Fusion Reactor Shielding Materials (FURESHMA): Understanding In-service Degradation

Context and current state-of-the-art:
This co-created, business-inspired, fundamental research aims to enable Tokamak Energy Ltd (TE) to develop and improve fusion reactor centre-column designs by understanding the effect of irradiation, intense plasma-exposure and high-heat flux (HHF) on advanced shielding materials degradation. This partnership, with a long-term vision of contributing to fusion commercialization efforts, will be delivered in active collaboration with world-leading fusion centres in the EU, and further guided by a steering committee comprised of subject-matter experts from the US and the UK.
Meeting net-zero emissions by 2050, as outlined by the Net Zero Government Initiative, requires green innovation technologies such as fusion energy which promises carbon-free, safe, secure and abundant power. The UK-based TE aims to demonstrate commercial fusion in the 2030s by combining its spherical tokamak design with rare-earth barium copper oxide (REBCO) high-temperature superconducting magnet technology, thereby, opening a pathway for smaller more compact power-plants. Key to success is a robust “centre-column” design, a life-limiting component comprising of REBCO coils. However, these magnets are highly susceptible to radiation damage and heat. Smaller power-plants offer limited shielding volumes, necessitating high-performance advanced shielding materials, with a thorough understanding of their fusion-relevant in-service degradation phenomena. This is critical to enabling TE’s commercial spherical tokamaks.
Key Challenge:
Fusion in-vessel conditions are severe – high neutron bombardment (>100 displacements per atom, dpa), a wide temperature range (cryogenic in magnets to >1000 °C), intense plasma particle exposure (>1019 ions.m-2.s-1 of D,T, He, impurities etc.)  and HHF (tens of MW/m2 to several GW/m2 during disruptions). Given these synergistic challenges, the primary shielding candidates for TE’s centre-column are novel ceramic shielding materials: reduced-activation binder tungsten carbide (rab-WC) and di-tungsten pentaboride (W2B5), which are protected by potassium doped tungsten (K-doped W) in the plasma facing regions. Shielding failure in-service would result in failure of the centre-column. But little is known regarding in-service degradation of these materials, over their wide envisaged operating temperature range from cryogenic to >750 °C, which is a major design-limiting challenge.
Project Aims/Objectives:
To make progress towards the overarching goal, the following short-term objectives, to be completed within three years, are proposed:

Understanding radiation-induced degradation of ceramic shields from cryogenic to 800 °C (rab-WC, W2B5).
Quantifying the effect of plasma exposure and HHF on K-doped W and rab-WC.
Preliminary HHF testing of W-WC joints.
Baseline neutronic and Multiphysics assessment of damaged shielding materials to guide a preliminary centre-column design using data from (i), (ii) and (iii).

Applications and Benefits:
By enabling TE to develop robust fusion in-vessel component designs guided by materials degradation knowledge, this study will (i) enable the UK to be a global leader in the technologies needed to decarbonise our economies and transition to net zero, and (ii) directly support the UK’s plan for bringing about a Green Industrial Revolution by commercializing fusion energy technology. By building partnership with the University of Birmingham, which has notable fusion materials expertise, and coinvesting in discovery science and engineering, TE stands to become a world-leader in fusion energy, placing the UK at the forefront of the fusion landscape and benefiting the wider UK economy.