Analysis of the Total Instantaneous Blockage accident consequences in the innovative inherently-safe CADOR SFR core

Abstract Within the framework of long term prospective studies, an inherently-safe Sodium Fast Reactor (SFR) core, named CADOR (Core with Adding DOppleR effect), is studied at CEA (French commissariat a l’energie atomique et aux energies alternatives). This core concept mainly relies on its enhanced Doppler effect. The behavior of this innovative core design, when facing incidental or accidental transients, is currently assessed in order to demonstrate the benefits of such a core configuration in terms of whole core melting prevention. This paper focuses more specifically on the transient resulting from a Total Instantaneous Blockage (TIB). This sequence has been chosen because it is an enveloping initiator of local melting. Thus, it has to be demonstrated that this local core melting does not lead to a generalized core melting. Transient simulations were carried out with the analytical tool BETINa. This is a fast-running tool based on the coupling between low-dimensional models and advanced statistical techniques. Firstly, a reference transient study enables to highlight the slow kinetic of this transient in comparison with more conventional SFR cores such as SuperPhenix. This is explained by the low power of the CADOR sub-assemblies in this core concept and to their high thermal inertia compared to previous SFR cores. Then, a parametric analysis allows to further understand the core behavior, focusing on the influence of the thermal or hydrodynamic propagation of molten material to the neighbouring sub-assemblies and on the axial location of the hexcan failure. These parameters are indeed identified as explaining a large part of the total variability of the final molten fuel mass. Finally, a complete statistical study based on the variation of 27 uncertain input parameters enables to identify the most influential parameters on the final extend of the core degraded zone.