Restart of the Chalk River nuclear reactor has been pushed into April after welding problems at the facility delayed repairs, its operator Atomic Energy of Canada said.
The reactor, which supplies a third of the world's medical isotopes, was shut down in May after a small leak of heavy water was found.
The facility was originally scheduled to return to service some time in March.
AECL said the first medical isotopes, a very small quantity of radioactive material used to perform imaging tests, would be delivered about 10 days after the plant is restarted.
AECL was not immediately available for comment Thursday.
The shortage of isotopes has forced doctors around the world to reschedule or cancel medical procedures and sent companies such as Canada's MDS Inc , whose Nordion division depends on Chalk River for the bulk of its isotopes, to scramble for new supply sources.
Earlier this week, MDS repeated that it expects a $4-million a month hit to earnings before interest, taxes, depreciation and amortization, or EBITDA, because of the shutdown.