U.S. Nuclear Regulatory Commission (NRC) Information Notice (IN) 2012-14, “Motor-Operated Valve Inoperable Because of Stem-Disc Separation”, was issued to inform nuclear power-plant licensees of recent operating experience involving a motor-operated valve (MOV) that failed at the connection between the valve stem and disc. The NRC expectation was that recipients would review the information for applicability to their facilities and consider actions, as appropriate, to avoid similar problems. Additional regulatory suggestions and insights contained in the IN are not NRC requirements.
On closer examination of the events involved, it became apparent that the undetected stem-disc separation observed with the subject MOV was not necessarily limited to that type or style of valve. In fact, the vast majority of inservice testing (IST) valves, and the manner in which they are tested, could also be susceptible to loss of functionality going undetected. The intent of the compliance project performed at the R.E. Ginna Station nuclear power plant was to examine the current testing performed on each IST program valve and determine the level of confidence that stem-disc separation would be detected. If the level of confidence was deemed less than acceptable for a subject valve, one or more augmented actions, as deemed both practicable and viable, were recommended for implementation.
The purpose of this presentation paper is to describe the systematic methodology that was employed to validate the effectiveness of the current periodic IST valve testing conducted at the R.E. Ginna Station and the corrective-action recommendations that were made as deemed appropriate. The corrective action(s) were designed to preclude the occurrence of future stem-disc separation issues going undetected, which could result in the loss of valve and potentially the loss of the associated accident-mitigation system’s operational readiness condition.
Paper published with permission.
