Thermal-Hydraulic Characteristics of Local Blockage within a Wire-Wrapped Pin-Bundle Subassembly for Sodium Cooled Fast Reactors

The numerical simulation of a 271-rod fuel assembly of nuclear Sodium-cooled Fast Reactor (SFR) with an internal blockage has been carried out. Internal blockage within a subassembly is addressed in the safety assessment because it has potentially very serious consequences for the reactor as a whole. Three dimensional calculations were performed using the SABRE4 computer code for the range of blockage positions and sizes to investigate the seriousness and detectability of the internal blockage. The magnitude and location of the peak temperatures together with the temperature distribution at the subassembly exit were calculated in order to look at the potential for damage within the subassembly, and the possibility of blockage detection. The analysis result shows that the 6-subchannel blockage causes large temperature rise within an assembly with practically no change in the mixed mean temperature at the assembly exit.