The Effect of Radiation in UK Nuclear Waste Base Glasses

The glass compositions used in the UK to immobilise highly radioactive waste arising from the reprocessing of spent nuclear fuel are termed MW and CaZn. The structure of the pristine glass powders with varying Li2O contents were investigated primarily using Magic Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR) spectroscopy employing 6Li, 11B, 23Na, 27Al and 29Si nuclei. 11B MAS NMR revealed that at increasing Li2O contents results in the formation of [BO4]- sites at the expense of BO3. 11B{6Li} and 27Al{6Li} dipolar heteronuclear multiple quantum correlation (D-HMQC) NMR revealed lithium as a charge compensator for anionic tetrahedral sites with increased lithium. 29Si and 23Na MAS NMR spectra showed depolymerisation of the silicate network and shortening of Na-O bond lengths with increased lithium. A manuscript of this work has been submitted and is currently under review.
Gamma irradiations (0.5 MGy to 80 MGy) were carried out on the pristine glass powders to observe how the growth of paramagnetic defects varies with composition with an aim to identify the dose at which defect formation saturates. The assessment of paramagnetic defects formed after radiation was carried out primarily using semi-quantitative X-band Electron Paramagnetic Resonance (EPR) spectroscopy which revealed that when the Li2O content of the MW and CaZn networks was increased, the number of paramagnetic defects formed decreased. This suggests that lithium promotes stability against radiation induced changes/damage in the glass network. EPR results were related to the data obtained from NMR of the pristine glass structure to identify where the defects form in the network and lithium's role in governing defect formation.
Glass monoliths of the same compositions were prepared and irradiated with 8 MeV Au3+ ions to simulate alpha recoil damage in the network. Time-of-flight elastic recoil detection analysis (TOF-ERDA) has been employed to understand the radiation induced diffusion of elements in the glass network. Hardness testing was carried out using nanoindentation to correlate the diffusion of elements with the hardness of the glasses. TOF-ERDA was carried out on the pristine and irradiated samples, the results highlighted the inward diffusion of Li, Na and B and the outward diffusion of Si and O after irradiation. The results also revealed the diffusion of species is greater in the MW composition compared to CaZn suggesting CaZn has a higher radiation tolerance. This correlates with the results from nanoindentation testing which revealed a decrease in hardness upon irradiation, the largest decrease in hardness was observed for MW composition with the lowest lithium concentration. This promotes the hypothesis that a higher lithium content will help stabilise the glass network against radiation induced damage.

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.