The UK has been generating electricity from nuclear power for over sixty years. Nuclear power generates 15% of the UK's electricity as of 2023, and current government plans call for this percentage to rise to about 25% by 2050. Consequently, the issue of safely disposing of the UK's existing stockpile of radioactive waste, as well as any waste that may be generated in the future, is clearly posed. Current UK government policy is to dispose of the higher activity wastes in an underground geologic disposal facility, known as a GDF. Construction of such a facility will have an estimated cost of £20-53 billion, over a period of several decades. The purpose of a GDF is the safe disposal of radioactive waste for periods of tens of thousands of years, in a manner that ensures that any leakage of radioactive materials into the surrounding biosphere is kept below specified limits. One of the rock types that has been identified as a potentially suitable host rock for the location of a GDF are lower-strength sedimentary rocks, known as LSSRs. Siting and construction of a GDF in LSSR will require the development of a quantitative understanding of the physical and biogeochemical properties of the host rocks surrounding the GDF. However, many fundamental gaps still exist in our knowledge of the issues related to performance of these host rocks as a geological barrier to radionuclide transport. In their call "Derisking geological disposal of radioactive waste in the UK", NERC have grouped these knowledge gaps into three Challenge Areas: geological isolation of the waste, potential contaminant pathways for radioactivity to escape into the biosphere, and new advances in mathematical modelling of the relevant processes. To address these Challenges, we have assembled a multidisciplinary consortium composed of over twenty scientists at seven UK universities and research institutes, many of whom have extensive experience and expertise in various areas related to radioactive waste disposal, and/or in closely related areas of subsurface science and engineering. In addition to these investigators, seven PhD students will be funded by the participating institutions, to further support the objectives of this project. As the ultimate goal of this work is the safe geological disposal of radioactive waste, we have named our project "GeoSafe". The GeoSafe research consortium will carry out innovative research that will investigate fundamental behaviour of LSSRs in the context of the three Challenges. We will measure mechanical, flow, and transport properties of LSSR rocks over a range of scales, with an emphasis on quantifying the effects of heterogeneities such as sedimentary architecture, bedding, laminations, inclusions, and fractures. We will use cutting edge multi-scale imaging techniques, and novel experimental techniques for coupled measurements, that will reconstruct properties of the rocks of interest across scales. We will investigate the effects that chemical and biological changes in LSSR rocks will have on the rock's permeability and dispersivity, conducting novel radionuclide diffusion and advection experiments paired with dynamic multi-scale imaging. GeoSafe will investigate the effects of possible existing fractures, quantifying whether these are likely to seal, and what their effect on transport may be if they remain open. Numerical simulations will be performed to assess flow and transport of liquid and gas flowing fluids, and as well as reactive radionuclide transport, within the vicinity and in the surrounding region of the GDF. Taken as a whole, GeoSafe will produce and synthesise a unique set of data, and develop state of the art experimental and computational tools and methods, that will be essential in understanding the fundamental behaviour of lower-strength sedimentary rocks in the context of evaluating the performance of a UK Geological Disposal Facility.

Nuclear fusion, Generation IV fission reactors and aerospace gas turbines are critical to our future energy generation and transportation. Their operation at high temperatures necessitates construction from a variety of advanced materials. In order to withstand these extreme environments materials require high melting points, high temperature strength and environmental resistance, and, for nuclear, irradiation resistance. There are strong environmental and economic incentives to yet further increase the temperature capability of the materials used, in order to improve efficiency to reduce fuel use, as well as for improve performance, design life and safety. However, while iterative improvements are being made year on year the temperature gains are becoming ever harder to realise. In this Future Leaders Fellowship a step change in temperature capability is sought by the realisation of a new class of body-centred-cubic (bcc, an atomic crystal structure) superalloys based on (1) Tungsten, (2) Titanium, and (3) Steel, for the extreme environments of nuclear fusion and gen IV fission reactors as well as aerospace gas turbine engines. I have created a close network of industrial, national and international academic partners, that will enable translation of these advanced materials from concept through to scale-up. The collaborations will be split across the bcc-superalloys Work Packages: (WP1) Tungsten, linking in UKAEA, toward nuclear fusion and Gen IV fission; (WP2) Titanium, for aero-engines, working with Rolls Royce and TIMET; (WP3) Steels, part of a collaboration with UKAEA, Bangor University and University of Manchester. Bcc superalloys comprise a metal matrix, where the atoms are arranged in a bcc crystal structure, which are reinforced by forming precipitates of high strength ordered-bcc intermetallic compounds (e.g. TiFe or NiAl). This has parallels to the strategy used in current face-centred-cubic (fcc) nickel-based superalloys. However, changing the base metal's crystal structure, and therefore also the reinforcing intermetallic compound, represents a fundamental redesign and necessitates the development of new understanding. The key advantage of using a bcc refractory-metal-, titanium-, or steel- based superalloy is their increased melting point(s), which give the possibility of increased operating temperatures, as well as greatly reduced cost for the case of steels. However, the change in crystal structure requires a fundamentally new design strategy. While the limited investigations into bcc superalloys have indicated that they have attractive strength, and creep resistance, they have been held back by their low ductility. During this fellowship, I will thoroughly investigate multiple ductilisation strategies on bcc-superalloys to advance their technology readiness level (TRL) and so remove the current barrier to their commercialisation.

A re-assessment of the impact of uncertainties within the nuclear industry is of paramount importance, not only ensuring the continued safety of nuclear energy systems, but also to ensure the economic viability of nuclear power, allowing for continued reductions in CO2 emissions globally. Uncertainties are unavoidable, and complex systems such as nuclear reactors are designed to cope with them. A naive approach would be to consider worst cases scenarios individually without considering their dependencies. This approach can produce over-designed and expensive systems without guaranteeing their overall safety. Proper quantification and propagation of uncertainty across multi-physical components allows one to determine vulnerable componentry, prioritise investments, identify operational margins and adopt relevant measures to guarantee safety whilst at the same time reducing the overall cost of advanced nuclear design. Methods will be synthesised as part of this project to improve the estimation of uncertainty/safety, bringing together researchers specialising in reactor physics, fuel performance, structural materials and uncertainty quantification. Work package 1: In reactor physics the new methods will be tested by considering the uncertainties propagated through a severe nuclear reactor accident assessment, specifically a loss-of-coolant accident (LOCA). The project will attempt to target and reduce uncertainties related to properties including nuclear data associated with specific isotopes and temperature dependent effects corresponding to neutron capture cross-sections. Drawing on the expertise in the UK and India, the enhancements in the methods utilised will have far-reaching impacts. Work package 2: Fatigue failure of graphite components, especially at high service temperatures, is of serious concern for next generation reactors. A design tool is to be produced that can efficiently incorporate variances in the mechanical and thermal loading history, and material properties to quantify a probable component life. In addition to the simple uncertainties in boundary conditions, complications arise from both the load sequence and the temperatures at which loading occurs, coupled with the impacts arising from neutron irradiation, temperature and coolant interactions. The world-leading team in the UK and India will generate new knowledge on the high temperature cyclic response of advanced nuclear graphite and will utilise it in the development of a new probabilistic modelling framework. Work package 3: Nuclear fuel performance codes predict the behaviour of fuel in a reactor, allowing operating regimes to be tested that avoid fuel melting or fuel failure. The models improved over decades of experience in the UO2-Zr system remain highly empirical (i.e. not mechanistic) and large uncertainties exist that are to be quantified through the use of uncertainty modelling (depending on each model's impact) and reduced through the addition of mechanistic models. Novel fuels with greater uncertainties will also be considered. Here, uncertainty modelling will be used to target the most rapid reduction of uncertainty of behaviour possible to expedite licensing and commercial use of the fuel. Work package 4: The uncertainty models will be identified and commonalities will be linked to enable the overarching uncertainty methodology to be formulated. This is an important task that will ensure the outputs from the targeted examples (in work packages 1-3) have far reaching impact beyond themselves in other areas of nuclear engineering and beyond. In addition to linking the uncertainty modelling methods this work package will lead by communicating the results to the wider community through publications and workshops.

In the UK, electricity generation using Nuclear Power is key to energy security and to achieving Net Zero. After six decades of commercial nuclear fuel reprocessing by Sellafield Ltd (SL), the UK has the largest inventory of civil plutonium (Pu) worldwide. The current and future management of the UK's civil Pu inventory by SL on behalf of the Nuclear Decommissioning Authority (NDA) is one of the most important challenges presented by nuclear decommissioning. The difficulty and scale of the challenges are reflected in the provision of funding: £2 billion for the retreatment plant, £4 billion for storage until 2120, and £10 billion for future Pu management. The Pu inventory is in the form of actinide oxide AnO2 (An = uranium U, or Pu) or mixed-actinide oxide powders (MOX) and stored in gas-tight packages on the Sellafield site. Research commissioned by SL, undertaken by the National Nuclear Laboratory (NNL) at Central Lab, has revealed that there is a significant knowledge gap in the chemistry of actinide oxides. The data cannot currently be explained and show that the properties of the AnO2 have changed during storage. This has led to concerns about safety, and how to handle these materials going forward. Moreover, there is an urgent need to establish optimal operating conditions for Pu inventory retreatment and repackaging, which is scheduled to begin in 2027, and to ensure safe and secure inventory storage from 2027 onwards. This knowledge gap results from the complexity of Pu chemistry under industrial conditions, and the difficulty of experimental studies. My insight is that not only are new experimental actinide materials needed, but so are new ways of studying them. This has been developed and informed through my recent secondment at SL, and working closely with key stakeholders (SL, NNL, NDA). The FLF will enable the synthesis of a new class of actinide nanomaterials, with broad application potential in nuclear decommissioning. This Fellowship will provide crucial experimental data on actinide structure and bonding on an atomic level, which has previously only been possible to study theoretically. Catalysis technology will be used to probe and quantify reactivity of actinide nanomaterials with problem industrial contaminants. This is also the first application of knowledge and technologies used in industrial catalysis to address nuclear industry technical challenges. This work is in partnership with SL and NNL and has been designed to generate data directly comparable to ongoing industrial work. Advanced characterisation and reactivity studies will be supported by the development of new spectroscopic tools. Synchrotron and neutron science will be utilised, ultimately in combination with vibrational spectroscopies, and in operando experiments. These studies will be a world-first. The impact of the FLF science will be realised through working in partnership with industrial stakeholders both in the UK (SL, NNL, NDA) and internationally through joint UK/US programmes (Los Alamos National Laboratory) and the European Commission Joint Research Centre (Karlsruhe). The translation of scientific knowledge to meet real end-user needs in nuclear decommissioning is a major goal of the FLF. This will be achieved by contributing to the scientific evidence base, therefore informing safety cases, engineering designs, and ultimately future UK government decision-making on Pu management.

The safe decommissioning of facilities used in the nuclear fuel cycle (nuclear fuel reprocessing, research and development and energy production) is a major socio-economic challenge facing the UK, with a predicted total cost of £120bn over the next 120 years. The decommissioning process will generate large volumes of water-based waste (effluent) which is radioactive and must be treated. As well as a number of specific challenges associated with the current materials and processes used to treat effluent, many new challenges are likely arise in the near future as decommissioning activity gathers pace. Overcoming these challenges is critical in the context of establishing public confidence in the management of radioactive waste as well as underpinning the UK's long-term energy strategy. Graphene oxide, a derivative of graphene with a high oxygen content, has exceptional properties which have already been demonstrated in other fields (e.g. desalination), and may be able to overcome the limitations faced by the materials currently used in effluent treatment. Graphene oxide could be used to treat effluents in two separate ways. Firstly, graphene oxide flakes could be added to the effluent and used to directly bind radioactive species (adsorption). Alternatively, a semi-permeable membrane, fabricated from individual graphene oxide flakes, could be used to sieve out the radioactive species (filtration). In this innovative and ambitious project, the science underpinning the use of graphene oxide in nuclear effluent treatment will be developed using a methodology led by computer simulation. Firstly, the development of new 'coarse-grained' models of graphene oxide will significantly extend the length and time scales accessible to simulation and open up the possibility of investigating the stability of graphene oxide membranes and dispersions. Using the new models, the efficacy of graphene oxide for the treatment of effluents containing some of the most problematic and dangerous radioactive species (e.g. uranium, plutonium, caesium and strontium) will be assessed, delivering the relevant physical and thermodynamic data required for the next stage of process development. The design and performance of graphene oxide will be optimised to improve decontamination factors for specific effluent treatment challenges. As a result, the project has the potential to revolutionise the techniques used in the treatment of radioactive effluent.