Atomic Energy of Canada Ltd. said Friday that it's stopping development of its two MAPLE reactors at its laboratories in Chalk River, Ont.

The decision — based on a series of factors including cost, time frame and risks involved — is effective immediately, AECL said in a news release.

"This was a difficult choice given the tremendous efforts expended by our people on development of the MAPLE reactors," the release said.

The federal government expressed support for the decision while noting that it will have no impact on the supply of vital medical isotopes, which are used in diagnosing and treating cancer and heart ailments.

Natural Resources Minister Gary Lunn speaks with reporters on Parliament Hill about the decision by Atomic Energy of Canada Ltd. to stop development of two reactors at its laboratories in Chalk River, Ont. (CBC)"After 12 years, these reactors have never worked and never produced medical isotopes," the federal government said in a joint news release from Health Minister Tony Clement and Natural Resources Minister Gary Lunn.

The two MAPLE reactors had been promoted by AECL on its website as "the world's first reactors dedicated exclusively to medical isotope production."

AECL, a 4,800-employee federal Crown corporation, had said that the reactors would upon completion "be able to provide a reliable, uninterrupted supply of radioisotopes for decades to come."

The move to shut down work on the reactors did not come as a surprise to critics of AECL and the Chalk River facility.

"These reactors tended to race out of control, so you simply couldn't operate on them," said Gordon Edwards of the Canadian Coalition for Nuclear Responsibility.

Edwards called the shutdown inevitable since "the reactors have never worked," he said.

"It seems to be just a waste," he told CBC News from Montreal.

Plagued with problems

The reactors were supposed to replace the aging NRU reactor years ago, but have been plagued with technical problems and soaring costs.

Last November, the supply of medical isotopes for Canada and the world was affected by a 27-day shutdown of a research reactor at Chalk River. The shutdown stemmed from a safety dispute between AECL and the Canadian Nuclear Safety Commission.

Facing a crisis, Parliament voted to overrule the commission's safety objections and the reactor was restarted Dec. 16.

AECL's future is under review by the federal government. There are reports that it may be spun off into private hands or sold to a foreign company down the road.

Earlier this month, AECL announced it was withdrawing from the competition for a new nuclear reactor design in Britain.

The Crown company said that instead, it was "focusing its marketing and licensing resources for the advanced Candu reactor on the immediate needs of the Canadian domestic marketplace."

With files from the Canadian Press