• Nuclear Engineering and Technology
• /
• v.52 no.8
• /
• pp.1677-1688
• /
• 2020

In the sodium-cooled fast reactor, the steam generator is a heat exchange device between sodium and water, which may cause leakage, resulting in a sodium-water reaction accident, which in turn affects the safe operation of the entire nuclear reactor. To this end, the electromagnetic vortex flowmeter is used to detect leakage of the steam generator and its signal processing method is studied in this paper. The hydraulic experiment was carried out by using water instead of liquid sodium, and the sensor output signal of the electromagnetic vortex flowmeter under different gas injection volumes was collected. The bubble noise signal is reflected by the base line of the sensor output signal. According to the relationship between the proportion of the bubble noise signal in the sensor output signal and the gas injection volume, a signal processing method based on the energy ratio calculation is proposed to detect whether the water contains bubbles. The gas injection experiment of liquid sodium was conducted to verify the effectiveness of the signal processing method in the detection of bubbles in sodium, and the minimum detectable leak rate of water in the steam generator was detected to be 0.2 g/s.

• Journal of the Korean Geotechnical Society
• /
• v.19 no.6
• /
• pp.325-334
• /
• 2003

It is very difficult to rehabilitate the damaged earth dam core to manage it stably against development of flow path and increase of leakage by hydraulic fracture. In this study, application of CGS (Compaction Grouting System) to damaged earth dam core was noticed by analyzing and comparing the results of the in-situ data and FEM. Results of in-situ data showed that according as progress of rehabilitation works tip pressures increased and volume of injection decreased, voids of damaged dam core were filled with materials similar to origin dam core. Rehabilitations caused turbidity and volume of leakage to decrease at the same water level. Also, results of FEM analysis indicated that permeability decreased by rehabilitation. Through this study, it is proved that CGS is able to decrease permeability coefficient, volume of leakage and turbidity on damaged earth dam core.

• Journal of Korea Water Resources Association
• /
• v.39 no.6 s.167
• /
• pp.545-552
• /
• 2006

The purpose of this study is to develop an optimal, long-term planning model for improvement of water distribution networks. The water distribution system is divided into sub-zones and the decision of improvement plan is made for each sub-zone. Costs for replacement, rehabilitation and repair, benefits including reduced pumping and leakage costs, and hydraulic reliability are considered to make optimal decision for improvement planning of water network. Harmony search algorithm is applied to optimize the system and hydraulic analysis model EPANET is interfaced with the optimal decision model to check the hydraulic reliability, The developed model is applied to actual water distribution system in Daegu-city, South Korea. The new model which use durability, conveyance and cost as a decision variable is different from existing methods which use only burying period and pipe type and can be used as optimal decision making system for water distribution network.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.30 no.2
• /
• pp.61-68
• /
• 2018

This study was conducted to propose the optimum minimum requirement of cutoff system composed of the impermeable soil layer and vertical barrier in offshore landfill for prevention pollution leakage by seepage, advection, and dispersion numerical analyses under steady state. According to the study results, the minimum requirement of impermeable soil layer is below $1{\times}10^{-6}cm/s$ of hydraulic conductivity with more than 500 cm thickness or a system with equivalent cutoff effect. The minimum requirement of vertical barrier is below $1{\times}10^{-6}cm/s$ of hydraulic conductivity with more than 50 cm thickness or a system with equivalent cutoff effect. In addition, the vertical barrier should be embedded enough to seal securely with the impermeable soil layer for working cutoff effect.

• Journal of Korean Society of Water and Wastewater
• /
• v.26 no.5
• /
• pp.609-617
• /
• 2012

A dynamic water quality model is presented in order to simulate water quality under slowly varying flow conditions over time. To improve numerical accuracy, the proposed model uses a lumped system approach instead of extended period simulation, unlike the other available models. This approach can achieve computational efficiency by assuming liquid and pipe walls to be rigid, unlike the method of characteristics, which has been successfully implemented in rapidly varying flows. The discrete volume method is applied to resolve the advection and reaction terms of the transport equation for water quality constituents in pipes. Numerical applications are implemented to the pipe network examples under steady and unsteady conditions as well as hydraulic and water quality simulations. The numerical results are compared with EPANET2, which is a widely used simulation model for a water distribution system. The model results are in good agreement with EPANET2 for steady-state simulation. However, the hydraulic simulation results under unsteady flows differ from those of EPANET2, which causes a deviation in water quality prediction. The proposed model is expected to be a component of an integrated operation model for a water distribution system if it is combined with a computational model for rapidly varying flows to estimate leakage, pipe roughness, and intensive water quality.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.24 no.4
• /
• pp.172-179
• /
• 1988

A cartridge type hydraulic logic valve consists of simple two port valve whose poppet is closed or opened by means of pressure signal of a pilot line. Accordingly, the logic valve can be used not only for direction, flow and pressure control purpose but also for versatile function valve which enables all above mentioned functions. In addition, the valve has little internal leakage and pressure loss, superior response characteristics and easiness in making small block type valve. The above mentioned good performances being recognized recently, the logic valve has been used widely in the large scale hydraulic system such as a hydraulic press system, for the performance requirements of high speed operation and precise control characteristics. However, there are scarce reports until now, except for a few ones from Aachen Institute of Technology in West Germany, so it is necessary to be studied on development and investigation for practical application. This paper showed that the static and dynamic characteristics of a logic valve when the logic valve is used for directional control, to investigate the relations between the valve operating characteristics and the valve design conditions. From the above mentioned procedure, it was ascertained that the valve operation characteristics obtained by numerical analysis showed good agreements with experimental results. The representative results obtained are as follows; 1. During the valve is closing, the poppet velocity is almost constant in the logic valve. 2. The pilot pressure P sub(3) and the resistance R in the pilot line have much influences on the valve operation time. 3. Spring strength have not such a severe influence on the valve operating time. 4. The operation characteristics of the logic valve can be estimated with good accuracy comparatively by numerical analysis with the equations describing poppet motion.

• Journal of the Korean Geotechnical Society
• /
• v.23 no.7
• /
• pp.47-55
• /
• 2007

In this study, applicability of electrical conductivity monitoring technique for containment barrier such as soil-bentonite wall was evaluated. Laboratory tests including permeability tests and column tests were performed to understand variations in electrical conductivity at different bentonite contents, hydraulic conductivities, and heavy metal concentrations. The electrical conductivity of compacted soil-bentonite mixtures was found to increase proportionally with bentonite content. Accordingly, the hydraulic conductivity of compacted soil-bentonite mixtures which decreases linearly with increasing bentonite content was found to have an inversely proportional relationship with the electrical conductivity. In column tests, electrical conductivity breakthrough curves and concentration breakthrough curves were simultaneously obtained. These results indicated that electrical conductivity measurement can be an effective means of detecting heavy metal transport at the desired locations within barriers and verifying possible contaminant leakage. Experimental results obtained from this study showed that the electrical conductivity measurement can be a promising tool for monitoring of containment barrier.

• Journal of the Korean Geophysical Society
• /
• v.6 no.3
• /
• pp.189-207
• /
• 2003

The purpose of this paper is to analyze the behavior and to study the safety evaluation of the Unmun Dam located in Cheongdo-Gun of GyeongBuk Province, Korea. For this purpose, soil analyses including boring data, geophysical surveys and monitoring the buried geotechnical gauges, such as pore-pressure gauge, earth-pressure gauge, displacement gauge, multi-layer settlement gauge, leakage flow-meter, were conducted. In addition to these data, numerical analyses of behavior of dam were performed to predict and to compare the data which were obtained from the above methods. Since many defects, such as gravel and weathered rock blocks in the dam core, and lots of amounts of leakage, by boring analyses were found, reinforcement by compaction grouting system (CGS) has been conducted in some range of dam. Some geotechnical gauge data were also used to confirm the effects of reinforcement. Analyses of monitoring the data of geotechnical gauges buried in the dam, such as pore-pressure gauge, earth-pressure gauge, displacement gauge, multi-layer settlement gauge, and leakage flow-meter shows the load transfer of dam and the possibility of hydraulic fracturing. As a conclusion, some problems in the dam found. Especially, the dam near spillway shows the high possibility of leakage. It should be pointed out that only the left side of he dam has not a leakage problem. As a whole, the dam has problems of weakness, because of unsatisfactory construction. It is strongly recommended that highly intensive monitoring is required.

• Journal of the Korean Geotechnical Society
• /
• v.34 no.3
• /
• pp.29-41
• /
• 2018

In the case of the enlargement levee on the soft foundation, the existing levee and the enlargement levee connection can be damaged due to heterogeneous subsidence such as differential settlement at the joint of the box culvert passing through the levee. This study selected the downstream region of the Geum River and then confirmed the influence of the piping possibility on the levee by performing a 2D seepage analysis and analyzing the seepage tendency according to the position of the box culvert's gate. As a result, the flow velocity and the hydraulic gradient are larger in the upper breakage than the lower breakage, and the upper leak was more vulnerable to the piping than the lower leak. If leaks occur in the gate located on the riverside land, the risk of piping is increased when the water level rises and is maintained highly. In the case of the gate located on the inland, it could be predicted that the leakage could damage the stability of levee by increasing the water pressure inside the levee. As a result, if leakage occurs at any position in the box culvert, the pore water pressure is increased or decreased compared with the case when no leakage occurs. Therefore, if the pore water pressure is drastically reduced or increased compared with the normal case, leakage may occur. However, the result of this study is based on a 2D seepage analysis, and it is likely to be different from actual cases. Therefore, more detailed analysis by 3D analysis is recommended.

• Journal of the Korea Concrete Institute
• /
• v.20 no.3
• /
• pp.291-298
• /
• 2008

Cracks in concrete generally interconnect flow paths and increase concrete permeability. The increase in concrete permeability due to the progression of cracks allows more water or aggressive chemical ions to penetrate into concrete, facilitating deterioration. The goal of this research is to study the relationship between crack width and water permeability of cracked concrete. Tests have been carried out as a function of hydraulic pressure (0.1 $\sim$ 2 bar) and crack width (30 $\sim$ 100 ${\mu}m$). Splitting and reuniting method was used to manufacture cracked concrete specimens with controlled crack width. Crack widths are checked by using a microscope($\times$100). The results show a considerable increase of water transport with crack width and hydraulic pressure. When the crack width is smaller than 50${\mu}m$, the crack width has little effect on concrete permeability. Due to the autogenous healing, the water flow through the crack gradually reduces with time. When crack width is 100 ${\mu}m$ and hydraulic pressure increase from 0.1 bar to 0.25 bar, concrete permeability increases rapidly about 190 times according to the test results.