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The aging NRU research reactor at Chalk River has been leaking low-level radioactive water into the Ottawa River for about 50 years, a federal licensing tribunal has heard.
Atomic Energy of Canada Ltd. (AECL), owner-operator of the 53-year-old reactor, has been unable to halt tritiumlaced water seeping from the reactor’s control rod bays and is instead diluting the concentration of tritium with fresh water before it somehow leaks into the nearby Ottawa River, the Canadian Nuclear Safety Commission (CN-SC) tribunal was told.
The five-member CNSC panel is deliberating on an AECL application to renew the operating licence of the NRU and surrounding Chalk River Laboratories (CRL) to 2016. AECL officials have assured the panel that NRU can run for at least another five years without compromising safety. One of its chief missions is producing medical isotopes. The current operating licence expires Oct. 31.
Tritium is a low-energy, radioactive form of hydrogen generated in the heavy-water used to moderate nuclear fission.
The tribunal seemed surprised to learn of the leak and that it had been depositing small amounts of tritium into the Ottawa River since the 1960s.
AECL’s unsuccessful attempts to stop the flow highlight the challenge the newlyrestructured Crown corporation faces trying to keep the world’s oldest operating reactor in service. NRU’s containment vessel sprang a heavywater leak in 2009 that led to a 15-month, $70-million shutdown and a global shortage of medical isotopes. It followed another emergency safety shutdown in 2007 that ended when Parliament legislated the reactor to resume operating.
Under CNSC’s direction, AECL is diluting the concentration of tritium in bays so that lesser amounts migrate into the drinking water of nearby Petawawa, the tribunal heard. Commission staff say tritium concentrations in Petawawa’s drinking water typically measure seven to 10 becquerels (bq), well below the Ontario drinking-water limit of 7,000 bq per litre.
An AECL effort to further minimize the impact by replacing all heavy water in the control rod bays with fresh water is expected to be completed by spring.
“What we’ve determined so far is that there does not seem to be . any (repair) project that would give you high confidence that you would completely stop the leak given the design of the reactor building and the age of the bays,” CNSC staff expert Peter Elder told the panel.
Despite the problem, CNSC staff agreed the reactor was safe to operate and recommended the commission renew CRL’s licence, but with conditions.
One is that AECL, “move to a formal management system . in line with modern standards . and (to) require AE-CL to actively address its safety culture issues,” said Elder, head of nuclear cycle and facilities regulation.
Another is that AECL address “fitness-for-service” problems, particularly, “aging of infrastructure and weaknesses in maintenance programs” that have resulted in a number of other radioactive leaks.
The tribunal also heard AE-CL has yet to fully inspect all the repair welds in the NRU containment vessel as required by the CNSC.
Randy Lesco, AECL’s vicepresident of operations and chief nuclear officer, said another extended shutdown of the reactor in April would be required to properly inspect some of the welds. He did not say how long the reactor would be down, but a similar inspection shutdown last spring lasted 33 days.
The effect on the global supply of medical isotopes is expected to be manageable, in large part because the earlier NRU outages led other producers to increase their capacities and the medical isotope community to become more efficient with supplies.
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