DOE-HDBK-1019/2-93
Reactor Theory (Nuclear Parameters)
SAMARIUM AND OTHER FISSION PRODUCT POISONS
sufficient amount of tritium may decay to helium-3 to add a significant amount of negative
reactivity. Any helium-3 produced in the reactor during a shutdown period will be removed
during subsequent operation by a neutron-proton reaction.
Summary
The important information in this chapter is summarized below.
Samarium and Other Fission Product Poisons Summary
Samarium-149 is produced directly from fission and from the decay of
promethium-149 during reactor operation. Samarium-149 is removed from the
core by neutron absorption.
The equation for equilibrium samarium-149 concentration is stated below.
NSm(eq)
g Pm S
fuel
f
s
Sm
a
The equilibrium samarium-149 concentration is independent of power level.
Following a reactor shutdown, the samarium-149 concentration increases due to the
decay of the promethium-149 inventory of the core and the loss of the burnup
factor.
If the reactor is restarted following a shutdown, the samarium-149 concentration
decreases as samarium is burned up and returns to its equilibrium operating value.
Helium-3 will become a significant neutron poison if significant amounts of tritium
are left in a reactor during a shutdown period that lasts longer than several
months.
Rev. 0
NP-03
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