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PLANT EVENTS

last update June 16, 1997

As any good class room Instructor knows, it is highly effective, and desirable, to relate fundamentals material to the Control Room and to the Plant, whenever possible. Many of the fundamentals topics do not lend themselves to such a relationship. Even so, there is often a derth of such real life material, actual experience, available for those topics that do. If you have any good analogies, stories, or events that you find successful in the teaching of reactor behavior, we will pass them along to others. Of course the INPO collection of significant event reports should be a good source for this kind of information.

• Loss of criticality at the POAH: Apparently there have now been three similar events, all at different plants, where a fairly rapid power reduction to low levels, at or just above the Point-of-Adding-Heat, caused a peak xenon transient to initiate. The negative reactivity change introduced by xenon buildup brought the reactor subcritical, with a slow decrease in power into the Intermediate Range. The introduction of negative reactivity apparently went unnoticed by control room personnel, until well below the POAH, where, at least in some instances, withdrawal of control rods was undertaken to reestablish criticality and power, in violation of reactor startup procedures. After the first such instance, INPO had issued a red SOER on the event. In at least one event, station management and the NRC resident inspector were present and took no exception to it. It is said that, typically, the operator is taken by surprise when the xenon concentration increase works so quickly to bring the reactor subcritical. In at least one event, a high reactor rate occurred during the rod withdrawal.

  If you have any important detail to add, let us hear from you. We will have some comment on this later.

• Inadvertent criticality during shutdown: This is an older type event. I don't know if anything recent has occurred. We have some material on this which will be added in the near future.

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