Bulletin of the Atomic Scientists, 1 August 2013.
Written by Winifred BirdJane Braxton Little
Deep in the forested mountains of Fukushima Prefecture, in the town of Kawauchi, a woman in an apron and skirt stands in front of her house, solemnly scrutinizing her property. A group of workmen, crouched nearby drinking their afternoon tea, have cleared the property of all underbrush and grass. Beyond them a dry brown expanse slopes 20 meters up the hillside, its trees now branchless trunks poking upward between fresh-cut stumps.
The woman is one of thousands of residents and temporary workers who are using chainsaws, bamboo rakes, and their own hands to remove leaf litter, undergrowth, and trees from the periphery of houses and other buildings throughout the eastern part of the prefecture. Their target is anything that might harbor contamination from the March 2011 meltdown of three reactors at the Fukushima Daiichi Nuclear Power Station. Japanese officials believe that scouring the land will rid it of radionuclides so that evacuees can safely move back home. But while decontamination has already been declared finished in one town within the exclusion zone and is under way in others, vast stretches of heavily forested mountains—up to 86 percent of the land in some districts near the plant—are proving a major obstacle in the government’s cleanup and resettlement plan.
At Chernobyl, Ukraine, the site of the only nuclear accident worse than this one, government officials have taken an entirely different approach to managing irradiated forests. After Chernobyl’s No. 4 reactor exploded in 1986, sending radionuclides aloft as far as Sweden and Finland, officials completely evacuated 2,600 square kilometers. In this area, known as the exclusion zone, forests now cover 87 percent of the land. Left to themselves, the abandoned forests and fields trapped cesium, plutonium, strontium, and other airborne radionuclides through their natural life cycle: Contamination-coated leaves and needles dropped to the ground, where they became part of the litter and gradually migrated into the soil. In 2006, scientists found that up to 96 percent of all radionuclides remaining in the forests were concentrated in the soil, mostly in the top 10 centimeters.
Cesium around Fukushima is also migrating from trees and leaves into the soil. When scientists at the government-funded Forestry and Forest Products Research Institute surveyed the distribution of radiocesium at three forested sites in the fall of 2011, they found between a third and half of contaminants were in the leaf litter. Removing these fallen leaves, they suggested, would be a relatively efficient way to clean up forests. By the time the researchers re-tested the same three sites a year later, however, contaminants had shifted dramatically downward: Between 65 and 77 percent of radiocesium was in the soil, where it is much more difficult, expensive, and environmentally harmful to remove.
While officials in Japan grapple with these issues, their counterparts in Ukraine are struggling with one of the consequences of their decision to let nature take its course in the Chernobyl exclusion zone: fire. If these forests burn, strontium-90, cesium-137, plutonium-238, and other radioactive elements would be released, scientists say. And instead of being emitted by a single reactor, the radioactive contamination would come from trees covering a vast area. A worst-case-scenario study conducted in 2011 predicted that people living outside the exclusion zone would not have to be evacuated, and there would be no cause for panic in Kiev. But firefighters would be exposed to radiation beyond acceptable levels. In addition to external radiation, they would be exposed to internal radiation by inhaling radionuclides in the smoke.
Forest scientists in Japan say the risk of catastrophic forest fires in Fukushima is relatively low compared with Ukraine, and limited to a short dry season in spring. Nevertheless, the Chernobyl data present yet another dilemma for Japanese officials and forest residents.
As the sites of the world’s worst nuclear power plant accidents, Japan and Ukraine share the challenge of protecting their citizens even as they hope to return residents to the rural communities where forests sheltered and nurtured them. Whether Japan opts for the Chernobyl model, leaving forests to their slow but natural recovery, or pursues decontamination, local residents will inevitably pay a price.
Editor’s note: A grant from the Society of Environmental Journalists covered the authors’ travel costs for this article.