| The fuel rod is widely encountered in PWR(Pressurized Water Reactor),BWR(Boiling Water Reactor)and SCWR(Supercritical Water Cooled Reactor).Different from the land-based nuclear reactor,a nuclear propulsion ship sailing on the ocean is rocked by waves and currents,among which the rolling process of a ship shows significant effect on thermal-hydraulic behaviors of fluid and the operational characteristic of power plants.The investigations on flow resistance in 3×3 rod bundles under rolling condition have been carried out by experimental study,numerical simulation as well as theoretical analysis.The experimental loop was open loop and forced circulation.The experiments were conducted under ambient temperature and pressure,and water and air were used as the test fluids.The liquid Reynolds number and gas Reynolds number ranges were 1563~19590 and8~2166,respectively,and the rolling period and rolling amplitude were 8s~16s and 5°~15°,respectively.The experimental study on single-phase flow resistance was carried out.The flow rate fluctuates periodically or not under forced circulation condition has been investigated.Effects of rolling parameters,valve openings of bypass valve and inlet valve of test section on flow rate fluctuation were studied.On this basis,the influences of liquid flow velocity,rolling parameters and channel size on frictional pressure drop as well as local pressure drop were concerned.The calculated correlation for single-phase transient frictional resistance in rod bundle in rolling motion was developed by considering above factors.In addition,the mechanism that rolling motion affects fircitional resistance was explored with the help of FLUENT software.The void fraction and gas rising velocity were obtained under stagnant water condition based on pressure drop method.Evaluation of existing correlation on void fraction under vertical condition was conducted.The effects of inlet pressure,valve opening,rolling amplitude and rolling period on fluctuated characteristics of gas flow rate were studied.Time-averaged and transient void fraction and gas rising velocity in rolling motion were focused on.The transient correlations for calculating void fraction and gas rising velocity were established in stagnant water under rolling condition by considering the effects of gasflow rate,rolling parameters as well as test section dimensions on flow parameters.Based on vertical two-phase flow resistance experimental data,evaluations on homogeneous flow modle as well as separated flow model were carried out.The fluctuated characteristics of gas and liquid flow rate under rolling condition were investigated.The influences of rolling motion on two-phase time-averaged frictional and local pressure drop could be neglected.The two-phase flow resistance characteristics were largely depended on air-water two-phase flow rate,rolling parameters and test section dimensions.A calculated method for two-phase flow resistance in rolling motion was achieved by using dimensional analysis,which solved the calculated problem for two-phase transient resistance in dynamic rod bundle.A force modeling of volumetric force acted on bubble was setted up systematically under rolling condition.The volumetric force was discussed along the direction of perpendicular to flow and that of parallel to flow,respectively.The comparision of local parameter distributions under inclined and rolling condition was achieved,indicating the effect of additional volumetric force induced by rolling motion.The change rules of transient gas rising velocity under different rolling condition were studied,which could explain the fluctuated characteristics of two-phase frictional resistance.The rolling motion influences frictional resistance by changing slip ratio and interaction of the two phases. |
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