Fission products and nuclear fuel behavior under severe accident conditions Part 2: Fuel behavior in the VERDON-1 sample

International audienceWithin the framework of the International Source Term Programme (ISTP), the VERDON programme aims at quantifying the source term of radioactive materials in case of a hypothetical severe accident in a light water reactor (LWR). Tests were performed in a new experimental laboratory (VERDON) built in the LECA-STAR facility (CEA Cadarache). The VERDON-1 test was devoted to the study of a high burn-up UO$_2$ fuel and FP releases at very high temperature ($\approx$2600°C) in a reducing atmosphere. Post-test qualitative and quantitative characterisations of the VERDON-1 sample led to the proposal of a scenario explaining the phenomena occurring during the experimental sequence. Hence, the fuel and the cladding may have interacted which led to the melting of UO$_2$-ZrO$_2$ alloy. Although no relocation was observed during the test, it may have been imminent