The work presented in this thesis focuses on exploring the applicability of high entropy hydrides as shielding materials in commercially viable fusion reactors. This objective was pursued using a combination of computational and experimental methods to identify compositions of interest and to explore mechanisms that may potentially limit the feasibility of certain systems.

The exploration of potential high entropy alloy materials has often been complicated by the vast compositional space that can be employed. However, it has been shown in this work that implementing a selection criterion for both elements and resulting compositions can effectively reduce the compositional space that needs to be considered. Moreover, a neutron penetration study of the resulting compositions of interest, was conducted using Geant-4, whereby the results highlighted that the shielding capacities of the proposed HEA compositions, with a 𝐻/𝑀 ≈ 1, were comparable to the performance of W2B5 a proposed composition that has been determined as one of the most effective shielding materials for 14 MeV neutrons.

Density functional theory has been implemented for the modelling of numerous equiatomic high entropy alloy systems as well as (TiZrNbHfTa)Hx a system which has previously been explored in terms of hydrogen storage that may offer effective shielding performance. The thermodynamic process of vacancy formation has been explored for each of the systems of interest and a minimum expected formation enthalpy was proposed based on the electronegativity of a given chemical environment. The influence of hydrogen interstitials on the predicted equilibrium vacancy concentration of (TiZrNbHfTa)Hx, as well as an observed stabilising effect of monovacancies on neighbouring hydrogen interstitials, presents an iii alternative mechanistic basis for previous experimental observations. Furthermore, the stabilising effect of adjacent monovacancies on hydrogen interstitials was implemented in a model that accurately predicts the decomposition temperature range for (TiZrNbHfTa)Hx, providing a potential avenue to further refine the compositions of interest in terms of HEAs.

The synthesis and subsequent surface analysis of as-cast and heat-treated (TiZrNbHfTa)Hx has identified the impact of chemical homogeneity of the alloy on hydrogen-induced crack formation. Consequently, additional requirements are suggested for future HEA compositions of interest, predominantly focusing on the importance of single-phase microstructures to limit the influence of hydrogen-induced volumetric expansion. Moreover, a series of proposed computational and experimental studies is supplied that will provide valuable information regarding the radiation damage response of these materials, the influence of cryogenic temperatures on hydride precipitation, and the influence of isotopic effects on hydrogen retention.