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ORNL-TM-9756.txt
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'OAK RIDGE
'NATIONAL
LABORATORY
MARTIN MARIETTA |
* OPERATED BY
~ MARTIN MARIETTA ENERGY SYSTEMS, INC.
- FOR THE UNITED STATES '
DEPARTMENT OF ENERGY
ORNL/TM-9756
o e N‘! TN
oy MR LT
P s Y s It x @ L
COVER
Extended Storage-in-Place
of MSRE Fuel Salt and Flush Salt
Karl J. Notz
DIETRIRUTION OF THIS DOSUW ST IS UNLIKIT S
Eooad
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i
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I 3
TR E““i‘i
OV
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Printed in the United States of America. Available from
National Technical Information Service
U.S. Department of Commerce
5285 Port Royal Road, Springfield, Virginia 22161
NTIS price codes—Printed Copy: A07; Microfiche AO1
This report was prepared as an account of work sponsored by an agency of the
United States Government. Neither the U nited States Government nor any agency
thereof, nor any of their employees, makes any warranty, express or implied, or
assumes any legal liability or responsibility for the accuracy, completeness, or
usefulness of any information, apparatus, product, or process disclosed, or
represents thatits use would notinfringe privately owned rights. Reference herein
to any specific commercial product, process, or service by trade name, trademark,
manufacturer, or otherwise, does not necessarily constitute or imply its
endorsement, recommendation, or favoring by the United States Government or
any agency thereof. The views and opinions of authors expressed herein do not
necessarily state or reflect those of the United States Government or any agency
thereot.
e
ORNL/TM--9756
DE86 001720
Nuclear and Chemical Waste Programs
EXTENDED STORAGE-IN-PLACE OF MSRE FUEL SALT
AND FLUSH SALT
Karl J. Notz
Chemical Technology Division
With contributions from:
R. C. Ashline, Chemical Technology bivision
D. W. Byerly, University of Tennessee
L. R. Dole, Chemical Technology Division
D. Macdonald, Martin Marietta Energy Systems, Inc.,
Engineering
T. E. Myrick, Operations Division
F. Jo. Peretz, Martin Marietta Energy Systems, Inc.,
Engineering
L. P. Pugh, Operations Division
A. C. Williamson, Martin Marietta Energy Systems, Inc.,
Engineering
Date Published: September 1985
NOTICE This document contains information of a preliminary nature.
It is subject to revision or correction and therefore does not represent a
final report,
Work Sponsored by U.S. Department of Energy
Surplus Facilities Management Program
OAK RIDGE NATIONAL LABORATORY
Oak Ridge, Tennessee 37831
operated by
MARTIN MARIETTA ENERGY SYSTEMS, INC.
for the
U.S. DEPARTMENT OF ENERGY
under Contract No. DE-AC05-840R21400
&
DISTRIZUTION OF THIS DOCIITIENMT IS UMLIRITED
AB STRACT * * * * e . -* L] ® o * e
1.
EXECUTIVE SUMMARY < o « « &
l.1 HISTORY o o o o o o o &«
1.2 PROJECTIONS « ¢ ¢ o & &
1.3 CONCLUSIONS &« o « o o
INTRODUCTION « o ¢ o o o o
TORY e - e o . . . o * e
DESCRIPTION o« o o ¢ o &
PRIOR STUDIES « o ¢ o
OPTIONS « o o o o o o &
PROJECTIONS 4« o ¢ o o ¢ o
4,1 RADIOACTIVITY o ¢ o o
4.2 RADIOLYSIS o o s o o &
4,2.1 Pressure Rise .
4.2.2 Corrosion Rates
4.,2.3 Use of Getters .
HIS
3.1
3.2 SURVEILLANCE AND MAINTENANCE
3.3
3.4
4.3 INTEGRITY OF THE FACILITY
4.3.1 Cell Penetrations
4,3.2 Water Control .
»
iii
- *
4.3.3 Secondary Containment
4 GEOLOGY AND HYDROLOGY .
o> ENTOMBMENT + ¢« o o « o
6 UTILIZATION o o o o o
7 FINAL DISPOSAL « o o »
4e7.1 WIPP v o o o o o
4,7.2 Commercial Spent
4.8 IN-CELL ALTERATIONS .
4,9 CONTINGENCY PLANNING .
CONCLUSIONS o ¢ o o = o + @
5.1 EVALUATION OF OPTIONS .
5.2 SELECTION OF PLAN « « «
CONTENTS
Fuel Repository
4.7.3 Greater Confinement Disposal . .
Appendix
Appendix
Appendix
Appendix
Appendix
Appendix
A.
B.
C.
D.
E.
F.
BIBLIOGRAPHY AND REFERENCES o« ¢« ¢ ¢ ¢ ¢ o o o« &
SEMIQUANTITATIVE EVALUATION OF SIX MSRE OPTIONS
WIPP WASTE ACCEPTANCE CRITERIA .« & & 4 o ¢ o o
ANALYSIS OF MSRE CELL PENETRATIONS . « «. . . .
BUILDING 7503 DRAINAGE SYSTEMS « o ¢ o ¢ « & &
GEOLOGIC INVESTIGATIONS RELATIVE TO MOLTEN SALT
REACTOR DECOMMISSIONING e o o o« ¢ o ¢ o o o
lo
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111
125
EXTENDED STORAGE-IN-PLACE OF MSRE FUEL SALT
AND FLUSH SALT
Karl J. Notz
ABSTRACT
The solidified fuel salt and flush salt from the Molten
Salt Reactor Experiment (MSRE) have been stored at the QOak
Ridge National Laboratory (ORNL) since the reactor was shut
down in 1969. The fluoride salt eutectic, containing 37 kg of
uranium plus plutonium and fission products, is safely con-
tained in three heavy-walled Hastelloy tanks, which are located
inside a reinforced concrete cell. Removal of these salts to a
remote location is not feasible until an appropriate repository
has been identified, built, and placed in operation. Since
this may take many years, extended storage—-in-place was criti-
cally evaluated. The evaluation, which involved a preliminary
assessment of several options for enhancing the integrity of
in-place storage, including containment improvement, the addi-
tion of chemical getters and neutron poisons, and entombment in
concrete, showed that this approach was a rational and safe
solution to the problem for the short term. Entombment is
essentially nonreversible, but the other options are open-
ended; they do not 1limit the future selection of a final dispo-
sal option. Specific actions and improvements that would
enhance safe containment during extended storage and would also
be of future benefit, regardless of which disposal option is
finally selected, were identified.
1. EXECUTIVE SUMMARY
1.1 HISTORY
The Molten Salt Reactor Experiment (MSRE) was concluded in 1969
after several years of well-planned and highly successful work. This
homogeneous reactor concept was based on the thoriunrU-233 fuel cycle
and used a molten fluoride eutectic as the operating medium. This work
is thoroughly documented.
At shutdown, the fuel salt containing most of the uranium and
fission products was divided and drained into two separate tanks, thus
ensuring criticality safety. The flush salt, containing 1 to 2% of the
uranium and fission products, was drained into a third tank. The salts
were allowed to cool and freeze, thereby precluding any leakage and
decreasing further the already-low corrosion rate. The drain tanks are
made of heavy—-walled Hastelloy N, a special alloy created for the
program, which has superior strength at high temperatures and
outstanding corrosion resistance toward the eutectic fluoride system
used for the MSRE. These tanks are contained within a hermetically
sealed, stainless steel—lined, reinforced-concrete hot cell, located
below grade except for a double set of roof plugs.
A surveillance and monitoring program, which includes daily and
monthly measurements, has been in force since shutdown. There is also
an annual reheat (but not hot enough to remelt) to recombine any
fluorine that might have formed from radiolysis by (a,n) reactions on
the fluoride salt. There have been no adverse incidents or releases of
radioactivity since the reactor was shut down 16 years ago. Several
prior studies have been made of decontamination and decommissioning (D&D)
of the facility, based on removal and reprocessing of the salts and on
the assumption that a site or repository would be available to accept
this material. In fact, there is no such site or repository at present.
Nor is it feasible to reprocess the salts without major construction of
such capability, whflch would be very costly and would introduce a finite
probability of radiation exposure or release.
The present study focused on extended storage and any enhancements
to the storage mode that would benefit the storage period and also be
beneficial in view of eventual final disposal. Time frames of 1 to 20
years (short term), 20 to 100 years (near term), 100 to 1000 years
(midterm), and more than 1000 years (long term) were considered.
1.2 PROJECTIONS
The most important of these is the radioactivity projection, which
was carried out to 1 million years by using the ORIGEN2 code. (Prior
projections were truncated at 5 and 20 years.) This projection showed
two major aspects: decay of fission product (FP) activity, as antici-
pated; and decay/ingrowth/decay of actinide activity, which is somewhat
unusual and derives from the slow ingrowth of the U-233 decay chain. The
FP activity has declined by a factor of 50 since discharge, will decline
by another factor of 8 at 100 years after discharge, and will essentially
disappear at 1000 years. The fission products are the major source of
beta and gamma activity. The actinide activity will initially decay by a
factor of 4 at 1000 years but will then grow back in to about its origi-
nal level at 40,000 years before commencing final decay.
The actinide behavior is the net result of U-232 (half-life of 72
years) and plutonium decay, along with U-233 (half-life of 158,000 years)
ingrowth and then decay. Each actinide decay spawns an additional five
or six alpha decays (along with some beta—gamma activity). The alpha
activity is important for several reasons: it is a long—term source of
neutrons from (a,n) reactions on Be-9, F-19, and Li-7, which are major
components of the fluoride eutectic, and it contributes about 50 W of
decay energy for a very long time. The neutrons must be considered in
shielding calculations but do not pose an undue problem. The decay
energy is, indirectly, a problem, not because of heat but because of
radiolysis.
Radiolysis of fluoride yields fluorine plus free metal. At slightly
elevated temperatures (>150°F) recombination is rapid enough to preclude
a buildup of fluorine; however, at lower temperatures, free fluorine will
eventually form (after an incubation period of >5 years) and will then
continue to be produced., Unless the radiolysis problem is brought under
control, disposal of the salts in the fluoride form will present a signi-
ficant problem. One possible way to limit the formation of free fluorine
is by the addition of a getter - an active metal that reacts readily with
fluorine.
The physical integrity of the drain tanks and cell is of obvious
importance. This factor was considered in terms of penetrations and
control of water. No deficiencies that would jeopardize extended storage
are evident at this time in either area, but some additional work in
these areas would be beneficial.
1.3 CONCLUSIONS
At this time, extended storage of the solidified fuel salts is the
most prudent and rational course. Actions that can be easily taken out-
of-cell to enhance storage should be implemented. An eventual decision
to remove the fuel salts to a final disposal site will be tempered by
site availability in 20 years or so. A future decision concerning
whether to reprocess or not will be controlled by the ability to limit
radiolysis, which is an open question at this time but must be resolved
in the interim.
2. INTRODUCTION
The MSRE was a graphite-moderated, homogeneous—fueled reactor built
to investigate the practicality of the molten—salt reactor concept for
application to central power stations. It was operated from June 1965 to
December 1969 at a nominal full-power level of 8.0 MW. The circulating
fuel solution was a eutectic mixture of lithium and beryllium fluorides
containing uranium fluoride as the fuel and zirconium fluoride as a che-
mical stabilizer. The initial fuel charge was highly enriched 235U,
which was later replaced with a charge of 233y, Processing capabilities
were included as part of the facility for on—line fuel additions, removal
of impurities, and uranium recovery. A total of 105,737 MWh was accumu-
lated in the two phases of operation. Following reactor shutdown, the
fuel salt was drained into two critiéally safe storage tanks and isolated
in a sealed hot cell, along with a third tank containing the flush salt.
When the reactor was first shut down, the assumption was made that
the facility and the fuel and flush salts would probably be utilized
again at some later date. Therefore, the shutdown procedure was essen-
tially a mothballing operation followed by surveillance and maintenance
(S&M) procedures. These procedures were designed to ensure safe tem-
porary storage and to maintain the operational capability of the facility.
Some years later, it became evident that the facility would not be
restarted, at least not as a molten—salt reactor. A decommissioning
study was done in which two options were considered: (1) removal of the
fuel and flush salts, followed by complete dismantling of the hot cells;
and (2) removal of the fuel and flush salts, followed by entombment of
the structural compoments within the reactor and fuel drain cells. The
second option is far less costly than the first, but both are quite
expensive because of the removal of the radioactive salts, which must be
processed and repackaged. Obviously, both options require a repository
which will accept the processed and repackaged salts. No such repository
currently exists; nor is there any assurance that one will be available in
the reasonably near future, even though there are several possibilities.
Therefore, our task is to determine what steps should be taken to extend
the storage period safely and what measures, if any, should be adopted to
enhance the present storage conditions.
In dealing with these questions, there are several time frames that
represent various operational limits. These can be defined and described
as
1.
3.
4.
follows:
Short term: 1 to 20 years. This is the period during which in=-cell
operations can still be carried out with confidence. Final disposal
options will be more clearly defined at the end of this period.
During this time span, the fission product activities will decay to
about two—-thirds of their present level.
Near term: 20 to 100 years. During this period, institutional
control can be maintained; therefore, it is the logical time to
transfer the fuel (and flush) salts to the final repository. The
fission product activities will decay to about 15% of their present
level during this time span.
Midterm: 100 to 1000 years. This is a reasonable lifetime for a
man-made concrete structure. During this time, the fission product
activities will decay to essentially zero, while the U-232 and plu-
tonium activities will decay to about 3% of their present level;
however, the U-233 activity will grow in to about 180% of its pre-
sent level.
Long term: 1000 to 1l million years. Geology will be the
controlling factor for this period. During this time, only the
U-233 decay chain will have any significance. Its activity will
peak after 40,000 years at about 900% of the present level and will
then decay permanently.
3. HISTORY
3.1 DESCRIPTION
The primary reactor and drain system components are contained within
two interconnected cells; the coolant and fuel processing systems are
located separately within adjoining cells (Figs. 1 and 2). The reactor
and drain tank cells are sealed pressure vessels that serve as secondary
containment for the fuel. The reactor cell is a 24-ft-diam steel tank,
while the drain tank cell is a stainless steel—lined reinforced concrete
rectangular tank. Each cell has removable roof beams and shield blocks
with a stainless steel membrane seal that must be cut open for access.
The coolant system and fuel process systems are located within shielded
cells that are kept at a slightly negative pressure and are swept by a
containment ventilation system. Access is gained via removable top
shield plugs. The associated equipment is housed in a steel—concrete—
transite structure that has containment features. Both the containment
cells and the high-bay area are maintained under negative pressure, with
an active ventilation system consisting of centrifugal fans and roughing
and HEPA filters that exhaust through a 100-ft steel discharge stack.
The reactor heat dissipation system included a salt-to-air radiator
exhausting through a steel stack and a drain tank for storage of the
coolant salt, where this material now resides. This stored coolant salt
is essentially nonradioactive. Ancillary facilities at the site include
an office building, a diesel generator house, a utility building, a
blower house, a cooling—water tower, and a vapor condensing system.
These facilities have been described in detail in other reports.“’5’15’18
The three cells of most concern to this study (reactor, drain, and pro-
cessing) are described in terms of penetrations and "containment enve-
lopes” in Sect. 4.3
ffjor components of the material of construction,
« A fuel-salt drain tank is shown in Fig. 3; the
properties and the
Hastelloy N (also c4lled INOR-8), are listed in Table 1,19
The presence o!&the solidified, stored fuel and flush salts is the
most significant aspect of the MSRE. More than 4600 kg of fuel salt and
4300 kg of flush salt, containing about 37 kg of uranium (primarily U-233)
ORNL OWG 63-4347
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ADDIT
TANK ToR
FUEL DRAIN
THERMAL
TFANK NO. ¥
SLOWERS
SHIELD
BLOWER
*ELEC SERVICE AREA BELOW HOUSE ;
RADIATOR
HBLOWERS
Fig. 1. Basement level floor plan of Building 7503.
01
ORNL DWG. 64-597
/—0
1, l ll_,l -
7 /] _ ,
E / STark
30-TON GRANE 3 AND 10-TON
CRANES e ===
Pl waintenance ; |
} 1 CONTROL | C01 aNT
1t ROOM | i {'saLT pump ! = —
- — —J L B Lo F /
REACTOR CELL be====—= _1| | S!‘%E“’ - :
- : ocks ] b .
FUEL SALT - ; : | A
ADOITION . ANNLLUS L g / '
SHIELD BLOCKS STATION e _ N g
| o 341 swiElp
- o -1 ratecks
ExSE:TrEd‘\,W \ I'
HANG :
Sy
r——
LIQUID WASTE CELL ;
DECONTAMINATION |- ]
CELL
T
.- _ ..
\RAD!ATOR
- FUEL - i
STORAGE .. nY. Ea | A
TANK = 1 || RADIATOR
b i . BYPASS DUCT
FUELJ i i SN -
PROCESSING b ¥ .
CELL AL
- ot CODLANT SALT
Tl DRATN TANK
= FUEL “REACTOR VESSEL
FLUSH
THERAMAL SHIELD
FUEL TANK DRAIN _INE
R
e Lruee brain
NO TANK NO 2
MSRE PLANT LAYOUT, ELEVATION
Fig. 2. Elevations view of Building 7503.
T
12
OQRNL-LR-DWG 61719
INSPECTION, SAMPLER, AND
LEVEL PROBE ACGESS
STEAM QUTLET
STEAM DOME
GONDENSATE RETURN
WATER DOWNCOMER INLETS
CORRUGATED FLEXIBLE HOSE
STEAM RISER
BAYONET SUPPORT PLATE
BAYONET SUPPORT PLATE
HANGER CABLE
STRIP WOUND FLEX!BLE
HOSE WATER DOWNCCMER
‘e-untlu [}
GAS PRESSURIZATION
AND VENT LINES
T
INSTRUMENT THIMBLE
FUEL SaLl 57YSTEM
FILL AND DRAIN LINE
SUPPORT RING
FUEL SALT DRAIN TANK
BAYONET HEAT EXCHANGER
THIMBLES (32) TANK FiLL LINE
[}
o
o
PN
L
&
@
THIMBLE POSITIONING RINGS
FUEL SALT SYSTEM
FILL AND DRAIN LINE — TANK FiLL LINE
MSR Primary Drain and Fill Tank
Fig. 3. Fuel-salt drain tank.
Table 1.
13
Composition and properties of INOR-8
(also known as Hastelloy N)
Chemical compositon, 7
Ni
Mo
Cr
Fe, max
C
Ti + Al, max
S, max