The agency in charge of the nuclear reactor at Chalk River Ont., said Thursday it could be out of service longer than originally thought.

The 52-year-old NRU reactor, which supplies 80 per cent of the world's medical isotopes, was shut down May 14 after a power outage in parts of eastern Ontario and western Quebec.

A heavy water leak was detected within the facility the following day, and officials said it would be out of service for more than a month while repair options are considered.

But executives at Atomic Energy of Canada said Thursday they could not rule out a prolonged shutdown.

"We have said at this point that it will be more than a month to bring the NRU back into service," said Bill Pilkington, AECL's vice-president in charge of the plant, at a press conference.

"As to what it might be beyond that, that really depends on what we find in our inspections. So, your [reporters'] suggestion of it being in the order of eight months or more is certainly not crazy, but at the same time, we don't have facts yet to determine what that is."