Three Dimensional Neutronics Analysis of the ITER First Wall/Shield Module 13

Radiation shielding and energy removal for ITER are provided by an array of first wall/shield modules (FWS). Nuclear analysis of the shield modules is important for understanding their performance and lifetime in the system. While one-dimensional (1-D) analysis provides an adequate first approximation, three-dimensional (3-D) analysis is needed to validate the 1-D analysis and resolve fine geometric details that result from heterogeneities in the module. Using MCNPX-CGM, a coupling of traditional MCNPX with the Common Geometry Module (CGM), high-fidelity 3-D neutronics analysis is now possible. Particles are transported in the CAD geometry reducing analysis time, eliminating input error, and preserving geometric detail. A detailed 3-D CAD model of FWS module 13 is inserted into a 1-D radial approximation including homogenized representations of the inboard FWS, plasma, and vacuum vessel (VV). A 14.1 MeV uniform source between the inboard and outboard sides is used to simulate the ITER plasma. Reflecting boundary conditions approximate the full extent of ITER in the poloidal and toroidal directions. Heating, radiation damage, and helium production profiles through module 13 are determined using high-resolution mesh tallies. In the front manifold of the shield block, heating and helium production were found to be lower in steel than the homogenized 1-D model suggests. Peaking in nuclear heating and helium production in steel is observed at the interface with adjacent water zones.