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SE( ,h}

INTRODUC TION

x}‘uf h()llluxrl‘.(a U LA ‘.l‘llllfi~‘ 1€l reactor .A‘\‘)(‘lr\ to ollie i)['!'!lll.l‘

of efficient breeding and power generagtion, at a reasonable cost, However,

homogeneous reactors using water solutions of the fissionable material
cannot operate advantageously at high temperatures without the disadvantage
of very high pressures, Another class of fluids, the alkali metal hydroxides,

have a number of the attractive [eatures of water and will permit high-

temperature operation al low pressures,

’

The advantages of NaOH are a low ma iting point (605 F), satisfactory

nuclear properties, and favorable heat-transfer characteristics Because
of their smaller absorption cross scctions, LAa'"OH and Li'OD would appear
better for breeder application, although their melting points (~84. F) ar

higher than that of NaOH, and hittle 13 known of their chemical behavior,

Nhese factors
SURRest that a homogeneous breeder reactor using an alkali metal hvdroxide
solution might be feasible,

'he work rc';»wr!(‘.! here was undertaken to determine whether

a re
actor of this type 1y \.\".”llc Of breeding,
(Ii'\l'H/\l (.\).\5ll)}.l{/\ll\“\.:‘
For the reflected pile, 1t was necessary to assume a container mals
tial, core temperature, and thermal barrier, [hese ass imptions can b

only partially justified, since complete prool would require extensive labo-
ratory work,

l.h(‘ Choice Oof 21 rconium as a core container 1s based on recent

rnsum(“) and \‘xrld---tn-m;ti.( ) tests performed at Battelle, In 24-hour cor-

rosion tests, zirconium and L-nickel showed lLittle attack by sodium
hydroxide at 1000 F

AT onlum, because of its small .\Pwurp!lnn Cross section, 18 mi

tive than nickelgas a separator hetween core and blanket

[he \H‘l(l ‘~trlh\'.t'h ol Foote zirconiun 1s 3000 pst oal WO F, which i1s
.
adequate for this apphication, By adding tour per cent tin, this can be an
creased ta 24,000 pPsi without increasing the cross sechion appri vy
e CORE |

SECRET

. 10.

Corrosion tests also indicated that at present none of the metals or

allovs tested were suitable caustic containers at 1500 F.  These data made

it necessary to choose a core temperature of less than 1500 F, The tem-

perature used (1100 F) 1s a compromise between efficient power production
mnd severe corrosion,

[he use of heavy water as a reflector necessitates a low-reflector

temperature if high pressures are to be avoided, However, maintaining a

reflector temperature of 250 F requires a thermal barrier, Rough cal-
culations show that this barrier can be obtained by placing zirconium foil

in the dead-air space between the zirconium shells,

The feasibility of reactors using lithium hydroxide as a moderator is
dependent on large-scale production of highly enriched lithium 7,
useful as a moderator in a breeder,

o be
the amount of lithium 6 should not be

greater than 100 ppm,

BARE PILE

Bare-pile calculations for a homogeneous mixture of U¢ 33

and hy-
droxide were made as a quick

basis {or comparison ol various hydrn,\ulrs
as moderators, The standard two group —= one region equation was used,

Fhis equation assumes a continuous slowing-down process which 1s not

valid for a hydrogenous material, However, use of a modified age makes

the method sufficiently accurate for a preliminary feasibility study,

In calculatingr (Fernu age) {or the hydroxides,

it was assumed that
hydrogen behaves as it does in water,

Using a numerical integration method,

the hydrogen scattering cross section was adjusted to give the experimental

value ( r §3 cm*) for water, With the adjusted hydrogen cross seq tion,
a ssmilar calculation was made for NaOH and [h'OH, For the calculation
of r1.0p» the value ('U 132,.2 ¢m®) for heavy water was used, The re-
sults are Listed 1n Appendix |1

he values for p, the probability of escaping resonance capture,: and

¢« , the tast fission effect, were assumed equal to |,

SECRE]

Rl b i Ll b L ek e

i SECRET
| | R
The absorption cross sections for lithium, sodium, and hydrogen
were calculated for a temperature of 1100 F', assuming a 1 /v dependence,
Thermal values were taken {rom NBS 5), The scattering cross sections

for 0,074 ev were obtained {from Adal ). The scattering of uranium and
thorium was neglected in calculating macroscopic scattering cross sections,

Using the standard two group - one region method, calculations were
made for thorium-moderator mass ratios of zero and 0,2 with the thorium
homogeneously mixed in the core, The inclusion of thorium in the core was
proposed in the hope of obtaining sufficient internal breeding (BG = 0) to
replenish continuously the !ncl consumed, The net breeding gain was to be
obtained in a bhnhot. \

The three modontou. NaOH, u"on. Li’0OD, were considered,
The results of the criticality calculations are plotted in Figures i -« 3, Al-
though parasitic absorption is emaller in Li7OD than in the other moder-
ators, Figure 3 indicates that much larger critical radii are required in a
Li7OD-moderated pile, This is caused by the smaller slowing-down power
of the Li'OD, which permits a large number of fast neutrons to escape,

Therefore, a larger reactor is necessary to obtain sufficient moderation to
maintain crittcdlty.

For each point on the 20 per cent thorium-criticality curves, a breed-
ing ratio has been calculated, The breeding ratios have been plotted versus:
radius on their respective criticality curves, These data show that the

breeding ratios are less than 1 md, thus, all breeding gains are negative
since, by definition:

S e
BG=BR-1:=28__ .1, )
2

For a given radius, both a breeding ratio and a critical mass for the bare
pile may be obtained from Figures 1, 2, and 3, The results show that a
0.2 mass ratio of thorium to moderator in the core does not produce a

positive breeding gain, although it increases the fuel requirements by a
significant amount,

To evaluate further the possibilities of internal breeding, infinite
pile breeding gains were computed, To obtain these data, the follwlng
cquuom were solved simultaneously,

v-(l+t);.§.2

:I_‘ : (2)

BG =

‘lfch

” Nomenclature, ‘M L

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.41 3

Radius, centimeters
Breeding Rotio Versus Rodius )
04
:
§ 02
) m—r. 70 80 100
Radius, centimeters

FIGURE |. CRITICALI Y AND BREEDING RATIO CURVES FOR A HOMOGE-
NEOUS U®-NaoOH MODERATED BARE PILE

SECRET

A-I1979
Moss u‘ou r

-~ Radivs, centimeters

) l l

Breeding Ratio Versus Rod

.Breading gain = breeding rotio~ |
- ' l |

— 80 0 100 120 140
Rodius centimeters

FIGURE 2. CRITICALITY AND BREEDING RATIO CURVES FOR A HOMOGE-

NEOUS U*™-LI"OH MODERATED BARE PILE ety

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Breeding Goin

Breeding Gain

SECRET

0.4 ]
LI1"0D Moderotor !

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as}- oD : -

l /+/ AT [T

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v \ E

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Vs Mosse, kilogroms

04 \

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LI'OH Moderotor | | |
| | ‘l l
0.3 4 L 4
e e
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ag \ ] | | | JE
R X ) 27 28 29 30 LY 32

U™ Moss, kilogroms

FIGURE 8. BREEDING GAIN FOR Li"OH AND Li' OD REFLECTED

PILES

A-19012

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SECRET
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”

APPENDIX 1

Nomenclature

a Macroscopic absorption cross section of thorium,

a = Macroscopic absorption cross section of uranium,

BR = Breeding ratio,

BG = Breeding gain,
e
it
L. = Macroscopic capture cross section of v,

i¢ = Macroscopic fission cross section of U233,

Sp = Macroscopic parasitic ablorption'crou section,

v = Neutrons/fission,

ES ]
n

T3#= = Neutrons produced per neutron absorbed in fissionable
material

R; = Nyop/Ny
R; = Npy/Ny

Molecules/cm?>,

2
[

Resonance escape probability,

Fast fission effect coefficient,

SECRET

Ja 2D
A -~ Core

(1)

(2)

(3)

(4)

SECRE ]

- Y

APPENDIX Il

n e ' 2,70 u 0.15
P |
' |
LiOH 120D NaOH D,0 -ThO,
114,5 cm® 457, 2 c¢m? 104, 1 cm® 132, 2 cm®
(l‘, B9 « n.’l 0,00714 \m'l - 0,0320 « !h-l
: : > 0,0155 ¢m~ !
2.159 cm 2.552 cm - 4. 311 cm
0,354 ¢cm 1,156 ¢m - 0.313 ¢cm
; 2 : 0, 207 cm®
0, 288 (.”.;-l 0.8B04 cm= 1 0,762 (nn'l -

Assumptions

Hydrogen scattering cross section in hydroxide is the same as in
water,

Uranium scattering cross section may be neglected in calcula-

- tions of r and Lz.

For fast neutrons, the molecules of NaOH appear as ''free"
atoms of sodium, oxygen, and hydrogen, The transport cross

secthon for each atom 1s computed and the average for the
molecule calculated,

For thermal neutrons, the value for transport cross section
was obtained by averaging the scattering cross section and
then using molecular weight for A in the equation

11.t - l's[l -.;_;]

SEC 52..’1‘