Reactor Theory (Nuclear Parameters)
Xenon Summary (Cont.)
A xenon-135 oscillation may be caused by a rapid perturbation in the core power
distribution. The xenon-135 oscillation can change local power levels in the core
by a factor of three or more.
Following a reactor shutdown, xenon-135 concentration will increase due to the
decay of the iodine inventory of the core. Xenon-135 will peak approximately
10 hours after the shutdown (from 100%) and then decrease as xenon-135 decay
becomes greater than the iodine-135 decay.
The greater the pre-shutdown power level, the greater the peak value of xenon.
The core can be considered xenon-free about 3 days after shutdown.
A xenon precluded startup occurs when there is insufficient reactivity in the control
rods to overcome the negative reactivity of xenon-135.
Xenon dead time is the period of time where the reactor is unable to override the
effects of xenon.
After a power decrease, xenon-135 concentration will initially increase due to
production by iodine decay being greater than the burnout. Xenon-135 will reach a
maximum about 8 hours after the power decrease and then decrease to a new,
lower equilibrium value.