Calculations of radiation back-flux from neutron irradiation in fusion reactors

Conclusions and Future Work Used MCNP simulations to quantify the radiation back-fluxes from neutron irradiation in fusion reactors.-Neutron back-fluxes ~60-90% of incident fluxthis is an unexpectedly large value!-Gamma radiation back-fluxes ~15-50% of incident flux.-Electron back-fluxes ~2 orders magnitude lower than gamma ray back-fluxes. Characterized the impact of materials design configuration on back-fluxes.-Neutron back-flux magnitude depends primarily on the choice of structural material.-Gamma ray and electron back-fluxes depend primarily on tungsten first wall thickness. Computed the time-integrated build-up of delayed back-fluxes from radioactive decay.-Delayed gamma ray and electron back-fluxes ~2-7% of the prompt back-flux magnitude.-Iron-based materials and V-4Ti-4Cr reach terminal build-up levels; Inconel 718 does not (within ~30 years). Large back-flux magnitudes have significant implications for power handling and disruption mitigation. Future work: scaling up to perform reactor-relevant calculations!-Real reactor geometries require HPC resources -Explicit delayed back-flux solution with decay source distribution for better efficiency.-Coupling to plasma physics to quantify effects on plasma performance and disruption handling.