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.

Energy use, especially in the form of electricity is an essential requirement for modern life, and one that most of us could not even contemplate living without. From transport and travel to computers and televisions, the global demand for energy is on the increase. The drawback of recent technological advances however, is that greenhouse gases, in particular CO2 are emitted during the production of energy. Growing public awareness of climate change and its future impacts on the world as we know it have recently shifted the focus from fossil fuel usage to alternative energy sources, and legislation is now in place for reducing the carbon footprint. Among the alternative options, nuclear energy remains the most viable in the short term since the technology is already in place for proficient energy production. Nuclear electricity generation currently supplies around 17 % of the worldwide energy demand (18.4 % in the U.K.) and has already created a legacy of environmental problems due to high level radioactive wastes associated with waste storage and production. This proposal concentrates on the chemistry of the radioactive actinide ions (uranium, plutonium and neptunium) used in the nuclear fuel industry, ways to identify and 'clean up' toxic wastes from the environment and methods to eliminate the need for storing high level wastes in the future. Since the actinides used in current reactors are generated under conditions that are dissimilar to the natural environment, the chemistry of these metals outside of the reactor is completely different and they often exist in unusual oxidation states for a certain period of time before being further altered or reacting. In order to reduce the detrimental impact these radiotoxic wastes have on the environment, it is imperative that we understand their chemistry in full. This can only be achieved by studying the chemistry of these metals in their reactive unstable oxidation states in controlled laboratory conditions using specially designed chemistry. By doing this, we can identify methods of stabilizing these oxidation states and ways for selectively removing them from contaminated sites so that they can ultimately be recycled and used for further energy production. This project will initially examine the chemistry of uranium in the +V oxidation state by synthesizing a range of complexes stabilized by different organic groups under anaerobic conditions, and study the way the chemical groups around them inhibit or enhance reactivity. This chemistry will then be applied to the stabilization of the more radiotoxic elements plutonium and neptunium. At the core of the project is the development of a spectroscopic fingerprint (using time resolved luminescence spectroscopy) of unstable (and stable) oxidation states of these elements in order to develop a non-invasive method of identifying such species in the environment that may exist on a timescale that is too fast using current radiometric and chemical methods.

The rapid growth of the population worldwide and the drive for economic development rely on continuous supply of energy, with global needs estimated to increase by 50% by 2035. Although fossil fuels are still the primary energy source, the problems associated with security of supply and the environmental impact because of the CO2 emissions, are going to limit their use in the foreseeable future. Low carbon and renewable energy sources, such as nuclear and biofuels, which are increasingly used, will meet progressively these energy demands. Nuclear energy from fission is a low carbon source and can provide large amounts of electricity and process heat using only small amounts of raw material. However, one of the main concerns in the nuclear fuel cycle is the management of the radioactive waste which can remain toxic for thousands of years. The expansion in nuclear power generation makes the problem of nuclear waste management particularly acute. Reprocessing of nuclear fuel can potentially recover the remaining actinides and fission products, and reduce the volume and toxicity of the spent fuel for storage or disposal in geological repositories. However, reprocessing has been associated with high costs, making the direct storage and ultimate disposal of high level waste the preferred option. Liquid-liquid extraction technologies are essential in spent nuclear fuel reprocessing where currently used contactors are decades old and are not well characterised. In this project we will develop novel liquid-liquid contactors for extraction processes that will intensify the production of energy from alternative and sustainable sources. Intensification addresses the need for materials and energy savings and contributes significantly to the competitiveness of process industries worldwide by making industrial processes faster, more efficient and less damaging to the environment. Substantial process intensification is possible with the use of small scale contactors, where the reduced length scales result in thin fluid films which enhance mass transfer rates, while the increased surface to volume ratios enable the controlled formation of well characterised flow patterns. We will develop two concepts to intensify liquid-liquid extractions and increase throughputs to industrial levels. The first approach involves an intensified impinging-jets contactor, where the two liquid phases collide at high velocities in the small space of the contactors; the intense mixing and high energy dissipation rates at the zone of collision form dispersions with small drop sizes and narrow distributions that have large interfacial areas. The second approach involves scale up of the process by increasing the number of small channels used (scale out). This approach differs from conventional scale up where the unit size is increased, and depends on the design of the flow distributor that feeds the channels. The research will be carried out in collaboration with two industrial partners, i.e. NNL which develops nuclear fuel reprocessing technologies and Greenegy that produces biodiesel. The active involvement and support of the partners in the project will facilitate technology transfer.

One of the most pressing problems facing society today is the management of existing and future waste forms arising from nuclear energy production. Here, the redox chemistry of the actinide elements plays a crucial role in many aspects of nuclear fission including safe disposal strategies and new recovery and recycling routes. Understanding the chemistry of actinides in engineered environments is imperative for the management of existing and future fission products (nuclear waste) arising from nuclear power production, particularly for underground geological disposal. In particular, the redox chemistry of neptunium, a key radionuclide found in appreciable quantities in high level waste is complex, changeable and currently not well understood. Over the lifespan of the proposed geological disposal facility, one of the principal hazards is a change in chemistry of neptunium that may result in leaching from the repository, breaching primary containment and entering the engineered environment. Due to the particular complex redox and chemical speciation of neptunium, crucial mechanistic information on redox chemistry and speciation that affects its interactions with engineered and natural encapsulating materials including the host rock and backfill material is lacking and remains one of the principal chemical challenges facing this field. In this feasibility study, we will address the prospect of using one and two photon fluorescence and phosphorescence spectroscopy and microscopy as a non-destructive technique to address this problem. We aim to visualise, locate and spatially map the different oxidation states of neptunyl that can co-exist in solution in model conditions using well defined complexes and aqua ions in with the ubiquitous geologically relevant minerals silica, alumina and calcite at previously unseen levels of detail (sub micrometer resolution). We have recently demonstrated that neptunyl(V) and (VI) emission occurs in the green and blue regions of the electromagnetic spectrum and are equally as intense as the uranyl(VI) ion, whose optical properties are well known and have been used by us for fluorescence and phosphorescence microscopy imaging. This means that both oxidation states can be detected simultaneously so that highly sensitive, informative three-dimensional imaging can be used to understand neptunyl geochemistry below the micron scale. This will add much needed important information to the safety case for nuclear waste disposal in a range of heterogeneous systems.

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.