Comparison of Naturally and Artificially Aged Solenoid Valves in Accident Simulations

A qualification research program conducted on naturally and artificially aged solenoid valves revealed no significapt differences in performance during seismic tests, but some differences during main-steam- line-break/loss-of-coolant-accident (MSLB/LOCA) simulation. Although the naturally aged valves were subjected to less severe aging than the artificially aged valves, they failed earlier than the artificially aged valves in the MSLB/LOCA test. Only a valve with metal seats performed satisfactorily throughout the program. All other valves tested experienced failure or diminished functional capability as a consequence of degradation of the EPDM components (seals, seats, diaphragms). Degradation manifested itself in the form of severe compressive set, embrittlement, and adherence of tacky material to bounding metal parts. There were also two coil failures. This paper analyzes the causes of degradation and recommends ways of improving the qualification method.