Flow-characteristics Investigation On Core-assembly Abnormal Structure Of Sodium-cooled Fast Reactor

The core assembly is an important part of sodium-cooled fast reactor(SFR),and its flow characteristics have a decisive effect on the safety and economic operation of fast reactor.There are a number of abnormal structures in the core assembly.so it is difficult to investigate the flow characteristics of abnormal structures.On the one hand,the investigation mainly depends on the engineering experiments,but fails to summarize the geometrical parameters effect on the flow characteristics.On the other hand,many investigations focus on the numerical simulation based on computational fluid dynamics.Limited by the experiment data,the reliability of the numerical results has not been fully verified by experiments.Therefore,it is necessary to further investigate the flow characteristics of core-assembly abnormal structure.In this paper,based on the comprehensive hydraulic experiment system of SFR,the flow characteristics of various core-assembly abnormal structures are experimentally and numerically investigated,which provides a reference for structure designs and engineering applications.In the current investigation,the flow-characteristics hydraulic experiments are conducted for core assembly,entry tubes,uniformly wire-wrapped rod bundles,non-uniform wire-wrapped rod bundles,labyrinth seal and orifice throttle.Combined with numerical simulation,the geometrical parameters effects on the flow characteristics are investigated,such as pressure drop,resistance coefficient and flow velocity distribution.For entry tubes of core assembly,the selection scheme is defined under different application requirements.Furthermore,the recommended hole-diameter selection scheme of straight-through entry tube and alternative scheme of few-hole straight-through entry tube are formulated.The empirical correlations and empirical criterion equations of entry-tube resistance coefficient are obtained,which can be used to predict the entry-tube flow characteristics or model similar flow scenarios.For the multi-plate entry tube of fast reactor control assembly,the geometrical parameters,such as the location of the sodium hole,the length of the connecting rod and the spacing of the throttling plates,effects on the flow characteristics and the adjustment efficiency of the throttling plates under the non-uniform arrangement are evaluated,which provides the direction for the structure optimization.In this paper,the applicability of the resistance-coefficient empirical correlations of uniformly wire-wrapped rod bundles,non-uniformly wire-wrapped rod bundles and orifice throttle are evaluated.The CTS correlation can accurately predict the flow characteristics of uniformly wire-wrapped rod bundles,while the CTD correlation has irreplaceable advantages in predicting the flow characteristics of non-uniformly wire-wrapped rod bundles,which are the best empirical correlations recommended in this paper.It is necessary to modify the calculation parameters of BDD correlation,especially the wrapped wire effect on the flow characteristics of rod bundles.But the error of MBDD correlation is large.In this paper,the MBDD correlation with optimal wrapped-wire addition factor is proposed,which has the same calculation accuracy as CTS correlation,while the calculation process is simpler.Moreover,the Flow-resistance Handbook and R-G correlation have high calculation accuracy in predicting the flow characteristics and outflow coefficient of orifice throttle.By numerical simulation and stress evaluation,the open operation head with a sodium outlet hole of 30mm in diameter has the most superior performance,which is conducive to maintaining the pressure balance at the top of core assembly and has the engineering function of discharging residual gas.The non-rotating labyrinth seal with right-angle trapezoidal throttle tooth is designed and manufactured,and its flow characteristics are experimentally and numerically investigated.At the same time,the geometrical parameters effects on labyrinth-seal flow characteristics are evaluated.Increasing the throttle-tooth number,spacing and throttle-tooth thickness can improve the labyrinth-seal sealing performance,while increasing gap width is not conducive to the improvement of labyrinth-seal sealing performance.In addition,a leakage-coefficient empirical correlation of labyrinth seal is obtained,which can be used for the preliminary estimation of leakage flow rate in similar non-rotating seals.The main sealing mechanism of labyrinth seal is revealed,including throttling effect,jet,vortex and secondary transverse turbulence.