Modeling of emergency zones for protective actions planning in case of radiation emergency based on relevant data related to the Fukushima prefecture

The paper considers principles of design of advanced plan of action in potentially hazardous areas affected by an accident in nuclear facilities, as well as applicability of the developed algorithm of making decisions on further actions that should be taken after the active phase of the accident in the emergency actions zone. The areas are divided into specific zones for actions planning, such as zones for precautionary actions and for emergency actions. The planning actions are aimed at reduction of exposure of the public to radiation contamination, they include evacuation of people living in radioactively contaminated areas and deactivation measures. The decisions on emergency measures that should be taken are based on analysis of annual committed effective doses of external radiation. Modeling of zones for emergency planning and recommended boundaries of the zone for protective measures was performed. The models were based on relevant data related to the Fukushima Prefecture. Two options of planning zones were studied, i.e. municipal corporations and smaller administrative units, gathered into clusters with the use of mathematical models for zoning. When modeling of sensitivity of results to main parameters of decisions making, i.e. individual committed effective dose to residents, ranged from 10 to 100 mSv/yr and the relative fraction of residents with dose that exceeded the reference dose in each planning zone (the fraction varied from 5 to 30%) was tested. The number of people recommended for resettlement was compared with the number of people with doses exceeded the annual dose limit. Boundaries of recommended zones from which the residents should be relocated were compared with actual boundaries of zones for evacuation and resettlement in the Fukushima Prefecture in 2011. Finally, advance planning zones for protective measures is ready to practical use. Algorithm for decisions making based on analysis of distribution of committed effective dose will be ready to use after practical improvement of algorithms for automatic zoning of areas.