Nuclear watchdog investigates possible mass radiation exposure

As many as 217 workers involved in November incident at Ontario plant, according to filing from Nuclear Safety Commission

Globe and Mail: Martin Mittelstaedt - February 16, 2010

The Canadian Nuclear Safety Commission says as many as 217 workers may have been exposed to radioactivity at the Bruce nuclear power station on the shores of Lake Huron while refurbishing a reactor in late November.

It is believed to be one of the largest mass exposures to radiation at a Canadian nuclear site.

The station operator, Bruce Power, said a preliminary review of the radiation exposure indicates no one received an excessive dose. The company is taking the incident “very seriously,” said John Peevers, a Bruce spokesman, while cautioning that “all indications are that there is nothing there approaching the regulatory limit” for radiation.

The CNSC, Canada's nuclear safety watchdog, indicated the estimated number of people who may have been affected in a regulatory filing Tuesday in Ottawa. The incident will be discussed by its commissioners at a meeting Thursday and conditions around the reactor are being monitored by CNSC staff.

The CNSC said the workers were exposed to alpha contamination, a dangerous form of radiation that, if breathed in or ingested, poses a risk of cancer. Preliminary dose calculations indicated that an “action level for inhalation of airborne radioactivity may have been exceeded,” the CNSC said.

“Preliminary dose calculations were conservatively interpreted as a potential indication that an action level for inhalation of airborne radioactivity may have been exceeded,” the CNSC said.

The CNSC did not provide an explanation of what the “action level” was. But Mr. Peevers said Bruce has an exposure limit stricter than federal regulations, at 80 per cent of the maximum radiation permitted for nuclear employees.

Ottawa allows atomic workers to receive up to 50 millisieverts of radiation per year on the job, an amount 12.5 to 25 times the natural background radiation Canadians are exposed to from such sources as solar radiation, building materials and radioactive elements in soil.

One millisievert is the radiation a person would get from approximately 10 chest X-rays.

The precise number of people exposed is not known. Mr. Peevers said some workers do not appear to have received any extra radiation.

Nuclear critic Shawn-Patrick Stensil of Greenpeace said the CNSC estimate would make the Bruce workers the largest group he is aware of that has ever been exposed to radiation from a power plant in Canada.

Work in the area was stopped until the radiation was cleaned up. The CNSC said all those who may have breathed in the contaminants have been removed from any tasks exposing them to radioactivity until their doses are determined.

All of the contaminants were contained in the station, and there was no danger to the public, nor releases to the environment, according to the CNSC.

Bruce Power is Canada's only private nuclear-station operator. It leases from the Ontario government two generating plants, known as Bruce A and B, which have four reactors apiece. The stations supply about 20 per cent of the province's electricity.

The company is currently refurbishing Bruce A, a $5.25-billion project that is one of the largest construction undertakings in Canada outside of the oil sands. The overhaul includes repairs at two reactors that are already about two years behind schedule.

Alpha radiation suggests the workers came into contact with a leak from a damaged bundle of nuclear fuel.

The reactor where the incident occurred has been mothballed since 1997. Mr. Peevers said the damage happened 30 years ago when Ontario Hydro, a provincially owned utility, operated the plant