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ORNL- TM- 935
COPY NO.
DATE
-
-
September 11, 1964
MSRE NEUTRON SOURCE REQUIREMENTS
J. R. Engel
P. N. Haubenreich
B. E. Prince
.
86
NOTICE
T h i s document contains information of a preliminary nature and was prepared
primarily for internal use at the Oak Ridge National Laboratory. It i s subject
t o revision or correction and therefore does not represent a final report. The
information i s not t o be abstracted, reprinted or otherwise given public dissemination without the approval of the ORNL patent branch, L e g a l and Information Control Department.
4-
.
YLEG
This report was prepored a s an account of Government sponsored work.
Neither the United States,
nor the Commission, nor any person acting on behalf of the Commission:
A. Mokes any warranty or representation, expressed or implied, w i t h respect t o the accuracy,
completeness,
any
or usefulness of the information contained i n this report, or that the use of
information,
opporatus, method, or process disclosed i n this report may not infringe
privately owned rights; or
B.
Assumes any l i a b i l i t i e s w i t h respect t o the use of, or for damages resulting from the use of
any information, apparatus. method, or process disclosed i n this report.
A s used i n the above, “person acting on behalf of the Commission”
includes any employee or
controctor of the Commission, or employee of such contractor, to the extent that such employee
or contractor of the Commission, or employee of such contractor prepares, disseminates, or
provides occess to, any information pursuant t o his employment or controct with the Commission,
or his employment with such contractor.
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CONTENTS
Page
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I n t e r n a l Source . . . . . . . .
P r o v i s i o n f o r E x t e r n a l Source .
Neutron D e t e c t o r s . . . . . . .
F l u x i n S u b c r i t i c a l Reactor . .
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E f f e c t of keff on F l u x . . .
S a f e t y Requirements . . . . . . .
I n i t i a l S t a r t u p Experiments . . .
N o r m a l O p e r a t i o n a l Requirements .
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Introduction
F l u x Due t o I n t e r n a l Source
F l u x Due t o E x t e r n a l Source
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Second Stage S t a r t u p Requirement . . . .
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F i r s t S t a g e S t a r t u p Requirement . . . . . . . . . . . . . .
L i m i t i n g Requirement on Source S t r e n g t h . . . . . . . . . .
Other Considerations . . . . . . . . . . . . . . . . . . .
Recommendations . . . . . . . . . . . . . . . . . . . . . . . .
Appendix: C a l c u l a t i o n of F l u x from a n E x t e r n a l Source . . . . .
Geometric Approximations . . . . . . . . . . . . . . . . .
Nuclear Approximations . . . . . . . . . . . . . . . . . .
P a r t i a l and Complete Shutdown and S t a r t u p
1
9
10
12
16
19
24
26
26
27
28
28
29
30
30
31
MSRE NEUTRON SOURCE R E Q U I W T S
J. R . Engel, P. N. Haubenreich and B . E. Prince
The alpha-n source i n h e r e n t i n t h e f u e l s a l t meets
a l l t h e s a f e t y requirements f o r a neutron source i n t h e
Msm.
S u b c r i t i c a l f l u x d i s t r i b u t i o n s were c a l c u l a t e d t o
determine t h e combination o f e x t e r n a l source s t r e n g t h and
d e t e c t o r s e n s i t i v i t y r e q u i r e d f o r monitoring t h e r e a c t i v i t y .
I f more s e n s i t i v e d e t e c t o r s than t h e servo-driven f i s s i o n
chambers a r e i n s t a l l e d i n t h e instrument s h a f t to monitor
the f i l l i n g operation, the calculations indicate t h a t t h e
r e q u i r e d source s t r e n g t h can be reduced from 4 x lo7 n/sec
t o 7 x lo6 n / s e c . An antimony-beryllium source w i t h an
i n i t i a l s t r e n g t h of 4 x lo8 n/sec would s t i l l produce
7 x 10' n/sec one y e a r a f t e r i n s t a l l a t i o n .
Because t h e r e i s considerable u n c e r t a i n t y i n t h e
c a l c u l a t e d f l u x e s , t h e f i n a l s p e c i f i c a t i o n of source and
type should be made a f t e r p r e l i m i n a r y f l u x measurements
have been made i n t h e r e a c t o r .
LNTllOilUC'I'J (JN
Some source of neutrons t h a t i s independent o f t h e f i s s i o n chain
r e a c t i o n i s e s s e n t i a l t o t h e safe and o r d e r l y o p e r a t i o n of t h e
MSm.
The primary requirement f o r such a source i s t o i n s u r e t h a t whene v e r t h e r e a c t o r i s s u b c r i t i c a l , t h e neutron population i n t h e r e a c t o r
i s s t i l l high enough t h a t i n any conceivable r e a c t i v i t y excursion t h e
i n h e r e n t shutdown mechanisms and t h e a c t i o n of t h e s a f e t y system become
e f f e c t i v e i n t i m e t o p r e v e n t damaging power and temperature excursions.
Besides t h e s a f e t y requirements f o r a source, t h e r e i s another,
r e l a t e d t o t h e convenient and o r d e r l y o p e r a t i o n of t h e r e a c t o r .
This
i s t h a t t h e neutron f l u x a t t h e d e t e c t o r s be high enough t h a t t h e
f i s s i o n chain r e a c t i o n i n t h e core can be monitored a t a l l t i m e s .
The
source s t r e n g t h r e q u i r e d f o r t h i s purpose depends on t h e experiment
b e i n g conducted o r t h e c o n d i t i o n of t h e r e a c t o r and t h e l o c a t i o n and
s e n s i t i v i t y of t h e d e t e c t o r s .
T h i s r e p o r t d e s c r i b e s t h e c o n d i t i o n s t h a t w i l l e x i s t i n t h e MSRE
d u r i n g t h e i n i t i a l c r i t i c a l experiment and d u r i n g subsequent s t a r t u p s ,
b o t h b e f o r e and a f t e r extended o p e r a t i o n a t power.
The source r e q u i r e -
ments f o r t h e v a r i o u s c o n d i t i o n s a r e d e s c r i b e d and t h e e x t e n t t o which
t h e s e a r e s a t i s f i e d by t h e i n h e r e n t , i n t e r n a l sources i s d i s c u s s e d .
The requirements f o r an e x t e r n a l source t o supplement t h e i n h e r e n t
source are analyzed and recommendations are made f o r a n e x t e r n a l
source and mode of s t a r t u p o p e r a t i o n t h a t s a t i s f y t h e requirements
i n a reasonable f a s h i o n .
INTERNAL SOURCE
The f u e l s a l t i t s e l f provides a s u b s t a n t i a l source of neutrons
I n the clean f u e l the l a r g e s t contribution t o the
i n t h i s react0r.l
i n t e r n a l source i s from t h e alpha-n r e a c t i o n s of uranium a l p h a
p a r t i c l e s w i t h t h e f l u o r i n e and b e r y l l i u m i n t h e s a l t .
Neutrons from
spontaneous f i s s i o n of t h e uranium add t o t h e i n t e r n a l source b u t t h i s
c o n t r i b u t i o n i s much smaller t h a n t h e alpha-n c o n t r i b u t i o n .
The uranium i n t h e f u e l s a l t i s a mixture of f o u r i s o t o p e s ,
U234, U235, U236,
and
U238;
t h e p r o p o r t i o n s depend on t h e choice of
f u e l t o be used i n t h e r e a c t o r .
Table 1 g i v e s t h e compositions of
t h r e e mixtures t h a t have been considered, a l o n g w i t h t h e i s o t o p i c
composition of t h e uranium i n each.
A l l of t h e uranium i s o t o p e s
undergo a l p h a decay and any of t h e uranium a l p h a s can i n t e r a c t w i t h
t h e f l u o r i n e and b e r y l l i u m i n t h e s a l t t o produce n e u t r o n s .
The
more e n e r g e t i c of t h e a l p h a p a r t i c l e s can a l s o produce neut r o n s by i n t e r a c t i o n w i t h l i t h i u m , b u t t h e y i e l d i s n e g l e g i b l e i n
comparison w i t h t h a t from f l u o r i n e and b e r y l l i u m .
Table 2 g i v e s
t h e neutron source i n t h e c o r e due t o t h e v a r i o u s uranium i s o t o p e s
'P.
N. Haubenreich, " I n h e r e n t Neutron Sources i n Clean MSRE F u e l
S a l t , " USAEC r e p o r t
August
27, 1963.
ORNL-TM-611,
Oak Ridge National Laboratory,
V
3
Y
Table 1 Composition of MSRF: Fuel S a l t Mixtures
*
Fuel Type
A
Composition"(mo1e %)
LiFb
BeF2
Z rF4
ThF4
70
23.7
5
B
C
67
29
3 -8
1
0.3
0
0.2
u234
1
1
3 3 5
93
93
m4
65
29.2
5
0
0.8
Uranium I s o t o p i c
Composition (Atom %)
336
338
1
1
5
5
a
Clean, c r i t i c a l c o n d i t i o n .
b
99.9926% Li7,
0.0074% ~i~
c
Table 2
Inherent Neutron Source i n Clean MSRF: Fuela
Fuel Type
a, n
Source
u236
A
B
C
4.3 x io5 3.1 x io5
9.2 x io3
3 . 2 x lo3
u=8
6.4 x io3
2.3 x
2
4
40
23
io3
3.8 x io5
9.9 x io3
2.8 x io3
2 . 0 x lo2
sou.rce
Tot a1
4.6 x io5 3 . 2 x io5
2.4 x
3.9 x
lo2
io5
a"Effective" core, containing 25 f t 3 of f u e l s a l t of c l e a n
c r i t i c a l concentration.
4
f o r t h e clean, c r i t i c a l loading w i t h t h e t h r e e d i f f e r e n t f u e l s .
About
97% of t h e alpha-n neutrons are produced by a l p h a p a r t i c l e s
from
t h u s , t h i s source i s p r o p o r t i o n a l t o t h e amount of
$34;
$34
i n the fuel.
The most a c t i v e of t h e a v a i l a b l e uranium i s o t o p e s from t h e
s t a n d p o i n t of spontaneous f i s s i o n i s
$38
which c o n t a i n s a much l a r g e r p r o p o r t i o n of
.
As a r e s u l t , Fuel C ,
$38
than t h e o t h e r two
mixtures, has a s u b s t a n t i a l l y l a r g e r source of neutrons from
spontaneous f i s s i p n .
The i n h e r e n t neutron source from spontaneous
f i s s i o n i s l i s t e d i n Table 2 f o r each of t h e t h r e e f u e l s a l t mixtures.
The E R E w i l l o p e r a t e f i r s t w i t h Fuel C , and t h e i n i t i a l c r i t i c a l
experiment w i l l c o n s i s t of adding f u l l y enriched uranium t o a s a l t
a l r e a d y c o n t a i n i n g d e p l e t e d uranium t o b r i n g t h e composition up t o
t h a t shown i n Table 1. A t t h e beginning of t h e c r i t i c a l experiment
the salt w i l l contain
and
$35
97% of t h e 'if!38b u t only about 0.7% of t h e
i n the c r i t i c a l loading.
$34
The combined alpha-n and spontaneous
f i s s i o n source i n t h e core a t t h i s p o i n t w i l l be about 2 x
lo3
n/sec.
A f t e r t h e MSFE has been operated a t high power, t h e f u e l w i l l
produce a s i g n i f i c a n t number of photoneutrons from t h e i n t e r a c t i o n of
f i s s i o n - p r o d u c t decay gammas w i t h b e r y l l i u m .
energy f o r t h i s source i s
The t h r e s h o l d photon
1.67 Mev, so t h i s type of source i s
i n s i g n i f i c a n t b e f o r e o p e r a t i o n when only t h e uranium decay gammas
a r e present.
Since t h e c o n c e n t r a t i o n s of f i s s i o n products and
b e r y l l i u m do n o t vary widely with t h e choice o f f u e l , t h e photoneutron
source i s approximately t h e same f o r a l l t h r e e f u e l s .
Figures 1 and 2
show t h e r a t e of photoneutron production i n t h e MSRE c o r e a f t e r o p e r a t i o n
a t 10 Mw f o r p e r i o d s of 1 day, 1 week, and 1 month.
The source i s
p r o p o r t i o n a l t o t h e power, and t h e source a f t e r p e r i o d s of non-uniform
power o p e r a t i o n can be e s t i m a t e d by s u p e r p o s i t i o n of sources produced
by e q u i v a l e n t blocks of steady-power o p e r a t i o n .
Y
5
.
L
3
X
4
8
12
24
28
TIME AFTER SWTDOWN (hr)
F i g . 1. Photoneutron Source i n MSRE Core S h o r t l y A f t e r Various
P e r i o d s a t 10 Mw.
6
TIME AFrm" S
Fig. 2 .
at 10 Mw.
(days)
Photoneutron Source i n MSRE Core A f t e r Various P e r i o d s
7
v
The gamma-ray source used i n t h e c a l c u l a t i o n s i s group I V of Blomeke
and Todd,2 which includes a l l gamma rays above 1.70 Mev.
The p r o b a b i l i t y
of one of t h e s e gamma rays producing a photoneutron w a s approximated by
t h e r a t i o of t h e Be9 ( 7 , n ) c r o s s s e c t i o n t o t h e t o t a l c r o s s s e c t i o n f o r
gamma ray i n t e r a c t i o n i n a homogeneous mixture w i t h t h e composition of
the core.
A Be 9 (7, n ) microscopic c r o s s s e c t i o n of 0 . 5 m i l l i b a r n s w a s
used,3 and t h e t o t a l c r o s s s e c t i o n w a s evaluated a t 2 Mev.
These assump-
t i o n s l e a d t o a c o n s e r v a t i v e l y low e s t i m a t e of neutron source s t r e n g t h .
PROVISION FOR EX'I'ERNAI, SOURCE
For reasons which w i l l be discussed l a t e r , it i s d e s i r a b l e t o supplement t h e i n h e r e n t i n t e r n a l source w i t h a removable s o u r c e .
Therefore a
thimble i s provided i n t h e thermal s h i e l d , on t h e o p p o s i t e s i d e of t h e
r e a c t o r from t h e n u c l e a r instrument s h a f t .
s c h . 40 p i p e of
304 s t a i n l e s s
The thimble i s a 1-1/2 inch,
s t e e l , extending v e r t i c a l l y down t o about
2 f t below t h e midplane o f t h e c o r e .
It i s mounted as c l o s e as p o s s i b l e
t o t h e i n n e r s u r f a c e of t h e thermal s h i e l d f o r maximum e f f e c t i v e n e s s .
Location o f t h e source thimble i n t h e thermal s h i e l d provides w a t e r cooling
and avoids t h e high temperatures a s s o c i a t e d w i t h t h e r e a c t o r .
A l l t h e p e r m a n e n t l y - i n s t a l l e d core- neutron d e t e c t i n g instruments a r e
l o c a t e d i n t h e n u c l e a r instrument s h a f t .
This i s a w a t e r - f i l l e d , 3 f t -
diameter tube which s l o p e s down t o t h e i n n e r s u r f a c e o f t h e thermal s h i e l d
w i t h s e p a r a t e i n n e r tubes f o r t h e v a r i o u s chambers.
Among t h e permanent
instruments i n t h i s tube a r e two s e r v o - p o s i t i o n e d f i s s i o n chambers which
w i l l be used t o monitor r o u t i n e s t a r t u p s as w e l l as t o record t h e e n t i r e
power range of t h e r e a c t o r .
These chambers a r e about 1 i n . i n diameter
2
J. 0. Blomeke and M. F. Todd, "Uranium-235 Fission-Product Production
as a Function of Thermal Neutron Flux, I r r a d i a t i o n Time, and Decay Time,"
USAEC Report ORNL-2127, Oak Ridge National Laboratory, August 1957.
3See curve i n Reactor Handbook, 2nd E d i t i o n , Vol. I11 B "Shielding",
E . P. B l i z a r d , E d . , p . 23 ( I n t e r s c i e n c e , New York, 1962).
by
6
i n . long and have a r a t h e r low counting e f f i c i e n c y of 0.026 counts
p e r neutron/cm
2
.
( O t h e r chambers i n t h e tube which have no b e a r i n g on
t h e source requirement are 2 compensated ion chambers and
3 uncompensated
s a f e t y chambers.)
Two v e r t i c a l thimbles, s i m i l a r t o t h e source thimble b u t made of
2 i n . s c h . 10 p i p e , a r e i n s t a l l e d i n t h e thermal s h i e l d to accomodate
temporary d e t e c t o r s .
The two d e t e c t o r thimbles are l o c a t e d 120" and 170'
from t h e source thimble, one on e i t h e r s i d e of t h e permanent n u c l e a r
instrument s h a f t .
The advantage of t h e s e v e r t i c a l thimbles i s t h a t they
p l a c e t h e e n t i r e l e n g t h of a chamber c l o s e t o t h e i n n e r s u r f a c e of t h e
thermal s h i e l d , whereas a long chamber i n t h e s l o p i n g instrument s h a f t
would extend back i n t o a lower - f l u x region and t h u s be exposed t o a
lower average f l u x .
I n a d d i t i o n t o t h e s e p r o v i s i o n s , t h e r e a r e s p a r e tubes i n t h e n u c l e a r
instrument s h a f t which could accomodate a d d i t i o n a l d e t e c t o r s .
I n planning t h e use of source and d e t e c t o r s i n r e a c t o r experiments
and o p e r a t i o n , an important q u a n t i t y i s t h e r a t i o of counting r a t e t o
source s t r e n g t h under v a r i o u s c o n d i t i o n s .
The counting r a t e i s t h e p r o -
duct of t h e counting e f f i c i e n c y of t h e chamber and t h e average f l u x t o
which t h e chamber i s exposed.
source-its
The f l u x a t t h e chamber depends on t h e
s t r e n g t h , t h e energy o f i t s neutrons, and, i n t h e c a s e of
an e x t e r n a l source, i t s l o c a t i o n .
The f l u x a l s o depends on t h e amount
of m u l t i p l i c a t i o n by f i s s i o n s and t h e shape of t h e neutron f l u x d i s t r i b u t i o n i n t h e c o r e , which i s determined by t h e l o c a t i o n of t h e source
and t h e value of k i n t h e c o r e .
The f l u x d i s t r i b u t i o n s i n and around t h e r e a c t o r have been c a l c u l a t e d
f o r s e v e r a l d i f f e r e n t c a s e s t o provide a basis f o r planning f o r t h e source
and d e t e c t o r s .
Many approximations had t o be made t o render t h e computa-
t i o n s manageable and consequently t h e probabLe e r r o r i n t h e r e s u l t s i s
q u i t e l a r g e , perhaps as much as a f a c t o r of t e n .
Unless s p e c i f i c a l l y
s t a t e d otherwise, t h e f l u x e s and source s t r e n g t h requirements d e s c r i b e d
i n this r e p o r t do n o t c o n t a i n any allowance f o r probable e r r o r .
Flux Due t o I n t e r n a l Source
With an i n t e r n a l , d i s t r i b u t e d source of S
n/sec i n t h e core, t h e
in
s t e a d y - s t a t e production r a t e w i l l be approximately S . /(1 - k
) n/sec.
in
eff
The f l u x a t any p o i n t i s t h e n
'
1
=
in
3
in
(1 - knPP)
The f a c t o r fin f o r a given l o c a t i o n depends on t h e shape of t h e f l u x .
For
a f l a t source and low m u l t i p l i c a t i o n , fin a t an e x t e r n a l d e t e c t o r would be
somewhat h i g h e r than a t high m u l t i p l i c a t i o n , when neutrons a r e , on t h e
average, produced n e a r e r t o t h e c e n t e r of t h e c o r e .
When t h e m u l t i p l i c a t i o n i s high, i . e . , when (1 - k e f f ) i s q u i t e s m a l l ,
most of t h e neutrons a r e produced by f i s s i o n s i n t h e core, w i t h a s p a t i a l
source d i s t r i b u t i o n c l o s e t o t h e f i s s i o n d i s t r i b u t i o n i n a c r i t i c a l r e a c t o r .
The r e l a t i o n between t h e core power, o r f i s s i o n r a t e , i n t h e c r i t i c a l core
and t h e f l u x i n t h e thermal s h i e l d w a s c a l c u l a t e d i n t h e course of t h e
thermal s h i e l d design, using DSN,4 a multigroup, t r a n s p o r t - t h e o r y code.
For t h e c a s e of a t h i c k , w a t e r - f i l l e d thermal s h i e l d , when t h e core power
i s 10 Mw, t h e p r e d i c t e d thermal neutron f l u x reaches a peak, 1 inch i n s i d e
t h e w a t e r , of 1 . 2 x 1OI2 n/cm2-sec.
lo5
The r a t i o of peak f l u x t o power i s
1.5 x lom6 n/cm2-sec p e r n/sec produced i n t h e core. It was e s t i m a t e d t h a t a chamber, 6 i n . long, a t maximum
thus 1 . 2 x
n/cm2-sec p e r w a t t , o r
insertion in the instrument shaft would be exposed to an average flux of
roughly 1 x
n/crn"-sec
p e r n/sec produced.
A chamber 26 i n . long i n
t h e instrument s h a f t would s e e an average f l u x only a t h i r d as high because
t h e s h a f t s l o p e s away from t h e c o r e .
The f l u x i n one of t h e v e r t i c a l
thimbles n e a r t h e i n n e r w a l l of t h e thermal s h i e l d would be about 3 x
n/cm2-sec p e r n/sec produced.
1x
3x
and
3x
Thus as keff approaches u n i t y , fin approaches
f o r a 6 - i n . chamber i n t h e s h a f t , a
2 6 - i n chamber i n t h e s h a f t and any chamber i n a thimble, r e s p e c t i v e l y .
4B. Carlson, C . Lee, and J. Worlton, "The DSN and TDC Neutron T r a n s p o r t Codes, '' USAEC Report LAMS-2346, Los Alamos S c i e n t i f i c Laboratory,
February 1960.
10
Flux Due t o E x t e r n a l Source
If a l a r g e f r a c t i o n of t h e neutrons come from an e x t e r n a l source, t h e
f l u x shape w i l l d i f f e r markedly from t h e c r i t i c a l shape.
Flux d i s t r i b u t i o n s
i n t h e s u b c r i t i c a l r e a c t o r with a s t r o n g e x t e r n a l source were computed by
a two-group neutron d i f f u s i o n method.
Equipoise Burnout,
two-dimensional d i f f u s i o n - t h e o r y program w a s used.
a two-group,
The r e a c t o r w a s rep-
resented by a model i n which t h e c r o s s s e c t i o n of t h e r e a c t o r and thermal
s h i e l d a t t h e midplane of t h e core w a s approximated i n x-y geometry and
t h e a x i a l leakage w a s represented by an e q u i v a l e n t buckling.
I n order
t o make t h e a n n u l a r gap between t h e r e a c t o r and thermal s h i e l d manageable
by t h e d i f f u s i o n program, t h e m a t e r i a l s i n t h e gap ( e l e c t r i c h e a t e r s ,
h e a t e r thimbles, i n s u l a t i o n , and i n s u l a t i o n c l a d d i n g ) were uniformly
dispersed i n i t .
The source w a s represented by a l o c a l i z e d neutron-
producing region j u s t i n s i d e t h e thermal s h i e l d . 6
c a l c u l a t e d by t h i s method f o r two c a s e s - w i t h
Two-group f l u x e s were
no f u e l s a l t i n t h e core
and with t h e core f i l l e d w i t h s a l t c o n t a i n i n g enough
of
0.91 (about 0.76
335
to
give a k
eff
of t h e c r i t i c a l c o n c e n t r a t i o n ) .
Although t h e neutron d e t e c t o r s respond p r i m a r i l y t o thermal neutrons,
it i s e n l i g h t e n i n g t o look a t t h e f a s t neutron d i s t r i b u t i o n s because most
of t h e thermal neutrons reach t h e v i c i n i t y of t h e d e t e c t o r as f a s t neutrons
and a r e slowed down l o c a l l y .
Figure 3 shows t h e f a s t f l u x (normalized t o
one neutron from t h e e x t e r n a l source) a t t h e core midplane along a diameter
which i n t e r c e p t s t h e l o c a t i o n s of t h e neutron source and t h e f i s s i o n
chambers.
With no f u e l i n t h e r e a c t o r , t h e f a s t f l u x w a s h i g h e r i n t h e
gap between t h e r e a c t o r and thermal s h i e l d , on t h e o p p o s i t e s i d e of t h e
r e a c t o r from t h e source, than i n e i t h e r o f t h e immediately a d j a c e n t
regions.
This implies t h a t , under t h e s e c o n d i t i o n s , most of t h e f a s t
neutrons t h a t reached t h e v i c i n i t y of t h e f i s s i o n chambers a r r i v e d by way
of t h e annular gap and t h a t very few were t r a n s m i t t e d through t h e c o r e .
Code,
5D. R. Vondy and T. B. Fowler, "Equipoise Burnout: A Reactor Depletion
USAEC Report, O a k Ridge National Laboratory, ( i n p r e p a r a t i o n ) .
6A d i s c u s s i o n of t h e c a l c u l a t i o n a l procedure i s given i n t h e appendix.
11
Fig. 3 . Fast Flux P r o f i l e s at Midplane of MSRE Core Along a
Diameter Through the External Source.
12
The a d d i t i o n of f u e l t o t h e core i n c r e a s e d t h e f a s t neutron source by
adding f i s s i o n neutrons and leakage of some of t h e s e neutrons from t h e
3.
core r a i s e d t h e f a s t f l u x n e a r t h e f i s s i o n chambers by a f a c t o r of
The f a s t f l u x e s on t h e source s i d e of t h e r e a c t o r v e s s e l were n o t a f f e c t e d by t h e a d d i t i o n of f u e l a t t h i s c o n c e n t r a t i o n .
(It w a s assumed
t h a t t h e e x t e r n a l source w a s s t r o n g enough t h a t i n t e r n a l n o n - f i s s i o n
sources were n e g l i g i b l e i n comparison).
5 show p a r t s of s e v e r a l thermal f l u x contours a t t h e
core midplane w i t h no f u e l s a l t i n t h e r e a c t o r ( F i g . 4) and w i t h s a l t
c o n t a i n i n g 0.76 of t h e c r i t i c a l ?35 c o n c e n t r a t i o n ( F i g . 5 ) . The contour
Figures 4 and
l i n e s a r e superimposed on s c a l e d drawings of t h e r e a c t o r model used i n
t h e c a l c u l a t i o n s and t h e r e l a t i v e p o s i t i o n s of t h e e x t e r n a l source and
t h e neutron d e t e c t o r s a r e i n d i c a t e d .
Table 3 gives t h e r a t i o of t h e thermal neutron f l u x a t a chamber t o
t h e e x t e r n a l source s t r e n g t h .
I n t h e c a s e s o f t h e 120° and 150' v e r t i c a l
thimble l o c a t i o n s t h e f l u x i s t h a t a t t h e c e n t e r o f t h e thimble.
For t h e
tubes i n t h e instrument s h a f t , which s l o p e away from t h e r e a c t o r , t h e
average f l u x seen by a chamber depends on i t s l e n g t h .
Comparison o f t h e two f i g u r e s and t h e numbers i n t h e t a b l e shows
q u i t e c l e a r l y t h a t t h e thermal neutron f l u x i n t h e gap and i n t h e thermal
shield, f o r
8
considerable d i s t a n c e from t h e source, i s h i g h l y i n s e n s i t i v e
t o conditions i n the core.
A s a r e s u l t t h e counting r a t e o f a chamber
i n t h e 120" thimble i s a much poorer i n d i c a t i o n of changes i n t h e core
than i s t h e counting r a t e of a chamber i n t h e instrument s h a f t .
E f f e c t of k O f t on Flux
An approximate r e l a t i o n between t h e f l u x , o r counting rate,
can be obtained by i n t e r p o l a t i o n of t h e r e s u l t s c a l c u l a t e d f o r k
and k e f f
eff
of
0, 0.91 and 1.0.
The manner i n which t h e f l u x v a r i e s w i t h k
i n t h e following way.
can be approximated
eff
Represent t h e f l u x a t a p a r t i c u l a r l o c a t i o n by
= bSx
S
f x x' + f i n i n
+ 1 - k
1 - k
UNCL A S 5 l f IED
ORNL DWO. 66H18
Fission
150" Chamber
/ Chamber
1
0
40
Chamb'er
80
I20
T
U
w
160
200
240
280
320
0
40
80
y
.
I20
160
(4
Fig. 4. Thermal Flux Contours, P e r Unit Source S t r e n g t h , Midplane
of MSRE (No Fuel Salt in Reactor).
14
UNCLASSIFIED
ORNL DUO.
Fission
~Chember
1%"
Chamber
/
Fig. 5 . Thermal Flux Contours, Per U n i t Source Strength, at
Midplane o f MSRF:. (keff 2 0.91)
.
1
Table
3.
Thermal Flux From an E x t e r n a l Source
C hamb e r
Length
(in. )
Location
120° thimble
no f u e l
keff = 0.91
any
13 x io-"
4x
6
2 x lo-"
18 x lo-"
9 x lo-"
7 x 10-6
1.7 x
150" thimble
I n s t r . Shaft
(-180')
I n s t r . Shaft
The term bS
x
Av. Flux/Source S t r e n g t h
[ (,/em2 -see )i(( n/sec ) 1
26
6 x
i s t h e f l u x due t o neutrons bypassing t h e core and should
The f a c t o r fx i n c l u d e s t h e p r o b a b i l i t y t h a t
eff'
e x t e r n a l source neutrons w i l l g e t i n t o t h e core and a l s o a shape f a c t o r
be i n s e n s i t i v e t o k
and i s
eff'
probably q u i t e low a t k
e f f = 0, r e f l e c t i n g t h e low p r o b a b i l i t y t h a t source
neutrons w i l l be t r a n s m i t t e d through t h e c o r e . Assume a l i n e a r i n c r e a s e
f o r t h e f i s s i o n neutrons produced.
I t s value w i l l depend on k
The value of fin should n o t change as much w i t h k
so
eff'
eff'
assume t h a t it i s c o n s t a n t . With t h e s e assumptions
with k
where a, b and c a r e c o n s t a n t s .
The value of c f o r each chamber l o c a t i o n can be c a l c u l a t e d from t h e
c r i t i c a l flux distributions.
Values f o r a and b can be c a l c u l a t e d from
t h e two Equtpoise Burnout r e s u l t s a t k = 0 and k = 0.91. Values f o r t h e
v a r i o u s proposed l o c a t i o n s are given i n Table
4.
These r e l a t i o n s were
used t o e s t i m a t e t h e r e a c t o r behavior and source requirements under subc r i t i c a l conditions.
16
Table
Location
Chamber
Length
(in.)
120" thimble
any
150" thimble
any
I n s t r . Shaft
6
I n s t r . Shaft
26
Note:
4.
Flux/Source F a c t o r s
a(
b(
c(cm-2)
3 x
5
4
1 x 10'~
13 x
4
3 x
3
2 x
1
6x
3 x
See t e x t f o r d e f i n i t i o n of a, b and c .
SAFETY FEQUIRFJENTS
When excess r e a c t i v i t y i s added t o a r e a c t o r which i s i n i t i a l l y
o p e r a t i n g a t a very low power, t h e f i s s i o n r a t e must i n c r e a s e by s e v e r a l
o r d e r s of magnitude b e f o r e t h e i n h e r e n t shutdown mechanism of t h e n e g a t i v e
temperature c o e f f i c i e n t of r e a c t i v i t y becomes e f f e c t i v e o r a rod drop i s
i n i t i a t e d by t h e h i g h - l e v e l s a f e t y c i r c u i t s .
on t h e MSRF.)
(There i s no p e r i o d scram
Since t h i s power i n c r e a s e t a k e s some time, a s u b s t a n t i a l
amount of excess r e a c t i v i t y may be added by a continuing r e a c t i v i t y ramp
and t h e power may be i n c r e a s i n g w i t h a very s h o r t p e r i o d by t h e time t h e
v a r i o u s shutdown mechanisms begin t o a c t .
I n the so-called "startup
a c c i d e n t " so much excess r e a c t i v i t y i s added t h a t s e v e r e power and tempera t u r e t r a n s i e n t s may be produced d e s p i t e t h e a c t i o n of t h e shutdown
mechanisms.
I n such a c c i d e n t s , provided t h e f i s s i o n r a t e follows t h e behavior
p r e d i c t e d by t h e n u c l e a r k i n e t i c s equations, t h e s e v e r i t y of t h e temperat u r e excursion i s uniqdely determined by t h e rate of r e a c t i v i t y i n c r e a s e ,
t h e c h a r a c t e r i s t i c s of t h e i n h e r e n t and mechanical shutdown mechanisms,
and t h e i n i t i a l power ( t h e mean value of t h e i n i t i a l f i s s i o n r a t e ) .
If,
however, t h e i n i t i a l f i s s i o n r a t e i s extremely low, s t a t i s t i c a l f l u c t u a t i o n s about t h e mean may permit wide v a r i a t i o n s i n t h e amount of excess
r e a c t i v i t y which can be introduced b e f o r e t h e power reaches a s i g n i f i c a n t
The problem i s d e s c r i b e d by Hurwitz e t a l . i n a r e c e n t paper7 as
level.
follows.
"When a r e a c t o r i s s t a r t e d up with an extremely weak source,
t h e r e w i l l be an i n i t i a l p e r i o d of time during which t h e power l e v e l i s
so low t h a t s t a t i s t i c a l f l u c t u a t i o n s a r e important.
Eventually t h e power
l e v e l w i l l r i s e t o a s u f f i c i e n t l y high l e v e l s o t h a t f u r t h e r s t a t i s t i c a l
f l u c t u a t i o n s have n e g l i g i b l e e f f e c t .
The i n f l u e n c e of t h e s t a t i s t i c a l
f l u c t u a t i o n s i n t h e e a r l y s t a g e of t h e s t a r t u p w i l l , however, p e r s i s t
through t h e high l e v e l s t a g e i n t h e sense t h a t t h e e a r l y s t a t i s t i c a l
f l u c t u a t i o n s determine t h e i n i t i a l c o n d i t i o n s f o r t h e high l e v e l s t a g e . ' '
I n t h e case of t h e W E , t h e i n h e r e n t alpha-n source produces more than
lo5 neutrons/sec i n t h e core whenever t h e uranium r e q u i r e d f o r c r i t i c a l i t y
i s p r e s e n t , and t h e f i s s i o n r a t e i s a l r e a d y i n t h e high l e v e l s t a g e
( s t a t i s t i c a l f l u c t u a t i o n s unimportant) a t t h e o u t s e t of any s t a r t u p
accident.
Furthermore, k i n e t i c s c a l c u l a t i o n s have shown t h a t t h e i n i t i a l
f i s s i o n rate s u s t a i n e d by t h e i n h e r e n t alpha-n source i s high enough t o
make t o l e r a b l e t h e worst c r e d i b l e s t a r t u p a c c i d e n t , which i s d e s c r i b e d i n
t h e following paragraphs.
The maximum r a t e of r e a c t i v i t y a d d i t i o n t h a t can be achieved i n t h e
MSRE r e s u l t s from t h e u n c o n t r o l l e d , simultaneous withdrawal of a l l t h r e e
control rods.
The r a t e of r e a c t i v i t y a d d i t i o n depends on t h e type of
f u e l i n t h e r e a c t o r (which determines t h e c o n t r o l - r o d worth) and t h e
p o s i t i o n of t h e rods w i t h r e s p e c t t o t h e d i f f e r e n t i a l - w o r t h curve.
The
most severe rod-withdrawal a c c i d e n t involves f u e l C and t h e maximum r a t e
of reactivity addition is 0.08s 6k/k per see.
(A higher reactivity ad-
d i t i o n r a t e , 0.10%p e r s e e , can be obtained w i t h f i e 1 B, b u t t h i s mixture
a l s o has a l a r g e r n e g a t i v e temperature c o e f f i c i e n t o f r e a c t i v i t y so t h e
r e s u l t a n t power excursion i s less s e v e r e . )
For shutdown margins g r e a t e r than 2% 6k/k and r e a c t i v i t y ramps between
0.02 and O.l$ p e r s e e , t h e power l e v e l of t h e r e a c t o r when k = 1 i s about
2 m i l l i w a t t s i f o n l y t h e i n h e r e n t alpha-n source
(4 x lo5 n / s e c )
i s present.
6 shows t h e power and temperature excursions t h a t r e s u l t w i t h f u e l
Figure
C when a l l t h r e e c o n t r o l rods a r e moving i n t h e region of maximum
~
7H. Hurwitz, Jr., D. B. MacMillan, J. H. Smith and M. L . Storm,
"Kinetics of Low Source Reactor S t a r t u p s . P a r t I", Nucl. S e i . Eng.,
166-186 (1963 ) .
15
-7
18
h
F
v
TIME
(sec)
Fig. 6 . Power and Temperature Transients Produced by Uncontrolled
Rod Withdrawal, Fuel C.
d i f f e r e n t i a l worth when k = 1 f o r t h i s c o n d i t i o n .
In t h i s calculation
t h e n u c l e a r power reached 15 Mw ( t h e l e v e l a t which t h e r e a c t o r s a f e t y
curcuits i n i t i a t e corrective action)
achieved.
A t t h a t time
0.6% excess
7.?
s e e a f t e r c r i t i c a l i t y was
r e a c t i v i t y had been added and, s i n c e
*
t h e n u c l e a r average temperature of t h e f u e l ( T f ) had r i s e n less than
2'F,
almost none had been compensated by t h e temperature c o e f f i c i e n t ;
the reactor period w a s 0 . 1 see.
I n t h e absence of a c t i o n by t h e s a f e t y
system, i n t o l e r a b l y high f u e l temperatures would be produced by t h i s
a c c i d e n t , n o t as a r e s u l t of t h e i n i t i a l excursion b u t as a r e s u l t of
t h e continued r a p i d rod withdrawal a f t e r w a r d s .
Figure 7 shows t h e r e s u l t s of a c a l c u l a t i o n of t h e same a c c i d e n t
i n which two of t h e t h r e e c o n t r o l rods were dropped (with a 0.1-see d e l a y
time and an a c c e l e r a t i o n of
5 f t / s e c 2 ) 8 when t h e power reached 15 Mw.
The temperatures reached i n t h i s case would cause no damage.
Thus t h e
i n h e r e n t alpha-n neutron source i s adequate from t h e s t a n d p o i n t of
reactor safety.
Because t h e s t a r t u p a c c i d e n t i s s a f e l y l i m i t e d with only t h e i n h e r e n t
source i n t h e r e a c t o r , it i s n o t a s a f e t y requirement t h a t any a d d i t i o n a l
source be p r e s e n t d u r i n g s t a r t u p .
Nor i s it necessary f o r s a f e t y t h a t
i n s t r u m e n t a t i o n capable of "seeing" t h e i n h e r e n t source be i n s t a l l e d ,
because i t s presence i s c e r t a i n and does n o t have t o be confirmed b e f o r e
each s t a r t u p .
INITIAL STARTUP EXPERIMENTS
Although it i s n o t a s a f e t y requirement, t h e presence of a sourced e t e c t o r combination which permits monitoring of t h e f i s s i o n rate i n t h e
s u b c r i t i c a l core i s n e c e s s a r y f o r convenient and o r d e r l y experimentation
and o p e r a t i o n .
8These values a r e conservative e s t i m a t e s o f t h e rod c h a r a c t e r i s t i c s
based on t e s t s w i t h a prototype assembly.
20
6
8
u)
12
14
16
TIME (sec )
Fig. 7. E f f e c t of Dropping Two C o n t r o l Rods a t 15 Mw During
Uncontrolled Rod Withdrawal, F u e l C.
21
More s u b c r i t i c a l observations w i l l be made during t h e i n i t i a l n u c l e a r
L
s t a r t u p experiments than a t any o t h e r time.
For t h e s e experiments it w a s
expected t h a t temporary neutron counting channels would be s e t up, u s i n g
sensitive detectors.
The thimbles i n t h e thermal s h i e l d were included
f o r t h i s purpose, t o o b t a i n a h i g h e r average f l u x a t t h e chambers than
could be obtained i n t h e n u c l e a r instrument s h a f t and a l s o t o provide
f o r i n s t a l l a t i o n of d e t e c t o r s a t more than one l o c a t i o n .
The v e r t i c a l thimbles w i l l accomodate 30-in-long BF3 chambers, w i t h
a counting e f f i c i e n c y of
1 4 counts p e r n/cm2.
Even w i t h t h e s e s e n s i t i v e
chambers, t h e i n h e r e n t source i n t h e s a l t ( c o n t a i n i n g only t h e d e p l e t e d
uranium) b e f o r e t h e a d d i t i o n of t h e enriched uranium i s inadequate t o
give a s i g n i f i c a n t count r a t e .
Because it i s d e s i r a b l e t o have a r e f e r -
ence count r a t e a t p r a c t i c a l l y zero m u l t i p l i c a t i o n , an extraneous source
i s r e q u i r e d f o r t h e c r i t i c a l experiment.
Furthermore, i n t h e determination
of t h e c r i t i c a l p o i n t and p o s s i b l y i n t h e c a l i b r a t i o n of t h e c o n t r o l rods,
it i s convenient t o be a b l e t o remove t h e major neutron source and observe
t h e decay of t h e f l u x .
For t h e s e reasons, a removable e x t e r n a l source
should be provided f o r t h e s e experiments.
The f l u x a t t h e v a r i o u s chamber l o c a t i o n s , from an e x t e r n a l source,
a t any value of k
Table
4.
can be estimated from Eq. 2 and t h e f a c t o r s i n
eff
The i n t e r n a l source s t r e n g t h i n c r e a s e s l i n e a r l y with t h e
amount of enriched uranium i n t h e core, reaching about
4x
lo5 n/sec
a t the clean c r i t i c a l concentration.
The f l u x from t h i s source can a l s o
be e s t i m a t e d from Eq. 2 and Table 4.
The p r e d i c t e d v a r i a t i o n of k
eff
w i t h enriched U c o n c e n t r a t i o n i s necessary f o r t h i s c a l c u l a t i o n , and t h i s
r e l a t i o n i s shown i n F i g . 8.
The method of a t t a i n i n g t h e c r i t i c a l c o n c e n t r a t i o n w i l l be t o add
increments whose s i z e s a r e determined by a p l o t of i n v e r s e count r a t e vs
amount of enriched uranium a l r e a d y added.
F i g . 9 i s such a p l o t , generated
from t h e f l u x c a l c u l a t i o n s d e s c r i b e d above and t h e k vs C r e l a t i o n s h i p
from F i g . 8.
Neutrons from b o t h t h e i n t e r n a l source and an e x t e r n a l
source of lo7 n see a r e included.
The bowing of t h e curves i n F i g .
9 r e f l e c t s t h e c o n t r i b u t i o n of
neutrons which a r e s c a t t e r e d around t h e o u t s i d e of t h e r e a c t o r from t h e
source t o t h e d e t e c t o r s .
A s would be expected, t h e e r r o r i s l a r g e s t f o r
22
UNCLASSIFIED
ORNL DWG. 644220
1.0
0.8
0.6
0.4
0.2
0.6
Fig.
8.
Variation
of
keff
with
Fuel
U235
Concentration.
23
UNCLASSIFIED
ORNL DWG. 64.8221
1.0
0.8
0.6
0.4
0.2
0
0.4
0.6
Fig. 9. Inverse Count Rates vs U235 Concentration.
Source Strength:
lo7 n/see.
V
External
24
t h e d e t e c t o r l o c a t e d n e a r e s t t h e source.
Because t h e bowing makes ex-
t r a p o l a t i o n less a c c u r a t e , t h e instrument s h a f t i s t h e most s u i t a b l e
l o c a t i o n f o r d e t e c t o r s i n t h e approach t o c r i t i c a l .
Therefore t h e ex-
t e r n a l source f o r t h e c r i t i c a l experiment should be a t l e a s t s t r o n g
enough t o give a conveniently high count r a t e at. a chamber i n t h e i n s t r u ment s h a f t b e f o r e any enriched uranium i s added.
A source of 1 x lo6 n/sec
would give a count rate of 10 c/sec on a chamber w i t h a counting e f f i ciency of
1 4 c/sec/n/cm2-sec under t h e s e c o n d i t i o n s .
The s t r e n g t h requirement j u s t s t a t e d i s a minimum f o r s t a r t i n g t h e
c r i t i c a l experiment.
The i n i t i a l approach t o c r i t i c a l i t y w i l l include
experimental determinations of c o n t r o l - r o d worth and c o n c e n t r a t i o n c o e f f i c i e n t of r e a c t i v i t y .
These determinations are based on c o u n t - r a t e
measurements w i t h and without t h e e x t e r n a l source p r e s e n t .
Therefore,
it must be p o s s i b l e t o o b t a i n a s u b s t a n t i a l d i f f e r e n c e i n count r a t e by
removing t h e e x t e r n a l soilrce.
Since t h e i n t e r n a l , alpha-n source i n -
c r e a s e s i n i n t e n s i t y w i t h i n c r e a s i n g uranium c o n c e n t r a t i o n , t h e e x t e r n a l
source must be s t r o n g enough t o make t h e c o n t r i b u t i o n from t h e i n t e r n a l
source s m a l l by comparison when t h e uranium c o n c e n t r a t i o n i s n e a r t h e
c r i t i c a l value.
The f l u x c a l c u l a t i o n s i n d i c a t e t h a t an e x t e r n a l source
of 1 x lo7 n/sec would produce a f l u x i n t h e instrument s h a f t a t l e a s t
100 times t h a t from t h e i n t e r n a l source a t a l l p o i n t s d u r i n g t h e approach
to critical.
a source
The d i f f e r e n c e s i n count rate which can be obtained w i t h
of t h i s s t r e n g t h are i l l u s t r a t e d i n F i g . 10.
This f i g u r e shows
t h e r e c i p r o c a l s of t h e count r a t e s p r e d i c t e d f o r a BF3 chamber (counting
e f f i c i e n c y of
proached.
14) i n t h e instrument s h a f t as t h e c r i t i c a l p o i n t i s ap-
The two curves a r e f o r t h e i n t e r n a l source alone ( e x t e r n a l
source withdrawn) and w i t h both t h e i n t e r n a l source and t h e e x t e r n a l
source.
NORMAL OPERATIONAL REQUIRFMFmS
An e x t e r n a l source of neutrons i s r e q u i r e d during normal o p e r a t i o n
of t h e r e a c t o r t o permit t h e convenient monitoring of t h e r e a c t i v i t y
during r o u t i n e s t a r t u p s .
(The s a f e t y requirements f o r a source are
s a t i s f i e d by t h e i n h e r e n t alpha-n source. )
25
UNCLASSIFIED
ORNL QWG. 64-0111
0.7
0.6
0.5
+,
JE
0-4
0
e
0
d
0*3
0.2
0.1
0
0.76
Fig. 10.
0.80
0.84
0.88
0.92
1.00
Inverse Count Rates v s U235 Concentration Near C r i t i c a l .
BF3 Chamber i n Instrument S h a f t .
26
P a r t i a l and Complete Shutdown and S t a r t u p
Y
There a r e two degrees of normal shutdown i n t h e MSFE - p a r t i a l
and
I n a p a r t i a l shutdown, t h e f i s s i o n chain r e a c t i o n i s s h u t -
complete.
down by i n s e r t i n g t h e c o n t r o l rods t o t a k e t h e r e a c t o r s u b c r i t i c a l , while
t h e f u e l s a l t continues t o c i r c u l a t e a t t h e normal o p e r a t i n g temperature.
( E l e c t r i c h e a t e r s maintain t h e temperature. )
margin i s between 2 and
i n t h e core.
7% 6k/k,
The r e a c t i v i t y shutdown
depending mainly on t h e amount of xenon
Such p a r t i a l shutdowns w i l l occur f r e q u e n t l y during e x p e r i -
mental o p e r a t i o n of t h e r e a c t o r .
Less f r e q u e n t l y , t h e r e a c t o r w i l l be
completely shutdown by i n s e r t i n g t h e rods and d r a i n i n g t h e fuel from t h e
core i n t o a d r a i n t a n k .
A s t a r t u p from a completely shutdown c o n d i t i o n w i l l involve two
s t a g e s , and t h e source and d e t e c t o r requirements a r e d i f f e r e n t f o r t h e
two s t a g e s .
The f i r s t s t a g e involves p r e h e a t i n g , f i l l i n g t h e core, and
beginning c i r c u l a t i o n .
The second (which i s t h e only s t e p i n s t a r t i n g
up from a p a r t i a l shutdown) involves withdrawing t h e c o n t r o l rods t o t a k e
t h e r e a c t o r c r i t i c a l and on up t o t h e d e s i r e d power l e v e l .
Second Stage StartuD Reauirement
For t h e second s t a g e , it i s d e s i r a b l e t h a t one instrument follow t h e
f l u x continuously, from t h e beginning of rod withdrawal u n t i l t h e r e a c t o r
i s o p e r a t i n g a t f u l l power.
purpose.
The servo-driven f i s s i o n chambers s e r v e t h i s
Therefore t h e e x t e r n a l source should a t l e a s t be s t r o n g enough
t o give a s i g n i f i c a n t count r a t e on t h e f i s s i o n chambers when t h e core
i s full of s a l t b u t s u b c r i t i c a l by t h e m a x i m u m margin a t t a i n a b l e with t h e
c o n t r o l rods
(3% 6k/k).
A c o n t r o l i n t e r l o c k r e q u i r e s t h a t one of t h e
f i s s i o n chambers have a count rate of 2 c/sec b e f o r e t h e rods can be
withdrawn i n t h i s s t a g e of t h e o p e r a t i o n .
The c a l c u l a t e d f l u x d i s t r i -
b u t i o n s i n d i c a t e t h a t t o o b t a i n t h e r e q u i r e d count rate on t h e f i s s i o n
chambers, an e x t e r n a l source of a t least
i n t e r n a l source of
4 x lo7
7 x lo6 n/sec i s r e q u i r e d .
An
n/sec i n t h e core would a l s o c l e a r t h e i n t e r -
l o c k and permit rod withdrawal.
As shown i n F i g . 2, t h e f i s s i o n products
would produce photoneutrons a t a r a t e g r e a t e r t h a n t h i s f o r s e v e r a l weeks
a f t e r a few d a y s ' o p e r a t i o n a t 10 Mw.
W
F i r s t Stage S t a r t u p Requirements
I n t h e f i r s t s t a g e , t h e r e a c t i v i t y must be monitored from t h e time
f u e l begins t o e n t e r t h e core u n t i l t h e core i s completely f i l l e d .
Before
a f i l l can begin it i s r e q u i r e d t h a t t h e rods be withdrawn t o such a
w i l l reach about 0.98 when t h e core becomes full. This
eff
procedure allows a b n o r m a l i t i e s t o be d e t e c t e d , while r e t a i n i n g some r e -
position that k
a c t i v i t y c o n t r o l which i s i n s t a n t l y a v a i l a b l e by dropping t h e rods.
To
i n s u r e t h a t t h e monitoring system of source and d e t e c t o r s i s o p e r a t i v e ,
t h e r e are two c o n t r o l i n t e r l o c k s which r e q u i r e a count r a t e of a t l e a s t
2 c/sec.
One i s on rod withdrawel and t h e o t h e r i s on d r a i n tank p r e s -
surization.
An e x t e r n a l source of
4 x le7
n/sec would be necessary t o
g i v e 2 c/sec on t h e f i s s i o n chambers w i t h n o f u e i i n t h e core, according
t o the flux calculations.
Note t h a t t h i s i s over f i v e times t h e source
s t r e n g t h r e q u i r e d f o r t h e second s t a g e .
If BF3 chambers w i t h an a c t i v e
l e n g t h of 26 i n . and a counting e f f i c i e n c y of
14 (c/sec)/(n/cm2-sec)
are
used i n the instrument s h a f t , a count r a t e of 2 c / s e c w i t h no f u e l i n t h e
core would be produced by an e x t e r n a l source of only 2 x
lo5
n/sec.
(The
f a c t o r by which t h e r e q u i r e d source s t r e n g t h i s reduced i s less than t h e
r a t i o of counting e f f i c i e n c i e s because the longer BFs chambers a r e exposed
t o a lower average f l u x . )
Use of t h e BF3 chambers t o monitor t h e f i l l i n g o p e r a t i o n would r e q u i r e some changes i n t h e r e a c t o r c o n t r o l c i r c u i t s .
The o p e r a t i o n a l
i n t e r l o c k on c o n t r o l - r o d w i t h d r a w a l p r i o r t o f i l l i n g could be bypassed
by an i n t e r l o c k which permits rod withdrawal i f a l l ( o r most) of t h e f u e l
s a l t i s i n t h e d r a i n tank (as i n d i c a t e d by d r a i n - t a n k weight, f o r i n s t a n c e ) .
This would allow withdrawal of t h e rods t o s t a r t t h e f i l l b u t would proh i b i t fhrther withdrawal w i t h t h e r e a c t o r even p a r t l y full u n l e s s t h e
f i s s i o n chambers were i n d i c a t i n g r e l i a b l y .
The c o u n t - r a t e confidence
i n t e r l o c k which must be s a t i s f i e d b e f o r e helium can be admitted t o t h e
d r a i n tank t o s t a r t t h e f i l l could be based on a s i g n a l from t h e channels
served by t h e BF3 chambers.
28
Limiting Reauirement on Source S t r e n g t h
If t h e more s e n s i t i v e chambers a r e used i n p l a c e of t h e servo-driven
f i s s i o n chambers f o r monitoring t h e f i l l , t h e l i m i t i n g requirement on
t h e e x t e r n a l source i s s e t by t h e second s t a g e i n t e r l o c k on rod w i t h drawal a t 7 x lo6 n/sec.
Because t h e second-stage rod-withdrawal i n t e r l o c k i s encountered
a f t e r t h e f u e l i s i n The core, t h e presence of an i n t e r n a l source s t r o n g
enough t o clear t h e i n t e r l o c k would e l i m i n a t e t h i s p a r t i c u l a r requirement
f o r an e x t e r n a l source.
Thus f o r many s t a r t u p s a f t e r high power o p e r a t i o n
it would be p o s s i b l e 50 depend on t h e f i s s i o n - p r o d u c t photoneutrons t o
c l e a r t h e rod-withdrawal i n t e r l o c k and t h e e x t e r n a l source requirement
would be s e t by t h e f i r s t - s t a g e , f i l l i n g i n t e r l o c k .
Other Considerations
Because t h e MSRE i s expected t o o p e r a t e f o r s e v e r a l y e a r s , s e v e r a l
f a c t o r s must be considered i n t h e choice of an e x t e r n a l source.
An antimony-beryllium source has t h e advantages of low i n i t i a l c o s t ,
ready a v a i l a b i l i t y i n s t r e n g t h s w e l l above 1
0
'
n/sec ( i r r a d i a t e d i n t h e
LITR) and freedom from t h e hazards of a c c i d e n t a l r e l e a s e of a l p h a a c t i v i t y .
The most s e r i o u s drawback i s i t s s h o r t h a l f - l i f e .
There i s no s i g n i f i c a n t
r e g e n e r a t i o n of Sb12* i n t h e low neutron f l u x a t t h e source tube, s o t h e
i n i t i a l s t r e n g t h must allow f o r t h e decay of t h e source w i t h a 60-day
half-life.
Even s o it w i l l be necessary t o r e p l a c e t h e source p e r i o d i c a l l y
throughout t h e l i f e of t h e r e a c t o r .
For example, i n o r d e r t o have
7 x lo6 n/sec a f t e r 12 months decay, an Sb-Be source w i t h an i n i t i a l
s t r e n g t h of
4x
lo8 n/sec would be n e c e s s a r y .
Although Sb-Be sources
even s t r o n g e r than t h i s can be produced i n t h e LITR, it i s probably
more economical t o use a p a i r of smaller sources which are a l t e r n a t e l y
used i n t h e %RE
and regenerated i n t h e LITR.
The decay of t h e source i s not a problem i f a plutonium-beryllium
source (24,000 y e a r h a l f - l i f e ) i s used.
Standard Fu-Be sources which
a r e o b t a i n a b l e c o n t a i n from 1 t o 10 c u r i e s o f Pu239 and produce from
1 . 6 x lo6 t o 1.6 x lo7 n/sec.
(The l a r g e s t sources are t o o b i g t o f i t
W
i n t o t h e MSaE source tube, however.)
Although t h e problem of source
decay i s avoided, t h e Pu-Be source has s e v e r a l disadvantages.
The i n i t i a l
c o s t i s high and plutonium containment must be guaranteed a t a l l times.
Also, t h e h e a t g e n e r a t i o n by f i s s i o n i n t h e plutonium (about 10 kw a t a
r e a c t o r power of 10 M w ) would probably r e q u i r e t h a t t h e source be r e t r a c t e d during high-power o p e r a t i o n .
RF1C OMMENDATIONS
1.
I n s t a l l i n t h e s p a r e tubes i n t h e instrument s h a f t two a d d i t i o n a l
neutron chambers w i t h a much h i g h e r counting e f f i c i e n c y than t h e servod r i v e n f i s s i o n chambers.
Use t h e s e during t h e i n i t i a l c r i t i c a l e x p e r i -
ments and f o r monitoring t h e f i l l i n g s t a g e of r o u t i n e s t a r t u p s .
Change
t h e i n t e r l o c k r e q u i r i n g a dependable count r a t e p r i o r t o f i l l i n g from t h e
s e r v o - d r i v e n - f i s s i o n chambers t o t h e s e chambers.
2.
As soon as t h e i n s t a l l a t i o n of t h e r e a c t o r and equipment permits,
check t h e flux/source r a t i o c a l c u l a t e d f o r t h e core with no f u e l .
(This
w i l l g r e a t l y reduce t h e u n c e r t a i n t y i n t h e source s t r e n g t h requirements )
a
Any source of lo6 n/sec o r more w i l l s e r v e f o r t h i s p r e l i m i n a r y experiment.
3.
Procure o r manufacture a source which w i l l meet t h e o p e r a t i o n a l
requirements.
The choice of t h e source type and i t s s t r e n g t h must be
based on t h e observed flux/source s t r e n g t h r a t i o and th, c o n s i d e r a t i o n s
Q
d e s c r i b e d i n t h e preceding s e c t i o n .
I f t h e a c t u a l flux/source r a t i o i s
n e a r t h a t c a l c u l a t e d , t h e choice f o r a source would be e i t h e r a 2 - c u r i e
Pu-Be source (8 x lo6 n / s e c ) or a p a i r of Sb-Be sources which would produce
3 t o 3 x lo8 n/sec (from about 123 c u r i e s of Sb12')
a f t e r an 8-week
i r r a d i a t i o n i n t h e LITR. A f t e r one Sb-Be source had been i n t h e MSRF: f o r
about 10 months, t h e o t h e r would be p l a c e d i n t h e LITR f o r i r r a d i a t i o n t o
be ready f o r exchange when r e q u i r e d .
I f t h e Sb-Be sources a r e used, it
w i l l be d e s i r a b l e t o modify t h e e x i s t i n g p r o v i s i o n s f o r source i n s e r t i o n
and removal t o make t h e o p e r a t i o n less time-consuming and c o s t l y .
Speci-
f i c a l l y , an access p o r t should be provided through t h e s t e e l c e l l cover
and t h e lower s h i e l d plug d i r e c t l y over t h e source t u b e .
APPENDIX
CALCULATION OF FLUX FROM AN EXTEFiNAL SOURCE
The neutron source f o r t h e MSRE w i l l be i n s t a l l e d i n a thimble i n
t h e thermal s h i e l d , about 20 i n . from t h e o u t s i d e of t h e r e a c t o r v e s s e l .
The v a r i o u s neutron d e t e c t o r s w i l l a l s o be, i n e f f e c t , i n t h e thermal
shield at d i f f e r e n t circumferential positions.
This r e s u l t s i n a
h i g h l y unsymmetrical c y l i n d r i c a l geometry f o r c o n d i t i o n s i n which neutrons
from t h e source c o n t r i b u t e s u b s t a n t i a l l y t o t h e neutron f l u x .
The source
i s a l s o s h o r t , compared t o t h e h e i g h t of t h e r e a c t o r , so a n a c c u r a t e c a l c u l a t i o n of t h e f l u x a t t h e d e t e c t o r s r e s u l t i n g from t h e source would
r e q u i r e t h e use of 3-dimensiona1,
c y l i n d r i c a l ( r , e, z ) geometry.
S i n c e t h e r e i s no r e a c t o r program a v a i l a b l e f o r t r e a t i n g t h i s problem,
a number of approximations were made t o reduce t h e problem t o one which
could be handled w i t h e x i s t i n g programs.
Geometric Approximations
The progran used f o r t h e f l u x c a l c u l a t i o n s w a s t h e Equipoise Burnout Code, a 2-group, 2-dimension neutron d i f f u s i o n c a l c u l a t i o n w i t h provisions f o r c r i t i c a l i t y search.
and i s l i m i t e d t o
T h i s code uses r e c t a n g u l a r (X-Y)
geometry
1600 mesh p o i n t s .
I n o r d e r t o t r e a t t h e azimuthal non-symmetry, t h e c a l c u l a t i o n s were
made i n a h o r i z o n t a l plane through t h e r e a c t o r and thermal s h i e l d a t
t h e midplane of t h e c o r e .
The a x i a l dimension of t h e r e a c t o r was
r e p r e s e n t e d by a c o n s t a n t geometric buckling i n t h a t d i r e c t i o n .
Per-
t u r b a t i o n s caused by t h e neutron d e t e c t o r s were n e g l e c t e d , so t h e plane
of t h e c a l c u l a t i o n had a n axis of symmetry a l o n g t h e diameter which
i n t e r c e p t s t h e p o s i t i o n s of t h e source and t h e f i s s i o n chambers.
There-
f o r e , it w a s necessary t o d e s c r i b e o n l y one-half of t h e plane i n t h e
mathematical model.
The l i m i t a t i o n t o X-Y geometry r e q u i r e d that t h e
v a r i o u s r e g i o n s be r e p r e s e n t e d as c o l l e c t i o n s o f r e c t a n g l e s .
The
main p o r t i o n of t h e c o r e w a s made equal i n c r o s s - s e c t i o n a l area t o t h e
a c t u a l c o r e w i t h t h e t r a n s v e r s e dimensions equal t o c o r e r a d i i .
These
-+
two requirements determined t h e s i z e of t h e l l c u t o u t s l la t t h e c o r n e r s
of t h e otherwise square c o r e .
The regions surrounding t h e core ( i . e .
t h e p e r i p h e r a l r e g i o n s of t h e r e a c t o r , t h e gap between t h e r e a c t o r and
thermal s h i e l d , and t h e thermal s h i e l d ) were a s s i g n e d t r a n s v e r s e
dimensions equal t o t h e r a d i a l dimensions of t h e a c t u a l components.
F i g u r e 11 i s a diagram of t h e r e s u l t a n t model.
Because of t h e mesh p o i n t l i m i t a t i o n i n t h e Equipoise Burnout
program, it w a s n e c e s s a r y t o omit some p h y s i c a l d e t a i l i n t h e c a l c u l a t i o n a l model.
The c o n t r o l rod thimbles n e a r t h e c e n t e r of t h e
c o r e were n e g l e c t e d i n t h i s model, as were t h e v a r i a t i o n s i n f u e l
f r a c t i o n and g r a p h i t e f r a c t i o n i n t h a t region; t h e main p o r t i o n of
t h e c o r e w a s t r e a t e d as a s i n g l e homogeneous mixture.
The p e r i p h e r a l
r e g i o n s of t h e r e a c t o r , i n c l u d i n g t h e c o r e can, t h e f u e l annulus, and
t h e r e a c t o r v e s s e l w a l l , were a l l homogenized i n t o a s i n g l e r e g i o n
(reactor shell i n Fig.
11).
The materials i n t h e gap between t h e
r e a c t o r and t h e thermal s h i e l d ( h e a t e r s , h e a t e r thimbles, i n s u l a t i o n
and i n s u l a t i o n l i n e r ) were a l l homogenized and uniformly d i s t r i b u t e d
throughout t h e gap.
A l l t h e s t r u c t u r a l material i n s i d e t h e thermal
s h i e l d w a s a l s o neglected.
A t o t a l of 1225 mesh p o i n t s i n a 49-by-
25 a r r a y were used t o d e s c r i b e t h e c a l c u l a t i o n a l model.
Nuclear Approximations
Two-Group Constants
The Equipoise Burnout program has p r o v i s i o n s for c a l c u l a t i n g 2group n u c l e a r c o n s t a n t s i f t h e n e c e s s a r y microscopic c r o s s - s e c t i o n
d a t a are s u p p l i e d as i n p u t .
I n t h i s c a s e , however, it w a s more ex-
p e d i e n t t o c a l c u l a t e t h e 2-group c o n s t a n t s s e p a r a t e l y u s i n g MODRIC,
a 1-dimensional, 33-group c a l c u l a t i o n .
Multi-group c r o s s s e c t i o n s
were prepared f o r t h e MODRIC program u s i n g GAM-1 and t h e e x i s t i n g
c r o s s - s e c t i o n l i b r a r y f o r t h a t program.
A radial c r i t i c a l i t y cal-
c u l a t i o n w a s t h e n made w i t h MODFXC f o r t h e r e a c t o r model w i t h f u e l
s a l t c o n t a i n i n g 0 . 6 of t h e c r i t i c a l c o n c e n t r a t i o n of U235; t h e presence
w
c
32
0
-
UNCLASSIFIED
ORNL DWG. 64-8223
t
Fis s ion
130' BF3
chLullbe I'
a
40
Thermal
Shield
120'
80
BF3
'Chamber
D-
120
I;:~
Shell
E
v
160
X
I
Water
Core
200
It
I
u
St a i n l e s s
>Steel
2 40
I1
I
280
'
320
Source
:
m
0
v
80
40
Y
Fig. 11.
Calculations.
-
120
- 1do
(em)
Cross Section of Model Used in Subcritical Flux
33
of t h e e x t e r n a l source was neglected i n t h i s c a l c u l a t i o n ,
The 2-group
c o n s t a n t s generated by MODRIC were t h e n used t o c a l c u l a t e t h e f l u x
d i s t r i b u t i o n i n t h e 2-dimensional model w i t h t h e source p r e s e n t .
MODRIC c a l c u l a t i o n s were a l s o used t o e s t i m a t e t h e 2-group con-
s t a n t s f o r t h e c a s e w i t h no f u e l s a l t i n t h e r e a c t o r .
I n order t o
g e t group c o n s t a n t s f o r t h e core w i t h o n l y t h e g r a p h i t e moderator
p r e s e n t , c a l c u l a t i o n s were made f o r t h e normal d e n s i t y of t h e d i l u t e
f u e l and f o r d e n s i t i e s t h a t were 0.5, 0.25, and 0 . 1 of t h e normal
value.
The 2-group c o n s t a n t s obtained from t h e s e c a l c u l a t i o n s were
p l o t t e d as a f u n c t i o n of f u e l d e n s i t y and e x t r a p o l a t e d to z e r o d e n s i t y
t o g e t c o n s t a n t s f o r t h e r e a c t o r c o n t a i n i n g no f u e l ( o n l y g r a p h i t e ) .
F o r s e v e r a l reasons, t h e above procedure does not l e a d t o comp l e t e l y a c c u r a t e values for t h e 2-group c o n s t a n t s .
The f a s t - g r o u p
c o n s t a n t s i n a given r e g i o n depend, t o some e x t e n t , on t h e energy
d i s t r i b u t i o n of t h e neutrons i n t h e r e g i o n .
T h i s energy d i s t r i b u t i o n
i s d i f f e r e n t i f a l l of t h e neutrons are born i n t h e c o r e (as w a s
assumed i n t h e MODRIC c a l c u l a t i o n s ) t h a n i f a s u b s t a n t i a l number
are born i n a n e x t e r n a l source r e g i o n (as w a s t h e c a s e i n t h e 2dimensional c a l c u l a t i o n s )
.
Some a d d i t i o n a l e r r o r i s i n t r o d u c e d by
t h e f a c t t h a t neutrons born i n t h e r e a c t o r and t h o s e born i n t h e
e x t e r n a l source have d i f f e r e n t energy d i s t r i b u t i o n s a t b i r t h .
Neutrons
born i n t h e r e a c t o r a r e products of t h e f i s s i o n process and have a n
energy d i s t r i b u t i o n t h a t corresponds t o t h e f i s s i o n d i s t r i b u t i o n ; t h e
f a s t - g r o u p c o n s t a n t s were c a l c u l a t e d f o r t h i s b i r t h - e n e r g y d i s t r i b u t i o n
(10 t o 0.011 Mev w i t h a n average of about 2 Mev i n t h e MODRIC program
used).
The energy d i s t r i b u t i o n of neutrons produced by a source
depends on t h e n a t u r e of t h e s o u r c e .
neutron energy i s about 34 Kev.
F o r a n Sb-Be source, t h e average
I n t h e Equipoise Burnout c a l c u l a t i o n
t h e f a s t - g r o u p c o n s t a n t s c a l c u l a t e d f o r f i s s i o n - s o u r c e neutrons were
a p p l i e d t o a l l t h e f a s t neutrons, r e g a r d l e s s of t h e i r p o i n t of o r i g i n .
Since absorption cross sections generally increase with decreasing
neutron energy, t h i s t r e a t m e n t overestimated t h e neutron f l u x a t t h e
chambers f o r a given neutron source.
34
Source Configuration
Irr
I n t h e Equipoise Burnout c a l c u l a t i o n , t h e source r e g i o n w a s t r e a t e d
as a s l e n d e r (2 em by 2 . 6 e m > prism
of t h e r e a c t o r model,
extending a l o n g t h e e n t i r e h e i g h t
T h i s i s a consequence of a p p l y i n g a c o n s t a n t
a x i a l buckling t o a l l r e g i o n s .
A s a r e s u l t , t h i s source i s l e s s
e f f i c i e n t i n terms of producing a neutron f l u x a t t h e c o r e midplane
t h a n a s h o r t source of t h e same t o t a l s t r e n g t h l o c a t e d n e a r t h e midplane.
No c o r r e c t i o n was a p p l i e d f o r t h e h i g h e r e f f i c i e n c y of t h e
s h o r t source because t h i s underestimate tended t o c o u n t e r a c t t h e o w r e s t i n a t e inherent i n t h e cross-section treatment.
Composition of Thermal S h i e l d
The thermal s h i e l d i s f i l l e d w i t h s t e e l b a l l s t o provide a mixture
t h a t i s approximately
5%
i r o n and 5% water.
Rowever, t h i s mixture
does not f i l l a l l p o r t i o n s of t h e thermal s h i e l d .
The source thimble
and t h e s p e c i a l counter thimbles a r e p r o t e c t e d by h a l f - s e c t i o n s of 8 - i n .
pipe which were welded t o t h e i n s i d e of t h e s h i e l d t o prevent damage
t o t h e thimbles d u r i n g t h e a d d i t i o n of t h e s t e e l b a l l s .
As a result,
each of t h e thimbles i s surrounded by a l a y e r of pure water.
The
n u c l e a r i n s t r u n e n t s h a f t , which extends t o t h e i n n e r w a l l of t h e
thermal s h i e l d , c o n t a i n s no s t e e l b a l l s .
The o n l y m a t e r i a l i n t h i s
s h a f t , o t h e r t h a n water, i s t h e aluminum i n t h e guide t u b e s f o r t h e
neutron chambers.
The neutron f l u x a t t h e v a r i o u s chambers i s
infl-Jenced more by t h e water l a y e r i m - e d i a t e l y a d j a c e n t t o t h e
thirrbles t h a n by t h e iron-water mixture i n t h e r e s t of t h e thermal
shield.
Therefore, t h e presence of t h e s t e e l balls w a s n e g l e c t e d i n
the flux calculations.
everywhere
il?t h e
T h i s l e a d s t o h i g h l y erroneous f l u x e s
thermal s h i e l d except i n t h e immediate v i c i n i t y of
t h e neutron chambers.
U s e of D i f f u s i o n Theory
The Equipoise Burnout program which w a s used t o compute t h e f l u x
d i s t r i b u t i o n s i s based on a d i f f u s i o n t h e o r y t r e a t m e n t of t h e neutron
t r a n s p o r t problem.
T h i s program w a s used because i s w a s t h e o n l y one
35
U
judged t o be p r a c t i c a l for a n approximate c a l c u l a t i o n of t h e e x t e r n a l
source requirements for t h e MSRE.
It i s w e l l known t h a t d i f f u s i o n
t h e o r y has l i m i t a t i o n s which a r e imposed by t h e b a s i c assumptions i n
t h e development of t h e mathematical t r e a t m e n t .
These l i m i t a t i o n s
r e s t r i c t t h e accuracy of t h e t h e o r y i n r e g i o n s w i t h high a b s o r p t i o n
cross s e c t i o n , n e a r r e g i o n boundaries and i n regions where t h e neutron
mean f r e e p a t h s a r e l o n g .
Since a l l of t h e s e f a c t o r s were p r e s e n t i n
t h e c a l c u l a t i o n a l model, t h e r e s u l t s of t h e c a l c u l a t i o n s can be
regarded as no more t h a n p r e l i m i n a r y e s t i m a t e s .
It i s l i k e l y t h a t
t h e c a l c u l a t e d f l u x e s are a t l e a s t w i t h i n a n o r d e r of magnitude of
t h e c o r r e c t v a l u e s b u t it i s not p o s s i b l e t o d e f i n e t h e l i m i t s of t h e
probably e r r o r .
ORNL
I
TM-935
INTERNAL DISTRIBUTION
MSRP D i r e c t o r ' s O f f i c e
Rm. 219, 9204-1
R
.
K . Adams
2.
3. R . G . A f f e l
4. L . G . Alexander
A . H . Anderson
6. S . J. B a l l
7. S . E . B e a l l
8. E . S . B e t t i s
9. R . B l m b e r g
10. C . J. Borkowski
11. H . R . Brashear
12* G . H . Burger
13. J . L . Crowley
14. S . J. D i t t o
15. N . E . Dunwoody
16-20. J. R . Engel
21. E . P . E p l e r
22. E . N . F r a y
23. C . H . Gabbard
24. R . B . G a l l a h e r
25. J. J. G e i s t
26. R . H . Guymon
27. S . H . Hanauer
28. P . H . Harley
29. P . N. Haubenreich
30. P . G . Herndon
31 * E . C . Rise
32 V . D . Holt
33. P . P . Holz
34. A . Houtzeel
35. T . L. Hudson
36. R . J. Ked1
37. A . I . Krakoviak
38. J. W . Krewson
1
L.
B. Lindauer
D . Martin
41. H . G . MacPherson
42. H . C . McCurdy
43. W . B . McDonald
44. H . F . McDuffie
45. C . K . McGlothlan
46. R . L . Moore
47. H. R. Payne
48. A . M. P e r r y
49. H. B . P i p e r
50* B. E . P r i n c e
51. J. L . Redford
52. M . Richardson
53. R . C . Robertson
54. H . C R o l l e r
55. D . S c o t t
56. J. H. S h a f f e r
57. M . J . Skinner
58. A . N. Smith
59. I . Spiewak
60. R . C , S t e f f y
61. J . A . Swartout
62. A . Taboada
63 J. R . T a l l a c k s o n
64. R. E . Thoma
65. W . C . U l r i c h
66. B. H . Webster
67. A . M . Weinberg
68. K. W . West
69-70. Central Research Library
71-72. Document Reference S e c t i o n
73-74. Reactor D i v i s i o n L i b r a r y
75-77* Laboratory Record2
78. ORNL-RC
39. R .
40. C .
.
EXTERNAL DISTRIBUTION
79-80. D . F . Cope, Reactor D i v i s i o n , AEC, OR0
81. R . W . Garrison, AEC, Washington
82. R . L . P h i l i p p o n e , Reactor D i v i s i o n , AEC, OR0
83. H . M. Roth, D i v i s i o n of Research and Development, AEC,
84. W . L . Smalley, Reactor D i v i s i o n , AEC, OR0
85. M . J. Whitman, AEC, Washington
86-100. D i v i s i o n of Technical Information Extension, AEC, OR0
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