On August 14, 2003, Pickering Nuclear Generating Station experienced a loss of Bulk Electrical System (BES) event. This event was caused by a blackout that affected the electric grid supplying the Province of Ontario, Canada, and parts of the United States. As a result, all eight reactor units at Pickering A and B experienced a total loss of the on-site electric power (Class IV power).
At the time of the event, Pickering A had units 1, 2 and 3 in the guaranteed shutdown state and unit 4 running at 12% of full power but not synchronized to the grid. Pickering B station had units 5, 6 and 8 operating at full power while unit 7 was heating up as it returned to service from a planned outage.
All operating units were safely shutdown. However, for a period of approximately 5.5 hours, immediately following the blackout, cooling of the reactor units was achieved only by natural circulation. Additionally, the High Pressure Emergency Coolant Injection (HPECI) System (common to all Pickering units) which is required to protect the hot-shutdown or operating units at Pickering against accidents, if certain failures were to occur, was impaired. Units in the guaranteed shutdown state did not require the protection of the HPECI System. The impairment was due to the loss of all alternate Class IV power sources as a result of the loss of the BES. Another back-up heat sink, the Shutdown Cooling System, was also unavailable for 3 hours.
The impairment was terminated when power supply from the BES was restored to unit 8. At all times, on all units, reactor power was controlled, fuel was adequately cooled and containment was available.
Event date: Thu, 14-08-2003