Analysis of fission product behaviors in the Phebus-FPT1 test with IMPACT/SAMPSON code

Phebus FPT-1 test was analyzed as one of the verification studies for the super simulator 'SAMPSON'. This code has been developed to show that there exist certain safety margins for light water reactors under hypothetical severe accidents and to investigate realistic measures of accident management by simulating accidents with a parallel computer. This paper describes the analysis of fission product (FP) behaviors in the test train. The core region was modeled as 3 channels and the fuel rod is divided into 11 regions in the axis direction. The release of FPs from the fuel was analyzed by diffusion in the fuel pellets. The release of volatile FPs from the molten fuel was treated by the instant release proportional to the amount of molten fuels. The primary circuit and containment were divided into 21 nodes. The mass balance of FP nuclides was calculated considering depositions. The main deposition processes in the hot leg and the steam generator were adsorption, diffusion and thermophoresis. The gravitation and diffusiophoresis were dominant deposition mechanisms in the containment. Organic iodine was assumed to be formed from the reaction of iodine with paints on the wet condenser in the field of radiation. The SAMPSON code was proved to be capable for evaluating FP behaviors in LWR severe accident conditions. (author)