Intermediate range order effects in radioactive waste glasses: implications for aqueous durability and mechanical properties

Radioactive waste occurs as a wide variety of radioactive elements that must be immobilised in a matrix of glass or ceramic or a composite, before disposal in a geological repository. This matrix, commonly known as the waste form, must be able to accommodate the wide range of species present in the waste and be resistant to leaching and mechanical fracture for the lifetime of radioactive species, typically 10,000 years or more. Glass, having an amorphous structure, is able to accommodate a wide range of radioactive waste species. In addition, glass fabrication technology is well established to produce these waste forms at large scale and this has been carried out for some years in both the UK and India, among several other countries.
The proposed project aims to understand the phase stability, thermal and radiation effects in radioactive waste glasses, in light of atomic scale structural changes due to radiation effects. These modifications will then be correlated with glass dissolution and mechanical properties such as cracking/fracture. The glasses selected are critical to the radioactive waste management programs in the UK and India, thus complementing methods and scientific expertise to realise clean, safe and economical energy from nuclear technology whilst presenting the most robust safety case for waste disposal. Our specific aims will be to: (1) understand the phase stability of glasses as a function of different divalent cations and addition of waste species; (2) define 'radiation damage' in an already amorphous/disordered material system and predict how radiation-induced modifications will affect dissolution properties over long timescales; and (3) understand the evolution of glass structure and properties under a temperature gradient and after undergoing annealing treatments.
In order that radioactive waste should no longer be deemed as an 'issue' rather than a practice that can be trusted by public opinion, the methods and materials employed to immobilise radioactive waste must be fundamentally understood and scientifically verified. This project aims at improving this confidence. Our detailed User Engagement Strategy will ensure that groups from the public and members of communities that may be involved in selection of a geological disposal facility, as well as the nuclear industry and supply chain, government and civil servants, and a wide range of academics, will be engaged throughout and beyond this project to deliver maximum impact from our proposed research.

Radioactive waste is a problem affecting future generations. Hence, radioactive waste management is of primary concern for successful implementation of next generation nuclear technologies and safe clean-up and decommissioning of nuclear facilities. Radioactive waste destined for geological disposal must be immobilized in a waste-form. The primary requirements for qualifying any waste-form are high waste loading (the amount of waste immobilized as a proportion of waste form volume), and superior long-term durability under radiation and corrosion conditions. The results obtained from this project will improve our understanding of phase stability and durability of waste-forms, thus helping the design of new waste-forms with enhanced waste loading whilst providing the required properties. Unlike metals and, to some extent, simple crystalline ceramics, radiation effects in complex glasses is still an area which requires much research in order to more fully understand - and therefore be able to accurately predict - its effects. Thus, the novel approach taken in this project will actively fill critical gaps in our understanding of radiation effects in glasses. The research in this project is therefore of great national importance to both the UK and India since they share common challenges in radioactive waste management.
Our User Engagement Strategy will ensure that each of the following UK and international groups will be engaged and gain impact from the proposed research: (i) the nuclear industry, government and policymakers; (ii) academic researchers (see also 'Academic Beneficiaries' section of JeS form); and (iii) the public and society. This will be achieved through multiple mechanisms, detailed in the Pathways to Impact.
(i) Several industrial, governmental and policy organisations will directly benefit from the project outputs, creating impact in many areas including: enhanced safety case for geological disposal of radioactive waste forms, support for delivery of UK Industrial Strategy and Nuclear Sector Deal, improved understanding of waste form behaviour, and greater knowledge of alternative glass formulations and processes. The organisations benefiting from the impact of this work include some of the largest and most important in the UK nuclear sector (NDA, Sellafield Ltd, NNL, RWM, BEIS, and members of the supply chain).
(ii) Impact for UK, Indian and international academic researchers from the proposed research will be achieved through enhanced mechanistic understanding of the effects of radiation on (a) radioactive waste forms (nuclear researchers); and (b) glasses (glass scientists); and through improved, validated molecular dynamics and atomistic simulations of glasses and amorphous materials. Further impact will be delivered through exchange and training programmes for Early Career Researchers, in training the next generation of nuclear experts. Finally, additional impact will arise in the UK through transfer of knowledge in alternative waste form host materials and processing technologies from India, providing improved understanding of these factors in the UK; and impact in India through transfer of UK expertise in advanced synchrotron and neutron techniques and computer simulations of highly complex disordered materials.
(iii) Impact for the public and society will be achieved through activities aimed at communicating our research to a wide section of the public via multiple channels (events, social media, popular press and online). The UK Nuclear Sector Deal of the Industrial Strategy highlights the need to improve public confidence to accelerate implementation of geological disposal of radioactive waste forms. Our impact and user engagement activities will contribute towards meeting this national strategic need, and our public engagement will thus focus on how our research will be used to help assess risks, to a local community that may host the geological disposal facility.