Parametric SAS3D simulations of ULOF accidents for a reactor of the Superphenix-1 type

Unprotected loss of flow accidents have been analyzed for a SPX-1 type reactor core in a collaborative effort by the French CEA/DSN and by KfK. The results from this analysis that was performed with the SAS3D code for an end of equilibrium cycle core are summarized. The objective was to analyze the core behavior and the possible energy release of the primary excursion that is triggered by sodium boiling and that includes further enhancements from fuel motion and fuel thermal interactions with sodium after fuel pin failures (LOF/TOP effects). Parametric results yield a spectrum of consequences that were evaluated in terms of isentropic fuel expansion energies. The simulated ULOF sequence will be discussed for a best estimate case. Sensitivities to the fuel axial expansion, to failure conditions, and to the post failure modelling will be shown. The analysis was done with a refined modelling of the fission gas release from molten fuel which has a strong influence on the possible consequences. 14 refs