3D neutronic analysis on compact fusion reactors: PHITS-OpenMC cross-comparison

The development of high temperature superconducting tape technology enabled the design of compact fusion reactors, allowing faster development in the field. The reduced size makes even more important the evaluation of neutron flux on all components and at every region, including at the magnet position, to assess the lifetime of the materials and their performances during operations. Compactness, however, introduces new technological challenges, considering the reduced space available for shielding materials and the consequently harsher radiation environment for both structural and functional materials. Many different particle transport codes have been developed for nuclear engineering and fundamental physics purposes, each one relying on different algorithms and nuclear models, with different features and capabilities. In the present work the transport codes PHITS and OpenMC are compared, testing the impact on integral results such as the tritium breeding ratio and on spatially resolved neutron spectra of different nuclear libraries, nuclear models and codes, on a CAD imported 3D geometry of an ARC like fusion machine. The impact of different neutron source shapes is also investigated, from a simple ring-like source to a realistic toroidal plasma distribution, as well as the possibility of performing calculations on a 10°reduced domain, instead of on a full 360°geometry. The uncertainty introduced by each model and geometry choice is analyzed and the computational time required is briefly discussed.