Abstract
To enhance a safety of sodium-cooled fast reactors, decay heat removal systems under natural circulation with a dipped-type direct heat exchanger (D-DHX) installed in a hot pool of a reactor vessel (RV) have been investigated. During the D-DHX operation, the thermal-hydraulics of RV is complicated because the coolant at low temperature from the D-DHX flows into the core and the radial heat transfer through coolant in the interwrapper gap among assemblies occurs.
We have been constructing the practical model for physics in the RV in the design study which can achieve a lower computational cost while maintaining prediction accuracy using the computational fluid dynamics code (RV-CFD). The applicability of RV-CFD previously was confirmed through several numerical analyses of steady-state in a sodium experimental apparatus named PLANDTL-1. In this study, to expand the scope of applicability of RV-CFD to the transient-state, we develop the non-equilibrium thermal model which considers the thermal inertia in simulated fuel pins.
The transient analysis simulating the power reduction due to reactor scram from the steady-state operation in PLANDTL-1 is conducted. The result shows the thermal-hydraulic behavior in the RV during the transient can be predicted, and the core temperature in the transient can be reproduced. Thus, the applicability of RV-CFD using non-equilibrium model to the transient analysis for PLANDTL-1 is confirmed. Its applicability for an actual reactor will be investigated in the future.
