One-dimensional coupled dynamic thermal hydraulic model for density wave oscillations in molten salt steam generators

Molten-salt thermal energy storage is widely recognized as a promising technology for large-scale, long-duration energy storage. However, during load-following operation, molten-salt steam generators (MSSGs) may be susceptible to two-phase flow instabilities, which can compromise operational safety and reliability. In this study, a physical model of the key MSSG component is established, and a one-dimensional dynamic heat-transfer model is developed within the Adaptive System Thermal-hydraulics (ASYST) framework to analyze density-wave oscillations (DWO). The model is validated against experimental data, with overall deviations generally within 10–11%, and the predicted oscillation period of 9.2 s shows good agreement with the reference value of 8.5 s. 150 operating conditions are evaluated to construct a stability map and determine the stability boundary. An operating condition is classified as unstable when the mass-flux oscillation diverges and its amplitude exceeds 10% of the mean mass flux. Within the investigated ranges of outlet steam pressure (8–14 MPa), steam–water-side pressure drop (0.31–0.49 MPa), and inlet molten-salt mass flow rate (0.90–2.54 kg/s), increasing the operating pressure is found to enhance system stability, whereas increasing the molten-salt mass flow rate generally reduces stability. The results further clarify the feedback mechanism responsible for DWO and quantify the coupled molten-salt-side response, where the outlet molten-salt mass flow rate fluctuates between approximately 1.98 and 2.23 kg/s, corresponding to about ± 7% under representative conditions. This study defines the safe operating envelope of the MSSG and provides theoretical guidance as well as data support for its optimized design and operational control.