Nuclear power reactors contain large steel pressure vessels and high-pressure pipework which must be carefully designed and regularly inspected when they are service to guarantee safety. When a reactor is operating, these systems are loaded not just by internal pressure, but also by thermal stresses which arise from temperature gradients, and by residual stresses which are 'locked-in' during construction. Thermal and residual stresses are often termed 'secondary' stresses and they are generally more difficult to measure and predict than the stresses which result from directly applied forces. Often, this means that parts which are in fact safe are pre-emptively taken out of service due to secondary stress concerns, incurring large costs in addition to plant downtime. In this project, new techniques will be developed to accurately predict how complex and multi-axial secondary stresses in components behave as they are further stressed in-service. This will require the development of a generalised mathematical framework to describe multi-axial stress relaxation, along with new computational methods to enable the analysis of complicated real-world structures. The predictive accuracy of the new analysis techniques will be tested in a series of experiments using neutron and synchrotron diffraction to observe how residual stresses deep inside metallic components change as they are subjected to changing external loads. The analysis techniques developed during this project will be integrated with existing structural integrity assessment procedures, allowing them to be readily used in industry, and leading to cheaper and more reliable power plants.

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.

The safe operation of engineering structures is vital in safety-critical industries such as power generation, nuclear, aerospace and oil and gas. Structural failures can have catastrophic consequences in terms of loss of life and financial circumstances. Meanwhile there is a strong interest in reducing costs, light-weighting, increasing design life and life extension. To this end, reliable structural integrity assessments are essential at the design stage and through in-service life to ensure continuous profitable operation of assets. Residual stresses are inevitably introduced in engineering structures during manufacturing processes. Their presence can have adverse effects on the behaviour of structures and contribute to driving force promoting various degradation mechanisms. Therefore, it is of paramount importance that the state of residual stresses in engineering structures is carefully and reliably characterised so that remedial actions could be taken to enhance the lifetime of current materials or novel designs and manufacturing methods developed and optimised. The contour method, first presented in 2000, is emerging as a powerful technique for the measurement of residual stresses in bulky parts. The method involves making a straight cut in the component of interest along a nominally flat plane where residual stresses are desired to be determined. The created cut surfaces deform due to the relaxation of residual stresses. The deformation of the cut surfaces are measured and then used to back-calculate 2D distribution of residual stress that was present along the flat plane prior to the cut. Nevertheless, there are still several limitations associated with application of the contour method: a) only a straight cut over a flat plane is used to section components for contour measurements; b) the standard method can only measure 2D distribution of one component of the residual stress tensor over a flat plane; c) the method is limited to symmetric sectioning of the cut parts, d) like other mechanical strain relief techniques, the contour method is prone to plasticity-induced errors where the magnitude of stresses or level of triaxiality is very high and e) most historical measurements using the contour method have concerned simple geometries such as welded rectilinear plates. For the first time, the "Complex Contour Method" proposes to develop the use of complex cutting paths, for example non-planar and closed complex cutting paths instead of cutting along a flat plane. This innovative approach will radically bring new capabilities for the contour method in several ways: it will unlock map of residual stress in multiple directions simultaneously. Of a true step change is extending the application of the technique to measure 3D maps of residual stress. Enabling the technique to deal with complex cutting paths will inherently deal with limitations of the standard method regarding symmetry of the cut parts. Moreover, removing the constraint of a symmetric planar cut opens the potential to mitigate plasticity-induced errors that can accompany standard contour method cuts. Of another radical step change of the application of the complex cutting paths is that it enables the technique to be implemented on complex engineering structures. For example, the conventional contour method confined to symmetric planar cuts cannot be applied to complex components such as tube penetration welds for pressure vessel heads. The proposed research has the potential to provide far more complete residual stress information about safety critical components of high interest to engineers in the aerospace, petrochemical, power generation and nuclear industries. In addition for industrial applications, a single complex contour cut offers a far more cost effective tool compared to the cumbersome and time consuming conventional contour method using multiple-method and multiple-cut approaches.