All holders of operating licenses or construction permits for nuclear power reactors. This information notice is being provided to alert addressees to potential problems resulting from failures in instrument air system check valves intended to isolate safety-related air accumulators under accident conditions. It is expected that recipients will review the information for applicability to their facilities and consider actions, as appropriate, to avoid similar problems. The valves had not been previously tested or included in the plant surveillance program. The instrument air system supplying all air bubbler lines is not safety-related, seismically qualified or supplied with vital power.
Check valves separate each of the four accumulators from the instrument air system.
Failure of these check valves would cause the accumulators to fully or partially discharge through the instrument air system if instrument air pressure was lost. If premature switchover occurred, the containment sump might be dry or might have an inadequate water level to provide net positive suction pressure to the pumps during a design basis event. This could lead to damage of the pumps and their subsequent unavailability. Although the specific event described here occurred on a pressurized water reactor, failure of air check valves to seat when required to ensure availability of air from safety-related accumulators could be a problem on any type reactor. No specific action or written response is required by this information notice.