Numerical Study Of Coupled Heat Transfer In Primary And Secondary Sides Of LFR Helical Coiled Once-through Steam Generator

The Helical-coiled Once-Through Steam Generator(HOTSG)is a crucial heat transfer device in lead-cooled fast reactor nuclear power systems,and its safe and reliable operation is of paramount importance.During long-term operation,HOTSG may experience performance degradation,such as fouling deposition,chemical corrosion,and thermal stress fatigue,leading to a decrease in heat transfer power or tube rupture.The study of these issues requires a foundation in the three-dimensional flow and heat transfer characteristics of HOTSG shell side,which in turn is affected by the complex two-phase boiling heat transfer process inside the tube.Therefore,this paper investigates the thermohydraulic characteristics of HOTSG primary and secondary sides and the coupled heat transfer method to provide a basis for the design optimization of HOTSG three-dimensional heat transfer and the multidisciplinary analysis of performance degradation due to fouling deposition,chemical corrosion,thermal stress fatigue.Firstly,based on the structural characteristics and flow and heat transfer characteristics of the HOTSG shell side,a flow and heat transfer model suitable for liquid metal cross-flow helical-coiled tube bundles was established.The reliability of the numerical calculation model was verified by using Na K alloy cross-flow rod bundles for experimental validation.The grid sensitivity analysis was performed using a typical local bundle structure in the primary side to obtain the rule of the numerical calculation results of the flow and heat transfer in the bundle region affected by the grid size,which supports the refinement of the three-dimensional grid generation of the HOTSG shell side.Secondly,for the boiling heat transfer and two-phase flow on the HOTSG tube side,as well as the heat conduction process on the tube wall,a onedimensional system analysis code was used to establish a parallel multi-channel calculation model.The applicability of the one-dimensional calculation model was confirmed by two-phase flow boiling heat transfer experiments in a single helical-coiled tube,and the node sensitivity analysis was carried out using the HOTSG single spiral tube calculation model.Then,based on the established HOTSG shell side three-dimensional CFD calculation model and tube side onedimensional system program calculation model,an intermediate control program written in Python was used to establish the HOTSG primary and secondary sides coupling heat transfer model through explicit coupling,and the reliability of the coupling heat transfer model was verified by small helical-coiled heat exchanger experimental data.The HOTSG first and second-side coupling heat transfer model was applied to a certain type of lead-cooled fast reactor steam generator,and detailed flow and heat transfer characteristics inside and outside the tubes were obtained.Through analysis,it was found that although the tube length and external flow field of each layer of helical coil tubes were different,the distribution of thermal parameters inside and outside the tubes and heat transfer power was relatively uniform.Finally,the sensitivity analysis of the coupling boundary conditions showed that the combination of the second and third boundary conditions could achieve stable and fast convergence of the coupling iteration process.Through this study,the distribution of three-dimensional thermal-hydraulic parameters on the shell side and the distribution of thermal-hydraulic parameters on the tube wall and inside the tube along the axial direction were obtained,which can support the three-dimensional heat transfer design optimization of HOTSG and multidisciplinary performance degradation analysis such as fouling deposition,chemical corrosion,and thermal stress fatigue.