Numerical Study On Flow And Heat Transfer Characteristics Of Natural Circulation With Rod Bundle Under Typical Ocean Conditions

Marine nuclear power plant are the most effective way to solve the energy demand for ocean sailing,by selecting the natural circulation system,we can improve the safety performance of Marine nuclear power plant,but the ocean conditions including fluctuating,swing and inclining will cause significant impacts to the natural circulation of nuclear power plant,and may even lead to serious safety accidents.In this paper,Based on relap5 and fluent coupling platform,numerical simulation and analysis are carried out to research the pulsating flow rate of the natural circulation system with rod bundle channel under the ocean conditions and the flow and heat transfer characteristics in the rod bundle channel.After being reasonably simplified,the mathematical model for fluctuating,swing and inclining motions were was established.Through the user defined function(UDF)interface,the model of ocean conditions were added into Fluent,and based on the experimental data in the literature,the subcooled boiling model and the motion models was proved be feasible and accurate.By adding the additional force which generated by the ocean condition into the source term of the momentum conservation equation in the Relap5 source program,and coupling the Relap5 with the ocean condition and Fluent based on the coupling interface program,the simulation of the natural circulation with rod bundle channel under the ocean condition was realized,whose feasibility and accuracy was verified by experimental data.The flow characteristics of the natural circulation system under the ocean condition are different from those which under the static condition.Under inclining condition,the driving force and mass flow of the single-phase and two-phase systems will increase with the increment of the angle of inclination.moreover,the flow change under the positive slant is greater than that under the reverse slant because of the loop layout.Under swing condition,the fluctuation amplitude of system mass flow is mainly related to the swing period and amplitude,while the mean value is mainly related to the heating power and inlet temperature.In single-phase condition,the fluctuation amplitude of system flow is mainly affected by the additional driving force,while in two-phase condition,the fluctuation amplitude of system flow is determined by the fluctuation amplitude of the additional driving force and the gravity driving force.Under fluctuating condition,The fluctuation amplitude for flow rate of single-phase and two-phase systems will both increase with the increment of s fluctuating amplitude and decrease with the increment of period,and the fluctuation amplitude of two-phase condition is larger than that of singlephase condition.Ocean conditions also affect the flow and heat transfer characteristics in the rod bundle channel.Under inclining condition,the vapor phase migrates and accumulates in the opposite direction of inclining under the influence of buoyancy and lift,which causing the increase of local void fraction,wall temperature and the thermal stratification of the fluid in the slant direction.Under swing condition,due to the periodic fluctuation of system flow and the secondary flow in cross section,the vapor phase moves periodically through the channel,the position of each subchannel and local share of the cavitation will happen cyclical change,will be cyclical fluctuations,bundle wall temperature will lead to the coefficient of heat transfer with swing cycle,and the heating power,the change of inlet temperature fluctuations;Under the fluctuating condition,as the secondary flow in the channel is not as strong as the swing condition,the fluctuation amplitude of each physical quantity is smaller than that under the swing condition.besides,the time-averaged frictional resistance coefficient can no longer be predicted by the existing formula under the condition of swing and fluctuating,and the variation law of instantaneous frictional resistance coefficient obtained by the research has certain guiding significance for engineering practice.