Enhancement of heat transfer from multiple heat sources placed in low Prandtl fluid

In the case of a severe accident in sodium cooled fast breeder reactors, the decay heat from destroyed core is removed by the free convection established in the pool. Because of safety and design implications; the adequacy of this passive mode of heat transfer has to be assessed. In addition, modification in the core catcher has to be done to accommodate the thermal load of whole core debris. In the present numerical study, we propose, combination of multiple passive jets and slots for the collection trays dispersing the core debris on multiple trays and effective heat removal. The heat source is placed in the lower plenum of reactor filled with low Prandtl fluid, Pr=0.0045 (liquid sodium). The configuration makes the physical domain to analyze as fundamental problem with internal heat generation in a cylindrical enclosure. The time-dependent form of the continuity, momentum and energy conservation equations are solved by finite volume-based solver. The mathematical model is validated against an in-house experiment as well as data available in the open literature. Three different possible scenarios of debris dispersion have been analyzed on two trays with- (i) both trays as solid, (ii) upper having slot and lower as solid and (iii) upper tray with multiple slots while lower tray is having passive cooling jets. The choice of angle and orientation is based on the previous study by the same authors. It has been found that two trays with slots at top and multiple jets at bottom are able to support the heat load of 25 MW as compared to similar to 14 MW on single tray without exceeding threshold safe structure design limits. The flow field inside the domain indicates the elimination of stagnant sodium at the bottom due to the implementation of passive jets and enhancement in the coolability of heat source.