Nuclear leak’s risk is ‘minuscule’ for nearby adults

But study predicts risk of childhood thyroid cancer would rise 30 per cent

A catastrophic radiation leak at an Ontario nuclear power plant would result in a “minuscule” increased risk of cancer to nearby adult residents, according to a new federal study.

However, the research and computer projection modelling by Canadian Nuclear Safety Commission (CNSC), the country’s nuclear regulator, predicts the risk of childhood thyroid cancer would rise 30 per cent, to 1.3 per cent from the current one-per-cent risk in Canada and Ontario.

The CSNC says that finding needs to be considered in emergency planning, but cautions not to read too much into the statistical jump.

“It’s a 30-per-cent increase of something that’s very small,” Patsy Thompson, director-general of the CNSC’s directorate of environmental and radiation protection and assessment, said in an interview.

“Thyroid cancer is very treatable (and potassium iodide) is 100-percent effective in blocking uptake of radioactive iodine if you take (the pills) on time.”

Overall, “this work shows that even for something essentially catastrophic, the health consequences would not be catastrophic, that people can feel safe living around nuclear facilities,” she said.

This is the first time the federal nuclear watchdog has undertaken a scientific health study based on a Fukushima-like disaster.

Under one scenario, four reactors at a single nuclear power station such as Darlington, Pickering or Bruce are presumed to have suffered a severe, simultaneous, common-cause accident. All plant safety features as well as actions by control-room operators and other mitigation measures fail.

The dome-shaped, concrete containment buildings shielding each reactor from the outside world breach, releasing large amounts of cesium-137 and other radioactive contaminants into the surrounding atmosphere and landscape.

Researchers considered varying wind speeds and directions, rates of radioactive release, plume dispersion and human radiological dose calculations as well as psycho-social and mental health impacts.

They also assumed emergency management measures under the Ontario nuclear emergency response plan — evacuation, sheltering in place and consumption of potassium iodide pills by those living closest to the accident site — to be effective.

CNSC staff were directed by the commission to undertake the study after Greenpeace and several other parties complained the agency and Ontario Power Genera- tion lowballed radioactive release and other estimates in a severe accident scenario report submitted at a 2012 environmental assessment hearing for the proposed refurbishment of four reactors at Darlington.

Shawn-Patrick Stensil, a Greenpeace Canada nuclear analyst, dismissed the study results Wednesday, saying the radioactive release calculations, while larger, still do not approach the releases during the nuclear disasters at Fukushima and Chernobyl.

He called the report “disingenuous.”

“I think the CNSC still has a blind spot regarding the potential for major accidents in Canada. It overlooks Darlington’s known accident potential” and other potential effects of an accident, such as radioactive fallout contaminating Lake Ontario’s drinking water.

“You’re going to have moms in Toronto refusing to drink water.”

Stensil said the study should also have examined the contamination cesium-137 causes to land and soil, and the need for policies and procedures to deal with reclamation.

Throughout the study report, the CNSC stresses the scenario is hypothetical and that pre- and post-Fukushima safety and other measures have “practically eliminated” the likelihood of such a severe accident.

The predicted risk of developing any type of adult cancer is currently 49 per cent, or 49,114 chances per 100,000 people. The study’s findings include: The predicted impact on risk of developing childhood thyroid cancer increases by 0.3 per cent under a 24-hour release scenario in which four reactor cores breach and the children are sheltered 12 km to 20 km away, but take no potassium iodide pills to block radioiodine from their systems.

The risk for any type of cancer increases by 0.0004 per cent for people 20 km to 36 km from the reactor site and who stay sheltered in their homes for seven days after a one-hour release of radiation from one crippled reactor. That equates to an additional 0.42 per cent of a chance.

“It is minuscule,” said Thompson.

In 24-hour release scenario in which four reactor cores breach, the risk for any type of cancer increases by 0.005 per cent, or by 4.9 chances for people who shelter for seven days six km to 12 km from ground-zero.

In a scenario in which the radioactivity is released in one hour by one reactor, the risk of developing leukemia is an additional 0.025 per cent of a chance for people sheltering 20 km to 36 km away.

In a 24-hour release, four reactor scenario, the increase is 0.25 per cent of a chance for people sheltering for a week six km to 12 km away.