• Nuclear Engineering and Technology
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• v.55 no.8
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• pp.3088-3101
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• 2023

A pressurized vessel-pipe-safety valve (PVPSV) combination is a commonly used configuration in nuclear power plants, and a good numerical model is essential for the system design, sizing and performance optimization. However, owing to the large-scale and cross-scale features, it is still a challenge to build a system level numerical model with both high accuracy and efficiency. To overcome this, a novel system level modeling method which can synthesize the advantages of various models is proposed in this paper. For system modeling, the analytical approach, the method of characteristics (MOC) and the surrogate model approach are respectively adopted to predict the dynamics of the pressure vessel, the connecting pipe and the safety valve, and different models are connected through data interfaces. With this system model, dynamic simulations were carried out and both the stable and the unstable system responses were obtained. For the model verification purpose, the simulation results were compared with those obtained from experiments and full CFD simulations. A good agreement and a better efficiency were obtained, verifying the ability of the model and the feasibility of the modeling method proposed in this paper.

• Journal of Drive and Control
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• v.16 no.4
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• pp.93-100
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• 2019

Nuclear and thermal power plants must provide the turbines with an appropriate degree of high temperature and high pressure steam, to produce the optimum electricity. Additionally, in the event of system and power system failure during electrical production, the steam is immediately disabled, to protect the turbines and generators rotating at high speed. The plant thus uses a special steam control valve system for turbine control, which is opened by force of the hydraulic servo actuator and closed by a large steel spring force. In this study, the causes of failure of the turbine control valve system, a key device of the power plants, were analyzed, and the causes of failure were improved relative to reliability of the equipment.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1633-1638
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• 2003

In case that in-leakage through the valve disk occurs, a numerical study is performed to estimate on thermal stratification phenomenon in the Safety Injection piping connected with the Reactor Coolant System piping of Nuclear Power Plant. As the leakage flow rate increases, the temperature difference between top and bottom of horizontal piping has the inflection point. In the connection point of valve and piping, the maximum temperature difference between top and bottom was 185K and occurred in the condition of 10 times of standard leakage flow rate. In the connection point of elbow and horizontal piping, the maximum temperature difference was 145K and occurred in the condition of 15 times of standard leakage flow rate. In the vertical piping of Safety Injection piping, the near of connection point between elbow and vertical piping showed the outstanding thermal stratification phenomenon in comparison with another region because of turbulent penetration from Reactor Coolant System piping. In order to prevent damage of piping due to the thermal stratification when in-leakage through the valve disk occurs, the connection points between valve and piping, and the connection points between elbow and piping need to be inspected continually.

• Journal of Power System Engineering
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• v.11 no.3
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• pp.35-40
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• 2007

Leak would happen because of the damage of high temperature and high-pressure valve in nuclear power plant. condition based prevention maintenance is essential by using the suitable method based on local condition. Energy loss prevention can prevent from an accurate test, Local actually and ability. The methods of test for high energy fluid leak at present are analysis of ${\Delta}T$, AE(Acoustic Emission) analysis, and thermal image. The result for test of secondary system in nuclear power plant Unit reveals that the AE occurred clearly in leakage situation, but thermal image didn't occur. It is identified that leak is occurred when the orifice located front and back of valve operates. It shows that making a impatient judgment by using the single method if it is leakage is containing uncertainty. So we think that using the Multi-Measuring method is more sound judgment than single-measuring method.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.9
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• pp.1009-1015
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• 2012

Valves are one of the most important components of a pipeline system in a nuclear power plant, and it is important to ensure their structural safety under seismic loads. A crucial aspect of structural safety verification is the seismic qualification, and therefore, an optimal shape design and experimental seismic qualification is necessary in case the configuration of the valve parts needs to be modified and their performance needs to be improved. Recently, intensive numerical analyses have been performed before the experimental verification in order to determine the appropriate design variables that satisfy the performance requirements under seismic loads. In this study, static and dynamic numerical structural analyses of a 200A butterfly valve for a nuclear power plant were performed according to the KEPIC MFA. The result of static analysis considering an equivalent static load under SSE condition gave an applied stress of 135 MPa. In addition, the result of dynamic analysis gave an applied stress of 183 MPa, where the CQC method using response spectrums was taken into account. These values are under the allowable strength of the materials used for manufacturing the butterfly valve, and therefore, its structural safety satisfies the requirements of KEPIC MFA.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.568-573
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• 2003

When a safety valve equipped in a nuclear power plant opens in an instant by an accident, a moving shock wave propagates downstream the valve, inducing a complicated unsteady flow field. The moving shock wave may exert severe load to the structure. So, to reduce the load acting on the wall of POSRV, a gradual opening of POSRV is adopted in general. In theses connections, a numerical work is performed to investigate the effect of valve opening time on the unsteady flow fields downstream of the valve. Compressible, two-dimensional Navier-Stokes equations are used with the finite volume method. The obtained results show that sharp pressure rise through moving shock tor the case of instant opening is attenuated by employing the gradual opening of valve. It is turned that the flows for the two cases of gradual valve opening time show the similar to that of highly under-expanded one in jet structure having expansion and compression waves and Mach stem. Also, comparing with the results for the two cases of opening time, the shorter the valve opening is, the pressure gradient at the downstream of the valve becomes softly.

• 유체기계공업학회:학술대회논문집
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• 2004.12a
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• pp.315-320
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• 2004

Swing check valves are the most common type of check valve in nuclear power plant and need to be operated property to perform their functions and to keep the valve internals stable. However, for a swing check valve disc to remain stable, the opening characteristics should be identified and the upstream flow velocity should be enough to hold the disc fully open and without motion. Thus it is necessary to develop a model for predicting the flow velocity for a given disc opening. In the present study, the disc positions with mean flow velocity were measured for 3 inch and 6 inch swing check valves. Comparison of the measurements with the existing models showed that the models underestimate the mean flow velocity for a given disc position. Therefore, the existing model for predicting swing check valve disc position was improved with the realistic disc impingement area perpendicular to the flow stream and the experimental data. The result showed that the improved model with the best estimate of kb = 0.04 predicts well the disc openings of 6 inch swing check valve, especially in the low velocity region. For better prediction of the disc opening at high flow velocity, however, it is recommended to develop a kb correlation with the disc angle.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3512-3517
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• 2007

Nuclear power plant has many external fire hydrants that have to operate in the state of emergency such as facility fire, forest fire. The valve stem of one among them was broken 3 times for 4 years. It had long valve stem and operated under high water pressure. The elongation and the tensile strength for the broken valve stem was measured to examine the defect of material property. And the vibration level and the natural frequencies was detected to check the resonance. As the result of a diagnosis, the cause of this fault is proven buckling of long valve stem.

• Transactions of The Korea Fluid Power Systems Society
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• v.7 no.1
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• pp.20-27
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• 2010

Electromagnetic control valves have been used for almost 20 years. As the solenoid modulating technology advances, its applications are extending to various industrial fields such as nuclear and fossil fuel power plants, chemical plants and refineries. Proportional solenoid valve for large flow control is designed with two-stage configuration to meet the required actuating force on the main disc and its position is stabilized by the self-controlled system. In this research, main disc dynamics is analyzed with linearized system model which is derived from the mathematical equations describing its nonlinear behavior. Major design parameters of the valve control system that affect the response and stability are also studied with root locus method. The linear dynamic analysis results are verified with simulations in time-domain.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.284-289
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• 2004

The objective this study is to estimate the feasibility of acoustic emission method for the internal leak from the valves in nuclear power plants. From the experimental results, it was suggested that the acoustic emission method for monitoring of leak was feasible. When the background levels are higher than the acoustic signals from leak, we can detect the leak analyzing the spectrum of the remainders which take the background noise from the acoustic signals.