By contrast, Japan’s government is attempting to bring background radiation levels in the most highly contaminated evacuation zone to an average of 1 millisievert per year once all the work is completed.
That would be twice the background radiation level in Denver, or a sixth of the annual dose for the average American when all sources or radiation are taken into account. Japanese nuclear workers are limited to an accumulative exposure of 100 millisieverts over five years. Although radiation health experts assume that any incremental exposure to radiation increases risks for later cancers, the International Atomic Energy Agency say a statistically significant correlation only shows up at doses over that higher threshold.
The Japanese government decided to allow people to move back to areas with an average annual dose of less than 20 millisieverts in December 2011.
In an attempt to reach the tougher radiation target, thousands of temporary workers have been put to work scrubbing houses and roads, digging up topsoil and stripping trees of leaves into which invisible caesium particles have wormed.
Few of the hundreds of companies and small firms involved have any experience with radiation. Some workers have said they have been told to flush contaminated leaves away in rivers by supervisors to speed the job up and reduce waste, since storage remains a problem.
On a recent Saturday, a crew of 10 workers in jumpsuits, hardhats and surgical masks were clearing a roadside outside Kawauchi, picking up leaves and trimming weeds. The lower half of nearby forest slopes were stripped of saplings and shrubbery.
“That’s lovely,” Yokota told a visitor. “They’ve got it nice and clean.”
Some experts are doubtful about the payback of that effort.
“The truth of the matter is that from the European experience [after Chernobyl], remediation factors are disappointing,” said David Sanderson, a professor of environmental science at the University of Glasgow and an expert in radiation who has made numerous trips to Fukushima to map the fallout.