Some Canadians are questioning the safety of our nuclear reactors after a leak at the Pickering nuclear plant this week, even though officials say it caused virtually no risk to the public.

The leak sent tens of thousands of litres of "demineralized" water into Lake Ontario on Monday. The accident came at a time of increased sensitivity to nuclear disaster as the world watches the ongoing crisis at Japan's Fukushima generating station, where crews are working to prevent a meltdown.

Officials say the risk of radiation to people and the environment after Monday's incident east of Toronto is "negligible." But the Canadian Coalition for Nuclear Responsibility, a Montreal-based think tank and watchdog group, says the leak is a small example of a greater problem with how nuclear safety is regulated.

Spokesperson Gordon Edwards says the leak shows the potential for more significant nuclear contamination of Lake Ontario, adding there is no proof that Canadian-made CANDU reactors are any safer than other reactor designs.

"That water came from one of the spent fuel bays right into Lake Ontario," Edwards told CTV's "Canada AM" on Thursday. "The spent fuel bays in Japan are currently the source of some of the greatest radiation exposures. If there is an accident in Pickering, the fact that there is a direct pathway from the spent fuel bay into Lake Ontario should be quite alarming.

"In this case, there might be small amounts of radiation, but that's just luck."

He said his organization, which began calling for more stringent regulations on spent fuel bays after Sept. 11, 2001, would like to see a web-based system that allows citizens to view real-time totals of how much radioactive material is being released into the environment in Canada.

"Since (the reactors in Pickering and Darlington) started operating, the amount of radioactivity in Lake Ontario as measured has more than doubled," he said. "All of that comes from nuclear reactors, mostly the Canadians ones… We unfortunately still have a very smug and complacent nuclear industry in Canada."

Ontario Power Generation notified the Canadian Nuclear Safety Commission late Monday evening after the release of about 73,000 litres of demineralized water at the Pickering A nuclear generating station earlier that day. On Wednesday, the nuclear regulator said the leak appears to have been caused by a pump seal failure.

The leak has been stopped and the faulty pump seal is being replaced, OPG said Wednesday.

"People are concerned about nuclear power, but this particular incident is normal water with a bit of radiation. It is well below our regulatory and other limits," OPG's Ted Gruetzner told CTV News Channel on Wednesday afternoon.

John Luxat, a radiation expert with McMaster University, says demineralized water is essentially distilled water used to feed steam generators.

"It is not radioactive; it is not going through the reactors. It is actually just going through steam generators to produce steam to drive the turbines," Luxat told CTV News Channel.

"It is used to remove heat from the heavy water going into the generators, but it doesn't at any time go into the reactor."