On February 9, 2021, at 0153
CST, Cooper Nuclear Station experienced a spike in
Secondary Containment differential pressure which exceeded the Technical Specifications
Surveillance Requirements 3.6.4.1.1 limit of -0.25 inches of water
gauge.
Secondary Containment differential pressure oscillated coincident with barometric pressure oscillations. Three additional spikes occurred which exceed the Technical Specification limit. The duration of each spike was less than one minute. The last spike occurred at 0232
CST.
Secondary Containment differential pressure has restored to Technical Specification limits and further investigation is ongoing.
This unplanned Secondary Containment inoperability constitutes a condition reportable under 10CFR50.72(b)(3)(v)(C) and (D), "An event or condition that at the time of discovery could have prevented the fulfillment of the safety function of [Structures, Systems, and Components] SSCs that are needed to control the release of radioactive material and mitigate the consequences of an accident.
The NRC Senior Resident Inspector has been informed.
