Atmospheric 137cs Dispersion Following the Fukushima Daiichi Nuclear Accident: Local-scale Simulations Using CALMET and LAPMOD

This paper investigates a local-scale radionuclide dispersion modeling, focusing on the 20 km range of the Fukushima accident. The California Meteorological Model (CALMET) was used to calculate the diagnostic wind fields for simulation using on-site meteorological observations, and the Lagrangian Particle Model (LAPMOD) was used to simulate the dispersion of the 137Cs. The simulation was validated against the measurement from two 137Cs airborne concentration stations (Futaba and Naraha). A comprehensive sensitivity analysis was implemented to the source term, the number of particles per second, and the disturbance in wind speed and direction. The results show that the simulation agrees well with the measurement at Futaba (Geometric Mean Bias: 0.79, Fractional Mean Bias: 0.58) than that at Naraha (Geometric Mean Bias: 1.01, Fractional Mean Bias: 0.52), especially for the peak values. The sensitivity analysis indicates that the simulation is highly affected by the source term and the wind direction.