"Weld modelling" is a powerful tool in understanding the structural performance of welded structures. Conventional continuum-mechanics-based predictions of the stresses generated by welding have achieved considerable success in understanding the in-service performance and degradation mechanisms of welds in the UK's nuclear reactor fleet. However their practical use is currently limited to materials that do not undergo so-called solid state phase transformation (SSPT) during welding, since the presence of SSPT makes it necessary to predict changes in the material microstructure in order to predict the stresses. In addition, the microstructural changes imposed by welding have a profound influence on a weld's resistance to creep, thermal ageing, oxidation, stress corrosion and other in-service degradation mechanisms, and upon its sensitivity to the presence of cracking. The Fellowship research programme aims to extend conventional weld modelling into a multi-disciplinary tool that can predict both continuum parameters such as stress & distortion, and microstructural parameters such as grain size and shape, the occurrence of secondary phases, and precipitate distributions, and hence both directly predict long term structural performance and be used for "virtual prototyping " of weld processes and procedures for novel welding processes. Success offers the prospect of better understanding of in-service performance of welds in both the existing UK nuclear reactor fleet, and in any industrial sector where the long term structural performance of welds is important. It will also aid the choice of weldment materials, joint design and welding process for structural welds in new-build nuclear power plants, and in advanced Generation IV designs that may be built on a longer time frame.

Volcanic ash is the most widespread and frequent hazardous volcanic phenomenon, being produced in over 90% of all eruptions. The 2010 eruption of Eyjafjallajökull in Iceland and the resulting closure of Northern European airspace has focused attention on the international reach of ash even from relatively small volcanic eruptions. It is now important to rigorously assess potential impacts on nuclear power facilities in the UK from volcanoes in neighbouring regions. Thick volcanic ash accumulation might render a site temporarily inoperable but even minimal (a few mm) ash deposition in the vicinity of a nuclear facility has the potential to disrupt normal operations. This proposal will result in a robust, transparent and broadly-applicable methodology for evaluating the likelihood of volcanic ash threatening UK nuclear facilities. This will be based on state-of-the-art probabilistic hazard assessment methodologies developed through NERC-funded science at the University of Bristol, with new knowledge exchange mechanisms and collaborative research strands to adapt to the special circumstances of low probability events relevant to the UK nuclear industry. The hazard assessment will be directly linked to a case study of site management changes to mitigate this hazard, and the methodology will be intentionally transparent and generic to allow application to other volcanic regions hosting nuclear or other sensitive high-tech sites. This project has been developed through ongoing discussions with EDF Energy, and the skills, tools and outputs acquired through the project will be transferable to, and of benefit for, a wider range of the volcanic hazard assessment stakeholder community. The project builds on NERC science outputs from the consortium projects STREVA,CREDIBLE and VANAHEIM and also the Global Volcano Model (GVM) network, and consists of five components: 1. characterisation of eruption source parameters at regional volcanoes with potential to disperse ash over the UK, and the meteorological conditions affecting ash transport from eruption source to specific location; 2. a workshop with experts from EDF Energy and from academia to create the essential framework for relating volcanic activity probabilities and likelihood of site impacts to nuclear industry procedures, standards and regulatory requirements; 3. a probabilistic framework for modelling airborne and ground-based regional ash hazard arising from multiple volcanoes, and visualisation of ash hazard at UK nuclear facilities; 4. a new set of protocols for nuclear site preparedness and management in the event of volcanic activity; preliminary estimation of implementation costs, business disruption and supply chain issues; 5. generation and dissemination of reports and a scientific paper presenting the hazard assessment methodology for low probability volcanic activity. The project will provide a quantified volcanic ash hazard assessment for UK sites. The main benefit is improved understanding of credible, though extreme (1 in 10,000 year), volcanic ash hazard on the operation of nuclear power plants in the UK. The far-reaching impacts of volcanic ash means that preparedness and mitigation strategies developed on the basis of findings from this project will protect against unforeseen nuclear safety consequences and help ensure the reliability of electricity supply to the population of the UK. The impact of the exchanged knowledge will range from the development of new informed decision-making concerning the volcanic ash hazard management to the potential design of mitigation measures and procedures if required. EDF Energy Generation is committed to characterising the hazard due to volcanic ash for its nuclear sites. This project forms the first part of understanding this problem and may identify further research and Knowledge Exchange needs.