"We've given them an optimistic schedule but it's going to be more than a month," said Dale Coffin, a spokesman for AECL.
Medical authorities said the loss of the isotopes produced by the reactor could spark a health crisis. The isotopes produced by the National Research Universal reactor at Chalk River help about 20 million people in 80 countries around the world every year.
Medical authorities began planning to make up for the isotope shortage that they think could last for six to eight weeks.
But two engineers — one working at the Chalk River facility and one who spent years working there — said they doubt the repairs will be made even within eight months and, in fact, may never be complete.
"A month to repair is a dream," said the engineer who works at the facility, and who asked for anonymity for fears he would be dismissed.
"Sounds to me as if good ol' NRU is gone for good," said the other engineer, who, after working for AECL at several of its nuclear facilities including Chalk River, now works for the federal government. That individual also requested anonymity.
Natural Resources Minister Lisa Raitt, in Edmonton where she was giving a speech, said she is relying on AECL, a Crown corporation, and the Canadian Nuclear Safety Commission, the federal nuclear safety watchdog, to provide the best information about the timeline for repairs.
"It's a reality of having older infrastructure and that's why the world is coming together to come up with a plan in order to deal with the global supply of medical isotopes," Ms. Raitt said.
At the Chalk River facility, which is on the shores of the Ottawa River about 185 kilometres west of Ottawa, technicians are following special protocols to prevent radiation sickness from the radioactive tritium-laced heavy water that is leaking from the 50-year-old reactor.
Technicians are wearing special protective clothing if they are working near the reactor and heavy water that has leaked is being stored in drums behind special protective shields. Some of that heavy water is being recirculated back into the 10-metre tall aluminum vessel.
Last fall, when the reactor sprang a leak of heavy water, the radioactive water was eventually discharged in small doses into the Ottawa River. Those discharges were done with the blessing of the CNSC. Both the CNSC and AECL said the discharges of the heavy water posed no threat to human or aquatic health.
For now, AECL engineers are using special machinery to test every part of the vessel. It is that testing, Mr. Coffin said, that will take most of the next month. And AECL engineers will not be able to say for certain how long or what kind of repairs are required until that testing is complete.
Canwest News Service has learned that one likely option for repairs involves removing the fuel rods in the reactor and completely draining the vessel that holds the heavy water. That process would take eight months in the best-case scenario, sources said, but would more likely keep the NRU off-line for at least a year.
"We're not going to speculate on what the repair method might be until we've completed the entire process of examining the entire vessel," Mr. Coffin said.
Buying and installing a new vessel to hold the heavy water — the one that is leaking was installed in 1972 — would likely require significant design work and safety approvals that could take 18 to 24 months.
AECL could even consider the purchase and installation of a new off-the-shelf reactor. That, though, could take as long six years.
Heavy water has an extra hydrogen molecule making it about 11% more dense than regular water. In AECL's reactor designs, heavy water is a crucial component, helping to slow down neutrons so that they can react with uranium in the reactor and create energy. The heavy water makes this process more efficient.
The production and use of heavy water is regulated by nuclear safety authorities. It costs about $700 per kilogram.