Raising awareness of SOV [solenoid operated valves] problems at US light water reactors

The US Nuclear Regulatory Commission's Office for Analysis and Evaluation of Operational Data began studying solenoid-operated valve (SOV) problems at nuclear power plants as part of its follow-up to an event at the Brunswick 2 plant on 2 January 1988. The event involved the failure of four SOVs to shift on demand, resulting in the failure of four containment isolation valves to close. The simultaneous failure of two sets of redundant containment isolation valves in two lines leads to a reduction in plant safety margin not addressed in plant safety analyses. The study focused on the vulnerability of safety-related equipment to common-mode SOV failures and degradations. It provides information on many representative events in which common-mode SOV failures and degradations have cut across multiple trains of safety systems as well as multiple safety systems. (Author)