The Ontario Power Generation says there was no risk to the public during a leak at the Pickering nuclear power plant on Friday afternoon.

Radioactive heavy water was leaking inside the Pickering Nuclear Generating Station's Unit 7, the OPG says. It was shut down at the time due to a planned maintenance outage.

Heavy water is used as a coolant in many Canadian nuclear reactors. It slows down the fission process, allowing engineers to control the nuclear reaction.

CTV Toronto's Paul Bliss says nearly 7,000 litres of heavy water were leaked inside the building at approximately 4 p.m. Friday. He says the leak was caused by a faulty pipe valve in Unit 7.

No injuries were reported, and all water was contained.

OPG says the leak has been reported to the Pickering municipal government, the province of Ontario, and Ottawa.

The public company says Unit 7 has been shut down for a "maintenance outage," and an investigation into the cause of the leak has been launched.

OPG has not said what caused the valve to spring a leak from plant’s moderator unit.

With a report from CTV Toronto's Paul Bliss