Distribution of radiation in residential environment and its temporal change

Abstract

  Following the approval of the designated reconstruction and rehabilitation base areas, in the difficult-to-return areas in 2017, the evacuation issues are to be lifted in these base areas and the residents will be allowed to return and live within 5 years, taking into account the reduction of the dose. For the residents intending to return to their home and live there, information about distribution of radiation in residential environment is essential while assessing the consequences of the nuclear accident in the context of risk assessment, since most of the individuals spend a large portion of their time indoors. In particular, reduction factor, RF, which is the ratio of the indoor dose to the outdoor dose, is important for estimating residents’ external dose due to radionuclide exposure resulting from fallout deposit on the ground, however, measurement data for Japanese settlements were lacking when the Fukushima nuclear accident occurred in 2011. Immediately after the accident, we started to evaluate reduction factor for detached wooden houses based on survey results in evacuation zones, Fukushima Prefecture. In this report, we summarize the values of reduction factor for detached wooden houses, which were collected before and soon after decontamination work, and 6-7 years after decontamination work, and discussed its temporal change.