DOE-HDBK-1019/2-93
SAMARIUM AND OTHER FISSION PRODUCT POISONS
Reactor Theory (Nuclear Parameters)
For the purpose of examining the behavior of samarium-149, the 1.73 hour half-life of
neodymium-149 is sufficiently shorter than the 53.1 hour value for promethium-149 that the
promethium-149 may be considered as if it were formed directly from fission. This assumption,
and neglecting the small amount of promethium burnup, allows the situation to be described as
follows.
Rate of change of 149Pm = yield from fission - decay 149Pm concentration
therefore:
dNPm
dt
g Pm S
fuel
f
f lPm NPm
where:
NPm
=
149Pm concentration
gPm
=
149Pm fission yield
lPm
=
decay constant for 149Pm
Solving for the equilibrium value of promethium-149 gives the following.
NPm(eq)
g Pm S
fuel
f
f
lPm
The rate of samarium-149 formation is described as follows.
Rate of change of 149Sm = yield from fission + 149Pm decay - 149Sm burnup
therefore:
dNSm
dt
g Sm S
fuel
f
f lPm NPm NSm s
Sm
a
f
where:
NSm
=
149Sm concentration
gSm
=
149Sm fission yield
sa
Sm
=
microscopic absorption cross section of 149Sm
NP-03
Rev. 0
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