Validation of the Femaxi/simmer Coupling by Using the e9 CABRI-2 Experiment

Accidents prevention and mitigation of the related consequences are mandatory for the safety assessment of the Generation IV Sodium-cooled Fast Reactors (SFRs). In order to reach these goals, the accurate evaluation of the most challenging transients, which may lead to severe accidents, is fundamental. In particular, an accurate evaluation of the degradation of the thermo-mechanical properties of the fuel pins due to irradiation, affecting the course of accidental transient conditions, is necessary. In our studies, the reference calculation route for the analysis of a severe accident in SFRs is based on the sequential use of the SAS-SFR and the SIMMER-III/IV mechanistic codes for the initiation (up to hexcan failure of a fuel sub-assembly) and the late (with core melting) phases of the scenario, respectively. Nevertheless, the module devoted to the SAS-SFR/SIMMER data transfer shows some limitations when innovative pins and core designs are considered. Having this in mind, the present paper proposes an innovative approach based on the coupling of a fuel performance code FEMAXI and the SIMMER code. When applied to severe accident studies of new reactors designs, such an approach is expected to improve the consistency of the SIMMER results as well as to extend its range of application. The FEMAXI/SIMMER coupling is described in the paper. Further, the results of the code validation against the CABRI-2 E9 experimental test, performed at the CABRI reactor using an OPHELIE-6 annular fuel pin irradiated in the PHENIX reactor, are shown and discussed. In the E9 test, a slow power ramp non-failure transient, corresponding to control rod withdrawal conditions, was investigated. New FEMAXI/SIMMER results are compared also to stand-alone SAS-SFR and SIMMER evaluations.