Modelling the Fuel Performance and Structural Integrity of TRISO Nuclear Fuel

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Nuclear energy has great potential to generate low-carbon energy, however it has until now, largely done this by contributing to baseload electricity generation. High temperature reactors offer the opportunity to move beyond this and have been selected as the technology of choice for the UK's advanced nuclear reactor demonstration plant. By raising the outlet temperatures, nuclear power stations will be able to generate process heat as well as electricity. Higher coolant temperatures will however require a step change in fuel design. One design change being proposed is to move away from UO2 fuel pellets and utilise TRISO (tristructural isotropic) particle fuel. In these fuels, the UO2 is contained in a spherical fuel kernel, surrounded by a porous buffer layer and three coating layers, intended to retain fission products in the particle. Peridynamics is an emerging computational mechanics tool for predicting cracking in a diverse range of complicated materials and loadings. To date, the research team have built a 2D thermo-elastic peridynamic model for TRISO fuel. This model is able to capture cracking in each component of the TRISO coated fuel particle and has demonstrated the possibility of cracking in the buffer layer acting as a stress raiser in the overlying SiC layer which is tasked with providing a hermetic seal to prevent the egress of fission products from the fuel particle. This PhD will aim to further develop the current thermo-elastic peridynamics model by introducing creep and irradiation swelling, both of which are known to be anisotropic. This will enable the complete irradiation history of the fuel particle to be modelled and the current 1.5D commercial fuel performance models such as STRESS3 to be enriched. Key aims for the project are as follows:To develop a finite element model for the complete irradiation history in order to determine the impact of debonding of the kernel and buffer and enable benchmarking of peridynamic models.To develop a model for anisotropic creep in peridynamics for each material and benchmark this against finite element models.To develop a model for volumetric swelling in peridynamics for each material during the entire fuel history and benchmark this against finite element models.To combine these models into a peridynamic model for the irradiation of TRISO fuel particles and validate this against irradiation data made available by the UK National Nuclear Laboratory.To use the model to enrich the current 1.5D fuel performance models by modelling features observed in post-irradiation examination.