BWRs never are xenon precluded. They always, at all parts of the operating cycle, have sufficient hot excess reactivity to have xenon override capability. They also naturally stabilize spatial and axial xenon tilt based on their design and the boiling boundary effect.

Pwr plants have total xenon override until the last 5-8% of cycle, when they are essentially at max dilution. They do not have natural flux tilt stabilization so the operator has to manually make adjustments to control tilt within limits.

I have personally started up a commercial BWR in peak xenon. It was very weird to have the reactor go critical moving a corner rod from 00 to 04, not see the criticality (power actually appeared to be going down at the time we notched it out), then as xenon burnout started happening we saw only one SRM period on scale. The PPC displays, when you have period in trend mode, you can see an inflection when critical occurs, and we saw the signature only on one instrument which didn’t make much sense. So we stopped pulling rods to watch, as a minute or two later the second SRM started to come on scale, then the third and fourth, as xenon burnout reduced shielding around the SRMs and allowed the core to finally couple. Then reactor period advanced over the next 12-15 minutes to about 82 seconds, when we finally hit point of adding heat and everything stabilized. Not a common evolution and I can see where other operators pulled too far and tripped their units, because you don’t see the core go critical on peripherals for quite a while.