Transient CFD analysis of MSRE fuel drain tank

The Molten Salt Reactor (MSR) is one of the Generation IV reactors and it provides inherent safety and high efficiency. The Fuel Drain Tank (FDT) is a critical component in MSR for storing fuel salt in case of shutdown as well as emergency and has to be designed to remove decay heat reliably for long time. To design and predict the behavior of MSR FDT, the Oak Ridge National Lab (ORNL) assumed certain parameters in 1960s while designing the Molten Salt Reactor Experiment (MSRE). One of the key assumptions is the difference between the mixed-mean temperature of the fuel salt and the thimble tube surface temperature remains constant at 25 F. This assumption greatly simplifies the heat removal prediction as well as the design of FDT. However, the assumption was not revisited for verification in the open literature. Thus, this study attempted to verify the value using the three-dimensional transient CFD simulations which were verified through the hierarchical verification and validation methodology. Consequently, it was found that the difference between FDT mixed-mean temperature and thimble tube surface-averaged temperature was maintained around 20 K, not 25 F after thermal stratification was well-developed.