Research On Thermal-Hydraulic Characteristics Of The Steam Generator Based On The Drift-Flux Theory

U-tube steam generator is most widely used in second-generation nuclear power plantsas a heat exchanger for connecting the nuclear island and conventional island. Because of theimportance of work status, the complex structural properties, flow and heat transfercharacteristics and a high accident rate, the steam generator has become the focus of domesticand foreign scholars. The key problems have become clear that one is the exact two-phasemodel choice in the section of the steam generator secondary side of the boiling; the other ischange of steam generator water level in the whole system with the disturbance response withfurther research.In this paper, with reference to the actual operating parameters of the steam generator,the more accurate theoretical model of the drift-flux has been used in the section of two-phaseflow boiling in a secondary; the non-linear models of the steam generator water level and themodel of the height of preheating segment have been added in the general mathematicalmodel of the steam generator, which to improve the steam generator system the model. At100%,70%,50%and30%load, the error scope between the main parameters of the steamgenerator calculated by simulation and the actual value of the steam generator is3%to4%,which verifies the accuracy of the simulation model.For the two-phase flow part, the distribution parameterC0, which is the signatureparameter of the drift-flux theory; the two-phase multiplierΦ₁₀², which is the key parameter ofthe two-phase frictional pressure drop; the slip ratio S, with the respective experimental errorof3.6%,6.8%and12.9%, which verifies the drift-flux theory can predict and reflect the flowand heat transfer characteristics of two-phase flow in the steam generator.On the basis of calculation in steady state, the dynamic simulation for4kinds ofconditions has been analysised with step by5%increase in water flow and10%descend inwater temperature. The simulation results show that, with the added the disturbance of steamgenerator parameters （pressure, steam production, quality of gas, water and height of preheat,etc） show a reasonable change trend, and accurate simulate the "false water level"phenomenon. Meanwhile, the higher the load, the water level rises or falls of the first endwith rapidly changing, and the transition process of the level with the load increased graduallyshorten its duration, the magnitude of change in water level also decreases with the increaseof the load. That is, as the load increases, the response speed and degree of the water level ofdisturbance is greater.Two typical nuclear accidents, the primary coolant leak and steam outlet piping breach, have been simulated here by using simulation model. Then do the research on the change ofthe pressure, the quality of gas rate and a side exit temperature and water level and otherparameters and the influence of the steam generator due to these two accidents.In summary, the drift-flux theory applied in the boiling section of the steam generatorand the non-linear model of water level and the height model of the preheating section addedin the overall model perfected the steam generator thermal-hydraulic model. These couldprovide a theoretical support for the study of the steam generator operating characteristics inthe future.