Study on temperature field in porous blockage in a fuel subassembly. 37-pin bundle sodium experiment

Local blockage issue in a fuel subassembly is one of initiation of local fault in a fast reactor core. In existing studies, it is shown that blockage in a wire-spacer type pin bundle will consist of small particles coming through the bundle and will be porous. In order to evaluate the integrity of fuel pins covered by the porous blockage, we have to predict thermohydraulics in the blockage and also in the pin bundle. In this study sodium experiments were carried out using a 37-pin bundle test section with a porous blockage. The fuel pins are modeled by electric heater pins of 8.5 mm in diameter (full scale). The blockage is formed by stainless steel spheres of 0.3 mm in diameter. The blockage is set in the two rows of subchannels along one side of hexagonal wrapper tube. The length of blockage in axial direction is 35 mm and corresponds to 1/6th of wire wrapping pitch. The experimental parameters were power of the heater pins. The heater power was varied from 14% to 43% of the maximum linear heat rate of a real reactor (∼420 W/cm). The flow rate in the subassembly was set at 430 l/min corresponding to 93% of the Reynolds number in a fuel subassembly of real reactor under full power condition. The experimental results showed that the highest temperature was measured on the pin surface covered by the blockage and faced to the subchannel which was surrounded by the blockage. The height of peak temperature point was nearly top of the blockage. It means that the temperature field in the blockage is influenced by flow filed in the blockage significantly. The non-dimensional temperature profile in the blockage and in the pin bundle is independent on heater power. (author)