Research On Hydraulic Design And Transient Cavitation Characteristics Of CAP1400 Reactor Coolant Pump

The main circulating reactor coolant pump(namely the nuclear reactor coolant pump) is the only one rotating equipment in primary circuit of nuclear power plant, and is one of the most critical nuclear facilities. In loss of coolant accident conditions(LOCA conditions), cavitation phenomenon will occur in the impeller channels. It will increase the vibration of pump casing and system piping, and security risks in the primary circuit. When the head provided by the nuclear reactor coolant pump is too small, the heat in the reactor core cannot be taken away by the coolant and it may lead to departure from nucleate boiling by overheating of the reactor core, even let the fuel rods melted resulting in serious consequences. Nuclear reactor coolant pump reliable operation in the LOCA conditions is an important target of its performance assessment. Therefore, the research on cavitation issues of nuclear reactor coolant pump in LOCA conditions is very important.This paper takes the nuclear reactor coolant pump as the research object. In combination with cavitation characteristics in LOCA conditions and the existing hydraulic design method and theory of cavitation comparative, this paper gains a hydraulic model of nuclear reactor coolant pump which is suitable for the cavitation conditions. Numerical simulation and experiment of the transient hydrodynamic performance in cavitation conditions are researched in this paper. The main contents are as follows:1. The cavitation, control equations, turbulence model, cavitation model and other hydromechanics basic theory is introduced briefly. Layer constraint method is used for hydraulic design and structural design of nuclear reactor coolant pump based on velocity-coefficient method and the unequal head theories.2. In order to effectively control the bubble motion, the influence of constraint layer position on the hydraulic performance and the bubble is studied. The results showed that: layer constraints in the middle line of the blade can effectively control the nuclear reactor coolant pump hydraulic performance. The constraint layer near impeller shroud is relatively closer to streamline of the impeller channel, which can effectively block the development of the bubble in the impeller along the axial. Therefore, sacrificing part of the hydraulic performance, the layer constraints can get better cavitation performance at the same time.3. Impeller radial force of nuclear reactor coolant pump in transient cavitation process was borne by 12 petal distribution; Because of the interference between the impeller blades and vanes blade, leading to double peak characteristics existing in four directions at 90 ° intervals. Cavitation effect on axial force of impeller is bigger than radial force. The main reason is the movement and development of bubbles will affect the blade surface pressure distribution, thus influence the axial force change.4. By studying the total volume variation rule of vapor in impeller channels in transient cavitation process, found that the vapor volume fraction presents transient stability in the critical cavitation condition, then the vapor volume fraction increased dramatically; Because of the uneven distribution of pressure in the critical cavitation condition, distribution of bubble in each impeller channel is nonlinear. As the cavitation degree deepening, the distribution regularity of flow passage is converged. For the blade designed by layer constraint method, the bubble mainly concentrated in the back side of blade near the hub.5. The model pump of the nuclear reactor coolant pump has the advantages of high efficiency, wide high efficient area, and its flow- power curve has obvious no overload characteristics. The minimal vibration in the middle section of pump casing, and the vibration will increases after departing from the middle section; Pump casing vibration near the volute tongue is particularly evident in the low frequency range. Comparison of amplitude change at each monitoring point in different flow rate can be found that minimum vibration in the design point. In contrast, vibration under big flow rate conditions is greater than the small flow rate conditions, each monitoring point vibration changes correspondingly with the change of the flow rate.6. The change of trends of pressure in each monitoring point and flow- head curve is consistent as decrease of the flow rate. When the model pump runs at design conditions, the pressure pulsation of each monitoring point is still in the weak level. Pressure pulsation amplitude will increase when internal flow condition has deteriorated after deviating from the design conditions.