A simplified simulation method for selecting the most effective off-site protective action

In order to facilitate a number of calculations needed to quantify effectiveness of off-site protective actions for various emergency scenarios for emergency planning of nuclear facilities, we developed a simplified simulation method for selecting the most effective protective action among candidates of action. The protective actions considered are sheltering in houses, sheltering in public concrete building, evacuation, and iodine prophylaxis. The method has functions of (1) simulating the movement of members of the public under protective actions and calculating avertable dose by protective actions in short computing time, and (2) selecting the most effective protective action for divided areas around a nuclear site. To achieve short computing time in function (1), we applied a multivariate analysis method by using sample data obtained from results calculated with a program for simulating the movement of members of the public under protective actions with a detailed mathematical model that requires long computing time. As to function (2), we focused on net benefit, namely avertable dose minus an intervention level, of a protective action. Intervention levels used are those that IAEA proposed based on justification and optimization of protective actions by taking account of benefit and disadvantage due to protective actions. Analysis results by the simplified simulation method showed good agreement with those by the detailed simulation program. Application of the simplified method to a model nuclear site demonstrated that the method was useful as it provided the most effective protective action area depending on source terms, meteorological conditions, and so on.