Safety margins set out acceptable risk at nuclear plants and determine what systems must be in place in the event of an accident. Older plants must review and upgrade them to keep pace with current standards in the industry.
The warning was sent to Pickering owner Ontario Power Generation (OPG) in a letter April 7 as it seeks approval to keep the plant open until 2014 to meet the province's electricity needs. Safety commission staff "remain concerned with the trend in erosion of safety margins," said the lengthy and highly technical letter to Patrick McNeil, OPG's senior vice-president.
Despite the concern, staff at the safety commission has recommended a five-year operating licence renewal for Pickering B, said OPG spokesperson John Earl.
"Neither the regulator nor OPG would allow the plant to operate if it wasn't safe," he told the Star.
The commission said it expects "that OPG will address the identified outstanding issues, and, in particular, will develop and implement engineered solutions to re-establish robust safety margins."
The letter was obtained by Greenpeace, which will appear at a hearing in Ajax today to argue against OPG's request for a five-year operating licence renewal at Pickering B, built in the mid-1980s.
"They're discovering at Pickering B that it's worse than they thought," said Shawn Patrick Stensil, energy campaigner for Greenpeace.
"Pickering is closer to a major population centre than any other nuclear reactor in the world.
Officials at OPG sought to play down the letter from the nuclear safety commission as one in a long series of correspondence as the government-owned utility seeks the licence renewal. McNeil has gone on record saying that there is less than a "one in a million" chance for a problem.
"The safety margin is completely adequate to meet the needs of the plant."
Stensil said he does not take comfort from the fact that the commission is recommending a renewal, given the politics swirling around nuclear energy.
"On the one occasion that former (safety commission) president Linda Keen stood up to the nuclear industry she was fired by the Harper government," he noted, referring to the commission's safety concerns that resulted in the temporary closing of a nuclear reactor in Chalk River that produced materials for nuclear medicine.
Stensil called the firing "a frightening lesson in an industry where safety is paramount. It's very unlikely that the regulator will have the courage to stand up to the industry again."
There is another layer of politics in Ontario. Atomic Energy of Canada, a Crown corporation that designed the CANDU reactors at Pickering, is one of several companies seeking a contract to build more nuclear power reactors in the province. The province's decision on that is due by early next year.