• Nuclear Engineering and Technology
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• 제53권12호
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• pp.4003-4013
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• 2021

During the long-term cooling (LTC) phase of a loss-of-coolant accident (LOCA) in a pressurized water reactor (PWR), water is supplied from the containment sump to the reactor coolant system (RCS) by the flooded sump water to the Reactor Vessel (RV) through the broken pipes. As part of the technical efforts for resolving GSI-191 [( Reid and Crytzer, May. 2007) 1, consideration is needed for the consequences of debris penetrating the sump screen and propagating downstream into the RV. Injection of debris (fiberglass) into the RV during the LTC recirculation phase needs special attention to assure that reactor core cooling is maintained. The point of concern is the potential for debris to adversely affect the reactor core flow paths or heat transfer [2]. However, all the experiments for proving the coolability of RV have been done with the assumption of the most of debris would be transferred to the RV and the bottom nozzle of the FAs. The purpose of the tests is to quantify the amount of the debris that would be accumulated at the lower plenum and the debris that passes through the FAs since non-conservatism of other researches assumptions that have been used in the past experimental or analytical programs.

• 한국가시화정보학회지
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• 제9권3호
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• pp.59-64
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• 2011

In this study the change of free surface vortex is expressed through the time volume fraction using multiphase unsteady condition in sump, because in previous studies of the pump sump did not represent the behavior of the free surface vortex exactly due to the reason it was calculated using single phase and steady condition. The reliability of the computational analysis is verified through comparing experimental results with that of present numerical analysis. Homogeneous free surface model is used to apply interactions of air and water. The results show that the free surface vortex can be identified on the isotropic surface at air volume fraction 1%~5%. The vortices make an air column from the free surface to the sump intake and are created and destroyed repeatedly. The behavior of free surface vortex at numerical analysis is quite similar to experimental test. The result of vortex motion according to time, works on a cycle.

• 한국유체기계학회 논문집
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• 제15권5호
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• pp.60-66
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• 2012

One of commonly physical phenomena encountered in pump sump systems in which its significant influence to the hydraulic performance of pump system plays an important role in the field of fluid engineering, is the appearance of free surface and submerged vortices. In this paper, a study of the vortices behavior and their formative mechanism of asymmetry is considered in this paper by using numerical approach. The Reynolds-Averaged Navier-Stokes (RANS) equations and k-omega Shear Stress Transport turbulence model used to describe the properties of turbulent flows, in company with VOF multiphase model, are implemented by Fluent code with multi-block structured grid system. In the numerical simulation, the calculated elevation of air-water interface and vortex core contours are used to classify visually surface vortices as well as submerged vortices. It is shown that the free surface vortex is identified by the concavity of liquid region from the free surface and swirling flow at that own plane. To investigate the distinctive behavior of these vortices corresponding to each given flow rate at the same water level, some numerical testing of them are considered here in such a manner that the flow pattern of surface vortex are obtained similarly to the obtained results from experiment. Furthermore, the influence due to the change of grid refinement and the variation of depth of the concavity are also considered in this paper. From that, these influential factors will be implemented to design a good pump sump with higher performance in the future.

• 상하수도학회지
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• 제24권2호
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• pp.211-217
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• 2010

In order to suggest the methodology for achieving anti-vortex within multi pump intake well, the field test and CFD(Computational Fluid Dynamics) simulation were conducted. The filed test were carried out for domestic W_multi pump intake well according to usual operation condition through the naked observation. From the results, operating #4, #5, #8 and 9# pumps, the vortex and swirl occurred above #4 and #9 intake pipe within two wells. For qualitative analysis, a commercial CFD code, using sump model, was used to predict the vortex generation within the selected pump intake facility accurately. The analysed results by CFD show that the vortex structure and location are in accordance with the results of the field test.

• 한국유체기계학회 논문집
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• 제8권2호
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• pp.53-56
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• 2005

• 한국유체기계학회 논문집
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• 제8권2호
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• pp.57-61
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• 2005

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2005년도 연구개발 발표회 논문집
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• pp.575-581
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• 2005

• Nuclear Engineering and Technology
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• 제55권4호
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• pp.1518-1527
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• 2023

A method was proposed for in-situ evaluating the thickness and resistivity of the oxide/hydroxide film formed on the surface of aluminum alloy exposed to sump water formed in the containment after a loss-of-coolant accident. The evaluation entailed fitting a model for the film impedance, which has film thickness and other variables describing the resistivity profile of the film along its thickness direction as fitting parameters, to the practically measured electrochemical impedance data. The obtained resistivity profiles implied that the films formed at pHs_25℃ 7, 8, 9, 10, and 11 all had a duplex structure; compared to the outer layer in contact with the solution, the inner layer of the film had a much higher resistivity and was inferred to be denser and provide most of the protectiveness of the film. Both the thickness and the total resistance of the film decreased with the increasing solution pH_25℃, suggesting that the films formed in more alkaline solutions had less protectiveness against corrosion, consistent with the increasing aluminum alloy corrosion rates previously identified.

• Nuclear Engineering and Technology
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• 제56권5호
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• pp.1725-1732
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• 2024

In nuclear power plants, reactor coolant leakage can occur due to various reasons. Early detection of leaks is crucial for maintaining the safety of nuclear power plants. Currently, a detection system is being developed in Korea to identify reactor coolant system (RCS) leakage of less than 0.5 gpm. Typically, RCS leaks are detected by monitoring temperature, humidity, and radioactivity in the containment, and a water level in the sump. However, detecting small leaks proves challenging because the resulting changes in the containment humidity and temperature, and the sump water level are minimal. To address these issues and improve leak detection speed, it is necessary to quantify the leaks and develop an artificial intelligence-based leak detection system. In this study, we employed bidirectional long short-term memory, which are types of neural networks used in artificial intelligence, to predict the relative humidity in the leakage area for leak quantification. Additionally, an optimization technique was implemented to reduce learning time and enhance prediction performance. Through evaluation of the developed artificial intelligence model's prediction accuracy, we expect it to be valuable for future leak detection systems by accurately predicting the relative humidity in a leakage area.

• Nuclear Engineering and Technology
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• 제15권3호
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• pp.179-187
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• 1983

국내원자력 발전소중 고리 1호기 및 5,6호기의 LOCA 사고시 격납용기 살수용액과 썸프 용액의 pH값이 US NRC에서 요구하는 설계기준치를 만족하는가를 알아보기 위해 전산프로그램 “LOCAPH”를 개발하여 최대 pH경우와 최소 pH경우로 나누어 분석하였다. 고리 5,6호기의 경우, 썸프 용액의 pH는 설계기준(최소 8.5이상)을 잘 만족하고 있으며, 살수 용액의 pH는 설계기준(8.5에서 11.0사이)을 약간 벗어나고 있음을 볼 수 있었다. 그러나 고리 1호기의 경우를 보면 썸프 용액의 pH는 역시 설계기준을 잘 만족하고 있으나 살수 용액의 pH는 최대 pH 경우에 있어서 현재 설계에 반영되고 있는 설계기준을 상당히 벗어나고 있음을 알 수 있었다.(고리 1호기 설계시 살수 용액의 pH에 대한 설계 기준치는 없었음) 설계 기준을 만족시키기 위해 고리 1호기의 설계변수를 바꾸어가며 계산해 본 결과 격납용기 살수 용액의 공급원인 핵연료 재장전수 저장탱크(RWST)의 붕소 농도를 2750ppm에서 2850ppm 사이로 유지하거나, 격납용기 살수 용액에 첨가되는 NaOH의 유량을 10gpm에서 24gpm사이로 유지해야 함을 알 수 있었다.