A study on the stem friction coefficient behavior of motor-operated valves

This paper describes how to calculate the stem friction coefficient of safety related motor operated valves (MOVs) that reflects potential degradation with time by using diagnostic signals acquired in static field tests that have been conducted more than two times per valve. Based on the calculated stem friction coefficients, their behaviors with time were analyzed considering various parameters that could cause potential degradation. Most friction coefficients change randomly rather than increasing or decreasing continuously over time. From those trends, a threshold coefficient, which represents the highest expected value of the friction coefficient, was calculated and provided.     

A study on the phenomenon of rate of loading in motor operated gate valves

This study analyzed the rate of loading (ROL) phenomenon, which is generated during the operation of a motor operated valve (MOV) under fluid pressure conditions. ROL is one of the most important parameters for an MOV performance evaluation. This paper includes the analysis results for the characteristics of ROL and the effect of fluid pressure on the ROL. Dynamic and static test were performed to analyze the ROL effect for flexible wedge gate valve. The result of this analysis confirmed that the ROL is generated under fluid pressure condition and that the ROL value under high differential pressure condition appeared to be higher than under low differential pressure condition. According to the test results of multiple valves, the ROL appeared to become higher, as the differential pressure increased, and under the high differential pressure condition, it accounted for approximately 17.6% of the thrust loss. In addition, the ROL effect was negligible in valves with a low differential pressure (below 1100 kPa).     

A study on the actuator efficiency behavior of safety-related motor operated gate and globe valves

Periodically, the operability of the safety-related motor-operated valves (MOVs) in nuclear power plants must be verified. Because the actuator efficiency is one of the most important factors in the determination of the actuator output, it should be considered in ensuring the operability of MOVs during the verification duration. In particular, special consideration should be paid to its potential degradation, but the design efficiency provided by manufacturers is usually used because the actuator efficiency calculation is difficult and requires considerable time and effort. In this paper, a method is introduced to calculate actuator efficiency by using diagnostic signals acquired in field tests. The actuator efficiency was calculated from the estimated motor torque, the stem thrust measured in field tests, and overall gear ratio provided by manufactures. The motor torque was estimated by using an algorithm, which can calculate electric torque from the three phases of currents and voltages, resistances between phases acquired in field tests. The validation of the design efficiencies was evaluated by comparing those efficiencies with the calculated actuator efficiencies. And, the age-related degradation was analyzed through the behavior analysis over time of the calculated actuator efficiencies. Most of the actuator efficiencies were found not to be degraded over time and kept efficiency greater than the design efficiency. However, two actuator efficiencies with lower motor speed, overall gear ratio, and maximum motor torque rating are susceptible to be lower than the design efficiencies. For the two actuators, threshold efficiencies were calculated and provided to replace their design efficiencies.     

Analysis of the effect of lubrication performance on motor operated valve actuator output thrust

In this study, we performed theoretical analysis and test to identify an effect that lubricant performance has on actuator output thrust of MOV. Particularly, we introduced Stem Friction Coefficient (SFC) concept that means friction coefficient between a stem nut and a stem screw. By using SFC concept, an effect of lubricant performance on the actuator output thrust was analyzed quantitatively. The first phase test was performed to compare the lubrication performance between new lubricant and old lubricant and the second phase test was performed to compare the lubrication performance for the three kinds of representative lubricants (EP0, EP1, EP2) being used in Korea nuclear power plants. According to the test results, SFC value of old lubricant appeared higher than that of new lubricant and a old lubricant at TST point generated lower thrust value than a new lubricant at the same torque value. We can verify that the effect of lubrication performance has on power generated in an actuator was very large and SFC was a very useful variable in analyzing lubrication performance quantitatively.     

浮栅ROM器件γ辐射效应实验研究

给出了浮栅ROM器件的γ辐照效应实验结果。器件出现错误有个累积剂量阈值，当累积剂量小于某一值时，无数据错误。当累积剂量达到一定值时，开始出现数据错误。随着累积剂量的增加，错误数增加，动态监测和静态加电的器件都出现数据错误，且不能用编程器重新写入数据。然而不加电的器件在更高的累积剂量辐射下未出现错误，而且可以用编程器重新写入数据。     

Analytical prediction of turbulent friction factor for a rod bundle

An analytical calculation has been performed to predict the turbulent friction factor in a rod bundle. For each subchannel constituting a rod bundle, the geometry parameters are analytically derived by integrating the law of the wall over each subchannel with the consideration of a local shear stress distribution. The correlation equations for a local shear stress distribution are supplied from a numerical simulation for each subchannel. The explicit effect of a subchannel shape on the geometry parameter and the friction factor is reported. The friction factor of a corner subchannel converges to a constant value, while the friction factor of a central subchannel steadily increases with a rod distance ratio. The analysis for a rod bundle shows that the friction factor of a rod bundle is largely affected by the characteristics of each subchannel constituting a rod bundle. The present analytic calculations well predict the experimental results from the literature with rod bundles in circular, hexagonal, and square channels.     

Simulation study of BGO array for characteristic gamma rays from neutron-stimulated elements

Characteristic gamma rays of 100 keV to about 6 MeV from different elements stimulated by neutrons have been applied to diagnosis biological imaging.In this paper,BGO detectors are used for the spectrum simulation. Signals from a single crystal and after correction are both obtained,and the energy spectrum summing adjacent signals seems possible to achieve excellent energy resolution for such high-energy photons.Some ideal suppositions are in- troduced and some other information,such as spatial resolution and difficult electronics,should be considered after this correction.     

α石英E′心断代零点研究

根据野外地质观察以及扫描电子显微镜和阴极发光分析结果,总结出α石英E′心断代零点的四种基本情况。叙述了每种情况下α石英的相应特征并对ESR采样方法和累积剂量的确定方法提出了建议。     

An experimental study and assessment of existing friction factor correlations for wire-wrapped fuel assemblies

The main objective of the present study is to perform a comparative study of five existing correlations that have been selected and identify the best performing correlations in the subchannel pressure drop analysis of a wire-wrapped fuel assembly by means of directly comparing with experimental data obtained in the present work. For this purpose, a series of water experiments have been performed using a helical wire-wrapped 19-pin fuel assembly for various combinations of test parameters. Four different test sections that have different pitch to rod diameter ratios (P/D) and wire lead length to rod diameter ratios (H/D) have been fabricated. A series of pressure drop measurements were made to obtain friction factors for these four test sections. A total of 293 data were obtained and the present along with existing data are used in the present comparative study of existing correlations. The results of this study show that both the original and the simplified Cheng and Todreas correlations give the best agreement with experimental data for all flow regions.     

Development of a new bubbly-slug interfacial friction model for RELAP5

The development of a new bubbly-slug interfacial friction model for the Pressurized Water Reactor (PWR) safety code RELAP5 is described. The model is based on a set of best-estimate void fraction correlations which cover the full range of geometries and flow conditions encountered in PWR safety analysis. By exploiting the relationship between void fraction and interfacial friction that exists for steady, fully developed flow conditions, the correlations are converted into effective interfacial friction coefficients that can be applied in the code for transient as well as steady-state conditions. Assessments against separate effects tests indicate that the new model is more accurate than the existing model in many situations, particularly rod bundle geometries, and should never be significantly less accurate. The model has been implemented in a local version of RELAP5/MOD2 and in a pre-release version of RELAP5/MOD3 at Idaho National Engineering Laboratory (INEL).     

An experimental study on evaporative heat transfer coefficient and applications for passive cooling of AP600 steel containment

After TMI and Chernobyl accidents, many efforts have been made to enhance the nuclear safety with passive features. Among such passive features, the passive containment cooling system (PCCS) has been suggested by Westinghouse in the AP600 plant. The containment with PCCS is a dual containment, and consists of a stainless steel vessel and a concrete wall. In the gap between these structures, air and water can counter-currently pass and cool the steel surface. This paper experimentally investigates evaporative heat and mass transfer at the surface of a falling water film with counter-current air flow in a vertical duct with one-side heated plate. Experiments included various conditions of mass flow rate of film and air. Experimental results show the strong effects of water temperature and air mass flow rate, but little effect of the water flow rate. Also, simple analyses based on heat and mass transfer analogy were performed to evaluate the experimental results. With experimental data, a new correlation on evaporative mass transfer coefficient was developed, and with the correlation, the containment pressure and temperature was calculated for the design basis accident of AP600 by the use of CONTEMPT4/MOD5 code implementation.     

月表岩石诱发γ辐射场原始谱特征模拟

玄武岩、克里普岩、橄榄岩在月球表面广泛分布,并具有一定的代表性,并且岩石密度差异较大,高能粒子(Galactic Cosmic Rays,GCR;Solar Particle Event,SPE)与岩石相互作用后激发γ射线。利用蒙特卡罗软件FLUKA开展了月表高能质子诱发γ射线的研究,获取了月表多种成岩主元素的特征γ射线能量峰、正电子湮灭峰和γ辐射平衡峰等原始谱特征信息。通过数据分析表明特征峰强度与月表岩石密度呈正相关。原始谱特征的研究不仅可以为不同系列绕月γ数据的对比研究提供参考,也可为在全月表面进行基于核辐射方法的岩石密度填图研究提供理论支撑。     

An analytical study of the dynamics and stability of a spring loaded safety valve

Spring loaded self-actuating safety valves are employed as part of the overpressure protection systems in various industrial applications. In order to design and predict their performance it is necessary to study the dynamic behavior of the valve over a range of fluid and system conditions. A one-dimensional model has been developed to study the effects of different valve parameters such as the spring-mass characteristics, geometry of internal parts, adjustment ring settings, bellows etc. which influence the dynamic behavior and stability of the valve. Analytical results for steam flow conditions are presented to demonstrate the relative effects of these parameters on the valve opening time, maximum lift, blowdown (upstream pressure differential between the valve opening and closing) and any oscillations of the valve stem. If the valve is not properly backpressure compensated, it may become unstable as the stagnation pressure at the valve inlet decreases. Lowering of the guide adjustment ring position or raising the nozzle adjustment ring generally results in improved stability, shorter valve opening time, higher lift and longer blowdown. The effect of damping on the valve stability is also demonstrated. The model can be used to evaluate the design of safety valves and damping devices to eliminate unstable valve dynamic behavior.     

Combination of modal responses: A closed-form formulation for rigid response coefficient

Recent studies conducted by US Nuclear Regulatory Commission (USNRC) for combining modal responses in a response spectrum method of seismic analysis and design have emphasized that each modal response quantity should be separated into damped-periodic and rigid parts before combining the contributions from different modes. The damped-periodic parts of modal responses are combined using the double-sum equation whereas the rigid parts are combined algebraically. A particular modal response quantity is separated into damped-periodic and rigid parts using the “rigid response coefficient”. The USNRC sponsored study recommends the calculation of rigid response coefficient by either the Lindley–Yow approach or Gupta method. While Lindley–Yow's method has a heuristic basis and gives incorrect results in low frequency region, Gupta's method is based on numerical studies of free-field earthquake motions and works well in the frequency regions of interest for a free-field ground motion. A closed-form solution was developed by Hahn and Valenti in 1997 using a frequency domain approach. With appropriate simplifications, their work can be shown to result in an expression which is very similar to that given by Gupta. It must be noted that the earthquake input to the secondary systems such as piping and equipment is defined by a floor motion and not a free-field ground motion. The frequency characteristics of a floor motion are very different from those of a free-field ground motion. In this paper, we study the validity of existing formulations for the case of floor motions and develop a closed-form solution based on a time domain approach to explain the behavior of rigid response coefficient. The formulation is then used to explain the nature of variation in rigid response coefficient for ground as well as floor motions. It is shown that the proposed formulation and its simplified form gives results that are identical to those evaluated numerically in the complete frequency region of interest.     

栅氧化方式对注FMOSFET电离辐射效应的影响

对氢氧合成和干氧栅氧化后注Ｆ的Ｐ沟ＭＯＳＦＥＥＴ和Ｎ沟ＭＯＳＦＥＴ进行了γ射线辐照试验，比较了两种栅介质注Ｆ的电离辐射响应特性。研究表明，氢氧合成栅氧化后注Ｆ的ＭＯＳＦＥＴ具有较强的抑制辐射感生氧化物电荷和界面态生长的能力。用一个新的模型对实验结果进行了讨论，该新模型中用Ｓｉ－Ｆ结键替代其它在辐射场中易成为电荷陷阱的应力键，并考虑到不同氧化方式导致栅介质本身具有的电子陷阱数、空穴迁移率和氧化时所引     

Design of a MGy radiation tolerant resolver-to-digital convertor IC for remotely operated maintenance in harsh environments

During future ITER maintenance operations, sensors and their embarked electronics will be exposed to a hostile and radioactive environment. This paper presents the design of a MGy radiation tolerant 16 bit resolver-to-digital converter (RDC) in 130 nm CMOS technology. The RDC features a Type II digital tracking loop, able to track resolvers with speeds up to 300 rps, and excitation frequencies up to 4 kHz. The RDC uses two integrated ΔΣ-analog-to-digital converters (ADCs) to digitize the resolver outputs. The 16 bit, 10 kHz ADCs utilize a correlated double sampling technique to remove radiation induced offset and 1/f-noise. The front-end features a static angular resolution of 16 bits (4.2 arcsec_rms) and a resolution of 10 bits (6 arcmin_rms) at a rotor speed of 100 rps. The circuit has a simulated radiation tolerance exceeding 1 MGy. It has the ability to operate under temperatures up to 125 °C, and to allow multiplexing with signals from other conventional sensors for compact, robust read-out architectures.     

Experimental study and numerical analysis on electromagnetic force of direct action solenoid valve

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.     

A novel flexible plasma array for large-area uniform treatment of an irregular surface

In this work, we demonstrate a flexible multi-pin plasma generator with movable electrodes, which can change the shape of the electrode array freely, and then provide a large-area uniform plasma for the treatment of surfaces of different shapes. Discharge characteristics includingU–Iwaveforms and discharge images and sterilization performance under three different electrode configurations (flat–flat, flat–curve, curve–curve) are investigated. Very similar results are acquired between the flat–flat configuration and the curve–curve configuration, which is much better than that under flat–curve configuration. This flexible multi-pin plasma generator offers a simple method to treat different irregularly shaped surfaces uniformly with a single device. Moreover, this device provides a foundation for developing a self-adaption large-scale uniform plasma generator by further introducing automatic adjustment of the position of every electrode driven by motors with discharge current feedback in the following study. Thus it will promote the applications of atmospheric-pressure cold plasmas significantly     

Development of a swing check valve model for a low velocity pipe flow prediction

A swing check valve is commonly used to prevent a reverse flow in the pipe lines of a nuclear power plant. The flow resistance by the swing check valve varies with the location of the swing disk in the velocity range lower than the required minimum velocity for a full opening of the swing disk, thereby the fluid flow is significantly affected by the dynamic motion of the swing disk. Such a phenomenon is very important to analyze safety issues, one of which is the gravity feed following a loss of the residual heat removal (RHR) which occurs during a mid-loop operation. This paper focused on the development of a new check valve model to enhance the capability of the thermal-hydraulic system code. A new angular momentum equation for the disk of a swing check valve is proposed. The proposed model is implemented into the MARS code and verified through a comparison of the simulation results with the experimental data. In particular, the results of the simulation for the gravity feed line are comparably consistent with the real test data performed in a nuclear power plant.