Development of high performance BWR spacer by using swirl flow

Critical power is one of the important factors in BWR fuel design. The plant operating cost and reactor operating power strongly depend on the critical power. Therefore, many investigators have tried to develop a method for increasing the critical power Swirl flow is one of the attractive methods for increasing the critical power. The current BWR fuel assembly has seven spacers for maintaining a constant gap between fuel rods. Spacer design has a significant effect on the thermal hydraulic performance of a BWR fuel assembly. The purpose of this study is to develop a new BWR spacer design with the high critical power and low pressure drop performance by using swirl flow. The developed performance spacer is the ferrule type spacer with twisted tape. This spacer is called the CYCLONE spacer. Critical power and pressure drop have been measured at BEST (BWR Experimental Loop for stability and transient test) of TOSHIBA corporation. Test bundle consists of electrically heated rods in a 4x4 array configuration. These heater rods are indirect heated. The heated length and outer diameter of the heater rod, as well as the number and the axial locations of the spacers, are the same as for those for a BWR fuel assembly. The axial power shape is stepped cosine (1.4 of the maximum peaking factor). Two test assemblies with different radial power distribution have been used. One test assembly has the maximum power rods at center of the test assembly and the other has the maximum power rods near the channel wall. The results show that the critical power performance of the CYCLONE spacer is 10 to 25% higher than that of the ferrule spacer while the pressure drop for the CYCLONE spacer is nearly equal to the ferrule spacer.