Analysis of Thermal Stratification in the Upper Plenum of the "Monju" Reactor Vessel - Effect Of Chamfer Of Flow-Hole On Thermal Stratification -

Abstract

The analysis of thermal stratification in the upper plenum of the “Monju” reactor vessel is an IAEA Coordinated Research Program (CRP).In spite of many attempts to predict the height of the thermal stratification interface, all calculated results indicated a higher height at approximately 10 minutes after the transient than what was measured at “Monju”.Hence, the present paper discusses the effect of chamfer of the flow-holes and heat capacity of the upper instrumental structure (UIS) on the height of the thermal stratification interface, using the 3D CFD code. The chamfer hypothesis stems from the engineer’s intuition that the edges of the flow-holes should have a rounded edge or chamfer.A flow-hole with chamfer exhibits a much lower local friction loss coefficient of the sodium than a straight-edge flow- hole, resulting in a flow increase from the flow-holes.The presence of chamfer is assumed although there is no direct information about them.Three cases were calculated, one case without chamfer and one case with chamfer on the flow-hole edge, to investigate the effect on the interface behavior.Third one is a calculation taking into account the chamfer on the edge and heat capacity of UIS.In the case of calculation taking into account flow-holes with chamfer and the heat capacity of UIS, the height of the thermal stratification interface is closer to the experimental result.