Decontamination tech gets test drive in Fukushima

Aug 15 - McClatchy-Tribune Regional News - Setsuko Kitaguchi The Yomiuri Shimbun

Companies participating in the Environment Ministry's technology verification project for the decontamination of radioactive substances in Fukushima Prefecture are testing their cleanup solutions to determine whether they can be used widely.

Shimizu Corp., a major general contractor, has been cleaning contaminated soil in a large tent set up in an open area of the town of Hirono. Bubbles came to the surface of muddy water in tubs, making it appear to boil.

By exploiting radioactive cesium's tendency to adhere to small particles, specific agents are mixed with soil particles under two millimeters in diameter to absorb the cesium. The resulting substance is then sifted by a machine to remove the soil so it can be reused. About 80 percent of the soil is salvageable.

There is an estimated 150 million to 280 million cubic meters of contaminated soil to be removed through such decontamination work. To reduce this amount, Shimizu and four other companies are undertaking such projects with the aim of recovering as much soil as possible.

Decreasing the amount of contaminated soil will ultimately determine the size of facilities needed to store it temporarily, as well as intermediate facilities to be built in the future.

The ministry chose 22 technology verification projects out of 295 proposed by the private sector, and is promoting the development of their respective technologies.

A wide range of areas have been contaminated with radioactive substances released from the Fukushima No. 1 nuclear power plant following last year's Great East Japan Earthquake and tsunami.

Schools, school routes and residential areas are given top priority for decontamination work. Cleanup of the Joban Expressway linking Tokyo with Sendai also is being conducted in earnest because restoring this vital distribution artery will help speed up reconstruction.

Forests, which account for about 70 percent of the prefecture, are given a lower priority than residential zones, as such places see relatively few visitors. The Environment Ministry said, "There is little need to decontaminate woodlands in their entirety" except those within 20 kilometers of residential areas.

Eleven cities, towns and villages, including Tamura and Naraha, are subject to decontamination under the central government's direct administration.

The government plans to decontaminate the area until the annual radiation dose is reduced to 20 millisieverts or less--a level considered safe for residents to return--by the end of March 2014. In areas where radiation exposure is already below that level, decontamination will continue, with the aim of lowering the dose to one millisievert or less.

However, progress is expected to be much slower in some areas. In March, the Cabinet Office concluded that "it will be difficult to achieve the target of reducing radiation to 20 millisieverts or less over a short period in areas with levels of 40 millisieverts."

The Environment Ministry took over the decontamination projects from the Cabinet Office last month. In addition to soil decontamination, there are other projects to reduce radiation levels around the prefecture.

Fukushima Komatsu Forklift Co. in Koriyama, Fukushima Prefecture, is testing a moplike device that sprays high-pressure water on the road to loosen radioactive cesium. The wastewater is sucked up and stored inside a tank on a truck to prevent recontamination due to spraying and leakage.

Cesium in the stored water is absorbed by coagulants and 90 percent of the water is designed to be recycled after going through a filtering device. Through this process radiation levels can be reduced by 60 percent to 70 percent on asphalt-paved roads depending on the conditions, the company said.