Shortly after lunch on the 11th March 2011, a 15 m high tsunami triggered by the magnitude 9.0 Great Tohoku earthquake engulfed the Fukushima Daiichi Nuclear Power Plant (FDNPP) - crippling the site, its essential surrounding infrastructure and the multiple safety layers the provided emergency reactor core cooling. Resulting from this absence of sustained core cooling provision, over the following days and in response to critical temperatures and pressures within the reactors, seawater was injected as a final resort to provide emergency core cooling. However, this desperate effort was insufficient, and temperatures rose in each of the reactor pressure vessels (RPVs) to in-excess of 2,000C; causing the uranium contained within the nuclear fuel assemblies to melt (partially or fully) and corrode vertically downwards through the RPV, into base of the primary containment vessel (PCV) - as well as coating the internal volume of the extensive PCV. In the UK, the Sellafield site includes the first commercial power-generating station (Calder Hall, with four Magnox reactors) and the plutonium-producing Windscale Piles 1 and 2, that fuelled the UK's original nuclear weapons programme. The haste to assemble led to little planning for end-of-life retirement, waste management and post-operational decommissioning, meaning that such facilities still present high hazards. The hazard removal challenges at Sellafield are, however, not unique in the UK, with the large number of Magnox stations also embarking on "accelerated decommissioning" ahead of long-term "care and maintenance". Many of the most pressing and complex decommissioning challenges across the NDA estate concern the decontamination of radiologically contaminated surfaces, with numerous methods having been considered to address this, and laser cleaning emerging as the promising candidate. Laser ablation (or "laser cleaning") is an emerging decommissioning tool for the international nuclear industry to rapidly decontaminate surface-fixed radioactive materials, having recently been identified as a "promising technique" for use across the UK NDA Estate. It is particularly attractive for nuclear decommissioning as it is not only non-contact, but also produces much smaller volumes of secondary solid and aqueous wastes than alternative physical and chemical methods. However, some fundamental challenges remain which prevent widespread implementation of the technique: - The ablative nature of the technique can generate localised atmospheric contamination. - Waste collection and disposal are complicated due to the airborne particulate nature of the ablated, radioactive material. - Additional 'before' and 'after' characterisation surveys are necessary to plan the decontamination activities and assess the quality of laser cleaning. This timely, cross-disciplinary, and impactful proposal addresses these and other challenges by developing novel particulate containment and collection strategies, integrated with innovative optical characterisation, for planning and assessing cleaning activities. In this way, it will reduce the burden, risks and overheads of laser cleaning, leading to its broader international utilisation. This would be particularly applicable at FDNPP, but also at Sellafield and other legacy nuclear sites in the UK. We will use knowledge from the laboratory assessments to make a prototype fibre coupled, 'OptiClean' system for integration onto our LBR-SuperDroid, as developed for the NNUF programme. The platform consists of a SuperDroid HD2, a large tracked robotic platform, with a KUKA LBR IIWA 14 robotic manipulator mounted on the top. Its tracked nature allows for remote doorway-scale accesses with additional stair-climbing capabilities whilst the LBR is a seven degrees of-freedom robotic manipulator with force feedback sensing for human-safe interaction.

Ductile materials, like metals and alloys, are widely used in engineering structures either by themselves or as reinforcement. They usually can sustain a lot of plastic damage before failing. Engineers understand quite well the ways that metals fail and how tolerant they are to damage, so efficient and less massive structures may be designed with well-defined margins of safety or reserve strength to cope with extreme events. By comparison, elastic brittle materials such as glasses and ceramics can fail without prior warning, so much larger safety margins are needed. Quasi-brittle materials are an important class of structural materials. They are brittle materials with some tolerance to damage and include concrete, polygranular graphite, ceramic-matrix composites, geological structures like rocks and bio-medical materials such as bone and bone replacements. Although their damage tolerance is much less than many metals and alloys, it can be quite significant compared to brittle materials such as ceramics and glasses. But this is not accounted for very well when engineers design with, or assess, quasi-brittle materials, as there is not an adequate understanding of the role on their damage tolerance of factors such as the microstructure of the material or the state of stress. Quasi-brittle materials are usually treated as fully brittle, taking little or no account of their damage tolerance, so assessments incorporate very significant safety margins, leading to designs that may be inefficient and unnecessarily bulky. Even when some assessment of damage tolerance is included, the microstructure can change as the material ages over time, and we need ways to measure the effects of this and to predict what it will do to the safety of the structure. This project aims to develop a method to predict the performance and evaluate the integrity of structures and components made from quasi-brittle materials. This will extend opportunities for their use in engineering applications, enabling more efficient design with greater confidence in safety. Quasi-brittleness is a property that emerges from the material's microstructure. A quasi-brittle material can be made from a connected network of very brittle parts (for instance, a porous ceramic). It exhibits a characteristic "graceful" failure as parts break locally when loaded sufficiently, which gives it damage tolerance. The "gracefulness" of the failure is affected by the random variations of strength and stiffness of the network and the form of the connections. Such networks represent a key part of the microstructure of the material, and to understand quasi-brittle fracture we need to construct models that properly describe the microstructure. There is a need to understand and define the mechanisms that control the fracture at the small and the large scale within these quasi-brittle materials. This will allow us to capture sensitivity to microstructure differences and degradation, and to produce general models that are suitable for the wide range of quasi-brittle materials and applications. Three-dimensional models that are faithful to the microstructure can be created using modern 3D microscopy methods, such as X-ray computed tomography. But these models are far too complex to simply scale up to structures very large relative to the microstructure. There is no computer than can do this, yet. We will develop modelling methods that sufficiently represent the complexity of quasi-brittle microstructures over a wide range of length scales, such as cellular automata finite elements. We will use advanced tomography and strain mapping techniques to observe how damage develops and to test and refine our models. We will then use this and the understanding that we gain to design new material tests and characterisation methods so that our methods may be used in a wide range of materials, from concretes to advanced nuclear composites, bone replacement biomaterials and geological materials.