Study On Three-Dimensional Characteristics Of Reverse Flow Phenomena In Natural Circulation Steam Generator

The natural circulation loop of pressurized water reactor has a good passive safety characteristic.In the natural circulation process,the u-tube of steam generator will seriously endanger the safety of the reactor in case of reverse flow.The natural cycle characteristics of Marine PWR are affected by the Marine environment and the reverse flow characteristics are more complicated than those on land.Therefore,it is necessary to study the occurrence and development rules and influencing factors of reverse flow under land and Marine environments.In this paper,the small steam generator of pressurized water reactor under natural circulation condition is taken as the research object,and the u-tube reverse flow phenomenon of steam generator under terrestrial and Marine environment is simulated and calculated by using three-dimensional CFD porous media model.The reverse flow characteristics of a small natural cycle steam generator are studied,and the pressure,temperature distribution and flow distribution in the lower chamber of the steam generator are obtained.The general conclusions are as follows: the three-dimensional simulation method can effectively reflect the characteristics of the flow field in the lower chamber of the steam generator.The pressure distribution and flow distribution in the chamber are very complex and have a significant impact on the reverse flow.Once the reverse flow occurs,the pressure drop at the inlet and outlet of the steam generator is usually negative,and the more u-shaped heat pipe reverse flow occurs,the greater the system resistance will be.With the decrease of the total mass flow at the inlet of the steam generator,the number of reverse flow tubes of the U-type heat transfer pipe of the steam generator decreases.The area where reverse flow occurs first is not the longest or shortest pipe given by the theoretical research institute.Even if it is the same row of U-shaped heat pipe with the same length,there are reverse flow pipe and positive flow pipe at the same time,which is caused by the uneven spatial distribution of flow distribution and pressure in the cavity.The main factors that influence the reverse flow of steam generator under land conditions include inlet temperature of steam generator,length of straight pipe of U-shaped heat pipe,secondary side pressure of steam generator,secondary side water level and rate of natural circulation flow drop.Finally,Marine additional force program was developed based on three-dimensional CFD porous media model,covering typical Marine conditions such as tilt,sway and fluctuation.For the tilt condition,the tilt axis,the tilt direction and the tilt Angle all affect the reverse flow.The steam generator with the same tilt Angle is more sensitive to changes along the flow direction.The larger the tilt Angle is,the more obvious the enhancement or suppression effect will be.For the swing condition,the occurrence of reverse flow can be inhibited by reducing the swing amplitude and increasing the swing period,while the effect of the swing condition on reverse flow is very limited.By studying the reverse flow of the u-shaped heat pipe of the steam generator under the land condition and Marine environment,the three-dimensional spatial distribution characteristics of reverse flow are obtained,the occurrence and development law of reverse flow are analyzed,and the main factors affecting reverse flow are discussed.The related research results can provide technical support for the research on the reverse flow mechanism of the steam generator U-shaped heat transfer pipe and the safe operation of the reactor.