Spacer grid effect visualization experiments during reflood period in a uniformly heated vertical single rod

An experimental study has been performed to investigate an effect of spacer grid in an annulus flow channel with flat power shape single rod during the reflood phase with the variation of flooding velocity, inlet subcooling of water, and initial temperature of heater surface. Two types of spacer grid have been used. One type has swirl vane and the other has no swirl vane. Rewetting velocity through the swirl vane type spacer grid is faster than that of flat type grid and the temperature behavior of heater rod near the spacer grid is observed in a different pattern. Upper part of the heated length is cooled by top-down flooding phenomenon. The top-down flooding is mainly affected by the initial wall temperature. The present study is precursory one to 6 x 6 bundle reflood test, which will be launched at the near future by KAERI