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Safety official concerned about tritium released into air from Chalk River
Low level radiation seeping into the Ottawa Valley from the disabled nuclear reactor at Chalk River is double the “action level” at which officials must respond to control the situation, a new Canadian Nuclear Safety Commission document shows.
The quantity of radioactive tritium released into the surrounding air and then falling on to land and into the Ottawa River is well within current maximum health limits. But those limits have now been questioned by one federal nuclear safety commissioner, echoing a long-running debate over what constitutes a safe exposure level to the cancer-causing tritium, especially in drinking water.
“Today’s standards may not always be in existence,” commission member Alan Graham told officials with Atomic Energy of Canada Ltd., which operates the reactor, at a meeting in Ottawa last week.
“I’m just concerned that we are — you are loading the atmosphere, whether it’s air or in water, with excess tritium. Now I know it’s dispersed in huge amounts of atmosphere, but still, how much of that may be getting in — falling as excess or extra into the water supply, the Ottawa River and so on?” he said.
“When do we start becoming concerned with the amount of tritium that’s going into the atmosphere?”
Also at the meeting was former nuclear safety commission president Linda Keen, fired by the Harper government last year for her refusal over safety concerns to allow the reactor to restart.
The AECL executives appeared before the commission last Thursday to update the nuclear watchdog on the May 14 forced shutdown of the aging, isotope-producing NRU reactor, two hours northwest of Ottawa. Minutes of the meeting were released by the commission Thursday.
AECL officials explained the giant aluminum reactor vessel sprung a “pinhole” leak due to hidden corrosion. It initially allowed about five kilograms an hour of tritium-laced, heavy water to drip out of the vessel, but that was recently slowed to three to four to kilograms an hour by reducing the volume and weight of water in the unit.
But until the nuclear fuel and control rods can be safely removed from the reactor core and the vessel is drained, officials won’t be able to stop the leak. And that work isn’t expected to be completed until the end of the month.
In the meantime, most of the leaking water is being collected and stored in specially designed drums.
However, about 20 per cent of it will continue to evaporate, be drawn into the building’s ventilation system and then released into the atmosphere to prevent a dangerous buildup of tritium in the air inside the NRU building.
The resulting emissions are roughly 1/1,000 of the allowable regulatory health limit, or more than 100 terabecquerels of tritium a week. The AECL “action level” — the point at which it must take action to reduce the emissions — is 50 terabecquerels weekly.
(A becquerel [bq] is a measurement of the number of radioactive disintegrations in a substance per second. A terabecquerel is one trillion becquerels.)
Canadian Nuclear Safety Commission executive Peter Elder acknowledged the Crown corporation “gets concerned when it’s over the action level. But the action level is an indication not of a health risk. It’s an indication of loss of control, so my point is how much they are above the action level is sort of — frankly it’s irrelevant. It is, what actions are you taking to reduce it and really to stop it, not just to get below the action level.”
By comparison, Ontario allows 7,000 bq per litre of tritium in drinking water. Last week, the Ontario Drinking Water Advisory Council released a report on the dangers of tritium and called on the government to slash the limit to 20 bq/l. Europe has a standard of 100 bq/l and the United States is at 740. California has adopted a non-binding limit of 15 bq/l.
In the days immediately following the May 14 NRU shutdown, AECL press releases simply noted that the action limit had been reached. Beginning last week, the releases said the action level had been “exceeded,” but did not elaborate.
The AECL executives offered other new details about the leak and the state of affairs with the NRU, including:
- Five or six other spots on the 35-year-old aluminum reactor vessel are showing signs of corrosion similar to corrosion that caused the current leak.
- A 2004 inspection of the vessel failed to spot any of the current weak spots.
- AECL hopes to repair the vessel with a sophisticated “patch” and the work is expected to take until at least Aug. 15. Because the repair work will be complex and has never been attempted before, officials admit the timeline is their best guess.
- Officials believe they can repair the vessel, though they told the commission there is no immediate or simple solution. Should it have to be replaced, however, the shutdown will last considerably longer. When the current vessel was installed in 1974, the work took 26 months.
- In its current state, the reactor could continue to produce isotopes, despite the pinhole leak. But without knowing more about the exact extent of the corrosion and the potential for the leak to increase, “the safe and prudent thing to do is to shut down and do a complete inspection,” said Bill Pilkington, AECL senior vice-president and chief nuclear officer.
imacleod@thecitizen.canwest.com
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