Numerical investigation on the thermal load heterogeneity of multi-assembly helical coil steam generator in high temperature gas-cooled reactor

The thermal load heterogeneity will lead to inhomogeneous local heat flux and thermal stress, extremely detrimental to the operational stability of heat exchangers with multi-assembly structure. In this paper, a full-scale analysis method for the helical coil steam generator in industry was developed and implemented. The validation was performed against flow boiling heat transfer experiment of helical tube. The simulation of single assembly and full-scale helical coil steam generator in high temperature gas-cooled reactor was performed, and the distributions of thermal-hydraulic parameters in heat exchange region were obtained. The results show that the nonuniform helium flow distribution with the inhomogeneous factor D_m value of 34.83% has a significant influence on the heat transfer characteristics. The peak heat transfer power of central assembly increases by 33.76% against design condition, introducing large thermal load heterogeneity with the inhomogeneous factor D_p value of 30.45%, even threating the structural integrity of helical tube in long-term operation circumstances. The structural elements design in the superior compartment should be optimized to increase the helium mass flow rate of the assemblies below the nozzle and behind the helium baffle, improving flow distribution uniformity and reducing the peak value of local heat flux and thermal stress.