• Journal of the Korean Vacuum Society
• /
• v.15 no.5
• /
• pp.465-474
• /
• 2006

A gas fueling system composed of a gas reservoir, an on-off valve, and a gas transferring tube, which is the simplest construction for the pre-programmed gas puffing, was simulated by numerically solving the time-dependent one-dimensional gas flow equation. The purpose of the simulation is to establish the relationship between the gas flow pattern (the elapsed time to the maximum flow, the maximum flow rate, the gas pulse duration) and the system parameters (the filling pressure and the volume of the gas reservoir, and the length and the diameter of the gas transferring tube).

• Plant Journal
• /
• v.9 no.2
• /
• pp.36-41
• /
• 2013

For areas installed with one pump, the trend for expected sizes of pump room areas is observed once pump power and floor dimensions are provided. However, these pump rooms with auxiliary charging pumps, turbine driven auxiliary feedwater pumps, and pump rooms with a separate valve room have unique ways to determine the pump room area. No definite trends are identified for areas installed with two pumps using pump power and floor dimensions. The relationship between pump power and floor dimensions is also unable to be found.

• Journal of the Korean Society of Visualization
• /
• v.15 no.1
• /
• pp.11-18
• /
• 2017

A two-phase flow observed in a heat exchanger or nuclear power generation often has a profound effect on undesirable noise or flow characteristics. Void fraction, which refers to the ratio of gas (or liquid) to the total fluid, affects heat transfer coefficient, vibration and so forth. In other words, void fraction is one of most important parameters in two-phase flow since it contributes to comprehend the characteristics of two-phase flow. We developed a two-phase flow visualization system to measure cross-sectional and volumetric void fractions by using quick closing valves and image processing software. With this system, we could observe the plug, slug, and stratified flow patterns of two-phase flow and measure a myriad of void fractions. As a consequence of the experiment, we found that the estimated void fractions were largely coincident with the predictive values by Chisholm model.

• Proceedings of the KSME Conference
• /
• 2002.08a
• /
• pp.835-838
• /
• 2002

An experiment has been performed using a facility, which simulates the safety depressurization system (SDS) and in-containment refueling water storage tank (IRWST) of APR1400, an advanced PWR being developed in Korea, to investigate the dynamic load resulting from the blowdown of steam from a steam generator through a sparser. The influence of the key parameters, such as air mass, steam pressure, submergence, valve opening time, and pool temperature, on frequency and peak toads was investigated. The blowdown phenomenon was analyzed to find out the real cause of the initiation of bubble oscillation and discrepancy in frequencies between the experiment and calculation by conventional equation for bubble oscillation. The cause of significant damping was discussed and is presumed to be the highly tortuous flow path around bubble. The Rayleigh-Plesset equation, which is modified by introducing method of image, reasonably reproduces the bubble oscillation in a confined tank. Right after the completion of air discharge the steam discharge immediately follows and it condenses abruptly to provide low-pressure pocket. It may contribute to the negative maximum being greater than positive maximum. The subsequently discharging steam does not play as at the driving force anymore.

• Proceedings of the KIEE Conference
• /
• 2002.11c
• /
• pp.337-341
• /
• 2002

본 논문은 원자력 발전소의 안전에 있어 매우 큰 비중을 차지하는 모터 구동밸브(Motor-operated valve : MOV)의 성능진단에 직접 센서를 장착하지 않고 전기신호만을 이용하여 성능진단의 가능성을 보이기 위한 것이다. 모터 토크를 계산하기 위한 두 가지 방법으로서 D-Q frame 변환 방법과 Air-Gap 토크 식을 제시하였고, 계산된 두 토크 값은 정확하게 일치하였다. 부하를 변동하면서 토크미터로 측정된 토크 갑과는 1%의 오차범위 내에서 일치함을 확인했다. 따라서 두 토크 식은 모터구동 밸브의 성능진단을 위한 식으로 사용해도 좋다는 결론을 얻어낼 수 있었다. 계산된 토크를 주파수 분석함으로서 부하의 변동에 따라서 슬립 및 모터속도 주파수가 변화됨을 알 수 있었다. 즉 주파수 분석을 통해 MOV의 모터 및 구동기 부분의 성능 저하 감시에 유용한 단서를 제공해 줄 것이다. 결과적으로, MOV에서 전기신호의 분석은 시스템의 전기 및 기계적인 성능 저하 감시에 이용될 수 있을 것으로 기대된다.

• Transactions of the Korean Society of Pressure Vessels and Piping
• /
• v.11 no.1
• /
• pp.74-78
• /
• 2015

Nuclear power plant steam generator that is one of the main component has several thousands of thin tubes. And the steam generator tube is subject to damage because of the severe operation conditions such as the high temperature and pressure. Therefore periodic inspections are conducted to ensure the integrity of steam generator component. Hanul unit 3 also has been inspected in accordance with in-service inspection program and is scheduled to be replaced for exceeding the plugging rate which was recommended by manufacturer. During the steam generator replacement activity, we found several clustered porosity on inner surface of main feed water pipe. Additionally crack-like indications were found at weld interface between base material and weld of main feed water pipe. This paper describes the field experience and visual testing results for inner surface of main feed water pipes. The destructive test result had shown that these indications were porosities which were caused by manufacturing process not by operation service.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.15 no.3
• /
• pp.239-245
• /
• 2003

In the nuclear power plant, emergency core coolant system (ECCS) is furnished at reactor coolant system (RCS) in order to cool down high temperature water in case of emergency. However, in this coolant system, thermal stratification phenomenon can occur due to coolant leaking in the check valve. The thermal stratification produces excessive thermal stresses at the pipe wall so as to yield thermal fatigue crack (TFC) accident. In the present study, effects of turbulence penetration on the thermal stratification into T-branches with square cross-section in the modeled ECCS are analysed numerically. $textsc{k}$-$\varepsilon$ model is employed to calculate the Reynolds stresses in momentum equations. Results show that the length and strength of thermal stratification are primarily affected by the leak flow rate of coolant and the Reynolds number of the main flow in the duct. Turbulence penetration into the T-branch of ECCS shows two counteracting effects on the thermal stratification. Heat transport by turbulence penetration from the main duct to leaking flow region may enhance thermal stratification while the turbulent diffusion may weaken it.

• Nuclear Engineering and Technology
• /
• v.27 no.5
• /
• pp.645-660
• /
• 1995

The loss of Residual Heat Removal System (RHRS) event during reduced inventory operation for the Korean Standard Nuclear Power Plants (KSNPPS) is simulated by RELAP5/MOD3 and RELAP5/MOD3.1 Tn cases are considered : Base case for an intact Reactor Coolant System (RCS) with no tent and a vent case for an open system. Comparative simulations of base case are peformed by RELAP5/MOD3 and RELAP5/MOD3. 1 computer codes. The results of too simulations are generally in good qualitative and quantitative agreement. However, since the results of RELAP5/MOD3 simulation reveals the deficiency of RELAP5/MOD3 wall heat model, the RELAP5/AOD3.1 computer code is used for the simulation of the vent case. The analysis result of base case show that two steam generators are insufficient to remove decay heat at one day after shutdown, where the RCS is closed. The RCS pressure increased continuously and reached the RCS temporary boundaries design pressure of 0.24 MPa around 4,000 seconds. In the vent case with a flow capacity equivalent to three times the capacity of Pressurizer Safety Valve (PSV), it is shown that the RCS Pressure does not reach 0.24 MPa and core uncovery does not occur until 10,000 seconds. The detailed discussions on the results of this study suggest the feasibility of RELAP5/AOD3.1 as an analysis tool for the simulation of the loss of RHRS event at reduced inventory operation. The results of this study also provide insight for the determination of proper vent capacity.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.40 no.6
• /
• pp.397-402
• /
• 2016

To produce adequate electricity in nuclear and thermal power plants, an optimal amount of steam should be supplied to a generator connected to high- and low-pressure steam turbines. A turbine output control device, which is a special steam valve employed to supply or interrupt the steam to the turbine, is operated using a hydraulic servo actuator. In power plants, the performance of servo actuators is degraded by the air generated from the hydraulic system, or causes frequent failures owing to an increase in the wear of the seal. This is due to the seal being burnt as generated heat using the produced compressed air. Some power plants have exhausted air using a fixed orifice, and thus they encounter power loss due to mass flow exhaust. Failures are generated in hydraulic pumps, electric motors, and valves, which are frequently operated. In this study, we perform modeling and analysis of the load-sensing air-exhaust valves, which can be passed through very fine flow under normal use conditions, and exhaust mass flow air at the beginning stage as with existing fixed orifices. Then, we propose a method to prevent failures due to the compressed air, and to ensure the control accuracy of hydraulic servo actuators.

• The Korean Journal of Nuclear Medicine Technology
• /
• v.23 no.1
• /
• pp.75-79
• /
• 2019

Purpose Cadmium-zinc-telluride (CZT) camera with semiconductor detector is capable of dynamic myocardial perfusion SPECT for coronary flow reserve (CFR). Image acquisition with the heart positioned within 2 cm in the center of the quality field of view (QFOV) is recommended because the CZT detector based on focused multi-pinhole collimators and is stationary gantry without rotation. The aim of this study was to investigate the optimal method for measuring position of the heart within the center of the QFOV when performing dynamic myocardial perfusion SPECT with the Discovery NM 530c camera. Materials and Methods From June to September 2018, 45 patients were subject to dynamic myocardial perfusion SPECT with D530c. For accurate heart positioning, the patient's heart was scanned with a mobile ultrasound and marked at the top of the probe where the mitral valve (MV) was visible in the parasternal long-axis view (PLAX). And, the marked point on the patient's body matched with the reference point indicated CZT detector in dynamic stress. The heart was positioned to be in the center of the QFOV in rest. The coordinates of dynamic stress and rest were compared statistically. Results The coordinates of the dynamic stress using mobile ultrasound and those taken of the rest were recorded for comparative analysis with regard to the position of the couch and analyzed. There were no statistically significant differences in the coordinates of Table in & out, Table up & down, and Detector in & out (P > 0.05). The difference in distance between the 2 groups was measured at $0.25{\pm}1.00$, $0.24{\pm}0.96$ and $0.25{\pm}0.82cm$ respectively, with no difference greater than 2 cm in all categories. Conclusion The position of the heart taken using mobile ultrasound did not differ significantly from that of the center of the QFOV. Therefore, The use of mobile ultrasound in dynamic stress will help to select the correct position of the heart, which will be effective in clinical diagnosis by minimizing the image quality improvement and the patient's exposure to radiation.