ORNL-4191 - the Molten Salt Energy Technologies Web Site

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B CALCULATED WITH STATIC
INHOUR FORMULA, USING
RCCUCED VALUES OF DE-
LAYED NEUTRON FRAC
TIONS
C CALCIJILATFD WITH NU
MERICAI. INTEGRATION /
1
7
60
n -
0001 0002 0005 0.01 002 005 01 0.2 05 1 2
INVERSL STABLE PERIOD (set?)
/
ORNL-DWG 67-11803
ING
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1- 1
5 40
Fig. 4.11. Reactivity Addition Required to Produce a Given Stable Period in the MSRE with 233U Fuel Loading.
"static" inhour equation, 7s8 using the (rjl given in
column 3 of Table 4.4. As a first approximation to
the corresponding relation for the circulating con-
dition, curve B is also calculated with the static
inhour equation, using the reduced p, given in
column 4 of Table 4.4. Finally, in curve C, we
show the relation obtained from the numerical integration
program, which gives the complete treatment
of the precursor production, motion, and
decay, when the reactor is on a stable period. In
the rangc 0.001 5 0) 5 1.0, curve C "bows" away
from curve B, illustrating the fact that the effective
reductions in the delay fractions are actually
dependent on the reactor period.6 As w becomes
large compared with the precursor decay constants,
A,, it can be shown that curve C approaches curve
B asymptotically Furthermore, curve B differs
asymptotically from curve A, on the vertical reactivity
scale, by an amount equal to the initial
reactivity loss caused by circulation (0.093% 6k/k,
from Table 4.4).
Samarium Poisoning Effects
At the end of 60,000 Mwhr of operation with the
current fuel charge, the ' 49Sm will be very near its
equilibrium concentration corresponding to 7.4 Mw.
~. . .. . . ..
7A. F. Henry, Nucl. SCI. Eng. 3, 52-70 (1958).
'E. E. Gross and J. H. Marable, Nucl Sa. Eng. 7,
281-91 (1960).
The ' 'Sm will achieve approximately 30% of its
equilibrium concentration. After shutdown the
149Sm will be further enhanced by about 8%, owing
to decay of '"Pm. These samarium poison con-
centrations will be present in the salt when the
reactor is brought to power with the 233U fuel
loadjng. For this new loading, however, the thermal
flux will be approximately 2.2 times that for the
235U fuel. In addition, the yields of the 149 and
151 fission product chains are lower than those for
the 235U (0.77 and 0.35% for 233U, vs 1.13 and
0.44% for 235U, based on ref. 9). The net result
is that the samarium initially present in the salt
will act as a burnable poison during the first part
of reactor operation with 233U. Figure 4.12 (top
curve) shows the result of calculations of the
reactivity change corresponding to burnout of the
initial samarium and achievement of the equilibrium
poisoning at the higher flux level. Continuous
operation at a power level of 7.4 Mw is assumed.
The lower curve in Fig. 4.12 shows the coirespond-
ing reactivity change caused by burnup of 233U
during this period. 'The algebraic sum of these two
curves (dashed curve) gives the approximate re-
activity effect which must be compensated for by
motion of the regulating rod. (There will be addi-
tional corrections due to other isotopic changes,
but these will be small compared with the samarium
........
'T. R. England. Time-Dependent Fission Product
?'hemal and Resonance Absorption Cross Sections.
WAPD-TM-333, Addendum No. 1 (January 1965).