Reviewing online monitoring data led engineers at a U. S. domestic power plant to discover some periodic transient activity occurring in the unisolable sections of the plant's safety injection (SI) lines. This activity typically occurred when the plant approached hot standby conditions after an outage. After performing an investigation, it was concluded that the activity was caused by periodic SI check valve testing. Effective review and disposition of the monitoring results supported engineering feedback to operations personnel with recommendations for performing check valve testing to mitigate further thermal shocks on the downstream components. Engineering was also able to classify the observed transient activity as one of the transients in the SI line licensing basis, to justify continued operation without significant engineering analysis, using the WESTEMS™ Design Envelopes approach to transient cycle counting. This paper describes the approaches used to identify the unexpected transient activity, evaluate and classify the activity using an efficient automated approach, and to develop recommendations for mitigating actions for plant operation.
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