Evaluation of Dose Equivalent Rates for a New Exclusive Ship “Seiei Maru” for Transporting Low-Level Radioactive Waste by Monte Carlo Particle Transport Calculation Using Variance Reduction Parameter Derived by FW-CADIS Method

The forward weighted consistent adjoint driven importance sampling (FW-CADIS) method has been proposed as a method for obtaining variance reduction parameters to estimate flux or dose rate distribution over a wide area, or responses at multiple localized detectors for a particle transport calculation based on the stochastic Monte Carlo method with a reasonable and high accuracy. The method has been applied to estimating the dose equivalent rate around the Japanese exclusive ship, “Seiei Maru”, which transports low-level radioactive waste. The particle transport calculation was performed using a mesh tally on the entire surface of the hatch cover above low-level radioactive waste packages stacked in the cargo hold and point detector tallies at each measurement point. The statistical error is spatially uniform for the mesh tally and is reduced only around the vicinity of each point detector tally. It is suggested that the estimated dose equivalent rate obtained by the calculation is equivalent to the measured result, and it is shown that this method is effective for the radiation safety evaluation of low-level radioactive waste transport ships.