In nuclear reactor vessels, the temperatures reached in the core, or heart of the reactor is extremely high. Keeping the process under control is vital in order to avoid accidents, which can be created by core material heat up, core material oxidation and melting and molten material relocation. The core melt process is characterised by two phases. Initially it involves damage occurring between the initial fuel and control rod damage and the melting and relocation of metallic material. The melting of ceramic material, loss of core geometry and molten material relocation follow this. The name given to the complex mixture of partially melted materials that may interact with the internal structure of the reactor, the concrete or the reactor containment is corium. Eurocore have studied the stabilisation and recovery of this material, considering, in particular, five different core stabilisation concepts: In-vessel retention with external cooling, core concrete interaction with top cooling, ex-vessel spreading with top flooding, water injection by bottom flooding, and crucible concept with sacrificial material. One of the major outcomes of the study indicated that further detailed scenarios for late accident sequences were needed. The study effectively highlighted modelling criteria and areas for these scenarios, additionally contributing towards the improvement of accident management.
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2 December 2020