Radiation shielding effect of typical residential houses in Japan in reactor accidents

Radiation shielding effect against γ-rays from radioactive noble gas cloud resulting from a major reactor accident was investigated for three typical residential houses in Japan; prefabricated, wooden and ferroconcrete houses. The shielding factors of the houses, the ratio of indoor dose rate to outdoor one, were estimated for the submersion and cylindrical plume trailing overhead, which contain monoenergetic γ-ray sources or γ-emitting noble gas radioactive nuclides. The shielding factors against the noble gas cloud decrease gradually with the release delay time and maintain the minima after 50 hours while 133Xe predominates in the cloud. Neither the mixing of iodine nuclides in the cloud nor the cloud shape affects significantly the shielding factors. Finally the shielding factors for the use of emergency planning were proposed as 0.4 for ferroconcrete residential houses and 0.9 for other ordinary residential ones. (author)