An Ontario nuclear reactor resumed operations Sunday and new supplies of medical isotopes will be ready for distribution within days to ease a worldwide shortage, the Atomic Energy of Canada says.

The Crown corporation said its National Research Universal reactor in Chalk River started up at 3:44 a.m. ET Sunday, a few days after Parliament pushed through legislation to get it back online as soon as possible.

The facility was originally shut down for a week of maintenance on Nov. 18, but the Canadian Nuclear Safety Commission refused to allow it to resume production until a host of safety issues were resolved.

However, the Chalk River facility produces about two-thirds of the world's supply of radioisotopes — nuclear material essential for medical imaging and diagnostic scans for fractures, cancers and heart conditions.

The shutdown created a global shortage of radioisotopes, which can't be stockpiled because they have a short shelf life.

The AECL said Sunday that new supplies of medical isotopes would be processed and ready for distribution within four days.

The Conservative government's bill, which was passed by MPs on Tuesday, effectively bypassed the Canadian Nuclear Safety Commission's order for the reactor to stay closed until the safety concerns were addressed. Late Wednesday, the Senate passed the legislation.

On Friday, Prime Minister Stephen Harper said he had accepted the resignation of Michael Burns, chair of the AECL, and appointed Glenna Carr, a former Ontario senior bureaucrat, to replace him.