Sensitivity analysis of the radioactive monitoring data in the Fukushima Daiichi Nuclear Power Plant

A large amount of radioactive materials was released into the atmosphere during the Fukushima Daiichi Nuclear Power Plant (FDNPP1) accident in March 2011 and the gamma dose rates measured by the monitoring sites in FDNPP1 greatly increased accordingly. The atmospheric dispersion simulations of the radioactive source term of FDNPP1 have been made in many researches, but the near-field radiation dose monitoring data in FDNPP1 were rarely analyzed. In this study, sensitivity analysis of the radioactive monitoring data in FDNPP1 is carried out with atmospheric dispersion simulations coupling the Risø Mesoscale Puff model (RIMPUFF) and different source term patterns. The simulation results show that the temporal profiles of the near-field radiation dose monitoring data are determined by several different factors in different ways, among which the meteorological data are the most determinant factors for the peak position and amplitude of the temporal profiles of the dose monitoring data. The trajectory of the radioactive plume and the half-life of radionuclides determine the declining of these peaks. The baseline of the dose monitoring data is determined by the deposition process and it is most sensitive to the composition of deposited radionuclides. (author)