• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.4
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• pp.405-413
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• 2015

In the US, the number of cases of subterranean water contamination from tritium leaking through a damaged buried nuclear power plant pipe continues to increase, and the degradation of the buried metal piping is emerging as a major issue. A pipe blocked from corrosion and/or degradation can lead to loss of cooling capacity in safety-related piping resulting in critical issues related to the safety and integrity of nuclear power plant operation. The ASME Boiler and Pressure Vessel Codes Committee (BPVC) has recently approved Code Case N-755 that describes the requirements for the use of polyethylene (PE) pipe for the construction of Section III, Division 1 Class 3 buried piping systems for service water applications in nuclear power plants. This paper contains tensile and slow crack growth (SCG) test results for high-density polyethylene (HDPE) pipe welds under the environmental conditions of a nuclear power plant. Based on these tests, the fracture surface of the PENT specimen was analyzed, and the fracture mechanisms of each fracture area were determined. Finally, by using 3D finite element analysis, limit loads of HDPE related to premature failure were verified.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2008.03a
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• pp.79-88
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• 2008

Since the hydraulic fracturing field testing method was introduced first to Korean geotechnical engineers in 1994, there have been lots of progresses in a hardware system as well as an interpretation tool. The hydrofracturing system of first generation was the pipe-line type, so it was not easy to handle. It had been modified to a wire-line system at their second generation. It was more compact one but it also needed an additional air-compressor. Our current system is much more compact and operated by all-in-one system, so it doesn't need an additional air-compressor. With a progress in a hardware system, the software for analyzing the in-situ stress regime has also been progressed. For example, the shut-in pressure, which is the most ambiguous parameter to be obtained from hydrofracturing pressure curves, can now be acquired automatically from the various methods. While the hardware and software for hydrofracturing tests are being developed during the last decade, the author could accumulate the field test results which can cover the almost whole area of South Korea. Currently these field data are used widely in a feasibility study or a preliminary design step for tunnel construction in Korea. Regarding the difficulties in a site selection and a test performance for the in-situ stress measurement at an off-shore area, the in-situ stress regime obtained from the field experiences in the land area can be used indirectly for the design of a sub-sea tunnel. From the hydrofracturing stress measurements, the trend of magnitude and direction of in-situ stress field was shown identically with the geological information in Korea.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.5
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• pp.375-382
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• 2007

Nondestructive testing (NDT) by using the electromagnetic methods are useful for detecting cracks on the surface and subsurface of the metal. However, when the material contains both ferromagnetic and paramagnetic materials, it is difficult for NDT to detect and analyze cracks using this method. In addition the existence of a partial ferromagnetic material can be incorrectly characterized as a crack in the several cases. On the other hand a large crack has sometimes been misunderstood as a partially magnetized region. Inconel 600 is an important material in atomic energy plant. A nickel film is coated when a crack a appears on an Inconel substrate. Cracks are difficult to detect on the combined material of an Inconel substrate with a nickel film, which are paramagnetic and ferromagnetic material respectively. In this paper, a scan type magnetic camera, which uses a complex induced current-magnetic flux leakage (CIC-MFL) method as a magnetic source and a linearly integrated Hall sensor array (LIHaS) on a wafer as the magnetic sensors, was examined for its ability to detect cracks on the combined material. The evaluation probability of a crack is discussed. In addition the detection probability of the minimum depth was reported.

• Proceedings of the Korean Nuclear Society Conference
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• 1998.05b
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• pp.305-311
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• 1998

최근들어 고려된 LBB(Leak Before Break) 적용요건중 동적파괴시힘 절차에는 울진 3&4호기 이후 파단전누설개념이 적용되는 배관이 탄소강으로 제작될 경우. 이 배관이 Dynamic Strain Aging (DSA)에 의해 파괴저항치가 감소되지 않는다는 것이 정량적으로 입증되지 않는 한, 동 배관의 파괴 물성치 결정시 DSA의 영향이 고려되어야 하며, DSA 영향을 평가하기 위해서는 동적과괴시험이 수행되어야 함을 요건화 하고 있다. 본 연구에서는 DSA 효과에 의한 파괴저항(J-R) 특성의 저하가차세대원전 원자로냉각재배관 파단전누설개넘(LBB) 적용시 설계 안전여유도에 영향을 미치지 않는 정도임을 평가하는데 있다. 따라서 ASME Section III에서 탄소강으로 분류하고 있는 강종별 파괴인성 변화를 고찰하고, 차세대원전 주냉각재배관 재료인 SA508 Class la의 최대 파괴인성 감소치를 예측하여, 울진 3&4호기에서 측정된 엘보우용 SA516-Gr.70 강의 DSA 영향 평가 결과와 비교 분석하여 차세대원전 주냉각재배관의 DSA영향을 평가하였다. 도출된 결론으로는 DSA 영향을 고려한 SA508 Class la의 J 및 dJ/dA 값은 극히 보수적으로 추정할 때 50% 이상 감소하는 것으로 예측된다. 이러한 DSA 영향을 고려하였을 경우 배관재 모재의 파괴인성치는 Weld-SAW의 J/T 값 수준으로 감소하였다. 그러나 현 LRB 해석이 가장 낮은 J/T값을 갖는 Weld-SAW Auto의 균열길이 2a인 J/T선도에 의거하여 수행되고 있다는 점을 고려한다면 비록 DSA가 배관재에 영향을 주는 가장 보수적인 값(J 및 dJ/dA값을 50% 이상)을 사용한다고 하더라도 차세대원전 LBB 적용에 문제가 되지 않음을 알 수 있다. 즉 차세대원자로 주냉각재배관에 LBB를 적용하는데는 DSA 영향은 상대적으로 중요하지 않다는 결론을 얻었다. 표면에 수소화물이 농축되어 있는 hydride layer가 형성됨을 관찰하였으며 ～5,000ppm 이상의 경우에는 수소화물의 방향성이 random하였으며 특히, ZIRLO$^{TM}$ 시편의 경우에서는 원주방향으로 길게 이어진 수소화물과 기계적 성질에 치명적인 반경방향의 수소화물이 평행하게 배열된 것을 관찰하였다.하였을 때는 Li$_2$O의 첨가에 의해 치밀화가 주로 일어났고, 반면에 $N_2$-7vol.%H$_2$ 분위기에서 소결하면 Li$_2$O의 첨가에 의해 작은 기공은 소멸되고 큰 기공이 생성되었다.지나치게 모국어의 영향만 강조하고 다른 요인들에 대해서는 다분히 추상적인 언급으로 끝났지만 이 분석을 통 해서 배경어, 목표어, 특히 중간규칙의 역할이 괄목할 만한 것임을 가시적으로 관찰할 수 있 다. 이와 같은 오류분석 방법은 학습자의 모국어 및 관련 외국어의 음운규칙만 알면 어느 학습대상 외국어에라도 적용할 수 있는 보편성을 지니는 것으로 사료된다.없다. 그렇다면 겹의문사를 [-wh]의리를 지 닌 의문사의 병렬로 분석할 수 없다. 예를 들어 누구누구를 [주구-이-ν가] [누구누구-이- ν가]로부터 생성되었다고 볼 수 없다. 그러므로 [-wh] 겹의문사는 복수 의미를 지닐 수 없 다. 그러면 단수 의미는 어떻게 생성되는가\ulcorner 본 논문에서는 표면적 형태에도 불구하고 [-wh]의미의 겹의문사는 병렬적 관계의 합성어가 아니라 내부구조를 지니지 않은 단순한 단어(minimal $X^{0}$ elements)로 가정한다. 즉, [+wh] 의미의 겹의문사는 동일한 구성요 소를 지닌 병렬적 합성어([$[W1]_{XO-}$ $[W1]_{XO}$ ]$_{XO}$)로

• Journal of the Korean Electrochemical Society
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• v.4 no.3
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• pp.87-93
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• 2001

Pressure-balanced external Ag/AgCl electrode has been extensively used for both Pressurized Water Reactor (PWR) and Boiling Water Reactor (PWR) environments. The use of KCI-based buffer solution often becomes the source of electrode potential drift due to slow leakage through its porous plug, typically made of zirconia. It is reported that results of our effort to improve the stability of electrode potential by using high purity water as the filling solution in which $Cl^-$ ion activity can be established and maintained at the solubility of AgCl even with the sustained leakage for a long period. Stability tests have been made in boron and lithium mixture solution at $288^{\circ}C$. The electrode potential remained stable within 10 mV over one week period. And after a thermal cycle between 288 to $240^{\circ}C$ the potential shift of Ag/AgCl electrodes did not exceed 15 mV By using the limiting equivalent ionic conductances and Agar's hydrodynamic theory, the thermal liquid junction potential (TLJP) of the electrode has been predicted. The calculated values for the water-fiued Ag/AgCl electrode potential, in which the chlorine concentration in the filling solution was derived from the measured data at ambient temperature, had a good agreement with the experimental values.

• Journal of Radiation Protection and Research
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• v.35 no.1
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• pp.21-25
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• 2010

Burnup of spent fuel should be determined accurately for the safety control of spent fuel. Especially, it is necessary to measure the burnup profile along the nuclear fuel axis. In the present work, an ionization chamber was designed and fabricated to measure the gamma ray profile inside the guide tube of spent fuel. The ionization chamber was composed of three parts; induction part, gas-inlet part, and sensor part. The sensor part had two electrodes; cathode and anode. A guide electrode was considered in the ionization chamber design to make the ionization chamber to be inserted easily into the guide tube. Pure gas (argon and xenon) was inserted into the ionization chamber, and the leakage current and saturation curve were measured to determine the operation characteristics of the ionization chamber. The gamma ray radiation was also measured in relatively high dose environment. The gamma ray profile of the spent fuel will be measured with the ionization chamber.

• Journal of the Korean Society for Nondestructive Testing
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• v.34 no.2
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• pp.176-183
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• 2014

Acoustic emission testing (AET) of cylinders is advantageous in that it can be directly conducted on cylinders installed in a car, without needing to dissemble them on a real-time basis. Therefore, users prefer AET over other nondestructive testing methods. Owing to these advantages of AET, it has been approved by the Department of Transportation of the U.S. as a safety evaluation method for pressure containers or as an alternative to the hydroproof testing method. This paper presents a study of the quantitative evaluation criteria for a container having ultrasonic testing defects and also for Type 1 and Type 2 gas cylinders, which are defective seamless pressure containers provided by NK, a manufacturer of pressure containers. For the Type 1 cylinder, the process from crack growth to leak was observed in a repetitive fatigue test using a 113 L container according to ASTM E 1419-02. Further, for the Type 2 cylinder, integrity was evaluated using a 119 L sound container and a container damaged by hydraulic pressure, by the slow-fill method according to ASTM E 2191-02. Based on the AET results of the Type 1 and Type 2 cylinders, quantitative evaluation criteria were established for a defective and non-defective container.

• The Journal of the Korea Contents Association
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• v.10 no.9
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• pp.267-275
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• 2010

Quality management of an x-ray unit drastically differs according to the type of establishment of medical institutions. Many primary medical institutions have it, but they do not pay much attention to quality management. In the study, Gyeongbuk area has been divided into four zones from January 4, 2010 to September 3, 2010, and four places were designated by city. Among medical institutions located at a total of 16 sites, the target was 8 places with X-ray emission equipment 10 years or more in use as well as 8 places with X-ray emission equipment less than 10 years in use. The 5 essential items of quality control were tested. In the test that checked for equipment it was found that sites with X-ray emission equipment 10 years or more in use didn't have ground connection (6.25%) while all of them passed the current leak test. In the exposure dose reproducibility test 4 sites with X-ray emission equipment 10 years or more in use (25%) and 1 site with X-ray emission equipment less than 10 years in use didn't pass the test. In the KVp accuracy test 5 sites with X-ray emission equipment 10 years or more in use (31.25%) and 2 sites with X-ray emission equipment less than 10 years in use (12.5%) didn't pass the test. In the tube current and tube current amount test 3 sites with X-ray emission equipment 10 years or more in use (18.75%) and 1 site with less than 10 years in use (6.25%) didn't pass the test. According to the findings of the present research, quality control at medical institutions with X-ray equipment 10 years or more in use was poorer than medical institutions with X-ray equipment less than 10 years in use. In this regard, administrative and technical measures need to be taken as soon as possible. In addition, owners of medical clinics or unit managers need to raise awareness, and it is necessary to revise a regular test cycle every year or every two years if they have old equipment or if the equipment is not used on a frequent basis. And it is also important to provide regular educational programs for quality management.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.205-205
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• 2012

Korea Superconducting Tokamak Advanced Research (KSTAR) 장치는 국내 유일의 초전도 자석을 이용한 핵융합 연구 장치로서 초고온의 플라즈마를 생성하여 차세대 에너지원인 핵융합 에너지를 획득하는 것을 목표로 두고 있다. 플라즈마를 생성부터 유지하기 위해서는 수소 동위원소를 토카막 내부로 공급해 주어야 하는데 이러한 수소동위원소를 "연료"라 부르며, 이 연료를 토카막 내부로 공급해 주는 시스템을 연료주입 시스템(Fueling System)이라고 한다. KSTAR에서는 토카막 내부로 고속의 연료 주입이 필요하고 정밀한 양의 연료를 공급하는 밸브를 사용하여야 하며, 이러한 밸브를 제어 할 수 있는 제어기를 필요로 한다. 위의 사항에 적합한 피에조 밸브(Piezoelectric Valve)는 2 msec 이내의 개폐시간과 500 Torr ${\ell}$/s 이상의 유량을 흘려줄 수 있는 피에조 밸브로 압전소자에 가해지는 전압(0~250 V)에 따라 변위의 양에 비례하여 연료가 진공용기 내로 유입된다. 압전소자의 변위는 최대 140 ${\mu}m$로 최적화되어 있어야 하며, 정전용량(Capacitance)는 30~40 nF이어야 한다. 또한 소자에 힘(Force)를 가해 최대 7 N으로 136 ${\mu}m$의 변위를 가진 소자를 사용해야 한다. 피에조 밸브의 특성으로는 아날로그 신호로 작동이 되어야 하며, 유량신호를 피드백하여 밸브의 구동 전압을 정밀하게 제어 되어야 한다. 피드백 제어를 위해 압력센서는 XCS-190 Series를 사용하여 낮은 유량에서도 민감하게 반응하도록 제작하였으며, 고전압이 유기 되었을 때 제어기를 보호하기 위한 정션박스를 설치하였다. 밸브 제어기는 피에조 밸브의 개방 속도를 높이기 위해 밸브 구동 전압을 순간적으로 높이는 POP 전압을 생성하는 기능과 유량 신호를 피드백해서 밸브 구동 전압을 정밀 제어 하는 기능을 가지고 있다. 제어장치는 아날로그 및 디지털 제어회로의 전원용 +15 V DC와 밸브 구동용 +250 V DC 출력용의 전원 공급 장치(Power supply unit), 펄스 및 트리거 신호를 생성하는 Master Programmer unit), Pop 전압과 피드백의 중요한 기능을 수행하는 Valve controller unit로 제작 되었다. 피에조 밸브와 제어기는 상호 작용하여 동작을 원활히 할 수 있도록 특성 실험을 진행하여야 하며, 진공상태에서 Lack의 유무를 확인하여야 한다. 현재 개발 제작된 밸브의 진공누설시험 및 특성실험을 진행하고 있으며, KSTAR 5차 캠페인에 적용할 계획이다.

• Journal of the Korean Institute of Gas
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• v.15 no.3
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• pp.67-73
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• 2011

One of the important topics to prepare the up-coming era of so-called ‘hydrogen economy’ is hydrogen transmission. Pipeline is conceivably the most economic way to consistently and safely transport a large amount of hydrogen over a long distance, which may be strongly requested in hydrogen economy era. As a good starting point for the purpose, one might wonder whether conventional API pipeline steels as designed for natural gas transmission can be used as the hydrogen pipeline materials or not. To answer the question, here we performed a series of micro-/nano-indentations together with tensile tests on the hydrogen-charged API X65, X70 and X100 steels having different strength level. In this paper, from the results of tensile tests, the hydrogen effects on the mechanical behavior in the API steels are systematically evaluated.