&nbsp; &nbsp; Due to the Great East Japan Earthquake and the accompanying tsunami, the Fukushima Daiichi Nuclear Power Plant lost all power, which led to the core meltdown. Severe accident (SA) codes were used to reproduce the accident progress, which can treat the behaviors of melting and dropping processes, deposition location, amount, and radioactivity of the molten core. However, the models after the core meltdown include large uncertainty. To improve the reliability of SA codes, it is necessary to clarify the dynamic characteristics of spreading behaviors of molten core and improve the model based on experimental results. Although researches on the spreading of the molten core on the floor has been conducted in the past, many of them simulated horizontal flow of molten debris to evaluate performance of a core catcher. There are few open literatures of molten metal experiments with floor impingement.&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; In the current study, experiments using molten Sn were performed to obtain fundamental data regarding spreading behavior of molten core on a wet floor. And, effect of hydrodynamical and thermal experimental conditions on the spreading behavior was analyzed using dimensionless parameters.Sn was melted with a high-frequency induction heating device and fell to on a stainless plate in a water tank. The spreading behaviors were observed with a high-speed camera. The spreading area and the deposition thickness of the solidified metal were also measured. The experimental parameters were nozzle diameter, fallen height, degree of superheat of molten metal, and water level.&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Local-pressure increment due to the molten metal-water interaction in the water pool occurred in some experiments (hereinafter, this phenomenon is called local steam explosion). Our results indicated that the spreading area and the shape of solidified metals strongly depended on the local steam explosion in the water pool. When the superheat of the molten metal was high, spontaneous steam explosion hardly occurred. However, the impact of the local steam explosion on the spreading areas were larger than those of low superheat conditions when the explosion occurred during floor collision process. We analyzed the effects on the spreading behaviors using dimensionless numbers such as falling height to nozzle diameter ratio L/d, Reynolds number, Peclet number, Weber number so on.

Spreading Behavior of Molten Metal on Flat Plate in a Shallow Water Pool

Paper Proceedings: https://asmedigitalcollection.asme.org/ICONE/ICONE28/volume/85246

2021 28th International Conference on Nuclear Engineering (ICONE28)

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