Numerical Study On Flow And Heat Transfer In The Primary Side Of Inverted U-tube Steam Generation Under Natural Circulation Condition

At present,nuclear power is in a period of great development.China's nuclear power technology has been relatively mature.While steadily promoting the development of nuclear power,it is especially important to strengthen the safety of nuclear power equipment.The steam generator is the hub that connects the first and second circuits in nuclear power plants system,which is an important device in the nuclear power plant.Natural circulation is that the power source generated by cold and hot fluid density difference under the action of gravity drives circulating flow,instead of external power source in close system.Natural circulation can effectively enhance the passive safety of the reactor,reduce the non-uniformity of the flow distribution in each channel of the core and improve the integrated capability of reactor.Therefore,natural circulation technology plays an important role in the design and operation of reactors.However,when studying on the ability of flow and heat in primary side under the natural circulation condition,it is found that there is a significant non-uniform flow in vertical U-shaped steam generator(UTSG)heat transfer tubes and revers flow of single-phase coolant in some tubes.Reverse flow reduces the effective heat transfer area of the UTSG and less flow goes through the reactor core.Therefore,the study of UTSG tube reverse flow in natural circulation is of great significance.In this paper,three-dimensional numerical simulation program FLUENT has been used to simulate the primary side of the UTSG under natural circulation conditions.The positive and negative values of the flow in the parallel U-tubes act as the criterion of normal flow and reverse flow or not.The results are compared with the calculation results of thermal hydraulics analysis program RELAP5 and agree well.The main contents of this research include in this paper:under natural circulation,doing research on the reverse flow characteristics of U-tubes in primary side of UTSG;Studying the influences of tube length,initial inlet flow rate,primary inlet mass flow rate and primary inlet temperature on reverse flow in UTSG;Researching on reverse flow characteristics of U-tubes of the UTSG under different inclining conditions and different inclining angles.This research is of great significance for the thermal hydraulic design of the evaporators and the safe operation of reactors in the marine environment.