Thermal hydraulic analysis of parallel-channel supercritical natural circulation loop: A numerical approach

In this numerical study, a closed supercritical natural circulation loop (SCNCL) with a parallel-channel configuration is analyzed from a thermal-hydraulic (TH) perspective. An in-house numerical model is developed to capture the axial variation of TH field variables in each heated channel. The model incorporates local property variations at supercritical pressures and integrates sub-models for the pressurizer, cooling heat exchanger (CHX), and wall heat conduction to accurately represent the behavior of the loop. Validation is carried out using benchmarks from the literature, covering steady state and transient conditions. Steady state simulations are performed to evaluate the flow distribution and overall loop performance under varying operating conditions. Emphasis is placed on identifying the effects of property variations and geometric parameters on flow across channels. Transient simulations are carried out to investigate the possibility of onset of core-wide (in-phase) loop and regional (out-of-phase) modes of the instabilities. While validating against the available experimental data, inlet mass flow rates at the two heated channels are found to be undergoing regional mode of oscillations. For the SCNCL with parallel heated channels considered in this analysis, and under the selected operating conditions, any instability observed in the core occurs without phase differences between the corresponding field variables in the parallel heated channels. This indicates that regional (out-of-phase) oscillations do not occur. Consequently, the marginal stability boundary (MSB) for the core-wide oscillation mode is determined, and a comprehensive parametric study is performed to examine the effects of key parameters, such as heater inlet temperature, loop pressure, loop height, and the number of channels, on the stability thresholds of the entire SCNCL system. • A thermal hydraulic model is developed for a closed SCNCL with parallel-channels. • Predictions are verified against the numerical benchmarks. • Influence of system parameters on the marginal stability boundary is investigated. • Comparative analysis of single and parallel-channel configurations.