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Event Report Forms (ERFs) are filed to the IAEA. Sometimes there are multiple event reports, updating the rating, the event description. Here you only see the latest event report

ERF send date: Tue, 21-05-1996
ERF description: Units, 1,5,6,7 & 8 at the Pickering Nuclear Generating were shut down in an orderly manner on April 20 & 21, to allow repairs to an emergency coolant injection system (ECIS) check valve (units 2,3 &4 were already shut down for maintenance). During testing the position of one of two parallel redundant check valves between the ECIS storage tank and the ECIS pump suction header could not be verified. The check valves are required to reseat to prevent loss of inventory and flow of contaminated water to the storage tank during the ECIS recovery phase. The back up motorized valve to prevent this is tested once every 10 years, during a planned 8-unit outage as its closure results in a total impairment of the ECIS function. The MV tested satisfactorily on shutdown. The check valves cannot be isolated, so a station outage for 8 - 10 days was taken for their repair. The failure constitutes a loss of redundancy of ECIS function. Continued operation is allowed but station policy is to suspend reactor fuelling for impairments where no safety function redundancy remains for response to a fuelling-induced (small) LOCA. Lack of fuelling would have forced shutdown in the near future anyway. When the NV opened the position indicating rod was found bent, causing the NV to be stuck in the partially open position. The position indicating mechanisms have been removed from both NVs to eliminate this failure mechanism and a new testing procedure developed.
This event is rated at level 1 on "degradation of defence in depth" without an initiator for a "possible" initiator (small LOCA) with "adequate" safety function.
ERF rating date: 02-05-1996
ERF contact person: Mr. W. Andersen
ERF address: 700 University Avenue, Canada
ERF affiliation: Ontario Hydro H11-B1, Nuclear Technology Services Division

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