• Journal of the Korean Society for Nondestructive Testing
• /
• v.28 no.4
• /
• pp.339-345
• /
• 2008

The heat exchanger tube in nuclear power plants is mainly fabricated from nonferromagnetic material such as a copper, titanium, and inconel alloy, but the moisture separator & reheater tube in the turbine system is fabricated from ferromagnetic material such as a carbon steel or ferrite stainless steel which has a good mechanical properties in harsh environments of high pressure and temperature. Especially, the moisture separator & reheater tubes, which use steam as a heat transfer media, typically employ a tubing with integral fins to furnish higher heat transfer rates. The ferromagnetic tube typically shows superior properties in high pressure and temperature environments than a nonferromagnetic material, but can make a trouble during the normal operation of power plants because the ferrous tube has service-induced damage forms including a steam cutting, erosion, mechanical wear, stress corrosion cracking, etc. Therefore, nondestructive examination is periodically performed to evaluate the tube integrity. Now, the remote field testing(RFT) technique is one of the solution for examination of ferromagnetic tube because the conventional eddy current technique typically can not be applied to ferromagnetic tube such as a ferrite stainless steel due to the high electrical permeability of ferrous tube. In this study, we have designed RFT probes, calibration standards, artificial flaw specimen, and probe pusher-puller necessary for field application, and have successfully carry out RFT examination of the moisture separator & reheater tube of nuclear power plants.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.20 no.2
• /
• pp.7-13
• /
• 2019

This study aims to develop a FE Model to simulate dissimilar friction stir welding and to address its potential for fundamental analysis and practical applications. The FE model is based on Coupled Eulerian-Lagrangian approach. Multiphysics systems are calculated using explicit time integration algorithm, and heat generations by friction and inelastic heat conversion as well as heat transfer through the bottom surface are included. Using the developed model, friction stir welding between an Al6061T6 plate and an AZ61 plate were simulated. Three simulations are carried out varying the welding parameters. The model is capable of predicting the temperature and plastic strain fields and the distribution of void. The simulation results showed that temperature was generally greater in Mg plates and that, as a rotation speed increase, not the maximum temperature of Mg plate increased, but did the temperature of Al plate. In addition, the model could predict flash defects, however, the prediction of void near the welding tool was not satisfactory. Since the model includes the complex physics closely occurring during FSW, the model possibly analyze a lot of phenomena hard to discovered by experiments. However, practical applications may be limited due to huge simulation time.

• The Journal of Engineering Geology
• /
• v.29 no.1
• /
• pp.1-12
• /
• 2019

Earthquake can change underground stress condition around the hypocenter and affect the fracture systems of the rocks. In Korea, the M5.8 Gyeongju earthquake on September 12, 2016 and M5.4 Pohang earthquake on November 15, 2017 occurred inside the Yangsan fault zone and possibly affected the fracture systems in the Yangsan fault zone and nearby rock masses. In this study, the characteristics of the fracture system (fracture orientation, number of the fractures, fracture spacing and aperture, dip angle, fracture density along depth, and relative rock strength) of the rocks in the low/intermediate level radioactive waste repository site located in the coastal area of the East Sea are analyzed by the impact of the Gyeongju and Pohang earthquakes using acoustic televiewer data taken from the boreholes at the radioactive waste repository site in 2005 and 2018. As a result of acoustic televiewer logging analysis, the fracture numbers, fracture aperture, and fracture density along depth overall increased in 2018 comparing to those in 2005. This increase tendency may be due to changes in the fracture system due to the impact of the earthquakes, or due to weathering of the wall of the boreholes for a long period longer than 10 years after the installation of the boreholes in 2005. In the borehole KB-14, on the whole, the orientation of the fractures and the average fracture spacing are slightly different between 2005 and 2018, while dip angle and relative rock strength in 2005 and 2018 are similar each other.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.10 no.3
• /
• pp.276-284
• /
• 2022

In this study, performance evaluation and rheological characteristics were analyzed for recycling the fine powder of nuclear power plant dismantled waste concrete as a solidifying agent for radioactive waste disposal. The radioactive concrete fine powder was used to prepare a simulated sample, and the test specimen was prepared using Di-water, CoCl₂, and 1 mol CsCl aqueous solution as mixing water. Regardless of the aggregate mixing ratio and the type of mixing water, it satisfies the performance standard of 3.45 MPa for compressive strength at 28 days of age. All specimens satisfied the criteria for submersion strength, and the thermal cycle compressive strength satisfies the criteria for all specimens except Plain-50. As a result of evaluating the rheological properties of the solidifying agent, it was found that the increase in the aggregate mixing rate decreased the yield stress and plastic viscosity. The leaching index for cobalt and cesium of all specimens was 6 or higher, which satisfies the standard. In order to secure the stable performance of the solidifying agent, it is considered effective to use 40 % or less of the aggregate component in the solidifying agent.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.30 no.3A
• /
• pp.329-336
• /
• 2010

An experimental study to evaluate bursting behavior in anchorage zone of the standard PSC I girders (span length : 30 m) has been carried out. The arrangement of bursting reinforcement in anchorage zone of the standard PSC I girders is considered to be designed without accurately reflecting the stress flows in the end zone of the PSC I girders caused by presstressing forces of the tendons. Also, due to excessive arrangement of the bursting bars, the workability of the girder is decreased greatly. In this study, three specimens with the same dimensions as the end zone of the standard PSC I girder are prepared and the experiment is carried out by applying PS forces. The bursting reinforcement of each specimen consists of 100 mm, 200 mm, and 300mm spacings, respectively. The experimental results show that the range of the PS forces to cause crack in the anchorage zone of the specimen are more than 1.6 times of the design PS forces. The bursting cracks occur in the vertical direction on the inside of all specimens. After applying 2.7 times of the design PS force, some of the transverse bursting reinforcements only in the specimen reinforced by 300 mm spacing yielded. The experimental results show that the anchorage zone of the standard PSC I girders arranged by 300 mm spacing of the bursting reinforcements which is the maximum spacing allowed in the road bridge design specifications, can be considered safe enough.

• KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
• /
• v.30 no.1
• /
• pp.63-72
• /
• 2024

Poly (butylene adipate-co-terephthalate) (PBAT) is one of the representative biodegradable polymers with high ductility and processability to replace petroleum-based polymers. Many investigations have been conducted to broaden the applications of PBAT in a variety of industries, including the food packaging, agricultural mulching film, and logistics and distribution fields. Foaming process is widely known technique to generate the cell structure within the polymer matrix, offering the insulation and light weight properties. However, there was no commercially feasible foam product based on biodegradable polymers, especially PBAT, and maintaining a proper melt viscosity of the polymer would be a key parameter for the foaming process. In this study, chemical foaming agent and cross-linking agent were introduced to PBAT, and a compression molding process was applied to prepare a foam sheet. The correlation between cell morphological structures and mechanical and physical properties was evaluated. It was found that PBAT with foam structures effectively reduced the density and thermal conductivity, allowing them to be suitable for applications such as insulation and lightweight packaging or cushion materials.

• Journal of the Microelectronics and Packaging Society
• /
• v.31 no.2
• /
• pp.23-27
• /
• 2024

In this study, the time-dependent warpage behavior caused by the viscoelastic properties of prepreg in a printed circuit board (PCB) was analyzed by finite element method (FEM). The accurate viscoelastic properties of the prepreg were measured by stress relaxation test, which were then incorporated into constructed warpage analysis model. When the PCB was subjected to repeated thermal cycles, the warpage of the PCB was restored to its initial state when only the elastic properties of the prepreg were considered, but when the viscoelastic properties were also considered, the warpage was not restored and permanent warpage change occurred. The warpage analysis for three different types of prepreg was conducted to compare their mechanical reliability, and the results showed that materials with elastic properties dominating over viscoelastic properties experienced less warpage, resulting in better mechanical reliability.

• Journal of the korean academy of Pediatric Dentistry
• /
• v.34 no.3
• /
• pp.359-369
• /
• 2007

This in vitro study was performed to assess the effect of surface sealing on the microleakage of class V composite resin restorations that underwent several aging treatments. Class V cavities were prepared on the buccal surface of 100 sound extracted premolars and restored with a hybrid light-cured composite resin according to the manufacturer's instructions. They were randomly divided into two groups consisting of 50 samples: group I, without surface sealing, and group II, in which margins were etched and surface sealant was applied. After thermocycling, each group was divided into five subgroups, respectively, to represent the five aging treatments: group A = no further treatment (only thermocycling), B = toothbrushing, C = load cycling, D = toothbrushing followed by load cycling, and E = aging treatment in deionized water for six months. Microleakage was assessed by examining the penetration of 2% methylene blue dye. The following results were obtained: 1. At occlusal and cervical margins in groups without surface sealing, there was no significant difference in microleakage after the several aging treatments (p>0.05). 2. The occlusal margins of groups with surface sealing showed no significant differences after the several aging treatments (p>0.05). 3. In the cervical margins of groups with surface sealing, microleakage significantly increased after load cycling or aging in deionized water for six months (p<0.05). 4. The no-further-treatment group and the toothbrushing group with surface sealing showed less microleakage than the corresponding groups without surface sealing (p<0.05). 5. The surface-sealed groups with load cycling or aging in deionized water showed no significant difference in microleakage to the corresponding groups without surface sealing (p>0.05). In conclusion, the results of this study suggest that the surface sealant infiltrating through the gap of the cervical margin exerted a positive effect on microleakage at the initial stage, but the effect was not sufficient to overcome the stress generated by the cuspal flexure during occlusal loading and water absorption.

• Journal of the Korea Institute of Building Construction
• /
• v.9 no.4
• /
• pp.55-61
• /
• 2009

Recently, the number of high-rise buildings being built in Korea by major construction companies for residential and commercial use has been increasing. When constructing a high-rise building, it is necessary to apply massive amounts of concrete to form a mat foundation that can withstand the huge load of the upper structure. However, it is of increasing concern that due to limitations in terms of the amount of placing equipment, available job-sites and systems for mass concrete placement in the construction field, it is not always possible to place a great quantity of concrete simultaneously in a large-scale mat foundation, and for this reason consistency between placement lift cannot be secured. In addition, a mat foundation Is likely to crack due to the stress caused by differences inhydration heat generation time. To derive a solution for these problems, this study provides test results of a hydration heat crack reduction method by applying placement lift change and setting time control with a super retarding agent for mass concrete in a large-scale mat foundation. Mock-up specimens with different mixtures and placement liftswere prepared at the job-site of a newly-constructed high-rise building. The test results show that slump flow of concrete before and after adding the super retarding agent somewhat Increases as the target retarding time gets longer, while the air content shows no great difference. The setting time was observed to be retarded as the target retarding time gets longer. As the target retarding time gets longer, compressive strength appears to be decreased at an early stage, but as time goes by, compressive strength gets higher, and the compressive strength at 28 days becomes equal or higher to that of plain concrete without a super retarding agent. For the effect of placement lift change and super retarding agent on the reduction of hydration heat, the application of 2 and 4 placement lifts and a super retarding agent makes it possible to secure consistency and reduce temperature difference between placement lifts, while also extending the time to reach peak temperature. This implies that the possibility of thermal crack induced by hydration heat is reduced. The best results are shown in the case of applying 4 placement lifts.

• Economic and Environmental Geology
• /
• v.28 no.6
• /
• pp.579-585
• /
• 1995

The Samkwang mine is Cretaceous gold-silver-bearing deposits located in the western part of the Ogcheon belt The ore deposits have been emplaced within granite gneiss of the Precambrian age. The Au-Ag deposits are hydrothermal-vein type, characterized by arsenic-, gold- and silver-bearing sulphides, in addition to the principal ore-forming sulphides arsenopyrite, galena, sphalerite, chalcopyrite, pyrite and pyrrhotite. Their proven reserves are 355,000 MT, and grades are 8.4 g Au/t and 13.6 g Ag/t. On the basis of their structural characters, the Au-Ag-bearing quartz veins are classified into three types of ore veins; (1) The Main vein shows $N40^{\circ}-80^{\circ}E$ strike and $55^{\circ}-90^{\circ}SE$ dip, (2) the Sangban vein shows E-W strike and $30^{\circ}-40^{\circ}S$ dip, and (3) the Gukseong vein has $N25^{\circ}-40^{\circ}W$strike and $65^{\circ}-80^{\circ}SW$ dip. The emplacements of the ore veins are closely related to the minimum stress axis $({\sigma}_3)$ during the strike-slip movement of the study area. The ore-bearing veins filled with extension fractures during strike-slip movements were sequentially emplaced as follows: I) When ${\sigma}_1$ operates obliquely to NE-series discontinous surface, the Main fault zone $(F_1)$ developes. 2) During the same time, extension fractures ($T_1$ Gukseong veins) take place. 3) When the fault progress continuously, the existing $T_1$, may be high angle and $T_2$ (Daehung vein) developes continuously. 4) When ${\sigma}_1$ changes to sinistral sense, $T_3$ (basic dyke) occurs. 5) When a reverse fault becomes active, the Sangban vein is branched from the Guksabong vein.