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RIDGE UliION
NATIONAL LABORATORY operated byCARBIDE
for U.S. ATOMIC
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the
ENERGY
COMMISSION ORNL - TM - 2282 COPY NO. DATE
PRELIMINARY
STUDY
OF A MOLTEN-SALT
BURST REACT0
A. M. Perry H. F. Bauman )W. B. McDonald J. T. Mihalczo Distribution 1. 2. 3.4.
F,
Dr. Victor Raievski, M. J. Skinner DTIE
ISPRA
NOTICEThis document contains information of o preliminary noture and was prepared primarily for internal use at the Oak Ridge National It is subicct to revision or correction ond therefore does Laboratarv.
- July
3
.
lo,
1968
..
3
..
A. M. Perry E. F. Bauman
w.
:B. McknaEd J. T. Mihslczo
The cpestion has been poscd whether one could. pulse a molten-salt
r e a c t o r s o as -to achieve an integrated f . ~ u xof
PP nsutrons/cm2
per
b u r s t i n a t e s t cavity a t the center of the reactor, and, i f so, what energy y i e l d would be required and what would be the shape of t h e pulse? The nominal objectives appear to be:
a> 1-2 x
neutrons/crn2 per burst, without a t i g h t specification
on %he neutron spec-imij 2)
a buyst width i n t h e neighborhood of 10 msec o r l e s s .
Since it appears t h a t the second objective sksuld be easy t o s a t i s f y ,
we have looked a t the p o s s i b i l i t y of achieving the f i r s t without much regard f o r f a c t o r s which mighc, influence the b u r s t shape, znd have sub-
sequently estinated the b u r s t width f o r m e of s e v e r a l reactor configurations one might contemplate using.
I. Selection of S a l t The calculztions were based on use of thd salt L i F (73 mole UF4 ( 2 7 m o l e
$1,
and
for each r e a c t o r considered, the c r i t i c a l enrich-
-ment of t h e uranixq was determined. used
5)
Separated Li7 would of course be
I
Relevant properkies of the salt are:
490
Melting point, "C Specific heat of t h e melt, cal/gm 'C Density o f t h e m e l t , gm/crf13 2.
0.217
3.26 - 9.3
X
IO-" T("C)
Allowable Energy Input
We postulate that the ternperature os" the salt could be allowed t o
rise 1090째C, i . e . , nominaLl!-y frorrl 500째C t o l'jO0"C. The p r c p e r t i e s given above yleld the following val-ues a t LO00"C (average tei-ipcszture) :
I
..
.
4
_,
,t
4.33 gm/crn13 4 wsec/cm3
Density §peeific heat
I
Thus, t h e integrated f l u x t h a t can be obialned. i n t h e t e s t c a v i t y
corresponds t o a maximum energy density of
3.
4 kwsec/cn?
per burst.
Geometry -
For t h e purposes of t h i s preliminary expl-oration, we postulate s-gherical geometry, with concentric regions and dimensions as follows :
T e s t cavity (void)
15 cm radius
Ni shell
1 cm thick
fieled s a l t
Ni s h e l l
2-7 t o 60 cm t h i c k 3 cm t h i c k
Graphite s h e l l
23 crn t h i c k
case wzs examined with the thickness of t h e outer Ni cont a i n e r increased to E? cm, end t h e graphite shell omitted; this was done for a 60-cm-thick s a l t region.
4.
c
Results
integrated f l u x e s obtainable i n the t e s t cavity a r e shown f o r
!â‚Ź!he
each case i n Table 1, along with geometrical specifications and other derived r e s u l t s .
Some of these r e s u l t s e r e a l s o p l o t t e d i n Fig. 1.
The neutron spectrum for case
#s, with
92-cn-BB core ( 3 ft) is
shown i n Fig. 2, a s t h e i n t e g r a l above energy E, as a function of E,
E where the time i n t e g r a t i o n i s taken over t h e duration of t h e burst. ,
~
,
For
comparison, t h e f i s s i o n spectmm i s a l s o g.iven, narr;.ialized to 1 X IO1" neutrons.
In
case
#?, which w z s the same
8s
case #13 except t h a t the 3-cm X i
and 23-cm grhphite shells were repl.accd by a single 23-cm N i shell, both
4
t h e pezk-to-average power density ratio and t h e integrated flux i n the
2.
t e s t cavity were t h e same as i n case #I-*
Q
Table 1.
Burst
Charadterfstics
vs Core Size
Integrated Flux in Test Cavity
.
Case Number
FueP Outside Dimeter :4
4
152
1821
17.5
854
1.545
3.4
0.97
4714
1
122 112 102
1-9.7
493 398
1.423
3.1 3.0 2.8 2.7
0.95 0.94 0.92 0.91
5333
92
934 718 538 : 391
82
'272
72
3-78
62
108
27.3 32.1 41.4
2.3 2.2 1.7
0.88 0.84 0.77
6
7 8 9 10 11 a shell
Fuel Volume (liters)
Far all cases shown, catity thickness = 5 cm, graphite
Critical Enrichment ($)
21.1 22.2 24.2
235u xass 0%)
253 200 12Q
!hta1 (neutrons/cm*
1.378 1.331 1.282
333
153
R p a%
*
1.231 1.1.78 I.123
outside diameter = 30 cm, inner shell thickness = 25 cm.
shell
thickness
>lOO kev x 1QWx6)
Burst Yield (Mw set)
2084
1615 12x4
= 1 cm, outer
883 605 382
6 d
e
.
*:<<3
.. ...i..i.i.i.i... Y
b
n
<:c9
.
.
h
B,'
FIG. 2
.
. n
h
8 h estimate of the buret width was made f o r ease #2 (not l i s t e d i n Table 1) which w a s the sme as ease #l except t h a t the graphite s h e l l thickness was PO em.
The Rossi a a t delayed c r i t i c a l , a&, was calcu-
lated, by use sf the DTF transport eoae, and f o n d t o be 9 x PO'
seceP.
The b u s t width was estimated approximately fmm the e x g r e s s i ~ n l
where M =
(p-I)
and p i s the r e a c t i v i t y i n doPPass.
mus, f o r p =
2 dollars, t h e burst width a t half m a f i m i s estimated t o be 0.4 msec. me r e a c t o r s smaller than case #2 w o u hive ~ narrower bursts.
5.
Discussion
Several i n t e r e s t i n g f e a t u r e s a r e apparent from these results. a)
me reactors are all f a s t , i.e.,
from 25 t o 40$ of the t o t a
integrate& flux is above 188 kev, and essential%y 81% of %he f1u.x is above P kev. b) The flux sf neutrons above 100 kev i s quite i n s e n s i t i v e t o r e a c t o r $ i z e , when t h e n o m b i z a t i o n i s for a given maxinun energy density (e.g.,
4 kwsec/c$).
mis
is so because t h e peak-to-average
~ ee 4ehe power density r a t i o rises with increasing core s i z e (see ~ a b 1)
t o t a l f l u x f a l l s o f f f a i r l y sharply w i t h decreasing core size below perhaps 30 i n . dian. e>
A s i n g l e nickel container shell, perhaps
6 i n . thick, appears L
t o be a s a t i s f a c t o r y reflector, yielding q u i t e flat power d i s t r i b u t i o n s ,
at Peast f o r the case studied.
It i s possible that some gains could be -
'
realized by optimizing the container-reflector regions of the assembly. ci)
Buss% widths.
While t h e b u r s t widths have not been calculated
with great care, the r e s u l t s obtained for one of the Largest cores studfea appear to s0m.m the expectation that the pulses of the desirea
magnitude w i l l be l e s s than 1 ansee i n widkh.
.. .<.<.2
Very
$râ&#x20AC;&#x2DC;
of
PittEe
a practical
ex@mr;ion sf
attention
the
bur3t
Qf the gesmetri
spbericab
Cal
will
ve33eP Details
fsr
be
and
the
intrcackcing
as the
of
the
the~free
in
imy
any
on
by
detafPe
mre
(e .g; )
Pi&id
surface.
be ext%nded
event
the
core
su~stanti~~.'~chanic~
probably
veaseb
3hockr;.
be required. and
mechanisms, very
of
aspects
aepenaing
affected
shape
and
gas,
sl" withstanding
reactih6y
engineering
can 'be p&d&ted
cover
contrsl
to
mechanism,
location
that
wi%% therefore of
the
temperatures
capable
given
quenching
such
arrangement,
the
been
can be significantly
fueb,
by pressurizing
heave to
A thick
The
QF cy'bindrical)~,
somewhat
SQ far
reactor.
Piquiel
e of I
has
rapidly,
in
wil$.
partictiar
of
require
the
t%evices
coneiderab.Je
6. swary A first prohu2e
0 I
2-3 e
intense,
This
&h.meter, of
about
a third than
at
the
sham
having
IL m3ec.
the
per
of burst
can be accomplished a vohme
700 Mw set-
of
possibilfty
bursts
neutrons/cm2
x 10""
cavity.
..
look
ri?haxis
of
about
91ae neutrons above
100
of neutron3
using
a molten-sa.ILt
indicates
can be achieved with
a core
200
liter33
are
essentially
kev.
that in
reactor fluxes
of
a centr&l
perhaps 3.1~2 with aU.
test
30 %n. in
outer
a burst
yield
above
7333e3tim3.tea buret
ts
31 kev,
wrath is
&pad fess
One of the above reactors, operating i n b u r s t mode with a m a x i m
energy density of
4 %Iw
s e c l l i t e r , may be compared with a similar r e a c t o r
operating a t constant ,power with a maxim power density sf
and with a coolant temperature r i s e , AT, equal t o P080'C residence time of the f u e l i n the core, i n seconds.
4 Wj'liter
times the
The implication i s
of course t h a t a r e a c t o r Like case #lo, f o r example, a t a power Bevel of 608 W ,w o a d pmillace a totab (fast) f l u i n the t e s t cavity of 2
x 1 0 ~ ~
neutssas/cm2sec. The power density of
4 Mw/liter
is probably a t t a i n a b l e .
One is
l e d t o speculate that such a reactor, w i t h cooling adequate f o r 600-Mw
operation, could be operated i n pulsed mode w i t h a pulse repetitlorn rate
of' l / s e c .
Since t h e pulses could then not be i n i t i a t e d from a very low
neutron Eevel, it is d a u b t r n that pulses as short as those c i t e d above could be achieved.
We have not yet estimated what pulse shape might be
obtained a t such a h i
r e p e t i t i o n r a t e , but t h e s e appear ta be sC%m
i n t e r e s t i n g p o s s i b i l i t i e s here worth f'urtlner investigation. -%
L
..,.,
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