Rigorous mcnp based shutdown dose rate calculations: computational scheme, verification calculations and application to ITER

A rigorous 2-step (R2S) computational system has been developed for the calculation of shutdown dose rate distributions in full three-dimensional geometry. The system is based on the use of the mcnp transport and the fispact inventory code linked through a suitable coupling scheme for the automated routing of decay gamma sources and neutron flux spectra. The decay gamma source distribution is sampled in a source routine linked to mcnp according to the distribution provided by preceding mcnp neutron transport and fispact inventory calculations. A detailed description of the flow scheme and the interfaces of the R2S code system is given. Validation of the system has been achieved through the computational analysis of an International Thermonuclear Experimental Reactor (ITER) shutdown dose rate experiment. The application to the ITER device has demonstrated the suitability of the R2S system for handling shutdown dose rate analyses of large and complex fusion reactor systems.