Critical Analysis of Spent Fuel Structure in Radionuclide Release

As a result of 60 years of using nuclear energy in civil and defence operations, the UK has generated a large legacy of nuclear waste, with a total volume capable of filling Wembley Stadium (450,000m3). The hazards posed to the general public from the radiation arising from this waste make its disposal extremely challenging; any solution must be long-lived as the waste will be radioactive for more than 100,000 years. For this reason, the Governments of several countries, including the UK, propose that the long-term disposal of this waste should be in a deep geological facility, several hundreds of metres below the ground. The formal term for an engineered geological disposal site is a Geological Disposal Facility (GDF). This man-made facility will be used to isolate the waste from future populations by using multiple layers of containment carefully designed to prevent radioactive elements (radionuclides) from entering the underground rock environment and eventually reaching the surface. Arguably, the most important part of the GDF is the nuclear waste itself; the release of radionuclides to the environment is controlled by the interaction of groundwater with the waste - if this material can be shown to be particularly durable in the presence of ground water, the release of radionuclides will be very small and the risk to future populations from the GDF will be low.

The focus of my Fellowship is on understanding the release of radionuclides from one particular type of nuclear waste, known as spent fuel, upon contact with groundwater. Many countries are planning to dispose of spent fuel in a GDF (e.g. Sweden, Finland), however the spent fuel in the UK is unique, because it originates from nuclear reactors that only exist in the UK. This is problematic because the potential behaviour of this material when it comes into contact with groundwater is poorly understood; this gives rise to uncertainty in the long-term safety of this material in a GDF. Therefore, the goal of this Fellowship is to develop an understanding of UK spent fuel, of how its structure and chemistry affect the release of radionuclides upon contact with water, and to evaluate its performance compared to other spent fuel types. Because real spent fuel is extremely hazardous, the Fellowship research team will develop an analogue for spent fuel, known as HIP-SIMFUEL, using state-of-the-art material processing technologies. The development of HIP-SIMFUEL, which will resemble spent fuel more closely than any other analogue currently available, represents a significant advancement for scientists working in the field of spent fuel research. Using HIP-SIMFUEL and a suite of advanced, high-resolution microscopy techniques, we will build the first ever atomic-scale understanding of the structure and chemistry of UK spent fuel, and we will develop novel imaging techniques to assess the role of these features in the mechanisms and rate of radionuclide release to groundwater. The results from experiments with HIP-SIMFUEL will be compared with those from real spent fuel particles; my team will examine particles of spent fuel that were discharged to the environment during the Chernobyl accident, which have subsequently been leached by natural groundwater for many years.

My Fellowship is particularly timely, given the UK Government's ongoing task of selecting a site for the disposal facility. The research represents a significant step in the understanding of the long-term performance of nuclear waste in the GDF, will enhance predictive models of future GDF behaviour and will help optimise the design of the containment system. Ultimately, this will lead to enhanced safety of the long-term management of nuclear waste in the UK and worldwide, and will increase public confidence of geological disposal concepts.

By providing a robust scientific underpinning of the post-closure safety case for geological disposal of spent fuel, my Fellowship research has the potential to directly impact the implementation of a geological disposal facility in the UK and to influence public confidence in the disposal concepts under consideration. Such confidence is necessary for the success of the ongoing UK voluntary site selection process. Once a site has been successfully selected, indications from Government are that significant investment in future nuclear power will be made, which will have far-reaching impacts to the economy, the environment and society.

The impacts will be realised through the primary beneficiaries of this Fellowship, which include geological disposal site host communities, other interested publics, and Governmental, policy and technical bodies, for example, the geological disposal policy implementers (Radioactive Waste Management Limited, RWM) and the geological disposal policy makers (DECC). Secondary beneficiaries include the media and school teachers; the Fellow and Fellowship PDRAs will also benefit from several activities. The benefit to these groups, over the whole fellowship lifecycle, include:

- New scientific understanding and data required to model the source term for radionuclide release from UK spent AGR fuel, for use in the post-closure safety case for geological disposal;
- Demonstration of a new approach and methodology to understand the rate and mechanism of spent fuel analogue and simulant dissolution, relevant to national and international geological disposal concepts;
- Potential reduction of the estimated £18Bn cost of radioactive waste disposal in the UK, through more appropriate disposal facility design led by an improved understanding and confidence in spent fuel durability;
- Improved public confidence in UK radioactive waste disposal strategy, through provision of underpinning scientific understanding and data, which are currently absent for AGR spent fuel;
- Five highly skilled and knowledgeable post-doctoral scientists for potential recruitment by the nuclear industry.

In a novel approach, the Pathways to Impact plan targets both social and technical aspects of nuclear waste geo-disposal, thus making a significant additional contribution to socio-technical research in topics associated with the nuclear fuel cycle. With a focus on the interlinked areas of publics and policies, several activities are proposed that will directly impact the on-going debate and actions surrounding the current implementation of the UK GDF site selection process. These activities briefly comprise:

1. In the absence of forthcoming information on aspects of the geological disposal "engineered barrier" from policy makers and implementers, I will initiate and manage a new academic-led, multi-purpose web platform, The Nuclear Waste Repository, with the primary role of hosting information on UK nuclear waste and geological disposal in an easy-to-understand, lay-person format.
2. Building on my previous public engagement and media experiences, I will promote wide, public dissemination of relevant information on nuclear waste disposal by undertaking filming of a short, creative nuclear waste geo-disposal documentary, in collaboration with award-winning film makers (Sort of Films). This will be showcased at multiple national and international venues.
3. I will organise a series of reciprocal knowledge exchanges with key beneficiaries, including RWM, DECC, the Swedish Geological Disposal Implementers and the Science Media Centre. The exchanges will encourage understanding of the science and policy behind the safety case for geological disposal and will be facilitated by an experienced sociologist, who will act as a knowledge broker and will prepare high impact outputs for publication (journal articles, policy briefs).