Radiation-Induced Evolution of Tungsten Carbide in Fusion Reactors: Accommodation of Defect Clusters and Transmutation Elements

Abstract

The development of suitable shielding material is a key challenge in the advancement of spherical tokamak fusion reactors. Tungsten carbide (WC) is a promising candidate material owing to its low neutron and gamma attenuation lengths resulting from the combination of high-Z and low-Z elements, but its behaviour under prolonged exposure to fusion neutrons is poorly understood. Here, we shed light on the microstructural evolution of WC under neutron irradiation by investigating the formation and clustering of defects using density functional theory atomic simulations. It is found that deviation from stoichiometry is accommodated entirely by C defects (vacancies and interstitials) while the disorder induced by radiation damage may be accommodated by three competing processes (C-Frenkel, anti-site and Schottky) with similar energetics. Vacancy clusters involving a combination of both tungsten and carbon vacancies show increasingly favourable binding energies with increasing cluster size and may lead to the fo...