• Journal of Energy Engineering
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• v.8 no.4
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• pp.605-611
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• 1999

Conventional methods for assessing remaining life of critical high temperature components in fossil power plants rely on nondestructive inspection practices and accompanying life analysis based on fracture mechanics By using these conventional methods. It has been difficult to perform uninterrupted in-service inspection for life prediction. Thus, efforts have been made for developing on-line remaining life monitoring systems employing information on the shape of structures, operating variables and material properties. In thus study, a software for on-line life monitoring system which performs real-time life evaluation of a high temperature system headers was developed. The software is capable of evaluating creep and fatigue life usage from the real-time stress data calculated by using temperatures/stress transfer Green functions derived in advance for the specific headers. The major benefits of the developed software life in determining future operating schedule, inspection interval, and replacement plan by monitoring real-time life usage based on prior operating history.

• 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 Soil and Groundwater Environment
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• v.9 no.2
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• pp.28-40
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• 2004

Box experiments were performed to evaluate the removal efficiency of SVE (soil vapor extraction) for gasoline in soil. An activated carbon sorption tower and a biofilter were operated as post-treatment processes to remove VOCs extracted from extraction wells of SVE. An acrylic resin box (65 cm${\times}$20 cm${\times}$30 cm) was used to make artificial soil layers and two injection wells and one extraction well were built for SVE process in the box. Gases from extraction wells flew into the activated carbon sorption tower or the biofilter. Gasoline concentrations of VOCs emitted from the extraction well were compared with those after post treatments. More than 92% of initial gasoline mass in soil were removed by SVE within few days, suggesting that SVE is very available to remove VOCs from contaminated soils. To treat VOCs from extraction wells of SVE, an activated carbon sorption tower and a biofilter were attached to SVE process and their gasoline removal efficiencies were measured. These post treatment systems lowered gasoline concentrations to below 1.0 ppm within few days. Average remediation efficiency was 98% of gasoline for the activated carbon sorption tower and 84.1% for the biofilter. The maximum removal capacity of a biofilter was 10.7 g/L/hr, which was ten times higher than general biofilter removal capacity. Results from the study suggest that the activated carbon sorption tower and the biofilter would be available for the post treatment process to remove VOCs generated from SVE process.

• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.6
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• pp.504-509
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• 2016

Defects in dissimilar metal welds are reported to be on the increase during the operating lifespan and aging of nuclear power plants. In Korea, reported cases of defects due to dissimilar metal welds include the drain nozzle of a steam generator and RCS hot tube sampling nozzles. Therefore, there is an urgent need to develop a reliable automated nondestructive inspection technique and a system for the inspection of dissimilar metal welds of small diameter nozzles in a high radiation area of a nuclear power plant. In this study, to ensure effective defect inspection of small diameter nozzles (RCS high-temperature tube sampling nozzle) of a nuclear power plant, three different methods were developed. These include: (1) optimum inspection probe design by beam simulation, (2) multi-directions UT optimum inspection technique for the inspection of small diameters of different welded parts, and (3) remote control automatic inspection system. The developed technique and systems have been verified to be suitable for use in the inspection of defects in smaller diameter nozzles in nuclear power plants.

• Journal of the Korean Society of Propulsion Engineers
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• v.2 no.2
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• pp.74-82
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• 1998

Combined cycle power plant is a system where a gas turbine or a steam turbine is used to produce shaft power to drive a generator for producing electrical power and the steam from the HRSG is expanded in a steam turbine for additional shaft power. The temperature of the exhaust gases from a gas turbine ranges from $400{\sim}650^{\circ}C$, and can be used effectively in a heat recovery steam generator to produce steam. Combined cycle can be classed as a topping and bottoming cycle. The first cycle, to which most of the heat is supplied, is a Brayton gas turbine cycle. The wasted heat it produces is then utilized in a second process which operates at a lower temperature level is a steam turbine cycle. The combined gas and steam turbine power plant have been widely accepted because, first, each separate system has already proven themselves in power plants as an independent cycle, therefore, the development costs are low. Secondly, using the air as a working medium, the operation is relatively non- problematic and inexpensive and can be used in gas turbines at an elevated temperature level over $1000^{\circ}C$. The steam process uses water, which is likewise inexpensive and widely available, but better suited for the medium and low temperature ranges. It therefore, is quite reasonable to use the steam process for the bottoming cycle. Recently gas turbine attained inlet temperature that make it possible to design a highly efficient combined cycle. In the present study, performance analysis of a 3 pressured combined cycle power plant is carried out to investigate the influence of topping cycle to combined cycle performance. Present calculation is compared with acceptance performance test data from SeoInchon combined cycle power plant. Present results is expected to shed some light to design and manufacture 150~200MW class heavy duty gas turbine whose conceptual design is already being undertaken.

• Journal of Energy Engineering
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• v.7 no.2
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• pp.194-201
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• 1998

In electric commuter trains using AC motors, lots of GTO thyristors and diodes are needed for power controls. These semiconductors generate heat about 1~2 kW, and for cooling which perfluorocarbon(PFC) heat pipes have been in use for the last two decades. The present study was investigated on the effects of such important design parameters as structure of internal surface (grooved or smooth), fill charge ratio, and inclinating angle from a vertical on heat transfer coefficients at both evaporators and condensers. To obtain experimental data, several heat pipes of the same geometry of 520 mm long and diameter of 15.88 mm but different in fill charge ratio and internal surface structure were designed and fabricated. For prediction of the heat transfer coefficients, related expressions were examined and the results of calculations were compared with experimental data. Performance tests were conducted while heat pipes operated at mode of thermosyphons. High enhancements of heat transfer coefficient were obtained internal grooves. In these cases, the evaporating heat transfer coefficients distributed in the range of 2~5.5 kW/$m^2$K, with an increase of heat flux from 15~45 kW/$m^2$. These experimental data were in good agreement with Rohsenow's expression based on nucleate boiling when correction factor $C_R$=1.3 was encountered. In addition, the condensation heat transfer coefficients were distributed from 1.5 to 3.5 kW/$m^2$K, and the data were in good agreements with Nusselt's correlation, based on filmwise condensation on vertical plate, when choosing a correction factor $C_N=4$. A fill charge ratio of 40~100% were recommended, and the in clination angle effects were negligible when the angle was higher then 30$^{\circ}$.

• Journal of Chest Surgery
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• v.37 no.2
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• pp.146-153
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• 2004

As the experience of coronary artery bypass grafting (CABG) has been accumulated, the number of reoperation after CABG is increasing. We analyzed our clinical experience of redo-CABG. Material and Method: Fourteen patients who underwent redo-CABG between Jan. 1994 and Dec. 2002 were included in this study. The mean period from the first operation to reoperation was 66$\pm$56 (3∼157) months, and the average ages were 62.8$\pm$8.7 (51∼78) years. The survivors were followed up 39$\pm$29 (4∼101) months postoperatively. Indications of reoperation were stenosis or occlusion of previous grafts in 11 patients, progression of native coronary artery disease in one patient, and both etiologies in two patients. Result: There were two in-hospital mortalities (14.3%) resulting from low cardiac output syndrome, Postoperative morbidities were perioperative myocardiac infarction in 2 patients (14.3%), mediastinitis in one patient (7.2%), duodenal perforation in one patient, ischemic necrosis of the lower extremity in one patient, gastric perforation after mesenteric infarct in one patient, delayed brain infarct in one patient, and intraoperative splenic rupture in one patient. There was one late mortality at six months postoperatively during the follow up. There was no angina recurrence during the follow up. Conclusion: Although redo CABG demonstrated relatively high operative mortalities and morbidities, postoperative status and clinical outcome of the survivors were favorable.

• Radiation Oncology Journal
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• v.11 no.1
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• pp.43-50
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• 1993

We evaluated frequency and types of chromosomal aberrations by ionizing radiation in cancer patients treated with radiotherapy in our institution. Twenty-five patients with various types of carcinomas such as lung, uterine cervix, esophagus, rectum, head and neck and pancreatic cancers were studied immediately before and after external beam radiotherapy. The frequency of aberrant metaphase prior to treatment was $4.93{\%}$, which was higher than that of control group. Especially in lung cancer, the freuqency of aberrant metaphase was three times higher than control group. A comparison of chromosomal abnormalities observed before and after radiotherapy demonstrated that proportion of aberrant rnetaphases was significantly inreased to $22.13{\%}$. Major chromosomal aberrations like structural abnormalities showed remarkalbe increase from 65.45 to $88.45{\%}$ after the treatment. Also the numbers of chromosomal alterations per cell were increased by a factor of 6.5. Aberrations with two or more break points were more prominently increased, compared with aberrations with single break point. The number of chromosomal break points was noted to be higher than expected value in No.1, 3, 8 and 11 chromosomes and lower in No.13, 15, 17 and 21 chromosomes. Based on this study, we believe that the distribution of chromosomal breakage is related with gene and chromosomal rearrangement which could result in the development of cancers.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.43-43
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• 2009

단련용 다결정 Ni기 초내열합금은 우수한 가공성, 내산화성, 고온특성 등으로 가스터빈 연소기, 디스크, 증기발생기 전열관 등 발전용 고온부품 소재에 널리 적용되고 있다. 최근 발전설비의 고효율화를 꾀하기 위해 작동 온도를 현격히 증가시키는 기술방향으로 발전하고 있고, 소재측면에서는 기존의 초내열합금 대비 고기능성을 확보할 수 있는 차세대 Ni기 초내열합금 개발이 유럽, 미국, 일본, 중국 등을 중심으로 활발히 이루어지고 있다. 이러한 소재의 고온강도 (온도수용성)를 향상시키기 위해서는 통상 규칙격자 금속간화합물인 $Ni_3(Al,Ti)-{\gamma}'$상의 분율을 증가시킬 수 있지만, ${\gamma}'$상분율이 증가할 경우 용접 및 후열처리 동안 용접열영향부 (HAZ)에서 액화균열이 발생할 가능성이 높아진다. 결정립계를 따라 발생하는 HAZ 액화균열은 입계특성에 의해 크게 영향을 받을 것으로 판단된다. 한편, 본 연구자들은 최근 입계 serration 현상을 단련용 합금에 도입시키는 특별한 열처리를 이론적 접근법을 통해 개발하였다. 형성된 파형입계는 결정학적인 관점에서 조밀 {111} 입계면을 갖도록 분해 (dissociation)되어 낮은 계면에너지를 갖게 됨을 확인하였으며, 입계형상 변화뿐만 아니라 탄화물 특성변화까지 유도하여 크리프 수명을 기존대비 약 40% 정도 향상시킴을 확인하였다. 이러한 직선형 입계 대비 'special boundary'로 간주되는 파형입계가 도입될 경우, HAZ 결정립크기 변화 및 액화거동에 미치는 영향을 고찰하고, 아울러 입계특성 제어가 용접성/용접부 품질 향상에 기여할 수 있는 가능성도 토의하고자 하였다. 본 연구에서는 재현 HAZ 열사이클 시험을 통해 미세구조를 정량적으로 비교하였다. 상대적으로 입계구조가 안정된 파형입계의 이동속도가 高계면 에너지를 갖는 직선형 입계보다 느려 HAZ 결정립 성장이 효과적으로 억제됨을 확인할 수 있었다. 입계 액화거동을 살펴보면, 두 시편 모두 $M_{23}C_6$, MC 등 입계탄화물 계면이 빠른 승온중 액화반응 (constitutional liquation)에 의해 입계가 액화되었으며, 이후 급냉에 의해 입계에 액상막이 존재한 흔적이 발견되었다. 최고온도별로 입계액화 폭/비율을 정량적으로 비교한 결과, 파형입계가 직선입계 대비 대체로 낮음을 확인할 수 있었으며, 때때로 액화되지 않고 잔존하는 입계 탄화물이 관찰되었다. 재현 HAZ 미세조직을 통해 Hot ductility 시험 결과를 유추하자면, 파형입계가 직선입계 보다 좁은 취성온도영역 (Brittle Temperature Range)을 나타낼 것으로 예상되어, 입계특성제어에 의해 Ni기 초내열합금의 용접성을 향상 가능성을 확인하였다.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.2
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• pp.90-98
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• 2006

Signals captured from a Combo calibration standard tube paly a crucial role in the evaluation of motorized rotating pancake coil (MRPC) probe signals from steam generator (SG) tubes in nuclear power plants (NPPs). Therefore, the Combo tube signals should be consistent and accurate. However, MRPC probe signals are very easily affected by various factors around the tubes so that they can be distorted in their amplitudes and phase angles which are the values specifically used in the evaluation. To overcome this problem, in this study, we explored possibility of simulation to be used as a practical calibration tool far the evaluation of real field signals. For this purpose, we investigated the characteristics of a MRPC probe and a Combo tube. And then using commercial software (VIC-3D) we simulated a set of calibration signals and compared to the experimental signals. From this comparison, we verified the accuracy of the simulated signals. Finally, we evaluated two defects using the simulated Combo tube signals, and the results were compared with those obtained using the actual field calibration signals.