The date for starting up the nuclear reactor at Chalk River, Ont., that produces most of Canada's medical isotopes has been delayed until at least next spring.

On Wednesday, officials with Atomic Energy of Canada Ltd. announced they expect the so-called NRU reactor to return to service in the first quarter of 2010.

AECL said its analysis has determined that nine sites likely need repairs at the 52-year-old reactor, which has been down since the middle of May, after officials discovered a leak of radioactive water inside it.

"In addition, high-resolution scanning data available recently has identified both wall thinning and localized pitting that suggests different corrosion effects," AECL, a Crown corporation tapped for sale by the Conservative government, said in a release.

The repairs pose no threat to workers, the public, the environment or nuclear safety, AECL said.

The Chalk River reactor normally produces about a third of the world's supply of medical isotopes, which are required for cancer and heart disease tests around the world.

In a statement late Wednesday, federal Health Minister Leona Aglukkaq and federal Natural Resources Minister Lisa Raitt said they were "very disappointed" at AECL's latest announcement.

The ministers said they have asked the operator to provide a firm return-to-service plan as soon as possible that is "consistent with maintaining the highest standards of safety and security.

"We understand this news will cause some concern for Canadians and their families," the ministers said. "Be assured, our government continues to take every step necessary to protect the health and safety of all Canadians."

Hospital isotope bills pile up

The announcement comes as Canadian doctors opened their mail last week and found bills up to $30,000 higher than usual from isotope suppliers who have come to collect after hiking their prices in the spring, when Chalk River was shut down.

The added costs along the isotope supply chain have forced hospitals to go into debt or cut from other departments to pay for the procedures.

In the wake of the shutdown, the Conservative government has created a $6-million fund to find substitutes for radioactive isotopes.

A panel of experts has also been convened to review 22 proposals for new sources of medical isotopes in Canada. Its report is due at the end of November.

This week, a spokeswoman for the operator of a new Australian nuclear reactor said the facility is still a "few months" away from shipping isotopes to Canada and elsewhere.

With files from The Canadian Press