Community Information Bulletin

NRU Electrical Circuit Breaker Testing Event

Chalk River, 2016 June 10 – The following information bulletin is in accordance with Canadian Nuclear Laboratories (CNL) ongoing commitment to voluntary public disclosure of events related to the Chalk River Laboratories (CRL).

On Thursday June 09, with the NRU reactor shut down for its planned maintenance outage, NRU staff performed a routine equipment test that simulates a loss of grid power to the main cooling pumps. The test was successfully completed and equipment performed as required. At approximately 4:30 p.m. and upon restoring grid power to the system from the Powerhouse, smoke was detected and local fire alarms actuated in an electrical room.
Staff at the Powerhouse were contacted, and the feeder line to the equipment was opened to isolate the power. Chalk River site Emergency Services quickly responded to NRU.

Responders confirmed that the source of the smoke was an electrical circuit breaker.
Investigation revealed that a DC-powered relay coil that closes the breaker overheated, and as a result generated smoke and a burning smell. The breaker was removed and a spare breaker installed. By 7:30 p.m. Thursday evening, normal power configuration was restored throughout the facility. The NRU reactor remained in its planned maintenance safe shutdown state throughout the event.

There were no injuries related to this event and there have been no radiological releases, to the public, environment or employees. Work on the planned NRU maintenance outage continues.


Patrick Quinn
Director, Corporate Communications
CNL, 1-866-886-2325