Study for shielding efficiency of evacuation facilities in nuclear emergency

Sheltering is one of the protective actions to reduce external exposures from both the radioactive plume and the deposited radionuclides in a nuclear emergency. The aim of the present study is to provide the data of characteristics of evacuation facilities regarding building materials and structures, and preliminary estimates of shielding efficiency for the use of emergency planning. To achieve this aim, surveys were performed on the evacuation facilities actually used in Japan. In addition, for air submersion and deposited radionuclides, the shielding factors were calculated based on the survey results. The findings indicate that the shielding factors for the radiation due to air submersion were almost within the range of the previous works. The shielding factors, which were calculated with considerations of the radionuclides deposited only on the ground surface, were greater than those of the previous works. To explain the differences between the present study and previous works, an evaluation should be needed taking into account contributions of contaminated roofs.