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Radioactive water has stopped leaking from the nuclear reactor at Chalk River, Ont., ending two months of low-level radiation seeping into the atmosphere near Ottawa.
Workers with Atomic Energy of Canada Ltd. recently completed draining the reactor’s 65,000-litre vessel and are now preparing to dispatch a remote-controlled ultra-sonic probe deep into the disabled machine to inspect the site of a pinhole leak of tritium-laced heavy water that began May 14.
What it reveals will help determine what is expected to be a delicate, complex and potentially costly repair strategy.
Most of the leaking water was slowly captured and stored in special drums and is to be reused when the National Research Universal reactor restarts. But about 20% evaporated and was drawn into the building’s ventilation system. To prevent a dangerous buildup of tritium inside the NRU building, the airborne tritium was steadily released into the atmosphere as the leak progressed.
The quantity going into the surrounding air, some of which then fell on land and into the Ottawa River, was well within current maximum health limits. Still, those limits were publicly questioned in June by the federal nuclear safety commissioner, echoing a long-running debate over what constitutes safe exposure to cancer-causing tritium, especially in drinking water.
It took workers until two weeks ago to drain the last of the heavy water from the vessel.
The shutdown of the world’s top reactor for producing medical isotopes has triggered price increases for the hospitals, clinics and millions of patients relying on isotopes to treat cancer, heart and other diseases. Medical experts fear longer-term shortages as the shutdown continues.
Dale Coffin, AECL’s chief spokesman, said Wednesday the commercial Crown corporation remains confident that the leaking vessel that houses the reactor core can be repaired, but the reactor won’t be back in service until “at least” late this year.
The leak, plus several other “areas of interest,” are blamed on hidden corrosion of the huge, cylindrical aluminum vessel, which also holds the heavy water used to cool the reactor. A 2004 inspection of the vessel failed to spot any of those areas. At least three, in addition to the leak site, require repair.
Should the vessel have to be replaced, the shutdown will last considerably longer. When the current vessel was installed in 1974, the work took 26 months.
Meanwhile, a blue-ribbon coalition of U.S. nuclear medicine groups urged their government on Wednesday to explore a public-private partnership to speed the ability of the United States to produce its own isotopes, instead of relying on supplies from Canada, Europe and South Africa.
Further, the group wants the U.S. government to reduce proliferation concerns by encouraging a switch to isotope production using low enriched uranium, rather than the bomb-grade, highly enriched uranium used in the NRU.
Even before the latest Chalk River shutdown, the U.S. government had been eyeing the possibility of developing its own isotope production using LEU. But the new NRU crisis, following another unscheduled closure last year, prompted a Senate committee this month to approve $20-million in spending to begin domestic production of medical isotopes.