The evaluation for radiation shielding ability of the soil materials and application to design for construction

The 2011 off-the Pacific coast of Tohoku earthquake affected Japan, wreaking severe damage to a nuclear power plant in Fukushima. During decommissioning, ensuring worker safety is important in relation to fuel debris retrieval. Given that background, the authors specifically examined the use of heavy bentonite-based slurry as a filling material in a nuclear reactor. Heavy slurry can shield gamma rays and neutron beams because of its high specific gravity and water contents. Also, soil materials are used for soil cover type storage facilities for radioactive waste without evaluation for shielding. This research was conducted to investigate and define the radiation shielding capability of soil materials for controlling nuclear accidents. To quantify the radiation shielding capability, the authors measured the transmitted radiation dose through soil materials under some conditions of pass length. Results show that the reduction of the gamma ray dose has a proportional relation with wet density of materials, and show that the reduction of the neutron beam dose is related with the volume water content of materials. The research described in this paper is a proposal for application to the design for construction using soils for decommissioning of the Fukushima Daiichi Nuclear Power Station.