be calculated from the
triangular area of the tailings represented by triangle ACD. In this
study we choose to let the maximum value of dj be 30.5 m (100 ft). The
cross-sectional area of the tailings (triangle ACD) can easily be cal-
culated in terms of dj, using a Hewlett-Packard model HP-67 programmable
calculator and the Triangles Program Card (Standard Pac SD-07-07).
Relationships of the triangular areas to d, and the relationships of

dy, to the various sides of the triangles used to calculate the surface
areas of the tailings and the pond, are given in Table A.6.1. The
calculated value of dy required to contain the 20-year accumulation of
tailings (5.86E6 m?®; 207E8 ft3) is 441 m (1450 ft). 1In this study the

evaporation rates of water from the pond were sufficiently high to permit

ORNL DWG 78-5028

 

26°
POND AREA

I78°
2e /7 ¢C
SOLID TAILINGS AREA

DAM

152°
27°

€ 0

 

Fig. A.6.1. Cross section of the natural wedge-shaped basin.
Ab-4

Table A.6.1. Relationship of triangular areas and sides
to the dam height (dh)

 

. a
Geometric term Relation to dh

Triangular areas

ACD 14.3057dh2
ABC 15.3206dh2

Triangle sides

AB 59.2526d

AC 29.6308d:
BC 29.6308dh
CD 27.6679dh
AD 2.2027dh

 

adh = AE (in Fig. A.6.1).
the dy and dy values for containment of the tailings to also be sufficient
to contain all of the pond liquor. Since this calculation is only approx-
imate, no contingency was allowed for abnormal weather conditions.

Once the values of dj and d; have been determined for containment
of the 20-year accumulation of tailings, it is a relatively simple matter
to calculate the surface area of the tailings. The surface area, A,
presented by the rectangular top of the tailings pile is proportional to

the one-half power of the volume of tailings, V., in the impoundment

basin:

AL =k, V2 (1)
where

ky, = a constant that is calculated from the geometric constants

in Table A.6.1.

A sample calculation of k, is as follows:

V. = 14.306d,°dy , (2)
A= de - (AC) , (3)
AC = 29.631dy, . (&)
A6~5

Combining Eqs. (2), (3), and (4), Eq. (5) is obtained:

A_ = 1.645 x 102 v 1/2, (5)
Therefore, k, is equal to 1.645 X 102 m}/2., Since there is a fixed
addition rate of tailings (9.29 x 10-3 m3/sec), Eq. (5) is more useful

if time is substituted for Vt in Eq. (5):

A_ = 8.906 x 10* g1/2 (6)

where the units of A, are m? and those of t are years.

The calculated values of A, at yearly intervals of the 20~year mill
operation are given in Table A.6.2. The value of AC is also listed,
since it is used in Appendix 7 to calculate the area of tailings

covered by pond liquor.

Table A.6.2. Characteristics of model tailings pile

 

 

Time (years) Surface area (m? x E5) AC (m)
1 0.9% 202
2 1.3 286
3 1.5 350
4 1.8 404
5 2.0 451
6 2.2 495
7 2.4 334
8 2.5 562
9 2.7 606
10 2.8 639
11 3.0 670
12 3.1 700
13 3.2 728
14 3.3 756
15 3.5 782
16 3.6 808
17 3.7 832
18 3.8 as7
19 3.9 880
20 4.0 903
Average 2.8 623

 

TRead as 0.9 x 10° m?.
Appendix 7

CALCULATION OF AREAS FOR DRY TAILINGS BEACH AND POND DURING
THE 20-YEAR OPERATION OF THE MILL

A7-1
A7~3

Calculation of the volume of the pond and its surface area as a
function time is more complicated than is the same calculation for the
tailings, by virtue of the fact that the water is continuously lost by
evaporation at a variable rate until the volume becomes constant at
steady state. An equation for calculating the volume of the pond as a
function of time was derived with the assistance of H. W. Godbee of
ORNL. The calculated volume in tura could be used to calculate the
surface area of the pond. We assumed no loss from the pond by seepage.

The derivation is as follows:

Let
I = input of liquid to the pond,
0 = output of liquid from the pond by evaporation,
de = change in volume of pond:

then
1 -0 = de . (1)

Because there is a fixed rate of addition of liquid to the pond, R,

the increase of I with time is described by Eq. (2):
1 = Rdt . (2)

Since it was shown in Appendix 6 that surface area of the top of a

triangular wedge is given by

>
I

o = ko Vpl/2, (3)

Ap = surface area of pond, m2,

= volume of pond, m3,

<
o]
|

geometric constant, ml/z;

O??‘
I
A7~4
therefore
0 =k ko V72, (4)

where
k] = evaporation constant, m/sec.

After combining the two constants, Eq. (5) is obtained:

0 = RV,? . (5)
By substituting for I and 0 in Eq. (1), Eq. (6) is obtained:

Rdt - KV,1/? dt = avy . (6)

Integration of Eq. (6) yielded Eq. (7), which was named the Bond-Godbee

equation:

_ 2R . R 2. 31/2 2R R Ko/ \
t 2 1n 5 % Vp 2 1n (2 > Vp . (7)

It is relatively easy to solve this equation by "trial and error,"
using a programmable caleculator such as the Hewlett-Packard model HP-67.
Programs were written to evaluate Vp at time t and for the value of R
necessary to yield a given value of Vp at time t. Note that the Bond-
GCodbee equation is only valid for volumes of VP less than that at steady

state. The steady-state volume is given by Eq. (8):
(Vp) steady state = K% K=? (8)

Values of k,, K, and the calculated value of Vp at steady state are given
in Table A.7.1 for the water addition rate (1.94 x 1072 m3/sec) to the

model tailings impoundments. The calculated rate of addition of water to
keep the tailings completely covered during the 20~year operation of the

mill is given in Table A.7.2. For the evaporation rate of 1.93 x 1078 m/sec
A7-5

Table A.7.1. Constants used in Bond-Gedbee equation and the
calculated steady-state volume of the tailings pond

 

 

Evaporation
Location rate (m/sec) ko(ml/z) K (m3/2/sec) Vp at steady state (m3)
Montana 1.93E-84 3.179E2 6.133E-6 9.97E6
Coelorado 2.90E-8 3.179E2 9.218E-6 4.43E6

 

%Read as 1.93 x 1078,

Table A.7.2. Calculated values of the minimum water addition rate
required to keep tailings under water over the 20-year
life of mill

 

 

Location Evaporation Minimm rate (m®/sec) Ratio of calculated rate
rate (m/sec) to the rate for model mill

Montana 1.93E-82 2.13E-2

Celorado 2.90E-8 2.77E-2 1.4

 

“Read as 1.93 x 1078,

(2 ft/year), a 10% increase in the flow rate (obtained by adding water
to the mill discharge) would keep the tailings covered over the 20-year
operation. However, at an evaporation rate of 2.90 x 1078 m/sec

(3 ft/year) an increase in flow rate of about 407 would be required.

Calculated values of the pond volume at yearly intervals are shown in

Table A.7.3 for the model pond at the Montana and Colorado sites, where
the respective evaporation rates are 1.93 x 107% and 2.90 x 1078 m/sec.
At an evaporation rate of 1.93 x 10~% m/sec, the pond volume after

20 years reaches about 557 of its potential steady-state value; whereas

at 2.90 x 10~% m/sec, it reaches about 80%. From the geometric relation-

ships (Table A.6.1, Appendix 6) and the pond volumes (Table A.7.3), values

of the area of exposed tailings, the area of tailings covered by the
pond liquor, and the total surface area of the pond were calculated.

Results of these calculations are shown in Tables A.7.4 and A.7.5.
A7-6

Table A.7.3. Change in volume of pond (V)
with time as a result of evaporation

Water input rate (R) = 1.94E-2 m?/sec

 

3 ,
Time (years) VP (m” % B6)"

 

 

Montana Ceclorado

1 0.52% 0.48
2 0.96 0.85
3 1.36 1.17
4 1.74 1.45
5 2.08 1.70
6 2.40 1.92
7 2.70 2.12
8 2.99 2.30
9 3.26 2.46
10 3.51 2.61
11 3.75 2.74
12 3.98 2.87
13 4,21 2.98
14 4.41 3.09
15 4.61 3.19
16 4.80 3.27
17 4.99 3.36
18 5.16 3.43
19 5.33 3.50
20 5.49 3.57
Average 3.41 2,45

 

 

aRead as 0.52 x 10% m3.

Table A.7.4. Evaporation surface area of tailings pond (Ap) and values of AC used to

calculate area of tailings underneath the pond

 

Time (years)

 

 

1 2 3 4 5 10 15 20 av?
A, m? x E5
p
Montana 2.31b 3.12 3.72 4.17 4.57 5.95  6.84  7.45 5.71
Colorado 2.19 2.91 3. 44 3,84 4.13 5.14  5.67  5.99 4.86
ac,%m
Montana 259 354 421 475 521 677 774 844 646
Colorado 249 332 390 433 469 582 643 680 552

 

aAverage of values calculated at yearly intervals for the 20-year operation of the mill.

bRead as 2.13 x 10° m?.

“Area of tailings covered by pond liquor is equal to AC x da.
A7-7

Table A.7.5. Calculated values for the area of taillings covered

by water and of the dry tailings beach

 

Time (years)

 

 

1 2 3 4 5 10 15 20 Av?
Tailings beach, m? x E3
Montana 0 0 0 0 4b 24 4
Colorado 0 0 0 20 60 160 40
Tailings under water, m? x B4
Montana 9c 13 15 18 20 28 34 37 27
Colorado 9 13 15 18 20 26 28 30 24

 

aAverage of values calculated at yearly intervals for the 20-year operation of the mill.

bRead as 4 x 103 m2,
C'Read as 9 x 10% m?2.
Appendix 8

EVAPORATION OF THE TAILINGS POND AFTER MILL CLOSING AND EXPOSURE
OF DRY TAILINGS SURFACE

A8-1
A8-3

The equation used to calculate the evaporation area of the pond as
a function of time was obtained by integrating Eq. (6), Appendix 7, with

a water input rate of zero (i.e., R = (Q):

thl/2 = vpill2 - 2Kt , (1)

Vpi = volume of liquid in the pond at mill closing, m3,

Vpr = volume of liquid after evaporation time t, m3,

K = evaporation constant, m3/2/sec (values for Colorado and Montana

sites previously given in Table A.7.1, Appendix 7),

t = time, sec.

Volumes of the ponds at the two locations as a function of elapsed
time are given in Table A.8.1. From these volumes, values of the areas
of the dry beach and of the pond were calculated by the same method used

in Appendix 7. The values obtained were listed in Table 4.5 (Sect. 4.2).

Table A.8.1. Volume of liquid in the tailings
pond (V) as a function of elapsed time
after closing the thorium mill

 

 

 

Elapsed time Vp (m3 x E6)
(years)
Montana Colorado
1 3.8ER4 9.7E5
2 2.5Eb 1.6E5
3 1.4E6 0P
4 6.2E5 0
5 1.6E5 0
6 2.8E2 0

 

@Read as 3.8 x 10° m3.

bCalculation by Eq. (1) estimates the pond is completely
evaporated after 2.7 years,
Appendix 9

RADON-220 FLUX FROM THE DRY TAILINGS AND FROM THE POND SURFACE

A9~1
A9-3
Dry Tailings Surface

The 220Rn flux from the dry tailings surface during mill operations

was calculated using Eq. (5) from Appendix 2 as follows:

Jo = 445p(kp—1)1/2 ,
Jo = 455 x 1.64 x 103 x 103 x (5 x 1078)1/2 |
Jo = 1.67 kBq/m? » sec (or 4.51 x 10" pCi/m? « sec) .

1

The following values of p and kp ' were utilized:

1.64 x 10° kg/m3 ,

P

kp~! = 5 x 107¢ m?/sec

These values were utilized by previous investigators (ref. 4, Sect. 4.2.8)
as being applicable to uranium mill tailings.

A factor of 0.6 was applied for decay of 224pa in calculating the
flux after shutdown of the mill. This factor was determined from a

graphical plot of the data listed in Table A.5.2, Appendix 5.
Surface of Pond

It was assumed that radium daughters of the thorium decay chain had
the same solubility as that observed in the pond liquor of a uranium mill.

Using Eq. (4), Appendix 2, the source term is as follows:

i

J 5.14 x 10% x 103 x (0.0125)1/2 (1.13 x 107%)1/2 |

O

Jo = 19.3 Bq/m? « sec (or 522 pCi/m? + sec)
The following values for Cgg of 224Ra, p, and kp~! were utilized:

Cra = 5-14 x 103 Bq/kg of 22%Ra ,

1 x 103 kg/m3 ,

p=
i

1.13 x 107° m?/sec ,

P;-I

lUI
facd
i

= 0,0125/sec .

>
)
ro
o

!
A9-4

This calculation probably yields a source term that is optimistically
low. The action of the prevailing wind on the surface of the pond would
cause mixing of the upper liquid layer and hence enhance diffusion of the
220Rn, However, we were unable to locate a model in the literature which

took such a mixing process into account.
~ Pl

Ln
I

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