Effect of burn-up on mechanical and chemical stability of spent fuel during wet and dry storage

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Within this decade, the two plants currently reprocessing spent fuel (SF) in the UK will close. With Advanced Gas Cooled Reactors (AGR) and Pressurized Water Reactors (PWR) still operational in the UK, it is anticipated that in excess of 5000 tonnes of unprocessed AGR and PWR fuel will be generated. With no final disposal solution, these fuels will be cooled in ponds, prior to storage for up to 100 years in dry casks. Due to the highly hazardous nature of spent nuclear fuels, their behaviour under these storage conditions must be fully understood.One outstanding issue is the effect of burn-up on the integrity SF under storage conditions. High-burn up fuels have a higher accumulation of fission products and have been subject to prolonged heating and irradiation within the reactor. As such, the chemical and mechanical properties are expected to change, detrimentally, as a function of burn-up. For example:1. Higher incorporation of fission products could lead to swelling of the fuel which may cause the cladding to be breached;2. Prolonged heating can result in loss of mechanical integrity, e.g. through cracking and grain growth;3. Exposure to irradiation for longer time periods results in enhanced lattice damage and further swelling.We aim to synthesise and characterise a series of UO2 analogues for spent AGR & PWR fuel, representative of the characteristics described above, at a range of different "burn-up". Synthesis will be performed using conventional solid state methods, and also by hot isostatic pressing, which will allow the incorporation of volatile fission product surrogates, e.g. Cs, I. We will perform a study to understand how burn-up influences the corrosion of SF under conditions representative of cooling pond conditions and failed dry cask scenarios, to support safety assessment of these storage practices.