Analysis on stress and modal characteristics of molten salt pump rotor system under thermal decomposition conditions

When a molten salt pump operates at high temperatures, the thermal decomposition of internal molten salt generates gas-liquid two-phase flow, which impairs operational stability and hydraulic performance. Nevertheless, systematic research concerning the structural response of the rotor induced by this phenomenon remains insufficient. Taking the 16ENH-2 two-stage molten salt pump used in the Dunhuang project as the research subject, this paper incorporates the gas generation effect from thermal decomposition into rotor analysis. A one-way fluid-thermal-solid coupling method is adopted to investigate the influences of gas generation rate, flow rate and temperature on rotor stress, deformation and modal characteristics. The results reveal that, compared with the gas-free condition k ₀ , thermally decomposed gas reduces the maximum equivalent stress of the second-stage impeller by 68.5% at 0.2 times the design flow rate and effectively suppresses stress fluctuation. Meanwhile, structural deformation exhibits a slight increase under the same conditions. Gas generation slightly decreases the natural frequencies and critical speeds and marginally raises the vibration amplitude of low-order modes, yet the mode shapes remain unchanged. The first-order critical speed under all working conditions exceeds the rated rotational speed, and the maximum equivalent stress is lower than the allowable stress of the material. Gas produced by molten salt thermal decomposition exerts dual effects on the rotor, namely stress reduction and vibration regulation.