Buoyancy phenomena in tube bundles and plena of liquid sodium heat exchangers for LMFBR's

Buoyancy effects in LMFBRs occur in the plena of heat exchangers at low speed convective flow: mixed convection. In decay heat removal systems buoyancy is the only flow driving force: natural convection. The computation of the thermal hydraulics of both situations are asking for different treatments as shown. The main aim of the calculations is the prediction of the thermal stress in the solid structures. Equations describing the mixed convective flows in plena of heat exchangers are presented. Numerical computations of the thermal-hydraulic behavior of a decay heat cooler are described