Computation fluid dynamics analysis of the Reactor Cavity Cooling System for Very High Temperature Gas-Cooled Reactors

• The correct radiation/convection energy repartition is predicted inside the RCCS.
• The change of fluid properties inside the RCCS impacts the numerical solution.
• The fin-panel design shows an improved heat removal capability from the RCCS.
• Symmetric lateral boundary conditions can be used if three standpipes are modeled.
• No significant temperature gradients were found at the standpipes inner wall.

The design of passive heat removal systems is one of the main characteristics of the modular Very High Temperature Gas-Cooled Reactors (VHTR) vessel cavity. The Reactor Cavity Cooling System (RCCS) is a key heat removal system during normal and off normal conditions. The design and validation of the RCCS is necessary to demonstrate that VHTRs can survive the postulated accidents. The commercial Computational Fluid Dynamics (CFD) STAR-CCM+/V5.02.009 code was used for three-dimensional system modeling and analysis of the RCCS. Different RCCS geometries and configurations were investigated to analyze heat exchange in the VHTR cavity. Sensitivity analyses over the RCCS cavity height and cooling panel location with respect to the reactor pressure vessel (RPV) wall were performed. The objective of the present work was to use CFD tools for addressing the behavior of the RCCS following accident conditions.Heat removal from the RPV through the RCCS system during normal and off normal conditions is accomplished through radiation, convection and conduction heat transfer modes. The interaction of all three heat exchange mechanisms makes it very challenging to have an accurate description of the RCCS heat transfer dynamics during normal and transient conditions. A systematic analysis of the cavity layout was performed to address the influence of different geometrical parameters on the balance of heat transfer across the RCCS cavity. Mesh convergence was achieved with an intensive parametric study of the different geometrical configurations and boundary conditions selected. Based on the results of previous studies, the Realizable k–ε turbulence model with Two-Layer all y+ wall treatment was used for the analyses discussed in the present work. The numerical results demonstrated that the CFD analyses can resemble the behavior of the full RCCS system from an integral effect point of view, with the main physical phenomena accurately reproduced by the CFD model.