抄録
High critical-power fuel assemblies are needed for boiling water reactors to increase the thermal safety margin of the reactor core. There are seven spacers supporting the fuel rods in a BWR fuel assembly, and it is well known that the critical power is affected by the spacer geometry. Studies of spacer geometry are therefore important to the development of high critical-power fuel assemblies.
Recently, Morooka et al. reported that a twisted tape increased the critical power. The purpose of this study was to clarify the mechanism by which the twisted tape improves critical power by measuring the film flow rate on the fuel rod under air-water conditions. The test data demonstrate that the twisted tape increases the film flow rate in the annular dispersed flow regime. It is thought likely that a swirling flow is generated downstream of the twisted tape and that droplet deposition is promoted by the swirl. We believe this is why the twisted tape increases critical power.
