Corrosion Studies of Advanced Gas-cooled Reactor (AGR) Spent Nuclear Fuel

Huang, Yifeng and Boxall, Colin and Hambley, David (2025) Corrosion Studies of Advanced Gas-cooled Reactor (AGR) Spent Nuclear Fuel. PhD thesis, Lancaster University.

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Abstract

The UK’s nuclear fleet primarily comprises Advanced Gas-cooled Reactors (AGRs), utilising UO₂ as the fuel source. As of 2019, the UK’s inventory of AGR Spent Nuclear Fuel (SNF) was approximately 2200 tHM (tonnes of Heavy Metal), with projections exceeding 4000 tHM by 2030, destined for disposal in a Geological Disposal Facility (GDF). Interim storage of AGR SNF takes place in wet storage ponds containing caustic demineralised water (pH 11.4, chloride <1 ppm) to mitigate corrosion. However, in cases of fuel pin / cladding failure, water ingress may lead to fuel corrosion, the implications of which remain insufficiently understood. This study investigates the electrochemical corrosion behaviour of AGR SNF under conditions relevant to UK wet storage. A series of experiments were conducted to characterise the corrosion mechanisms of UO₂, AGR SIMFUELs, and AGR cladding materials, including coupled-electrode systems simulating cladding-fuel interactions in real AGR SNF. These baseline studies enabled direct comparison with the first-ever electrochemical investigation of legacy AGR SNF under hot-cell conditions. This two-part study examined electrochemical behaviour in Simplified Simulant Pond Water (SSPW) at various pH levels, followed by an assessment of chloride ion concentration effects. These preliminary results indicate that the electrochemical behaviour of legacy AGR SNF closely aligns with that of AGR SIMFUELs, validating their use as SNF simulants. Furthermore, findings confirm that current AGR wet storage conditions effectively suppress and prevent further corrosion of SNF during interim pond storage. These insights contribute to the fundamental understanding of AGR SNF corrosion and inform the long-term management of AGR SNF in the UK.