Numerical thermal hydraulic analysis of supercritical natural circulation loop

In the present numerical study, a supercritical natural circulation loop (SCNCL) with a closed configuration is analyzed from a thermal-hydraulic (TH) perspective. An in-house model is developed to capture the axial variation of TH field variables considering a single channel in the heated section. This TH model efficiently accounts for local property variations at supercritical pressures and is integrated with models for the pressurizer, cooling heat exchanger (CHX), and wall heat conduction to accurately represent the behavior of a closed SCNCL. To evaluate the predictive capability of the integrated TH model, validation is performed against both experimental data and numerical results available in the literature, covering steady state and transient scenarios. Steady state simulations are then conducted to assess the SCNCL performance and determine the mass flow rate under various operating conditions, with an emphasis on identifying the underlying physical mechanisms. Finally, transient simulations are carried out to investigate the risk of density wave oscillations (DWOs) and to determine the marginal stability boundary (MSB). A comprehensive parametric study is performed to explore the influence of different factors on the MSB.