Finite element models for radiation effects in nuclear applications

Fusion reactor components will be exposed to fluxes of high energy neutrons while also being subjected to thermal, mechanical and magnetic loads. Exposure to neutron irradiation has numerous consequences, including swelling and dimensional changes, comparable in magnitude to the peak transient thermal deformations of plasma-facing components. Irradiation also dynamically alters the various thermo-mechanical properties, relating the operating temperature, stress and swelling in a strongly non-linear way. The available experimental data spanning the design parameter space are too sparse; computer simulations ought to be used to mechanistically assess the effect of neutron exposure to enable designing a fusion power plant on time and on budget. In this study we explore the equivalence between the body force/surface traction approach and the eigenstrain formalism for treating anisotropic irradiation-induced swelling. We find that both commercial and massively parallelised open source software for finite element method (FEM) simulations are suitable for assessing the effect of neutron exposure on the mechanically loaded reactor components. We demonstrate how the two primary effects of irradiation, radiation swelling and the degradation of thermal conductivity, affect the distributions of stress and temperature in a divertor. Significant uncertainties characterising the magnitude of swelling and models for treating it suggest that on the basis of the available data, only an order of magnitude estimate can be given to the stress developing in reactor components during service.