Investigation of thermal stratification phenomena in reactor vessel (4); Investigation of algebraic stress model

Muramatsu, Toshiharu; Ninokata, Hisashi

For the purpose of the establishment of analytical model for turbulent flow behavior related to in-vessel thermal stratification phenomena, an algebraic stress turbulent model (ASM) has been implemented into AQUA in the place of the k- turbulence model. The new turbulence model has provided high-accurate results in thermal stratification analysis due to the fact that empirical constants such as the turbulence prandtl number prt have been eliminated. From the analyses of water and sodium experiments using the new model, the following results have been obtained: [Water experiment] (1)Calculated speed of stratification interface rise agreed well with the experiment under the conditions that the internal sloshing behavior of the stratification interface was not observed. (2)While under the experimental conditions with the internal sloshing behavior being present, a calculated sloshing amplitude was slightly underestimated by the ASM. One of the reasons is considered to be that the model constants were derived for steady-state flows and not for transient turbulent flows. [Sodium experiment] In general, calculated speed of stratification interface rise has agreed well with the experiment. From the above results, it was confirmed that the algebraic stress turbulence model is superior to the conventional k- turbulence model on accuracy for an analysis of thermal stratification phenomenon.