Assessment of MOV stroke time testing as a condition-directed PM task

Abstract

This research focuses specifically on motor-operated valves (MOVs) in the Emergency Core Cooling System (ECCS) for a Boiling Water Reactor (BWR). The possible use of stroke time testing as a condition-directed Preventive Maintenance (PM) task for MOVs is evaluated. The MOV failure modes included: packing failures, control switch related failures, mechanical failures, and motor/electrical-related failures. MOV stroke time test data for the MOVs in the High Pressure Coolant Injection (HPCI), Reactor Core Isolation Cooling (RCIC), Low Pressure Coolant Injection (LPCI), and Low Pressure Core Spray (LPCS) systems were gathered and analyzed from PECO Energy's Peach Bottom Atomic Power Station in order to assess the value of stroke time testing. This analysis shows that MOV stroke time testing should not be used as a condition-directed PM task. Regression analyses and attempts to identify large stroke time deviations failed to predict possible or eminent MOV failures. Stroke time testing should only be considered as ‘go/no-go’ test, and is therefore limited to only proving operability under no-load conditions.