Fuel behavior and fission product release under realistic hydrogen conditions with comparisons between Heva 06 test results and Vulcain computations

Because of the importance of source term predictions for LWR beyond design basis safety analyses, the CEA/IPSN has developed an extensive program to characterize the source of fission products (F.P.) released from overheated fuel and their evolution in the primary coolant system. The Vulcain code is an module of the Escadre system which is the French LWR accident analysis computer code package. It describes the thermal behavior of the core during its dewatering up to its loss of geometry, the release kinetics of F.P. and structure materials, and the thermal hydraulics in the primary coolant system, with a view to providing the main parameters governing the vapor and aerosol transport mechanisms. The Heva program, a series of 8 experiments performed to date, is aimed at characterizing the fission product source associated with postulated severe accident conditions. These test were carried out in the Heva loop with spent fuel reirradiated in the Siloe or Melusine reactors just prior to the experiment. The purpose of this paper is to show how the Vulcain code was used to define the HEVA 06 test with realistically simulated reactor accident conditions and, reciprocally, how large benefits may be achieved by performing such an experiment for the prediction of volatile F.P. release