Experimental study for the effects of ballooned rod bundle on the convective heat transfer by single-phase steam flow

For a large break loss-of-coolant accident (LBLOCA) conditions in a pressurized-water reactor, the cladding temperature increases until the reflood phase and the increased temperature can make a ballooned fuel rods. As a result, the flow passage area of sub-channel is reduced and it leads the redistribution of flow and heat transfer in sub-channels. During the single-phase steam flow in the early phase of the reflood, the cladding temperature may increase and have a peak value due to low heat transfer from the fuel to the steam. If a LBLOCA condition and ballooned fuel rods are occurred, the effect of reduced flow passage on the convective heat transfer by single-phase steam flow is important phenomena to analyze the safety of a reactor. The present experiments were performed in various Reynolds numbers (about 2600∼13000) to investigate the effect of the Ballooned fuel rods on heat transfer phenomena by single-phase steam flow. The experiments were performed in two rod bundles in KAERI reflood ATHER test facility. One is a non-deformed 6x6 rod bundle, which consists of 36 non-deformed heater rods. The other is a deformed 5x5 rod bundle that consists of 9 deformed heater rods and 16 non-deformed heater rods. The cladding temperature and convective heat transfer for two rod bundles are compared for each flow conditions and the effects of experimental parameters are analyzed. (author)