Radiation risks questioned

02 December 2009

The risks of small radiation doses could have been exaggerated, the Electric Power Research Institute (EPRI) has found, while an industry group has sharply criticized the drive for ever-lower doses absent from real-world concerns.


The health effects of radiation have been noted many times in research dating back to military workers' exposure to nuclear weapons tests, but observable effects only come with very large doses of radiation. The risks from small doses over longer periods have been largely assumed under the 'linear-no threshold' model, which implies that any level of radiation exposure - no matter how small - would cause a corresponding level of biological damage.


After collating more than 200 peer-reviewed publications on the topic, EPRI was able to conclude that this methodology may have been over-estimating the risks. Different mechanisms are at work at each end of the scale, EPRI found from recent studies, and "when radiation is delivered at a low dose rate (i.e. over a longer time period), it is much less effective in producing biological changes than when the same dose is delivered in a short time period."


Nuclear power plant workers are the most studied in the world in terms of radiation, with doses logged for everyone who regularly enters nuclear sites. Strict average annual limits are imposed by national regulators while most companies have even stricter limits of their own.


But in all this data, which covers more than 100,000 workers per year at US nuclear power plants, nobody has been exposed to more than the US regulatory annual limit of 5 rem (0.05 Sv) since 1989. "Doses of less than 10 rem (0.1 Sv) in a single exposure are too small to allow detection of any statistically significant excess cancers," said EPRI.


Theoretical safety gains


"It is a disservice to the public interest to set safety standards on the implicit premise that all radiation is harmful, even at extremely low doses," wrote John Ritch, head of the World Nuclear Association, in a letter to the International Atomic Energy Agency (IAEA) last month.  Ritch's letter was co-signed by WNA Board members Ichiro Takekuro, chief nuclear officer of Tokyo Electric Power Company, and Chris Crane, president and chief operating officer of Exelon. Takekuro and Crane represent the largest nuclear operators in Japan and the USA, respectively.


The Ritch letter focused on the currently ongoing revision of the IAEA Basic Safety Standards and a proposal to reduce dose limits for the public from 1 mSv per year to 0.3 mSv. Ritch warned that a "wholly theoretical gain in radiation safety could take precedence over, and act to the detriment of, the real gains in public health and environmental protection that can be achieved through a worldwide expansion of nuclear power."


The tendency to strive for ever-lower radiation doses in the absence of evidence of real health gains "undercuts the fundamental, well-established principle of optimisation of doses, which entails that a judicious balance be struck among real risks and benefits," said Ritch.


In practical terms, a constant drive for lower doses would lead to increasing cost and complication for nuclear operators and regulators, with no measurable benefit for workers or the public. Meanwhile, the benefits of nuclear power in terms of energy security, development and climate change abatement would be available only at higher cost.