Radiation levels on school playgrounds near the disaster-crippled Fukushima No. 1 Nuclear Power Plant can be cut by up to 99 percent by removing contaminated soil, the Ministry of Education, Culture, Sports, Science and Technology has announced.
The ministry concluded on May 11 that radiation levels on school playgrounds and other locations near the troubled plant can be effectively reduced by replacing irradiated topsoil with earth from deeper down, or removing the top layer and burying it. The government's Nuclear Safety Commission has also acknowledged both methods are effective in lowering soil radiation levels to a certain extent.
The ministry will inform affected schools of how to exchange or remove contaminated soil through the prefectural board of education starting May 12, but whether to carry out the procedure or which of the two methods will be employed will be left up to each school.
On May 8, workers from the ministry and other institutions measured radiation levels in the soil in the city of Fukushima, detecting toxic radioactive substances up to 5 centimeters deep.
By removing the topsoil to a depth of 10 centimeters and replacing it with dirt from about 50 centimeters below the surface, the amount of radiation on the surface decreased by about 90 percent.
Furthermore, radiation levels at the test site dropped significantly as workers scraped off the topsoil, put it in a deep hole and covered the hole with clean soil. When the layer of clean soil covering the hole is 40 centimeters thick, the radiation dose on the surface is expected to drop by 99 percent.
The government is considering fully or partially covering the decontamination procedure expenses, said Ryuzo Sasaki, senior vice education minister during a press conference on May 11.
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(Mainichi Japan) May 12, 2011
東日本大震災：校庭の土汚染、９９％低減可能 文科省が原子力安全委に報告
東京電力福島第１原発事故で放出された放射性物質による福島県内の校庭の汚染について、文部科学省は１１日、有効な線量低減策として、表土と下層の土を入れ替える方法と、削った表土を１カ所に埋める方法の２通りを内閣府原子力安全委員会に報告した。安全委はいずれも一定の効果があるとしている。文科省は１２日以降、同県教委などを通じて各学校に低減策を通知するが、実施するかどうかや、どちらの方法を選ぶかの判断は各学校に委ねるという。
同省などが８日に福島市内で実施した調査によると、放射性物質は表面から地下５センチ程度までの間に分布。土を入れ替える場合、１０センチまで削った表土を深さ５０センチの土と入れ替えると、表土の線量が約１割に下がった。校庭の１カ所に深く掘った穴に、削った表土をまとめて埋める方法では、穴をふさぐ土を踏み固めることで、遮蔽（しゃへい）効果が向上。厚さ４０センチなら線量は９９％低減できると試算している。
こうした対策にかかる費用について、笹木竜三副文科相は１１日の会見で、国が全額または一部を補助するよう検討する考えを明らかにした。【岡田英、野田武】
英訳毎日新聞 2011年5月12日 東京朝刊
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