Sodium experiments of buoyancy driven penetration flow into low power subassemblies in a sodium cooled fast reactor during natural circulation decay heat removal

Kamide, Hideki ; Kobayashi, Jun ; Hayashi, Kenji

Natural circulation has a significant role in the decay heat removal function of a sodium cooled reactor. The dipped heat exchanger (DHX) immersed in a reactor upper plenum as the decay heat removal system provides cold sodium in the upper plenum during the decay heat removal operation. This cold sodium covers the top of the core under low flow rate conditions of the natural circulation. Sodium experiments were carried out to find onset condition and penetration depth of such partial reverse flow driven by buoyancy force. The onset conditions of the penetration flow were correlated with Gr and Re numbers as well as basic water experiments. The observed penetration depths were limited in the upper axial neutron shielding of the subassembly.