Atomic Energy of Canada president Hugh MacDiarmid waits to appear before the natural resources committee on Parliament Hill in Ottawa on Thursday. (Adrian Wyld/Canadian Press)

The operator of a shut-down nuclear reactor that usually supplies 30 per cent of the world's medical isotopes now says it will probably take longer to repair the aging facility than its earlier estimate.

"I think it'd be fair to say, simply three months is probably just judgmentally looking optimistic today," Atomic Energy of Canada Ltd. president Hugh MacDiarmid told a House of Commons committee on Thursday.

The Crown company's admission comes as the Conservative government is in hot water over the mishandling of secret documents related to Canada's nuclear industry and the reactor.

The 52-year-old reactor was shut down May 15 after inspectors detected a heavy-water leak inside the facility.

The shutdown has left doctors and medical researchers scrambling for a scarce supply from the world's four other isotope-producing reactors.

MacDiarmid said the company will know more about how long the repairs will take when it finishes its inspections in a few weeks.

Medical isotopes — tiny radioactive particles that can be injected into the body — have become the standard treatment for some cancers and have brought medical imaging to new levels.

Opposition parties have repeatedly lambasted the Tories over their handling of the current situation, as well as a previous shutdown in 2007.

During Thursday's question period in the House of Commons, opposition members slammed Prime Minister Stephen Harper for not accepting Natural Resources Minister Lisa Raitt's resignation offer after it was revealed documents related to AECL and the reactor were left behind at CTV's Ottawa news bureau for almost a week without anyone in the government noticing.

Netherlands boosting isotope output

The control room at the Chalk River nuclear facility is seen during a media tour in Chalk River in December, 2007. (Chris Wattie/Reuters)

A 26-year-old member of Raitt's staff resigned over the blunder on Wednesday, but critics have accused the prime minister of ignoring his own Accountability Act by allowing the ministerial aide to take the fall for Raitt.

Harper said Raitt held a "reasonable expectation" that the staff member would safeguard the documents and has taken "appropriate action."

Raitt told the House on Thursday that the Netherlands has agreed to increase its production of medical isotopes by 50 per cent, while Canada and the United States were holding a bilateral meeting on Friday to discuss ways to bridge the shortage.

According to a report among the documents, the federal government has provided AECL with $1.7 billion in funding since 2006. A talking-point memo describes the spending as "cleaning up a Liberal mess."

The 2009-10 federal budget shows that $351 million was earmarked for Atomic Energy of Canada Ltd. but the documents indicate that $72 million not previously revealed publicly will also be given to AECL this year for "maintaining the option of isotope production," CTV said.

With files from The Canadian Press