NUC K117 Chapter 4: Fission Product Poisons
3 Feb 2019
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Document Summary
Fission product poisons: two primary culprits, xe135 is a very big player, sm149 is a second big player (but not as big, both a ect thermal utilization and ke in a negative way. Te135 behavior: quickly decays to i135 (usually can be ignored due to very short half life) I135 behavior: viewed as the primary producer of the neutron poison xe135, continues to produce xe135 even after shutdown, causing a peak" period of excessive negative reactivity. Xe135 behavior: xe135 decays to cs135 with t1/2 of 9. 1 hr (a removal" process, xe135 also removed" by absorption of thermal neutrons (becomes xe136, which is not a poison) Two production mechanisms and two removal mechanisms operate at di erent rates. It is now di cult to determine what value or direction xenon concentration is taking versus time. It also means that reactivity is hard to track!
