Neutron irradiation & thermomechanical experiment (NITE) - design

For the reliable long-term operation of fusion power plants, it is crucial to understand and predict the lifetime of materials in use. These materials include all structural and functional materials utilized at the first wall, blanket, magnets, and shielding. The key challenge is that the harsh environment including high-heat fluxes, high thermal stress and stress cycling, neutron irradiation, and sputtering on such materials should not be viewed separately. Currently, the combined loads cannot be evaluated experimentally because of the lack of adequate facilities. The purpose of our work is to design a synergetic neutron irradiation and thermomechanical experiment for fusion materials. This design will leverage the existing Advanced Test Reactor, a fission reactor at Idaho National Laboratory. We also acknowledge that, with existing fission reactors, the exact fusion condition cannot be created and critically discuss the limitations. The combination of neutron irradiation with a high-heat flux is the focus. This is realized with an irradiation capsule design that includes a tristructural-isotropic-fueled region inside the capsule to enable a steady-state heat flux on one side of the specimen. The experimental design modeling showed that steady-state heat fluxes of 2.4 MW/m² with a thermal gradient above 50 °C/mm through the 5-mm-thick specimen can be achieved.