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Research on Transient Hydraulic Characteristics of Multiphase Flow of the Reactor Coolant Pump

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Tutor: YuanShouQi
School: Jiangsu University
Course: Fluid Machinery and Engineering
Keywords: The reactor coolant pump,Gas-vapor-liquid multiphase,Cavitation,Transition proce
CLC: TL353.12
Type: PhD thesis
Year:  2013
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Abstract:
The reactor coolant pump is one of the most critical nuclear-powered devices in the nuclear power plant. The functions of the reactor coolant pump are to drive the gas out of the system when water-filling, to circulated and heating the nuclear reactors before it starts work, to ensure that the primary coolant circuit work normally to cool the core of the reactor, and to prevent the nuclear accidents expanding under accident conditions. The reactor coolant pump¡¯s long-term stability, safe and reliable operation are of extremely importance to the coolant delivery, cool the reactor core, exhaust the heat and prevent the occurrence of nuclear accidents. The main tasks of this dissertation are to analyze the transient flow variation of gas-liquid two-phase mixture under a variety of accident conditions by numerical simulation, and use the five-hole probe, the pressure pulsation probe and vibration instrument for test validation. Some meaningful research and creative achievements are obtained and listed as follow:1. In order to ensure that the reactor coolant pump can work smoothly during variable flow conditions, adopting the test and numerical simulation during the transient operating conditions to study the dynamic characteristics of the complex impeller, which has different number of blades and guide vanes and different splitter inlet. The result shows that during the process of variable flow, when the blade number is five and the guide vane number is eleven, the radial force upon the impeller is the smallest. The pressure pulsation is the minimum under a variety of conditions, as the splitter blade inlet diameter is0.72D2.2. In the actual operation, for reactor coolant pump will encounter the flow transient problems, so the internal hydrodynamic characteristics in single-phase variable flow transition process was analysed firstly. Then the author conducted in-depth research of the gas-liquid two-phase transient flow law inside the reactor coolant pump, in the transition process of unchanged in flow rate and increase in gas content, gas content unchanged and flow increases, or the flow and gas content change together. The reactor coolant pump gas-liquid two-phase transient hydrodynamic flow characteristics under the different transient transition process are obtained.3. The hydrodynamic characteristics of three inertial rotation models was compared during the downtime transition process. It turn out that the hydrodynamic characteristics of the inertial rotation model with idler is the most stable one during the downtime idle process. Based on this, it continues to study deeply on the hydrodynamic characteristics of the single-phase and gas-liquid two-phase mixed conditions in the downtime transition process. From the study, the variation laws of tract pressure, speed, gas volume fraction, vorticity and radial force within the reactor coolant pump impeller are obtained during the downtime transition process.4. Considering the feature of invisible cavitation, which does greater harm to the reactor coolant pump impeller, the bubble phase flow variation law in the invisible cavitation transition process was elaborated, and found out that the exponential function variation law of the gas volume fraction with the pressure decreasing. The wavelet transform and Fourier transform methods are adopted to analyze the reactor coolant pump pressure pulsation in different stages of cavitation, and the characteristics of pressure pulsation in different cavitation stages was obtained. In the incipient cavitation conditions, the low frequency was predominantly factor in the fluctuation frequency of head of the reactor coolant pump,and the rotation frequency was predominantly factor in the main frequency of pressure fluctuation in impeller passages. The pressure fluctuation induced by the cavitation had little effects on the main frequency.In the developed cavitation condition,the pressure fluctuation induced by cavatation has come to matter much more to the dominant frequency, sub-main frequency and oscillation amplitude.The low and medium frequency were predominantly factors in the fluctuation frequency of head.In serious condition of cavitation,the pressure pulsations are composed of irregular high-frequency and regular the low and medium pressure pulsations.5. The relationship between the gas content and the cavitation was researched by CFD numerical simulation and experiment under the dehydration gas-liquid two-phase mixed conditions. The results showed that gas content on cavitation was very obvious impact. With the increase of gas content, cavitation area became smaller under the same conditions. The gas content impact on the cavitation fracture conditions was systematically analyzed under the conditions of gas-liquid two-phase. The result showed that gas content could delay the cavitation fracture conditions.6. Based on the fluid-structure coupling techniques to systematically study the relationship between the reactor coolant pump cavitation and the impellermaximum deformation, the variation laws of the impeller maximum deformation transient pulsation corresponding different cavitation stages and the impeller radial force imbalance variation law are obtained. The reactor coolant pump, with dynamical modal analysis and structural statics, was researched on the basis of considering the gas-liquid two-phase conditions. It was found that when the flow rate was unchanged, the gas content and the reactor coolant pump impeller maximum amount of deformation presented a linear variation, and when the gas content was unchanged with the flow rate increasing, the impeller maximum amount of deformation increased7. The comprehensive and systematic tests of static and transient internal flow field and the hydramic characteristics were conducted with the five-hole probe, the pressure pulsation probe, vibration instrument and the virtual instrument. It was also proved that the measured results were in accord with the calculated ones. The research results provide some reference for the reactor coolant pump or other gas-vapor-liquid multiphase pumps.
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