Steady-state tritium inventory in plasma-facing tungsten for fusion reactors: An effective calculation method and implications of calculation results

Abstract

The tritium inventory in plasma-facing components needs to be evaluated with sufficient accuracy since it is relevant to the safety and fuel-cycle sustainability of fusion reactors. Here, we propose an effective method to calculate the steady-state tritium inventory in plasma-facing tungsten. In this method, the surface and diffusion processes of hydrogen isotopes (HI) are first modelled by rate theory to obtain a steady-state concentration profile of HI dissolved in the lattice. Subsequently, trap effects are modelled by equilibrium theory. By decoupling the trapping/detrapping processes from the surface/diffusion processes and focusing only on the steady state, the calculation cost is largely reduced, and atomic resolution is realized in the rate model to describe surface processes in detail. The applicability and performance of the proposed method are demonstrated with a one-dimensional test case simulating the ITER tungsten mono-block. The calculation results show that tritium retention in the deep region becomes the main source of tritium inventory at a steady state due to the large temperature gradient in plasma-facing tungsten. Several implications for DEMO and beyond are obtained regarding tritium inventory and HI effects on mechanical integrity. The proposed method can be complementary to the macroscopic rate model for tritium inventory calculations.