Summary and interpretation of the CABRI REP-Na Program

Nuclear Technology, mars 2007, vol 157

J. Papin, B. Cazalis, J.M. Frizonnet, J. Desquines, F. Lemoine, V. Georgenthum, F. Lamare, M. Petit.

The CABRI REP-Na programme performed in the sodium loop of the CABRI reactor by the French “Institut de Radioprotection et de Sûreté Nucléaire”, aimed at studying the behaviour of high burn-up UO2 and MOX fuel submitted to a RIA (8 tests with UO2 and 4 with MOX fuel).The failures of some of the UO2 and MOX fuel rods at enthalpy levels ranging from 125 J/g to 472 J/g (30 to 113 cal/g) have underlined the need of evolution of the present safety criteria. The detailed interpretation led to identify 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, during the first phase of the transient, without significant clad temperature increase.
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 and internal pressure, and the post-failure phenomena (fuel ejection, fuel-coolant interaction with finely fragmented solid fuel); such issues will be addressed by the CABRI International Programme (CIP) tests under typical pressurised water conditions.