Modeling and Analysis on Flow Instability of Helical Coiled Tube Steam Generator of Liquid Metal Fast Reactor under Coupled Heat Transfer Conditions

A steady thermo-hydraulic model of the helical tube steam generator was first constructed to study the coupled heat transfer process between the primary and secondary sides based on a discrete modeling method, and obtain the heat flux density distribution along the steam generator. Then, taking the obtained coupled heat flux density distribution as the thermal boundary condition input, considering the dynamic variation of physical properties on the secondary side, a dynamic model based on the time-domain method suitable for two-phase flow instability among parallel multiple channels of the steam generator was constructed. Finally, taking the lead-bismuth fast reactor as an example, flow instability of the steam generator was analyzed under an inlet lead-bismuth temperature of 320°C~480°C and an inlet water temperature of 160°C~240°C. It was found that flow instability is less likely to occur under coupled heat conditions, compared with that under uniform or linear distribution. Flow excursion is prone to occur under low inlet temperature of the primary or secondary side. As the inlet lead bismuth temperature increases from 320°C to 480°C, average heat flux significantly increases by 2.5 times, and the non-uniformity of heat flux distribution increases of 49%. Meanwhile, the density wave oscillation amplitude gradually increases, and system stability weakens.