Synthesis of CABRI-RIA tests interpretation

The CABRI REP-Na programme performed in the sodium loop of the CABRI reactor by the French 'Institut de Radioprotection et de Surete Nucleaire', has been devoted to the study of the behaviour of high burn-up UO2 and MOX fuel submitted to a RIA (8 tests with UO2 and 4 with MOX fuel).The observed failures of some of the UO2 and MOX fuel rods at enthalpy levels ranging from 30 to 113 cal/g enthalpy levels have underlined the need of evolution of the present safety criteria. The detailed interpretation of the phenomena together with SCANAIR analysis, led to identify the key parameters during the first phase of the transient, without significant clad temperature increase, which are the deleterious influence of a high clad corrosion level with hydride concentrations on clad failure and the contribution of grain boundary gases on fission gas release and potential clad loading, mainly in case of MOX fuel. Pending questions still concern the transient fission gas behaviour and the impact on clad loading during the whole transient, the rod behaviour with high clad temperature, the high internal pressure effect and the post-failure phenomena (fuel ejection, fuel-coolant interaction with finely fragmented solid fuel). The CABRI International Programme (CIP) already launched in 2000 (two first tests performed in 2002), will provide under typical pressurised water conditions, relevant additional knowledge relative to high burn-up UO2 and MOX advanced fuels