Canadian Regulators Seek Stronger Controls on Alpha Radiation Exposure

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The Canadian Nuclear Safety Commission (CNSC) is re-evaluating alpha radiation protection measures at all its Candu licensees. It’s been working with Bruce Power on the issue since early this year, and sent letters last week to Ontario Power Generation, Hydro-Quebec and New Brunswick Power, requesting that they “perform a gap analyses on current work controls used to mitigate potential alpha exposures and implement any identified program improvements” by Jul. 30. The CNSC is scheduled to discuss the issue at its meeting Jun. 29.
The Canadian regulator’s actions stem from the exposure of workers at Bruce Power’s Bruce A Unit 1 in Ontario in November, which the company reported Jan. 7. Bruce is testing hundreds of workers for alpha exposure in connection with that incident. While the analysis of large-volume bioassays of the workers has been slowed by a lack of lab capacity in Canada, a company newsletter in March said that results showed that at least nine workers had been exposed to levels of alpha radiation ranging from 1,000 millirem to 3,000 millirem. None have exceeded their annual limits, Bruce says (the CNSC sets that limit at 5,000 millirem per year).
The CNSC released a statement saying that it “continues to monitor the situation and Bruce Power’s remedial activities. There is no risk to the public or the environment.” A CNSC spokesman last week declined to answer UIW’s questions about the incident, “because the matter is before the Commission.” But, according to the incident report Bruce Power filed with the CNSC in January, information from Bruce’s website and testimony from Bruce Power
executives before the CNSC since then, this is what happened: Bruce Power was conducting operations related to the restart of Units 1 and 2 of the Bruce A plant, which had been shut down along with Units 3 and 4 in the 1990s by Ontario Hydro, Ontario Power Generation’s predecessor.

OPG is the plant’s current owner. In November, workers at Unit 1 were grinding a feeder tube in the vault to prepare it for welding. They were wearing plastic suits with air supplies and had a vacuum sleeve over the work area. Routine air sampling showed beta radiation from cobalt-60, so they tented the area and put it under negative ventilation to partition it off from the rest of the vault and other workers who were not wearing the same level of protective gear. After the grinding work resumed, further analysis of air samples showed alpha activity. What was strange was that the ratio of beta to alpha was 7:1, while in normal operating plants the ratio of beta to alpha is assumed to be about 10,000:1, Bruce A Chief Nuclear Officer Norm Sawyer told the CNSC in February. So the assumption that protecting workers against beta would be enough to protect them against alpha, too, turned out to be wrong.

Bruce Power tested 195 workers it thought could have been exposed by working in the vault while the grinding was going on. It later opened the testing program to all workers, and the number tested “is over 500 now and they’re all well within regulatory levels,” Bruce Power
spokesman John Peevers said Friday. The company implemented new alpha monitoring and protection measures to guard against future exposures. But the issue didn’t end there. The revelation that the beta-to-alpha ratios it had been depending on for years had been wrong at Bruce A’s Unit 1 prompted Bruce Power to file another report with the CNSC last week, notifying regulators that it planned to start testing long-term fuel handling employees to determine whether “historical uptakes had occurred in operating units.” So far, the results from one employee have come back and it “indicated that dose-attributable alpha radiation has
been received,” according to Bruce Power’s latest CNSC filing. The company is now testing “38 or so employees that would be sort of higher priority,” Peevers said.
It’s unclear yet what the implications of Bruce’s experience in Ontario are for the industry. The CNSC has already been working with Candu operators in Canada to address the issues it raised, and there are Candus on three other continents to worry about, too. Bruce Power Chief
Executive Duncan Hawthorne suggested to the CNSC last month that it’s not just about Candus. “We’ve always, in our industry, assumed that by protecting for beta and gamma, we in turn protect for alpha, not recognizing that in certain plant conditions and parameters, that might
not be appropriate,” he said.
A spokesman for the World Association of Nuclear Operators said the organization was not conducting a special investigation into the issue, but was “taking the operating experience at Bruce A into account.”

Sam Tranum, Washington

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