The ISP 46 and some calculational results obtained with ATHLET-CD

The PHEBUS FPT-1 experiment was carried out in the PHEBUS experimental facility at the Cadarache research center in the south of France in July 1996. As an integral experiment, it served for studies of core degradation and fission product release into the containment by simulating loss of coolant in the cold leg of the primary system in a light water reactor. This experiment was nominated international standard problem 46 (ISP 46) by the OECD, thus serving for benchmarking accident analysis codes developed worldwide. RUB-LEE participated in ISP 46 with version 1.2D/1.1I of the ATHLET-CD code. In the introduction to the article, the reasons for improving accident analysis codes by means of integral experiments are explained. This is followed by a description of the organization of ISP 46, the PHEBUS experimental matrix, and the experimental facility. Information about the ATHLET-CD code used is supplemented by the model of the experimental facility in ATHLET-CD. The fuel rod temperatures, hydrogen generation, and the results obtained with respect to releases of fissile material and structural material are discussed next. The results for ISP 46 obtained with the ATHLET-CD code on the whole are excellent, especially as far as fuel temperatures and hydrogen generation are concerned. Details of proposed further developments of the code are mentioned, among them modeling the dislocation of molten fuel. Implementation of the MESOCO late-phase model in the respective code update has been scheduled for 2003.