Initially, the government implemented the evacuation measure in accordance with the IAEA document, which defined the Protected Action Zone (PAZ) as areas within 3km radius from the power station.As the extent of the accident became larger, the evacuation range was expanded based on the 10km radius of the Emergency Planning Zone (EPZ, 10km radius) stipulated in the Emergency Preparedness Guidelines by the Nuclear Safety Commission.The further propagation of the accident forced the government to expand the evacuation scope accordingly to concentric areas of a 20km radius.
On the other hand, the Nuclear Safety Commission's Emergency Preparedness Guidelines stipulate that evacuation measures be determined based on predicted radiation dose calculated by the SPEEDI Network System based on the status of radioactive material discharge, monitoring data and meteorological information.Although the dispersion of radioactive materials per unit of discharge was swiftly predicted and calculated immediately after this accident, monitoring data could not be gathered due to the actual situation of discharge and power blackout.As a result, the radiation dose could not be predicted, and therefore SPEEDI was not utilized for determining evacuation measures.