Prediction of ambient dose equivalent rates in the early phase of the Fukushima Daiichi Nuclear Power Plant accident

Honda, Fumiya*; Kinase, Sakae   

To obtain reliable estimates of external dose in the early phase of the Fukushima Daiichi Nuclear Power Plant accident, a prediction map of ambient dose equivalent rates was developed using a prediction model. The prediction model is described using a double exponential form with ecological half-lives. It was found that the high ambient dose equivalent rate distribution stretches northwest from the F1NPP. The maximum ambient dose equivalent rate of the first month following the accident was found to be about 300 Sv/h. Main contributing radionuclides were I-131, Cs-134 and Cs-137. Radiation emitted from I-131 contributes about 50% of the ambient dose equivalent rate.