Fission product speciation in the VERDON-3 and VERDON-4 MOX fuels samples

Abstract Within the framework of the International Source Term Programme, the VERDON-3 and VERDON-4 complementary tests were devoted to studying MOX fuel and fission product (FP) behaviour at very high temperature (>2300 °C) under oxidising and reducing atmospheres. Post-test qualitative and quantitative characterisations of the VERDON-3 and VERDON-4 samples were carried out in the LECA-STAR facility at the CEA Cadarache centre. This article focuses on the impact of the atmosphere on fission product speciation and more precisely on the behaviour of Cs, Mo and Ba. The well-known white inclusions composed of metallic Mo, Ru, Rh, Pd and Tc underwent transformations during the two tests implying melting and/or composition changes. The semi-volatile behaviour of Mo was once again confirmed. Almost no Cs was seen to remain in the samples after the VERDON-3 and VERDON-4 tests, which is consistent with its volatile behaviour. The behaviour of Ba, which is known to be released in high quantities in reducing atmospheres, provided complex to assess as significant releases seems to have taken place in both VERDON-3 and VERDON-4 tests.