Standard Values and Reference Levels with Respect to Radiation Safety

Reference Levels for Evacuation and Return

Reference levels have been proposed for deciding on an evacuation of local residents.

When a radiological accident has occurred, the decision whether to evacuate the local residents is made using reference levels for emergency exposure proposed by the International Commission on Radiological Protection (ICRP: a non-governmental international academic body that implements recommendations related to radiation protection from a specialist standpoint). These reference levels fall into three broad categories. In regions where the exposure of local residents exceeds 100 mSv, a total evacuation is prioritized. In areas where an annual exposure of 20 to 100 mSv is expected, standard values for the evacuation of local residents are determined with consideration to the situation including measures for recovery at that point. In the Fukushima nuclear accident, this value was indicated by the government as less than 20 mSv. When the level drops below the value for evacuation, the area is treated as a region in preparation for cancellation of evacuation, and infrastructure development begins. Exposure after the people return following development of their living environment is kept to between 1 and 20 mSv annually. The long-term objective from this situation is an annual exposure of 1.0 mSv. For the people who live in a region where an evacuation has been cancelled, exposure management is ongoing, and radiation protection is important so as to reduce the annual exposure to 1.0 mSv or less.