Canada Wednesday warned of a "critical shortage" of medical isotopes used for cancer and heart patients because a temporarily shuttered nuclear plant was to remain closed until the end of 2009 for repairs.

Ottawa's ministers of natural resources and health issued a joint statement warning of "a significant shortage of medical isotopes in Canada and in the world this summer" as a result of the longer-than-anticipated shutdown of the aging reactor at Chalk River in Ontario, some 200 kilometers (125 miles) west of Ottawa.

The government warning came after Atomic Energy of Canada Limited (AECL) said the nuclear facility -- shuttered in May after a leak of radioactive water inside the reactor -- would be out of service through at least the end of 2009.

AECL had earlier estimated that the National Research Universal (NRU) reactor at Chalk River would be back in action after three months.

"The unplanned shutdown... will result in a significant shortage of medical isotopes in Canada and in the world this summer," said Health Minister Leona Aglukkaq and Natural Resources Minister Lisa Raitt in a joint statement.

"We expect a period of more critical shortage during the month of August. For this reason, careful management of available supplies by the community and the successful identification of alternatives will remain essential," the statement said.

When operational, the half-century old NRU reactor at Chalk River produces one-third of isotopes used for medical radiation treatments around the world, particularly for diagnosing cancer and heart patients.