Single-Phase Flow And Heat Transfer Characteristics Of Natural Circulation System With Petal-Shaped Fuel Bundle Channel Under Rolling Motion Conditions

Nuclear energy is an environmentally friendly and efficient energy source that can effectively promote the achievement of China’s dual carbon goals.Nuclear energy technology is gradually improving,and nuclear power plants are gradually developing towards integration.The reactor and naval architecture are combined to build a sea-based nuclear power plant.It provides strong guarantees for the promotion and implementation of China’s maritime power.Petal-shaped fuel rods have significant advantages such as large specific surface area and strong lateral mixing.It can meet the requirements of high power density and long refueling cycles for sea-based nuclear power plants,and it has broad application prospects.To investigate the effects of rolling motion on the flow and heat transfer characteristics of the natural circulation system,a multi-scale coupled simulation study of natural circulation systems is conducted with 3 × 3 square arranged fuel bundle channel.The relevant research conclusions can provide theoretical guidance for the application of petal-shaped fuel elements in sea-based nuclear power plants.Firstly,a multi-scale coupled numerical model of 1D code and 3D STAR-CCM+ software under rolling motion condition is established.Then its reliability is verified by comparing with existing experimental data.The results show that the values obtained from the coupled simulation calculation are in good agreement with the experimental values,and the relative deviation is concentrated within 2%.Secondly,the local fluid field changes in the petal-shaped fuel bundle channel at different heights and rolling times are studied.The influence of rolling parameters on rolling start-up characteristics is analysed.The flow resistance in the petal-shaped fuel bundle channel under different rolling motion conditions and operating conditions has been studied.The results indicate that the axial flow rate and secondary flow rate are asymmetrically distributed under rolling motion conditions due to the influence of inertial forces.The results indicate that if the start-up direction of rolling motion is the same as the direction of natural circulation flow rate,rolling motion will cause a sharp decrease in flow rate at the initial moment.The results show that the increase of heating power and inlet temperature will increase the density contrast between cold and hot legs,and also increase the driving force of the system.This will lead to an increase in the mean value of natural circulation flow rate and resistance pressure drop,as well as a decrease in fluctuation amplitude.Both an increase in rolling angle and a decrease in rolling period will increase the range of additional inertial force and effective height difference.Them can cause a significant increase in the fluctuation amplitude of flow rate and resistance pressure drop.As the rolling period is reduced from 30 s to 20 s,the fluctuation amplitude of flow is increased by 161.83%.If the rolling angle is increased from 10 ° to 20 °,the flow fluctuation amplitude is increased by 105.79Finally,the heat transfer characteristics of the fuel bundle channel under different rolling motion conditions are studied.The research show that different rolling postures can cause changes in axial flow rate and secondary flow rate perpendicular to the rolling axis,resulting in significant changes in the peak temperature of the cross-section.Both an increase in rolling amplitude and a decrease in rolling period can cause a significant increase in the fluctuation amplitude of temperature.The increase in rolling angle increases the fluctuation amplitude of the average heat transfer coefficient.The rolling angle has different effects on the local heat transfer coefficient of different sub-channels.Among them,the fluctuation amplitude of flow rate in the sub-channel around the central rod is greater,and the fluctuation amplitude of heat transfer coefficient reaches108.34%.By considering the influence of acceleration Reynolds number,the Nusselt number correlation suitable for the natural circulation system of petal-shaped fuel bundle channel under rolling motion condition is obtained.In addition,by considering the influence of rolling period and rolling angle,the Nusselt number correlation in the start-up phase is constructed.