Experimental investigation of spray cooling behavior in 4×4 simulated fuel bundle

During the Fukushima Daiichi nuclear power plant accident, a failure of cooling systems for the spent fuel pool (SFP) occurred, and there was a concern that the spent fuels were damaged. Thus, safety measures for SFP cooling in severe accident conditions are required. As a countermeasure for the severe accident SFP, portable sprays are used to cool spent fuels under such conditions. In this paper, experiments were performed to understand the cooling phenomena and obtain validation data for the numerical simulation method which evaluates the applicability of the portable spray system. A cooling experiment using an electrically heated 4 × 4 simulated fuel assembly was performed, and the temperature distribution during the spray cooling process was measured. The results show that the temperature decrease in the upper region of the simulated fuel assembly was relatively uniform compared with that in the lower region. Also, the spray water temperature did not significantly affect the cooling process and the average velocity of the cooling front-edge.