The article written by Mure Dickie and Clive Cookson for Financial Times that appeared in November last year seems to have engendered a lively discussion in the comment section regarding what is the "safe" radiation dose, if there is one.
From Financial Times (11/11/2011):
Nuclear energy: A hotter topic than ever
By Mure Dickie and Clive Cookson
Divisions over radiation risk have been exposed after Fukushima
In front of the government office in Japan’s Iitate village, the radiation monitor – a large metal box topped by warning lights – displays airborne levels in real time on a glowing digital display. A handheld dosimeter carried by local forester Toru Anzai gives more personal readings. In the nearby prefectural capital, sophisticated germanium detectors hum into the night analysing the radioactivity of local foods.
Eight months after a tsunami sent the Fukushima Daiichi atomic power station into near meltdown, data are pouring in across Japan on the scale of contamination caused by the world’s worst nuclear crisis in 25 years. Yet none of these detectors or their data can tell their users just how worried they should be. For the crisis has laid bare an absence of scientific and social consensus on radiation risk, which is undermining a disaster response already weakened by fractious leadership and an often slow-moving bureaucracy.
Uncertainty about radiation danger is not a problem for Japan alone. Atomic plants around the world are ageing fast, and more are being built in developing countries where there is often limited public oversight and high levels of corruption. It would be foolish for the world to assume that this crisis will be the last.
On one side, analysts say bowing to exaggerated fears of radiation will stunt global development of nuclear power, slowing economic growth and increasing pollution and global warming from fossil fuels. On the other, experts accuse the nuclear industry and government officials of playing down the dangers.
In May, radiation safety researcher Toshiso Kosako tearfully resigned as a scientific adviser to Japan’s prime minister after the government decided to set the limit for exposure in schools at 20 millisieverts a year, a level usually applied to nuclear industry workers. “It’s unacceptable to apply this figure to infants, toddlers and primary school pupils,” Professor Kosako said.
But Wade Allison of Oxford university says the 20mSv a year limit for evacuation should be raised to 100mSv a month, arguing that the principal health threat posed by the Fukushima Daiichi crisis is “fear, uncertainty and enforced evacuation”.
Underlying such stark differences lies a lack of clarity about what radiation does to the body at doses below 100mSv per year, the level at which an increase in cancer becomes clearly evident in epidemiological surveys. Prof Allison and many other scientists believe that, below a certain threshold, radiation is likely in effect to do no harm to health at all. However, the mainstream assumption is that even very low doses carry some risk, even if it is not yet measurable.
The result has been highly precautionary limits on artificial radiation exposure, such as an international safety standard for the public of just 1mSv in a year. That is less than half the exposure most people receive naturally from background radioactivity in rocks, soil and building materials, and from cosmic rays. This may make sense in normal times – but it means that in a crisis people tend to assume exposure above the limit is dangerous. The problem for authorities is that it is next to impossible to judge exactly at what point it will be safer to move a population away from the radiation or to limit its exposure by, for example, keeping children indoors and closing schools. Such moves themselves have health risks: evacuation can kill the elderly and thrust younger people into unemployment. Disrupted education can mar children’s future careers. Loss of exercise habits makes people vulnerable to illness and obesity.
David Boilley, a nuclear physicist and head of the French citizens’ radiation testing group Acro, believes the Japanese evacuation line of 20mSv a year is too high, but acknowledges that a 1mSv level would be unrealistic. French government experts have suggested setting the evacuation trigger at 10mSv per year – although this could mean adding another 70,000 people to the 150,000-200,000 evacuated from areas near Fukushima Daiichi.
“Evacuation is terrible [and we] need to weigh the burden and benefit,” says Mr Boilley, whose group is helping with monitoring in Fukushima, adding that the appropriate trigger point varies not only by area and exposure but also by individual. “Where to put it? That’s a very hard question,” he says. “I am happy I am not a politician who has to decide.”
(Full article and the comment section at the link)
Professor Wade Allison left his comment, saying:
I have written and explained in accessible language, but in some depth, why the evacuation level should have been set in the region of 100 millisievert per month, that is 1200 per year -- that is 60 times the current value, not five times, as quoted in this FT article.
Hey that means I was right, saying in my post that Professor Allison's annual limit was 1.2 sievert...