Simulation of fission product behaviour in the primary circuit of PHEBUS FPT-1 (ISP-46)

The goal of the experimental program PHEBUS is to study the degradation phenomena and the behaviour of the fission products released in the reactor coolant system and the containment building. Four experiments have been performed so far. The test PHEBUS FPT-1 simulated a severe accident caused by a leak in the circuit's cold leg of the primary system of a Light Water Reactor (LWR). This test was selected as an International Standard Problem (ISP-46) organized by NEA/CSNI to assess the capability of computer codes to model in an integrated way the physical processes taking place during a severe accident. This paper presents results obtained in the frame of ISP-46 with the stand-alone version of the computer code SOPHAEROS 2.0. In this exercise the fission product behaviour on the primary circuit was simulated and the results were compared with the experiment. The PHEBUS FP (Fission Product) programme was initiated to investigate physical and chemical phenomena during a light water reactor severe accident and to validate the models in severe accident codes. The programme concentrates on processes not fully understood, i.g. oxidation of liquefied Zircaloy and the attended hydrogen production, the degradation of fuel and control rods resulting in melting or the release of fission products and structure material. The parameters are the burn-up of the fuel, oxidation rates in melts, different lengths of melting phase, varying cooling rates in the late release phase and the influence of absorber material. Main topics in the investigations are the material transport in the primary system, the deposition of aerosols in the containment and the revolatilisation of iodine through radiolysis and desorption. The results of the programme will provide a more accurate assessment and improvement of necessary steps to be taken in efficiently limiting the effects of the accident, a return of the reactor to a safe state and better management of any consequences involving possible radioactive release outside the reactor. The PHEBUS FP programme was founded in 1988 and has been carried out in collaboration of the 'Institut de Radioprotection et de Surete Nucleaire' (IRSN) with the Joint Research Center (JRC) of the European Commission (EC). Through the intermediary of the Commission, 25 organizations belonging to 10 European countries participate in the programme. Further partners are EDF (France), NRC (USA), NUPEC (Japan), JAERI (Japan), AECL and HYDRO (Canada), KAERI (South Korea), HSK and PSI (Switzerland). Six tests were planned over a period of about twelve years. Up to now four tests have been performed already (FPT-0 in December 1993, FPT-1 in July 1996, FPT-4 in July 1999 and FPT-2 in October 2000). The test FPT- 3 is scheduled for 2004 and FPT-5 has been cancelled