Three-pin cluster CABRI tests simulating the unprotected loss-of-flow accident in sodium-cooled fast reactors

Onoda, Yuichi ; Fukano, Yoshitaka  ; Sato, Ikken ; Marquie, C.*; Duc, B.*

Two three-pin cluster tests simulating the Unprotected Loss-of-Flow (ULOF) accident of Sodium-cooled Fast Reactors (SFRs) were conducted focusing on fuel relocation and freezing behavior. Based on detailed data evaluation and theoretical interpretation for the three-pin cluster tests, it is concluded that axial fuel relocation and freezing are dominated by local fuel enthalpy, and the relation between fuel dispersal and fuel enthalpy observed in these CABRI tests is basically applicable to the pin-bundle condition. It is also clarified that a fuel/steel mixture tends to create tight blockages near the axial ends of the relocating fuel. Part of the fission gas released from the fuel is expected to be trapped within the bottled-up region between the upper and lower blockages and will keep this region pressurized for a relatively long period.