Proton, alpha and gamma irradiation assisted stress corrosion cracking: understanding the fuel-stainless steel interface

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The student involved in this project will undertake an experimental research programme aimed at understanding radiation-driven mechanisms which lead to cracking of protective layers in spent fuels. The experimental programme will take place in UTGARD Lab at Lancaster University and at the Dalton Cumbrian Facility, the latter being a leading radiation science laboratory which is situated close to the heart of the UK nuclear industry. This will involve the irradiation of samples and development of their corrosion susceptibility in real time. The student involved will also perform complimentary modelling calculations, using state-of[1]the-art radiation transport and reaction-diffusion modelling software (SRIM calculations). Instruction in both the implementation of the irradiation and in the use of the modelling software will be provided in the first year of the PhD. The skills developed and the project location will make it ideal for someone with a longer-term ambition of entering the nuclear industry. Spent UK nuclear reactor fuel will be stored for at least 60 years before going into a Geological Disposal Facility (GDF). The cladding should not breach during this time. A better understanding of the effects of radiation, hydrogen, stress and water-environment is required to ensure safe storage and handling before the spent fuel is deposited in a GDF. Mechanisms underpinning crack growth, the precursor to cladding breach, are unknown and effects of stress are not currently well understood. The project will aim to develop a much better understanding of the processes at work. Proton irradiation of samples will be used in the first instance to expose them to reactor-levels of radiation damage. Subsequently, alpha and gamma irradiation will be used to mimic the damage effects caused by the fuel decay products. Radiation produces material damage and also changes in the water chemistry, producing highly reactive of oxidising species in a way which is distinct for each radiation type, hence the need for use of the various types of radiation. This combination is only available within the UK at DCF. This radiolytic production or reactive species in turn increases the corrosion potential which can initiate or accelerate crack formation and propagation. Microstructural effects manifest as key changes in the physico-chemical environment near grain boundaries, formation of dislocation loops, voids and precipitates, deformation and hardening. Through combining a range of techniques, including monitoring of electrochemical properties, chemical products and microscopy, it is hoped that precursors of crack-formation can be detected. This would in turn constitute a new candidate for on-site monitoring of spent fuels and hence make an important contribution to the UK's low-carbon energy provision.