Thermal-hydraulic test results of advanced BWR fuel bundles with spectral shift rods (SSR)

An advanced water rod was invented that we call a spectral shift rod (SSR). The SSR consists of an inlet hole, a wide ascending path, a narrow descending path and an outlet hole. In principle, the water level in the ascending path can be controlled by the core flow rate. Steady and transient tests were conducted under BWR operating conditions (up to 8.5 MPa). The SSR configuration parameters used were the cross-sectional shape of the ascending path, cross-sectional areas of the ascending and descending paths, and the diameters of the inlet and outlet holes. The thermal-hydraulic parameters used were the system pressure, bundle flow rate, bundle inlet subcooling, heat generation rate inside the SSR, and the heater rod power. It was confirmed that the SSR water level from the steady state test could be controlled by the flow rate, and the configuration parameters did not affect the SSR water level controllability. In the case of the transient tests, the change rates of the thermal-hydraulic parameters were determined from the result of ABWR's transient analyses. It was confirmed that the change rate of the SSR water level was less than that of the thermal-hydraulic parameters, and the use of a smaller sized inlet hole reduced the change rate of the SSR water level. (author)