Radioactive heavy water leaked from a reactor at the Pickering nuclear station on Friday, says Ontario Power Generation.
The company says the leak was contained within the building, and no workers were exposed to a dangerous level of radiation.
The reactor had been shut down for planned maintenance, and staff were working on a valve when the leak occurred, said OPG’s Neal Kelly. He wouldn’t say how much fluid leaked.
The heavy water that leaked is used as a moderator in the reactor, he said. It surrounds the uranium fuel and allows a nuclear reaction to take place by slowing the passage of neutrons emitted by the uranium.
Neutrons travelling at too high a speed bounce off other atoms, without splitting them and releasing energy.
The facility is designed to contain leaks, and no heavy water escaped the building, he said.
Other reactors at the station continued to operate during the clean-up, which was completed late Friday, Kelly said.
Staff from the Canadian Nuclear Safety Commission were in the station when the incident occurred, he said. OPG has reported it to the commission and to provincial and municipal authorities.