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

This paper presents the results of pretest calculations of the Phebus fission product release experiment FPT3. 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. The calculations were focused on the main phenomena occurring in the bundle, such as the thermal behavior, the hydrogen production mainly due to cladding oxidation, the massive degradation of spent fuel and the release of fission products and control rod and structure materials. Using the predefined 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 pressurized water 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 behavior. However, the spread in the calculated oxidized boron carbide masses indicates that modeling efforts are still necessary in all the codes in this respect.