In order to obtain experimental knowledge on fragmentation and cooling behavior of molten core material discharged into regions where the depth and volume of sodium are limited, a series of out-of-pile experiments using alumina (Al2O3) as a simulated molten core material was conducted at an experimental facility of National Nuclear Center of the Republic of Kazakhstan (NNC/RK). In this experimental series, approximately 9 kg of molten alumina was discharged through a duct of 40 mm in inner diameter into a test vessel (200 mm in depth and 300 mm in inner diameter) installed in an outer large vessel filled with sodium. The discharge mass of molten alumina and the dimension of the inner test vessel were determined so that the bulk temperature of sodium inside the test vessel could exceed its saturation temperature. Flow holes were provided in the top lid of the inner test vessel to allow sodium flow between the inner and outer vessels. The shape of solidified alumina recovered from the inner test vessel after this experiment was not ingot-like but fragmented debris. As a possible mechanism for such a debris shape, Fuel-Coolant Interaction (FCI) at the molten alumina jet impingement on the bottom of the test vessel might have promoted jet fragmentation, and heat exchange by sodium inflow and outflow through the flow holes might have contributed to effective cooling of molten alumina.

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