Xenon Summary

Xenon-135 Response to Reactor Power Changes

Xenon Summary (Cont.)

Nuclear Physics and Reactor Theory Volume 2 of 2
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Reactor Theory (Nuclear Parameters) DOE-HDBK-1019/2-93 XENON When reactor power is decreased from 100% to 50% power (t = 55 hours), the process is reversed. There is an immediate decrease in xenon burnup, which results in an increase in xenon-135 concentration. The iodine-135 concentration is still at the higher equilibrium level for 100% power and is therefore still producing xenon-135 at the higher rate. The xenon-135 concentration continues to rise until the rate of production of xenon-135 becomes equal to the rate of removal (roughly 7 to 8 hours after the initial reduction in power level). The xenon-135 concentration then gradually decreases to the new equilibrium level in about 50 to 60 hours. The magnitude of the xenon peak is greatest if the initial power level is very high. Maximum peak xenon occurs when a reactor that is operating at 100% equilibrium xenon concentration is suddenly shut down. The most rapid possible burnout of xenon occurs when a reactor is started up and operated at full power while this maximum peak xenon condition exists. Summary The important information in this chapter is summarized below. Xenon Summary Xenon-135 is produced directly as a fission product and by the decay of iodine-135 during reactor operation. Xenon-135 is removed from the core by radioactive decay and by neutron absorption during reactor operation. The equilibrium concentration for xenon-135 is determined by the following equation. or N_Xe (eq) g Xe S fuel f f lI NI lXe s Xe a f N_Xe (eq) g Xe g I S fuel f f lXe s Xe a f The xenon-135 concentration increases with increasing power level in a non-linear manner. Equilibrium xenon-135 concentration reaches a maximum at a flux of about 10¹⁵ neutrons/cm²-sec. After a power increase, xenon-135 concentration will initially decrease due to the increased removal by burnout. Xenon-135 will reach a minimum about 5 hours after the power increase and then increase to a new, higher equilibrium value as the production from iodine decay increases. NP-03 Rev. 0 Page 41

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