Analysis of thermal stratification in the upper plenum of the MONJU reactor vessel

An analysis of sodium circulation in the upper plenum of Monju fast reactor has been performed for validation of the multi-dimensional computational fluid dynamics (CFD) models using data from the turbine trip test conducted in December 1995. A simplified symmetric segment of the upper plenum model has been used with explicit geometric representation of the holes on the inner barrel to simulate the bypass flow. The calculations for the steady-state and transient conditions are performed and compared with the thermally stratified flow conditions observed during the test. Reasonable agreement with test data is observed for steady-state solutions. However, CFD simulations with various modeling options consistently predict a faster dissolution of the thermal stratification than the test data indicates, probably due to underestimating the bypass flow. (author)