• Journal of the Korean Society of Safety
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• v.37 no.5
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• pp.80-88
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• 2022

The Korean nuclear industry had developed the SPACE (Safety and Performance Analysis Code for nuclear power plants) code, which adopts a two-fluid, three-field model that is comprised of gas, continuous liquid and droplet fields and has the capability to simulate three-dimensional models. According to the revised law by the Nuclear Safety and Security Commission (NSSC) in Korea, the multiple failure accidents that must be considered for the accident management plan of a nuclear power plant was determined based on the lessons learned from the Fukushima accident. Generally, to improve the reliability of the calculation results of a safety analysis code, verification is required for the separate and integral effect experiments. Therefore, the goal of this work is to verify the calculation capability of the SPACE code for multiple failure accidents. For this purpose, an experiment was conducted to simulate a Control Element Drive Mechanism (CEDM) break with a safety injection failure using the ATLAS test facility, which is operated by Korea Atomic Energy Research Institute (KAERI). This experiment focused on the comparison between the experiment results and code calculation results to verify the performance of the SPACE code. The results of the overall system transient response using the SPACE code showed similar trends with the experimental results for parameters such as the system pressure, mass flow rate, and collapsed water level in component. In conclusion, it can be concluded that the SPACE code has sufficient capability to simulate a CEDM break with a safety injection failure accident.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.17 no.1
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• pp.18-27
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• 2021

This study aims to develop an improved evaluation technology for assessing CANDU-6 safety. For this purpose, the multiple steam generator tube rupture (mSGTR) followed by an unmitigated station blackout (SBO) in a CANDU-6 plant was selected as a hypothetical event scenario and the analysis model to evaluate the plant responses was envisioned into the MARS-KS input model. The model includes logic models for controlling the pressure and inventory of the primary heat transport system (PHTS) decreasing due to the u-tubes' rupture, as well as the main features of PHTS with a simplified model for the horizontal fuel channels, the secondary heat transport system including the shell side of steam generators, feedwater and main steam line, and moderator system. A steady state condition was successfully achieved to confirm the stable convergence of the key parameters. Until the turbine trip, the fuel channels were adequately cooled by forced circulation of coolant and supply of main feedwater. However, due to the continuous reduction of PHTS pressure and inventory, the reactor and turbine were shut down and the thermal-hydraulic behaviors between intact and broken loops got asymmetric. Furthermore, as the conditions of low-flow coolant and high void fraction in the broken loop persisted, leading to degradation of decay heat removal, it was evaluated that the peak cladding temperature (PCT) exceeded the limit criteria for ensuring nuclear fuel integrity. This study is expected to provide the technical bases to the accident management strategy for transient conditions with multiple events.

• Journal of Chest Surgery
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• v.36 no.3
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• pp.142-149
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• 2003

To know the feasibility of the coronary artery bypass graft (CABG) for multivessel coronary artery disease with purely bilateral internal thoracic arteries (ITAs), we analyzed the short-term clinical results and the coronary angiography of the patients. Material and Method: From March 2001 to June 2002, four hundred and five patients underwent CABG. Purely bilateral ITAs were used in 159 patients (39.3%). We analyzed these patients retrospectively The mean age of these patients was $61.2{\pm}8.5$ (range: 30 ~80) years and there were 123 male patients. The preoperative risk factors were as follows: diabetes in 54 patients (34.0%), history of acute myocardiac infarction within 4 weeks in 29 (18.2%), and emergency operation in 6 (3.8%). Off-pump CABG was carried out in 128 patients (80.5%). Associated procedures were mitral valvuloplasty (5), aortic valve replacement (3), Dor procedure (1), and so on. Result: The mean number of distal anastomoses was $3.1{\pm}0.9$ (range: 2~6), the mean duration of hospital stay was $8.4{\pm}4.5$ days. There was one (0.6%) operative death. Except for one early death, no other patients suffered from low cardiac output. The other postoperative complications were occurred as follows: reoperation due to bleeding in 3 patients, perioperative myocardiac infarction in 1, transient cardiac arrest in 2, transient cognitive dysfunction in 7, and transient ischemic attack in 1, and deep sternal wound infection in 1 patient. Recently, early postoperative angiography was performed in 19 patients who had triple vessel disease. The total number of distal anastomosis was 78 (mean $4.1{\pm}0.8$/patient). All distal anastomosis sites were patent, but competition flow was observed at the bypass sites where the native coronary artery stenosis was not significant. Conclusion: The CABG with purely bilateral ITAs for triple vessel disease was performed safely. The early patency rate was relatively good in small number of patients. However the long-term patency rate and the functional study to evaluate the sites where competition flow was observed should be followed.

• Nuclear Engineering and Technology
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• v.26 no.3
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• pp.440-452
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• 1994

Nuclear fuel bundles are designed such that the heat flux at a-fuel pin surface should not exceed the critical heat flux (CHF) during normal operation and anticipated transient. Therefore, evaluation of the CHF for fuel bundle is demanded in an exact and reliable manner. One of the major concerns with the current application of CHF correlations is that the CHF based on circular tubes is applied to the fuel bundle subchannel analysis, mainly in terms of the hydraulic diameter with correction factors which may result in a source of possibly large uncertainties in CHF prediction. The hydraulic diameter does not recognize the local properties of fluid nor such effect as the surface curvature; the turbulence action on the convex surface is much more pronounced than that on the concave surface. Even for the tube having concave curvature, the effect of tube diameter on CHF becomes important with decreasing diameter. These facts imply that the convex curvature effect is significant and crucial to the reliable CHF prediction. This paper reviews and discusses analytical and experimental aspects of effect of transverse convex curvature in incompressible turbulent flow and heat transfer, and on CHF. Flow models to quantify this effect are briefly mentioned and future works are recommended.

• Journal of the Korean Institute of Gas
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• v.17 no.4
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• pp.58-69
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• 2013

This paper presents production data analysis for two production wells located in the shale gas field, Canada, with the proper analysis method according to each production performance characteristics. In the case A production well, the analysis was performed by applying both time and superposition time because the production history has high variation. Firstly, the flow regimes were classified with a log-log plot, and as a result, only the transient flow was appeared. Then the area of simulated reservoir volume (SRV) analyzed based on flowing material balance plot was calculated to 180 acres of time, and 240 acres of superposition time. And the original gas in place (OGIP) also was estimated to 15, 20 Bscf, respectively. However, as the area of SRV was not analyzed with the boundary dominated flow data, it was regarded as the minimum one. Therefore, the production forecasting was conducted according to variation of b exponent and the area of SRV. As a result, estimated ultimate recovery (EUR) increased 1.2 and 1.4 times respectively depending on b exponent, which was 0.5 and 1. In addition, as the area of SRV increased from 240 to 360 acres, EUR increased 1.3 times. In the case B production well, the formation compressibility and permeability depending on the overburden were applied to the analysis of the overpressured reservoir. In comparison of the case that applied geomechanical factors and the case that did not, the area of SRV was increased 1.4 times, OGIP was increased 1.5 times respectively. As a result of analysis, the prediction of future productivity including OGIP and EUR may be quite different depending on the analysis method. Thus, it was found that proper analysis methods, such as pseudo-time, superposition time, geomechanical factors, need to be applied depending on the production data to gain accurate results.

• Parasites, Hosts and Diseases
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• v.54 no.2
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• pp.147-154
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• 2016

Toxoplasma gondii infection induces alteration of the host cell cycle and cell proliferation. These changes are not only seen in directly invaded host cells but also in neighboring cells. We tried to identify whether this alteration can be mediated by exosomes secreted by T. gondii-infected host cells. L6 cells, a rat myoblast cell line, and RH strain of T. gondii were selected for this study. L6 cells were infected with or without T. gondii to isolate exosomes. The cellular growth patterns were identified by cell counting with trypan blue under confocal microscopy, and cell cycle changes were investigated by flow cytometry. L6 cells infected with T. gondii showed decreased proliferation compared to uninfected L6 cells and revealed a tendency to stay at S or G2/M cell phase. The treatment of exosomes isolated from T. gondii-infected cells showed attenuation of cell proliferation and slight enhancement of S phase in L6 cells. The cell cycle alteration was not as obvious as reduction of the cell proliferation by the exosome treatment. These changes were transient and disappeared at 48 hr after the exosome treatment. Microarray analysis and web-based tools indicated that various exosomal miRNAs were crucial for the regulation of target genes related to cell proliferation. Collectively, our study demonstrated that the exosomes originating from T. gondii could change the host cell proliferation and alter the host cell cycle.

• Journal of Chest Surgery
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• v.10 no.2
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• pp.299-314
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• 1977

Clinical experience on 16 cases of open heart surgery under the extracorporeal circulation with mild or moderate hypothermia and partial hemodilution technique at the National Medical Center during the period from June 1976 to October 1977. Nine of sixteen were congenital heart disease and seven were acquired heart disease. The age of the patient ranged between 6 and 48 years. The body weight varied from 18.5kg to 60kg and body surface area 0. 79-1.70m2. The average priming volume of pump oxygenator was 2080 ml, which was consisted fresh ACD blood, buffered Hartmann`s solution, Mannitol, 50% dextrose in water and Vit. C. The average hemodilution rate was 27%. The average flow 2.3 L/min/m2 or 80 ml/min and the duration of perfusion varied from 31 min to 270 min with average of 107 min. The perfusion was carried out under the mild or moderate hypothermia using core cooling alone in 10 cases, core cooling and local myocardial cooling with $0-4^{\circ}C$ physiologic saline in 2 cases. From a hemodynamic point of view, the blood pressure dropped down around 80 mmHg after the initiation of perfusion follwed by increase to safety level and stable during the perfusion. The central venous pressure remained within normal limits. In most cases, hemoglobin and hematocrit decreased during and after the perfusion. Hemogiobin level was decreased, average of 20.6 %, hematocrit 18.6%, pletelets 55% postoperatively. Plasma hemoglobin increased moderately, from preperfusion average valve of 7.79 mg % to post-perfusion value of 54.7 mg %. Electrolytes changes during cardiopulmonary bypass showed definite hypokalemia but changes of Na, Ca were not definite. Arterial blood gas analysis during cardiopulmonary bypass suggested that the metabolic acidosis which was accompanied by respiratory alkalosis which was corrected postoperatively. As the opera tive complication, transient hemoglobinuria in 4 cases and neurological signs in 2 cases were all cured. There were 2 death cases and operative mortality rate was 12.5%.

• Journal of Korea Multimedia Society
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• v.8 no.10
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• pp.1322-1328
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• 2005

The circulation flows passing through the Ekman boundary layer on the rotating disk and transfer the angular momentum into the interior region of the container. Consequently, the circulation enhances the momentum transfer and the interior fluid is divided by a propagating shear front. This investigation focuses on computer vision and image processing technique for analysis of Non-Newtonian Fluids. To visualize marching velocity shear front for the transient flow, a particular shaped particles and light are used. To validate the proposed method, quantitative image are compared with the optical data acquired by a direct measurement of LDV (Laser Doppler Velocimetry).

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.50 no.12
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• pp.624-630
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• 2001

The trend of the regulations on environmental issues are getting tight. Responding to this trend new technologies such as moving electrodes, wide pitch and pulsed power supply are also introduced in the electrostatic precipitator(EP) systems. The introduction of wide pitch and moving electrodes enhances the system performance of the EPs by improving air-flow and by improving the ash reentrainment on rapping. The power supplies for the EPs developed up to date include thyristor-based dc or intermittent type, SMPS(switching mode power supply) type and the pulsed-power supply type. The use of the pulsed ones is known to improve dust-collecting efficiency of high resistivity ash and reduces back corona occurrence in the collecting plate. There are two kinds of pulsed-power supplies; one with pulsed transformers and the other with direct dc switching devices. The latter uses rotary spark gap switches or semiconductor switches. Both have the merits and demerits: the spark gap switches are simple and robust but has short life time, hence, high maintenance cost, whereas the semiconductor switches have long life time but are costly. In this study, A high voltage power supply with superimposing voltage pulse on dc source was developed for EPs. This study describes circuit topology, operating principle of the scheme, and analysis of experimental results on Dong-Hae Power Plant. The pulsed power supply consists of a variable dc power supply with ratings of 60kV, 800mA and pulse generator which is made of high voltage thyristor-diode switch strings, an LC resonant tank and a blocking inductor. The pulse generator generates variable pulse-voltage up to 70kV using a high frequency resonant inverter with a variable dc source. Two prototypes were built and tested on 250MW DongHae power plant to verify the possibility of the commercial use and the normal operation in the transient states.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.1
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• pp.65-72
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• 2013

This case study presents a practical method to reduce resonant vibration of large vertical pumps. The pumps are driven at 400 rpm rated speed by induction motor. The vibration was not significantly large when operated at this rated speed. Large vibration was occurred when the pump was operated below the rated speed for flow control. Due to the large vibration resonance, variable speed operation of the pump was not possible for several months at worst cases. To find an efficient vibration control method, the flexural responses of pumps for both normal and transient operations were measured. The measured modal characteristics were compared with those of finite element analysis. When the pump was operated at a specific rpm, the natural mode whose resonance frequency is twice the rotating angular speed induced the large vibration. The retrofit utilizing stiffeners to reduce this resonant vibration were performed. Effects of designed stiffeners on reducing vibration were validated through tests after actual installation.