Study on Forced-Convective Boiling Heat Transfer of Seawater with Sea Salt Deposition

Seawater was injected into reactor cores in the accident at the Fukushima Daiichi Nuclear Power Station. This study intended to provide base data to consider reactor core cooling by seawater. Pool nucleate boiling heat transfer experiments and vertical upward forced-convective boiling heat transfer experiments were conducted by using water and artificial seawater. In the pool nucleate boiling experiments of seawater, slow surface temperature excursion was initiated at some heat flux that was considerably lower than the critical heat flux although the surface heating rate was kept almost constant. The initiation of the surface temperature excursion coincided with the initiation of the deposition of calcium sulfate on the heat transfer surface. The temperature excursion was caused by the heat conduction resistance increase with an increase in deposition layer thickness. It was suggested that the deposition of calcium sulfate on the heat transfer surface starts when the seawater concentration at the vicinity of the heat transfer surface becomes lower than 11 wt%. In the forced-convective boiling heat transfer, even if the seawater concentration at the inlet was low, the sea salt concentration was enriched because of evaporation as flow proceeded, which resulted in the initiation of the surface temperature excursion.