During a core disruptive accident (CDA) in sodium-cooled fast reactors (SFRs), molten core material could be discharged through coolant channels, such as the control rod guide tubes, into the core inlet plenum under the core region. In such a case, a combined phenomenon of "jet impingement on a horizontal structure" and "Fuel-Coolant Interaction (FCI)" is expected to occur because of the limited sodium depth and volume of the reactor inlet plenum. However, there is a lack of experimental knowledge on such a complicated phenomenon under sodium-cooled conditions, which leads to a large uncertainty in fragmentation and cooling behavior of molten core material during a CDA of SFRs.In the present study, 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. In this experimental series, approximately 9 kg of molten Al2O3 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 Al2O3 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 Al2O3 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, FCI at the molten Al2O3 jet impingement on the bottom of the test vessel might have promote jet fragmentation, and heat exchange by sodium inflow and outflow through the flow holes might have contribute to effective cooling of molten Al2O3.

Fragmentation and Cooling Behavior of a Simulated Molten Core Material Discharged Into a Sodium Pool With Limited Depth and Volume

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

2021 28th International Conference on Nuclear Engineering (ICONE28)

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