This paper discusses a rational methodology to evaluate dose rate at the boundary of the interim storage facility using two methods; 1) a method taking into account “shade effect” which represents the self-shielding effect of interim storage containers, 2) utilization of a newly developed simplified code. It was proved that the method of the shade effect is applicable to the secondary gamma-ray, which dominates approximately 50% of the total effective dose rate. Thus, the effective dose rate attributed to the secondary gamma-ray depends on both the number of containers in the facility and the shade coefficient which represents the factor of the shade effect. Using this shade coefficient, the dose rate was estimated for the facility that stored 8 or 16 containers around the boundary of the facility and the results were consistent with that of the Monte Carlo calculation. In the present study, a simple neutron transport code, MCNP-ANISN_W, was newly developed aiming at the simplification of large-scale calculation. The results of the dose rate agreed well with that of the Monte Carlo calculation. The results of the present study show that the simple evaluation technique and the code developed in this study would be useful for the evaluation of dose rate around the boundary of the interim storage facility.
