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

在未来十年内，英国目前的两座乏燃料后处理工厂将关闭。随着先进气冷堆（AGR）和压水堆（PWR）在英国仍在运行，预计将产生超过5000吨未处理的AGR和压水堆燃料。由于没有最终处理方案，这些燃料将在池中冷却，然后在干桶中储存长达100年。由于乏核燃料的高度危险性，必须充分了解它们在这些储存条件下的行为。一个突出的问题是燃烧对存储条件下的完整性SF的影响。高燃烧燃料有较高的裂变产物积累，并且在反应堆内受到长时间的加热和辐照。因此，化学和机械性能预计会发生不利的变化，作为燃烧的函数。例如:1。裂变产物的高掺入可能导致燃料膨胀，从而可能导致包壳破裂；2 .长时间加热会导致机械完整性的丧失，例如通过开裂和晶粒生长；暴露于较长时间的辐射会导致晶格损伤加剧和进一步肿胀。我们的目标是合成和表征一系列用于AGR和PWR乏燃料的UO2类似物，代表上述特征，在不同的“燃烧”范围内。合成将使用传统的固态方法，也可以通过热等静压进行，这将允许纳入挥发性裂变产物替代品，例如Cs， i。我们将进行一项研究，以了解在冷却池条件和失效干桶情况下燃烧如何影响SF的腐蚀，以支持这些存储实践的安全评估。

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.