Stability threshold for stratification-induced flowrate oscillations in PLANDTL-2 sodium natural circulation experiment

Renaudie de Vaux, S.*; Li, S.*; Marrel, A.*; Ezure, Toshiki ; Tanaka, Masaaki  

In this study, experimental results on sodium natural circulation in PLANDTL-2 under eight transient scenarios were reported. The experimental parameters were the initial state of the primary circuit, the shutdown inertia of the secondary circuit, and the operating mode of the Decay Heat Removal system (DHRS). As the results, it was clarified that flow reversals can be observed in the primary circuit under rapid cooling cases by DHRS linked to an enhancement of thermal stratification in the plenum. A novel method was introduced to estimate the delay between DHR system activation and increase in stratification. In addition, some guidelines for future investigations were given in order to avoid the presently described instabilities.