The development of analytical method to predict and assess the current state of the reactor cores of Fukushima Daiichi nuclear power plant is required. Experimental researches are also required to obtain data to verify the analytical results and to understand the phenomena that are important to the accident progress evaluation.

In the Fukushima Daiichi nuclear power plant accident, seawater was injected into the reactors to cool down nuclear fuels. Core cooling with seawater has never been assumed and the effect of seawater on heat transfer in core is not clear. Then, effects of seawater on thermal-hydraulic behavior must be investigated to understand the phenomena occurred in the accident and to evaluate current state of the reactor cores.

In this series of research work, the effects of seawater on thermal-hydraulic behavior before and after degradation of the cores will be researched experimentally. Experimental results will be incorporated to numerical simulation codes to evaluate effects of seawater on the Fukushima Daiichi nuclear power plant accident. In the experimental research part, we have a plan performing two heat transfer experiments to evaluate thermal hydraulic performance of sea water and effects of salt precipitation. A precipitation state confirmation experiment is performed to obtain basic information required for the experiments with salt precipitation. In this paper, outline of the research plan is explained and the results of the precipitation state confirmation experiment is shown.

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