Preliminary applications of CFD methodology on analysis of the single-phase laminar natural circulation under swing conditions

•CFD method is used to predict natural circulation under swing motions.•CFD method can avoid using land-based correlations to swing system.•Pseudo-steady mass flux amplitude increases linearly with swing angles.•Swing phase difference significantly changes the pseudo-steady parameters.

In nuclear power systems, the natural circulation loop will startup to remove the residual heat after losing the power for the forced circulation. The natural circulation will startup if the driving force caused by the density difference is large enough to overcome the resistance of the loop, however, the system will encounter additional forces, including the transport force and the Coriolis force, which may change the driving force and break the stability of natural circulation. In this work, the CFD model for a natural circulation loop was developed to study the dynamic startup performances and the pseudo steady-state operations under swing conditions. Using CFD methodology can avoid employing the correlations for wall friction and heat transfer using in system code, which may be not applicable for swing systems. Based on the CFD analysis, parametric studies were carried out, including swing period, maximum swing angle, heat power, swing center and the swing phase difference. The swing angle, swing period, swing phase difference and heated power can significantly affect the thermohydraulics and stability of the natural circulation systems, while the swing radius has little influence. This work proved that CFD methodology may be qualified for analyzing the natural circulation system under swing conditions.