Decontamination of School Facilities in Fukushima-city
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Decontamination of School Facilities in Fukushima-city
Hideki Yoshikawa1,5, Kazuki Iijima1,5, Hiroshi Sasamoto1,5, Kenso Fujiwara1,5, Seiichiro Mitsui1,5, Akira Kitamura1, Hiroshi Kurikami1,5, Takayuki Tokizawa2,5, Mikazu Yui1,4, and Shinichi Nakayama3,5 1 Geological Isolation Research and Development Directorate, Japan Atomic Energy Agency 2 Ningyo-toge Enviromnental Engineering Center, Japan Atomic Energy Agency 3 Policy Planning and Administration Department, Japan Atomic Energy Agency 4 Nuclear Science Research Institute, Japan Atomic Energy Agency 5 (Present affiliation) Fukushima Environmental Safety Center, Headquarters of Fukushima Partnership Operations, Japan Atomic Energy Agency, Okitama-cho 1-29, Fukushima
ABSTRACT Following the release of radionuclides into the environment as a result of the accident at Fukushima Daiichi nuclear power plant, Japan Atomic Energy Agency (JAEA) had to develop an immediate and effective method of reducing the dose rate received by students in school facilities. A demonstration of a reducing method was carried out by JAEA at a junior high school ground and kindergarten yard in the center of Fukushima-city. Dose rates of the released radionuclides are largely controlled by the ground level contamination and accumulation of mainly Cesium137 (Cs-137) and Cesium 134 (Cs-134) in populated areas. An effective means of reducing dose rate was to remove the surface soil and to bury it on-site under fresh uncontaminated soil or soil collected under deep depth at the site for shielding. The dose rate at1 m above ground level was reduced from 2.5 μSv/h to 0.15 μSv/h. INTRODUCTION Two explosions at the Fukushima Daiichi nuclear power plant on 12th and 14th March 2011 caused an uncontrolled release of radionuclides into the environment. The majority of the released radionuclides were deposited on the ground and accumulated at various surfaces such as plants, roofs, roads, and soils near the nuclear plant. In populated areas, dose rates related to the released radionuclides are largely controlled by the surface contamination and accumulation of Cesium137 (Cs137). While elevated dose rates recorded after the accident generally continued to decrease daily, elevated dose rates were recorded in May 2011 in Fukushima city, located some 60 km NW of the Fukushima Daiichi plant. The Fukushima University Junior High School and the Kindergarten attached to Fukushima University are located in the central part of Fukushima city. About 450 students and about 70 pupils go to the school and the kindergarten. The junior high school covers a ground surface of about 15000m2 and the kindergarten an area of about 1200m2. They are surrounded by big trees, such as cherry and zelkova of over the 10m height, and make up a good educational environment. Both buildings of the junior high school and the kindergarten are made of concrete, therefore, air dose rate in these buildings are with less than 0.1 Sv / h lower than outside. After the accident, an educator and parents had declined to exercise in the outside in
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