Nonintrusive methods for monitoring the operational readiness of solenoid-operated values

Abstract

Solenoid-operated valves (SOVs) are being studied at Oak Ridge National Laboratory as part of the USNRC Nuclear Plant Aging Research (NPAR) Program. The primary of the study is to identify, evaluate, and recommend methods for inspection, surveillance, monitoring and maintenance of SOVs that can ensure their operational readiness — that is, their ability to perform required safety functions under all anticipated operating conditions. An earlier (Phase 1) study described SOV failure modes and causes and identified measurable parameters that might be used to monitor the various degradations that lead to functional failure. The present (Phase II) study focuses on devising and then demonstrating the effectiveness of techniques and/or equipment with which to measure the previously identified performance paramaters (or others) and thus detect and ascertain the trend of the progress of any degradation that may be occuring. Several nonintrusive techniques are presently under investigation. These include monitoring coil mean temperature during operation by means of DC coil resistance, monitoring valve position by means of coil AC impedance, verifying free SOV plunger movement by measuring current and volatage at their critical bistable (pickup/dropout) values, and detecting the presence of shorted turns or insulation breakdown within the solenoid coil using interrupted-current test methods. A technique slated for later investigation is monitoring coil hum or chatteringm, using acoustic sensors or electrical noise indications. Experimental results are presented demonstrating the technical feasibility and practicality of the diagnostic techniques being assessed in this continuing study.