Development of tritium release model for advanced Li8PbO6 breeder materials for compact spherical tokamaks

The proposed research will accelerate the development of advanced ceramic breeder materials for compact spherical tokamaks. As the limiting step in the tritium recovery process for solid breeders is tritium release from the crystal, this proposal will examine the atomic scale mechanisms responsible for tritium diffusion in a leading candidate ceramic, building on successful previous work.

An understanding of the tritium mobility will enable the development of strategies to limit tritium retention, thereby ensuring maximum tritium production to sustain the plasma. The subtle interactions between tritium atoms and defects present in the ceramic matrix will ultimately determine the rate of tritium release from the crystal. However, the nature of the defects in the material will change as the material ages and so it is critical that we understand the tritium release process across the material's lifetime.

Development of ceramic breeder materials for ITER and DEMO has focused on two key candidate materials, lithium metatitanate (Li2TiO3) and lithium orthosilicate (Li4SiO4). However, recent work has indicated that the high lithium density and excellent tritium release characteristics (at least in the stoichiometric material) mean that octalithium plumbate (Li8PbO6) is an interesting possible replacement for Li2TiO3 and Li4SiO4 for use in spherical tokamaks.

Therefore, this study will employ a mixture of atomistic simulation techniques (DFT and MD) to explore tritium release in Li8PbO6. The project will develop a tritium release model for Li8PbO6 similar to fission gas release models used in fission reactors.

In GREEN we envisage there are potentially Impacts in several domains: the nuclear Sector; the wider Clean Growth Agenda; Government Policy & Strategy; and the Wider Public.

The two major outputs from Green will be Human Capital and Knowledge:

Human Capital: The GREEN CDT will deliver a pipeline of approximately 90 highly skilled entrants to the nuclear sector, with a broad understanding of wider sector challenges (formed through the training element of the programme) and deep subject matter expertise (developed through their research project). As evidenced by our letters of support, our CDT graduates are in high demand by the sector. Indeed, our technical and skills development programme has been co-created with key sector employers, to ensure that it delivers graduates who will meet their future requirements, with the creativity, ambition, and relational skills to think critically & independently and grow as subject matter experts. Our graduates are therefore a primary conduit to delivering impact via outcomes of research projects (generally co-created and co-produced with end users); as intelligent and effective agents of change, through employment in the sector; and strong professional networks.

Knowledge: The research outcomes from GREEN will be disseminated by students as open access peer reviewed publications in appropriate quality titles (with a target of 2 per student, 180 in total) and at respected conferences. Data & codes will be managed & archived for open access in accordance with institutional policies, consistent with UKRI guidelines. We will collaborate with our counterpart CDTs in fission and fusion to deliver a national student conference as a focus for dissemination of research, professional networking, and development of wider peer networks.

There are three major areas where GREEN will provide impact: the nuclear sector; clean growth; Policy and Strategy and Outreach.

the nuclear sector: One of our most significant impacts will be to create the next generation of nuclear research leaders. We will achieve this by carefully matching student experience with user needs.

clean growth - The proposed GREEN CDT, as a provider of highly skilled entrants to the profession, is therefore a critical enabler in supporting delivery of both the Clean Growth agenda, Nuclear Industry Strategy, and Nuclear Sector Deal, as evidenced by the employment rate of our graduates (85% into the sector industry) and the attached letters of support.

Policy and Strategy: The GREEN leadership and supervisory team provide input and expert advice across all UK Governments, and also to the key actors in the nuclear industry (see Track Records, Sections 3.3 & 5.1, CfS). Thus, we are well positioned to inculcate an understanding of the rapidly changing nuclear strategy and policy landscape which will shape their future careers.

Outreach to the wider public: Building on our track record of high quality, and acclaimed activities, delivered in NGN, GREEN will deliver an active programme of public engagement which we will coordinate with activities of other nuclear CDTs. Our training programme provides skills based training in public and media communication, enabling our students to act as effective and authoritative communicators and ambassadors. Examples of such activities delivered during NGN include: The Big Bang Fair, Birmingham 2014 - 2017; British Science Week, 2013 - 2017; ScienceX, Manchester; 2016 - 2018; and The Infinity Festival, Cumbria, 2017.