Preliminary results of a comparative assessment of athlet-cd and melcor by simulating the experiment phebus fpt1

System codes like MELCOR (Methods for Estimation of Leakages and Consequences of Releases) and ATHLET-CD (Analysis of Thermal hydraulics of Leaks and Transients – Core Degradation) are tools to simulate severe accidents in nuclear power plants, which enable estimations and predictions on the course of (hypothetical) accidents. These codes need continuous validation to ensure the quality of the results. To support the validation and development progress of ATHLET-CD, in this work the code is used to simulate the in-pile experiment PHEBUS FPT1. Additionally, a MELCOR simulation is applied for comparison. The test was performed at IRSN (Institut de Radioprotection et de Sûreté Nucleaire) in France and was under research as International Standard Problem n°46 (ISP-46). First simulation results mainly show similar trends concerning the main parameters of the experiment, in particular thermal hydraulics, fuel rod temperatures and hydrogen generation. Deviations between the simulation results are more clearly visible regarding phenomena, which depend partly on more different model assumptions and influencing variables, like degradation of material or the release of fission products. Concluding, as far as the comparison is advanced, it can be stated that ATHLET-CD as well as MELCOR are able to simulate the experiment PHEBUS FPT1 basically with adequate accuracy. However, the results show specific deviations from the experiment which imply improvement potential of the codes.