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

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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.