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.

在国际源术语计划的框架内，VERDON-3和VERDON-4互补试验专门用于研究MOX燃料和裂变产物（FP）在极高温度（> 2300°C）下在氧化和还原气氛下的行为。VERDON-3和VERDON-4样品的测试后定性和定量表征是在CEA Cadarache中心的LECA-STAR设施中进行的。本文重点讨论了大气对裂变产物形态的影响，更准确地说，涉及Cs，Mo和Ba的行为。在两次测试中，由金属Mo，Ru，Rh，Pd和Tc组成的众所周知的白色夹杂物发生了转变，这意味着熔化和/或成分发生了变化。再次证实了Mo的半挥发性行为。在VERDON-3和VERDON-4测试后，几乎没有Cs残留在样品中，这与其挥发性行为一致。Ba的行为已知是在还原性气氛中大量释放，提供了评估的复杂性，因为在VERDON-3和VERDON-4测试中似乎都发生了显着释放。