Benchmark Study on Fuel Bundle Degradation in the FPT3 Phebus Test Using the Severe Accident Codes Athlet-CD, ICARE2 and MELCOR

This paper presents the results of pre-test calculations of the PHEBUS FPT3 experiment. The test scenario with the appropriate initial and boundary conditions was provided by the Institut de Radioprotection et de Sûreté Nucléaire. For the analyses, three severe accident codes were used: ATHLET-CD, ICARE2 and MELCOR, respectively. The calculations were focused on the main phenomena occurring in the bundle such as the thermal behaviour, the hydrogen production mainly due to cladding oxidation, the massive degradation of spent fuel and the release of fission products, control rod and structure materials. Using the pre-defined boundary and initial conditions, relatively small deviations between the code results were obtained, which demonstrates that the dominant processes occurring during a severe accident in the core of PWR reactors can be adequately simulated. By applying these codes to a large spectrum of integral tests as well as to plant analyses, one will obtain reliable results on the fuel bundle behaviour. However, the spread in the calculated oxidised boron carbide masses indicates that modelling efforts are still necessary in all the codes in this respect.JRC.F.4-Nuclear design safet