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.
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.
g Pm S
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
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