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Abstract: Control rod hydraulic drive mechanism (CRHDM) is a newly invented patent and Institute of Nuclear and New Energy Technology Tsinghua University owns CRHDM''s independent intellectual property rights. The Integrated valve which is made up of three direct action solenoid valves is the key part of this technology, so the performance of the solenoid valve directly affects the function of the integrated valve and the CRHDM. Based on the operation conditions of the Control Rod Hydraulic Drive System, the electromagnetic force of the direct action solenoid valve was analyzed by experiment and numerical method. The result shows that the electromagnetic force of the solenoid valve increases with the increasing current or the decreasing the length of the air gap. In addition, the electromagnetic force is saturated when the current goes up to the threshold, so the working input current should be the threshold. What is more, the electromagnetic force of the solenoid valve with the flat contact surface is larger than the one whose contact surface is cone. Finally, the operation time of the valve with the flat contact surface is shorter than the one with the cone contact surface on the condition that the length of the air gap is longer, but the result is opposite when the length of the air gap is shorter. In order to gain big electromagnetic force and short operation time, the structure of the solenoid valve is that the contact surface is flat with the seal ring. [Copyright &y& Elsevier]

Abstract: Control Rod Hydraulic Drive Mechanism (CRHDM) is a newly invented patent of the Institute of Nuclear and New Energy Technology Tsinghua University which owns CRHDM''s independent intellectual property rights while the integrated valve made up of three direct action solenoid valves is the key part of this mechanism. Therefore, the performance of the solenoid valve affects the integrated valve and the CRHDM directly. In this paper, we present a method to design the parameters of the direct action solenoid valve based on orthogonal experiment design, back propagation (BP) neural network and particle swarm optimization (PSO). The result proves that the method is feasible and accurate to design the parameters in order to obtain the biggest electromagnetic force. Besides, the result also shows that it is the current which influences the electromagnetic force of the direct action solenoid valve most. [Copyright &y& Elsevier]

Abstract: This paper discusses the behavior of the hydraulic control rod driving system (HCRDS) in cyclical swing. The first generation HCRDS with the hole–hole step cylinder, the important driving component, has been applied in 5MW nuclear heating reactor for several years and run well all along. The second generation with the chamfer-hole step cylinder has also been developed and studied. The HCRDS working principle, as well as the particular design of the hole–hole step cylinder, has been introduced in the paper. The control rod (CR) behavior when HCDRS vacillating in certain swing and cycle has been analyzed subsequently. The calculating result indicates that the CR can keep its balance in such unstable state and the operation of driving CR upwards or downwards can function properly likewise. In cyclical swing, the CR can drop down quickly and meet the reactor shut-down needs. The theoretical analysis proves the HCRDS reliable and safe, establishing basement for its further research and wide use. [Copyright &y& Elsevier]

• A new design of the capacitive control rods position indicator for SMRs is proposed in this paper. • The performance of the indicator is evaluated based on a theoretical model. • The maximum error of the indicator is ±0.05 mm. The position of control rods is one of the core parameters that can affect the power of nuclear reactors, and it is needed to be monitored by the position indicators. Based on the central shielding effect of the driving rod, the design of the coaxial capacitive position indicators is proposed in this paper. The theoretical rod position recognition model of the indicator is constructed by the conformal mapping, and it is verified by the numerical method. The results manifest that the performance of the indicator can be accurately analyzed by the theoretical model. The performance of the indicator is studied, and it is compared with that of the existing capacitive position indicator. The results show that compared with the existing design, the precision and the sensitivity of the new indicator can be enhanced by two orders of magnitude at the same time. [ABSTRACT FROM AUTHOR]

The control rod hydraulic driving system (CRHDS) is a new type of built-in control rod drive technology and the IV is the key control component. The working principle of integrated valve (IV) is analyzed and the IV hydraulic experiment is conducted. There is transient flow phenomenon in the valve opening process. The theoretical model of IV opening process is established by the loop system control equations and boundary conditions. The valve opening boundary condition equation is established based on the IV three dimensional flow field analysis results and the dynamic analysis of the valve core movement. The model calculation results are in good agreement with the experimental results. On this basis, the model is used to analyze the transient flow under high temperature condition. The peak pressure head is consistent with the one under room temperature and the pressure fluctuation period is longer than the one under room temperature. Furthermore, the changing rule of pressure transients with the fluid and loop structure parameters is analyzed. The peak pressure increases with the flow rate and the peak pressure decreases with the increase of the valve opening time. The pressure fluctuation period increases with the loop pipe length and the fluctuation amplitude remains largely unchanged under different equilibrium pressure conditions. The research results lay the base for the vibration reduction analysis of the CRHDS. [ABSTRACT FROM AUTHOR]

• A new bubble-layer-based mechanistic model for the boiling annular-mist flow is established. • The accuracy of this model is verified with experimental data and simulation results of void fraction and CHF with high accuracy. • The variations of two-phase flow parameters in the bubble layer region and the core region are described separately, and the dryout point can be predicted. Accurate prediction of the boiling annular-mist flow as well as the occurrence of the dryout is of particular importance for the safe operation of heat systems. Therefore, this paper focuses on the analysis of the boiling annular-mist flow and aims to propose a mechanistic model to describe this boiling process. Firstly, the physical model is established which divides the flow field into the bubble layer region and the core region in the radial direction. The bubble layer serves as a pseudo boundary for generating bubbles, whose thickness is adopted as the bubble departure diameter. In addition, the annular-mist flow is divided into the core region evaporation flow section and the bubble layer evaporation flow section in the axial direction, based on the relationship between the thickness of the bubble layer and the film thickness. Then, a set of two-dimensional steady-state conservation equations is proposed, which considers the energy, mass and momentum exchanges in both the bubble layer region and the core region. The accuracy of this model is verified with the experimental data and simulation results of void fraction and CHF. Based on this model, the variations of two-phase flow parameters in the bubble layer region and the core region can be obtained separately, such as the velocity, void fraction and pressure. The dryout point can be predicted based on the variation of the film thickness. These findings promote the fundamental understanding of the thermal–hydraulic characteristics of the annular-mist flow. [ABSTRACT FROM AUTHOR]

Absorber sphere pneumatic conveying is a special application of pneumatic conveying technique in the pebble bed High Temperature Gas-Cooled Reactor (HTGR or HTR). Granular discharge through a vertical pipe with a bend outlet is one of the control modes to determine solid mass flowrate which is an important parameter for the design of absorber sphere pneumatic conveying. Granular discharge rate through the vertical pipe with a bend outlet in the small absorber sphere system are investigated by discrete element method simulation. The effect of geometry parameters on discharge rate, the discharge rate fluctuation in the vertical pipe, and the effect of friction on steady discharge rate ( W s ) are analyzed and discussed. The phenomena of discharge rate fluctuation in the vertical pipe are observed, which are mainly resulted from the evolution of the average downward granular velocity. The steady discharge rate decreases rapidly with sliding friction coefficient increasing from 0.125 to 0.5, and gradually saturates with the friction coefficient further increasing from 0.5 to 1. It is interesting that the linear relation between W s 2/5 and pipe internal diameter D with zero intercept are found for the vertical pipe discharge with a bend outlet, which is different from the orifice discharge through a hopper or silo with none-zero intercept. A correlation similar to Beverloo’s correlation is developed to predict the steady discharge rate through the vertical pipe with a bend outlet. These results are helpful for the design of sphere discharge rate through the vertical pipe with a bend outlet in the small absorber sphere system of the pebble bed HTGR. [ABSTRACT FROM AUTHOR]

• The work concerns coarse particle conveying in the small absorber sphere system. • Present an overview of recent experiments and discrete element simulation at INET. • We present some CFD-DEM results of coarse particle conveying obtained so far. Pneumatic conveying of absorber spheres in the pebble-bed high-temperature gas-cooled reactor is a special application of pneumatic conveying technique in the nuclear engineering. It may be regarded as an intermittent circulation of absorber spheres between the side reflector boring and the storage bin in the reactor. The whole process consists of several sub-processes, e.g., the granular discharge from the sphere storage bin into the boring, granular discharge from the side reflector boring into the feeder, particle entrainment in the feeder, sphere conveying in the transport pipe, and gas-solid separation in the storage bin. We give a brief summary of the experimental and discrete element simulation work done recently at the Institute of Nuclear and New Energy Technology of Tsinghua University, mainly from the viewpoint of gas-solid flow and granular flow. CFD-DEM coupling simulation is recently conducted to investigate the coarse particle conveying in the small absorber sphere system. We present some CFD-DEM simulation results of coarse particle conveying in ambient air and high-pressure helium gas. Based on the needs of engineering practice and scientific research, some research requirements are suggested. Further work is still needed, to make a comprehensive understanding of the conveying process, and to optimize the design and operation of the conveying system. [ABSTRACT FROM AUTHOR]