Pool nucleate boiling heat transfer experiments of the 3.5 - 10wt% NaCl solution, the real seawater and the 3.5 - 10wt% artificial seawater solution as well as distilled water for the basis of comparison were performed to examine the effect of salts on boiling heat transfer. Seawater was injected into the reactor cores in the accident at the Fukushima Daiichi Nuclear Power Station of Tokyo Electric Power Company. This study intended to provide base data to consider reactor core cooling by seawater. Boiling curves of the 3.5 - 10wt% NaCl solution, the real seawater and the 3.5 - 10wt% artificial seawater solutions as well as distilled water were well predicted with the Rohsenow pool nucleate boiling heat transfer correlation although the curves were a little shifted to the higher wall superheat region. The formation of secondary coalescent large bubble was suppressed in the experiments of the NaCl solutions, real seawater and the artificial seawater solutions, and small primary bubbles detached directly from the heat transfer surface. Sea salt deposition was observed only in the experiments of the 7.0wt% and 10wt% artificial seawater solutions. The deposited salt was calcium sulfate. Slow heat transfer surface temperature excursion occurred in the experiments of the 7.0wt% and 10wt% artificial seawater solutions after the heat flux was raised to 600 kW/m2 and 120 kW/m2, respectively. The critical heat flux of the 7.0wt% and 10wt% artificial seawater solutions were 600 kW/m2 and 120 kW/m2, respectively if the occurrence of the slow heat transfer surface temperature excursion was defined as the critical heat flux condition. The heat transfer surface temperature excursion might be caused by the growth of the deposited salt layer.

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