Uranium has been the fuel for the world's commercial nuclear power stations. Its reserves are, however, finite and the demands of planned Generation III 'New Build' reactors could consume much of the available supply. Options are available to increase nuclear fuel sustainability: developing novel extraction methods (e.g. uranium from sea water and phosphate mining); nuclear fuel can be reprocessed; fuel efficient fast reactors can be developed; or thorium, which is 3-4 times more abundant than uranium, can be adopted as an alternative fuel. This research considers key aspects of the thorium option.Historically a handful of commercial reactors have been fuelled in part by thorium. Due to economic drivers the cycle has not been adopted in contemporary commercial reactors. In the future this may change. Notably India, and in particular its Bhabha Atomic Research Centre, has pioneered the use of thorium and intends for it to form an integral part of its energy generation plans. Its Kakrapar-1 reactor has used fuels containing thorium and major new thorium fuel developments are underway.Fuel selection has an important effect on sustainability and proliferation resistance. India has given much attention to re-processing fuel cycles. We seek to assess an alternative, the open or 'once-through' cycle, against a range of criteria. The open cycle will be considered in two broad domains: sustainability and proliferation resistance. In both domains some metrics and assessment frameworks already exist. Discussions of nuclear energy sustainability are often dominated by considerations of fuel resource depletion; economic, social and environmental sustainability are not emphasised. We intend to take full consideration of the impacts of thorium use from mineral extraction, through processing and reactor use to the disposal of all associated waste materials. Proliferation metrics are less mature, but methodologies for quantifying risks of nuclear proliferation are being developed.The proposed research aims to assess, validate and improve metric frameworks for nuclear sustainability and proliferation resistance. It will culminate with the creation of a single unified assessment framework. This work is driven by examining the particular attributes of proposed open cycle thorium reactors. The research programme is formed via three key areas of work:1) A review of proliferation resistance and sustainability assessment methodologies, with emphasis on quantitative measurements; where necessary methods will be improved. An umbrella assessment framework will be developed encompassing proliferation resistance and sustainability allowing for a harmonised and directly comparable assessment of different reactor designs.2) A review of proposed open cycle thorium-fuelled nuclear reactor designs. The review will include identifying the front- and back-end fuel composition of the designs. It will emphasise sustainability and proliferation resistance characteristics by addressing their wider resource and emission consequences and identifying associated proliferation risks. Our work will advance proliferation assessment to go beyond the attributes of the fuel itself, to include consideration of the infrastructure context.3) The reviewed reactor designs will be assessed within the newly developed umbrella sustainability and proliferation resistance framework. The relative positive and negative features of each of the designs will be measured. These designs will also be compared to mature light water reactor technology.The research will directly provide an improved understanding of the costs and benefits of thorium as an energy source. The assessment framework will improve quantitative assessments of proliferation risks and nuclear sustainability. The framework will be disseminated to the wider global nuclear community allowing them better to select technologies for the benefit of local and international populations.

Accidents at nuclear plants, such as those at Fukushima and Chernobyl, have increased the public awareness of the severe consequences that can result when system failures occur. However, as the demand for energy increases and low-carbon sources are required, many countries, including the UK and India, see nuclear power generation as an important contributor to meeting these needs. Risk analysis methods, which originated in the 1970s, require the evaluation of the frequency and consequences of the potential hazards which can occur on nuclear systems. It is these methods which have been used, and are still used, to ensure the safety of nuclear power generation. However, since the conception of the risk analysis approaches, the characteristics of engineering systems have undergone significant changes due to the advances which have occurred in technology. Computer control systems and the use of autonomous systems are now common and this introduces new vulnerabilities to the system. The range of failures and threat events which can cause safety issues is increasing with newly emerging threats due to the severe weather conditions associated with global warming and deliberate terrorist attacks and cyber-attacks of increasing concern. It is likely that new, currently unknown, threat types will continue to emerge. These changes in the systems, their vulnerabilities and their threats mean that new approaches, capable of dealing with these new requirements are needed to ensure the safety and security of nuclear energy production for future reactors. Resilience engineering is considered to offer significant benefits when considering the effectiveness of safety critical systems on potentially hazardous plants. This approach looks at designing systems which are capable of experiencing threats and have several approaches (known as dimensions) which enable the system to avoid, withstand, adapt to or recover from their effects. This project examines the benefits that resilience engineering could offer in the context of nuclear safety systems. It indicates the models and data required to predict the resilience of a nuclear power generation plant. Such models will be formulated and applied to a demonstrator system. Through this predictive tool modern nuclear systems can be designed and operated to achieve the high levels of safety demanded. Special attention in the framework will be given to deliberated, intended cyber-attacks and also the role in which humans can play in the recovery of the system following a threat.

There is considerable concern that uranium reserves are not sufficient to facilitate large scale international nuclear new build. Thorium is around four times more abundant than uranium, and could offer a potential alternative fuel cycle. Just as importantly, beyond ~500 years, thorium based spent fuel and associated reprocessed wastes are much less radioactive than those arising from conventional uranium fuels. Furthermore, because they generate only very small amounts of plutonium, thorium based fuels are not useful for the production of conventional nuclear weapons, which rely on plutonium - in this regard they are much more proliferation resistant. At present, except in India, thorium based fuels have only used in research or prototype energy generating reactors. This is because there have been and remain sufficient supplies of uranium. Conversely, in India, the lack of an indigenous uranium supply has driven the development of a thorium dioxide based approach to civil nuclear energy. India is on the verge of completing the second stage in that development. It will continue to develop experience in thorium based fuels for civil nuclear energy applications rapidly over the next decade. This requires a predictive capability to establish that fuel being irradiated in a civil reactor will behave in a manner that is compatible with its design criteria, especially the safety systems of the reactor. In a general sense, this mirrors the requirement for uranium dioxide based energy generation. The manner in which a safety case for civil reactor operation evolves is complex but takes advantage of developments over decades. For uranium dioxide based fuels, this has resulted in safe and secure operation that has seen a steady improvement in the efficiency with which nuclear fuel is utilised. Further increases in efficiency are certain, but will require modifications to existing strategies. In particular, more research must be undertaken that satisfies regulators that fission products are retained safely and securely within the fuel assembly as it spends more time within the reactor core. This translates to fuel that can retain the fission products within its crystal lattice for longer and that the thermal conductivity of the fuel does not deteriorate. However, unlike in the past where we only had access to experimental work on which to base the fuel performance predictions, we now have advanced modelling techniques that together with experiment can provide better understanding of the fundamental processes responsible for fuel behaviour. In this project we will use advanced materials simulation techniques to investigate the behaviour of thorium dioxide based materials. This includes the movement of fission products through the lattice and thermal conductivity. These will then be compared to predictions that are being made on civil uranium dioxide based materials in related projects. Comparison will also be made to experimental data already available concerning uranium dioxide and thorium dioxide but also data being generated by collaborators in India on thorium dioxide. This has the advantage of testing existing models that have been developed for uranium dioxide on a different system. We have developed models for existing fuels that include assumptions. Comparison to thorium dioxide provides a more stringent test of those models. It also allows us to understand to what extent it might be possible to translate the uranium dioxide based models to predict the evolution of thorium dioxide fuels. Collaboration will also proceed with modelling being carried out in India.

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.