• Nuclear Engineering and Technology
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• 제51권3호
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• pp.867-876
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• 2019

Second harmonic generation using nonlinear ultrasonic waves have been shown to be an early indicator of possible fatigue damage in nuclear power plant components. This technique relies on measuring amplitudes, making it highly susceptible to variations in transducer coupling and instrumentation. This paper proposes an experimental procedure for in-situ surface wave nonlinear ultrasound measurements on specimen with permanently mounted transducers under high cycle fatigue loading without interrupting the experiment. It allows continuous monitoring and minimizes variation due to transducer coupling. Moreover, relations describing the effects of the measurement system nonlinearity including the effects of the material transfer function on the measured nonlinearity parameter are derived. An in-situ high cycle fatigue test was conducted using two 304 stainless steel specimens with two different excitation frequencies. A comprehensive analysis of the nonlinear sources, which result in variations in the measured nonlinearity parameters, was performed and the effects of the system nonlinearities are explained and identified. In both specimens, monotonic trend was observed in nonlinear parameter when the value of fundamental amplitude was not changing.

• 한국정밀공학회지
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• 제21권10호
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• pp.102-108
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• 2004

In this paper, we studied a vibration problem that is critical and common to most precision measurement systems. For micro mechanical part measurements, results obtained from the vision-based precision measurement system may contain errors due to the vibration. In order to defeat this generic problem, for the current study, a PC based image processing technique was used first, to assess the effect of the vibration to the precision measurement and second, to develop an in-situ calibration algorithm that automatically compensate the measurement results in real time. We used a set of stereoscopic CCD cameras to acquire the images for the dimensional measurement and the reference measurement. The mapping function was obtained through the in-situ calibration to compensate the measurement results and the statistical analysis for the actual results is provided in the paper. Based on the current statistical study, it is expected to obtain high precision results for the micro measurement systems.

• 한국자동차공학회논문집
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• 제20권2호
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• pp.85-89
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• 2012

This paper presents a study on the system identification of the in-situ output shaft torque measurement system using a non-contacting magneto-elastic torque transducer installed in a vehicle drivline. The frequency response (transfer) function (FRF) analysis is conducted to interpret the dynamic interaction between the output shaft torque and road side excitation due to the road roughness. In order to identify the frequency response function of vehicle driveline system, two power spectral density (PSD) functions of two random signals: the road roughness profile synthesized from the road roughness index equation and the stationary noise torque extracted from the original torque signal, are first estimated. System identification results show that the output torque signal can be affected by the dynamic characteristics of vehicle driveline systems, as well as the road roughness.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2005년도 춘계 학술발표회 논문집
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• pp.1384-1389
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• 2005

A real-time monitoring system for in-situ soil remediation technologies is developed and then applied to electrokinetic remediation technique in the field trial tests during 150days. The developed system is consisted the controlled program based on internet web page, data logger, measurement instruments and so on. In the measured items there are pH, temperature, electrical current and potential, vacuum pressure. The results indicated that the system is successively applied to electrokinetic remediation technique, and further research considering economic view and multi purpose system for in-situ soil remediation technologies is needed.

• 산업기술연구
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• 제28권B호
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• pp.111-116
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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, and it has been developed to a wire-line system at their second generation. The current up-to-date system is more compact and is able to be operated by all-in-one system. With a progress in a hardware system, the software for analyzing in-situ stress regime has also been progressed. 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.

• 한국암반공학회:학술대회논문집
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• 한국암반공학회 2008년도 춘계학술발표회 논문집
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• pp.79-88
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• 2008

1994년 처음으로 국내 지반공학자들에게 소개된 수압파쇄 시험법은, 측정장비 및 해석방법에 있어서 많은 발전을 이루어 왔다. 파이프라인 타입이었던 제1세대 수압파쇄 시험장비는 다루기가 쉽지 않았고 파이프 연결부위에서의 압력 누설 문제가 대두되면서, 제2세대라 불리는 와이어라인 타입으로 보완된 바 있으나, 기존의 시스템에 비해 많은 장점을 가짐에도 불구하고 공기압축기를 별도로 설치해야 하는 문제점을 여전히 안고 있어, 2004년 이후 이를 모두 포함하는 현재의 제3세대 all-in-one 시스템으로 보완된 바 있다. 장비의 발전과 함께, 응력해석을 위한 소프트웨어의 발전도 꾸준히 진행되어온 바, 불확실한 결정값으로 인해 가장 다루기 어려운 균열폐쇄압력에 대하여 여러 가지 기법을 적용함으로써 가장 합리적인 값을 도출해내는 방법의 개발이 그 한 예가 될 것이다. 이러한 지난 10여년 간의 기술발전과 함께 국내 대부분의 지역에서 수행된 수압파쇄시험을 통하여 대한민국의 거의 전 지역에 대한 측정결과들을 축적할 수 있었으며, 현재 이 결과값은 터널굴착을 위한 기초설계단계에서 널리 활용되고 있다. 향후 해저터널의 건설과 관련하여 해상에서의 수압파쇄 초기응력측정법 또한 꾸준히 개발되고 있으나, 지금까지 축적된 내륙에서의 초기응력 측정값이 해저터널의 안전한 설계를 위해 직간접적으로 사용되어지길 기대하며, 현재까지 수압파쇄시험을 통해 얻어진 한반도의 초기응력의 평균 크기와 방향을 지질학적 특성결과와 관련 지어 제시하고자 한다.

• Nuclear Engineering and Technology
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• 제54권1호
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• pp.186-192
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• 2022

Flow accelerated corrosion (FAC) is a type of pipe corrosion in which the pipe thickness decreases depending on the fluid flow conditions. In nuclear power plants, FAC mainly occurs in the carbon steel pipes of a secondary system. However, because the temperature of a secondary system pipe is over 150 ℃, in situ monitoring using a conventional ultrasonic non-destructive testing method is difficult. In our previous study, we developed a waveguide ultrasonic thickness measurement system. In this study, we applied a waveguide ultrasonic thickness measurement system to monitor the thinning of the pipe according to the change in pH. The Korea Atomic Energy Research Institute installed FAC-proof facilities, enabling the monitoring of internal fluid flow conditions, which were fixed for ~1000 h to analyze the effect of the pH. The measurement system operated without failure for ~3000 h and the pipe thickness was found to be reduced by ~10% at pH 9 compared to that at pH 7. The thickness of the pipe was measured using a microscope after the experiment, and the reliability of the system was confirmed with less than 1% error. This technology is expected to also be applicable to the thickness-reduction monitoring of other high-temperature materials.

• 방사성폐기물학회지
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• 제12권2호
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• pp.171-178
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• 2014

원전 해체 시 원자력설비는 안전하게 해체되어야 한다. 고리 1호기나 월성 1호기와 같은 노후화된 원전의 경우 곧 원전 해체를 계획하고 있는 대상 원전이지만, 이 원전들의 가동 중단 후 해체 시 선원항 평가 기준, 제염 및 해체 기술 등의 독자적인 국내 기술 확보는 미흡한 실정이다. 본 연구의 목적은 원전 선원항 평가 기술 중 하나로 In-Situ 기법을 이용하여 대형 원전 기기를 직접 측정하여 측정대상체에 대한 선원항 평가방법을 개발하는 것이다. 원자로 헤드를 별도의 해체 없이 이동형 감마핵종분석기를 이용하여 직접 측정법으로 분석하고 간접 측정을 병행하여 측정 결과를 보완하였다. 그리고, 표면오염시료는 방사화학분석을 수행하였다. 분석 결과를 확장하여 원자로의 핵종 재고량을 계산하였다. 본 연구 결과를 토대로 각 핵종별 방사능량 변화에 따라 해체 시점을 결정할 수 있으며, 원전 해체 시 작업자의 피폭 저감에 도움이 될 것으로 기대한다.

• Nuclear Engineering and Technology
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• 제51권7호
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• pp.1828-1834
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• 2019

The performance of a plastic scintillator for use in an in situ measurement system was analyzed using simulation and experimental methods. The experimental results of four major pure beta-emitting radionuclides, namely $^3H$, $^{14}C$, $^{32}P$, and $^{90}Sr/^{90}Y$, were compared with those obtained using a Monte Carlo N-particle (MCNP) code simulation. The MCNP simulation and experimental results demonstrated good agreement for $^{32}P$ and $^{90}Sr/^{90}Y$, with a relative difference of 1.95% and 0.43% between experimental and simulation efficiencies for $^{32}P$ and $^{90}Sr/^{90}Y$, respectively. However, owing to the short range of beta particles in water, the efficiency for $^{14}C$ was extremely low, and $^3H$ could not be detected. To directly measure the low-energy beta radionuclides considering their short range, a system where the source could flow directly to the scintillator was developed. The optimal thickness of the plastic scintillator was determined based on the suggested diameter. Results showed that the detection efficiency decreases with an increase in the depth of the water. The detection efficiency decreased drastically to approximately 10 cm, and the tendency was gradually constant.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.181-181
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• 2013

Recently, nanostructure and the molecular orientation of organic thin films have been largely paid attention due to its importance in organic electronics such as organic thin film transistors (OTFTs), organic light emitting diodes (OLEDs), and organic photovoltaics (OPVs). Among various methods, the diffraction and scattering techniques based on synchrotron x-rays have shown powerful results in organic thin film systems. In this work, we introduce the in-situ annealing system installed at PLS-II (Pohang Light Source II) for organic thin films by simultaneously conducting various x-ray scattering measurements of x-ray reflectivity, conventional x-ray scattering, grazing incidence wide angle x-ray scattering (GI-WAXS) and so on. Using the in-situ measurement, we could obtain real time variation of nanostructure as well as molecular orientation during thermal annealing in metal-phthalocyanine thin films. The variation of surface and interface also could be simultaneously investigated by the x-ray reflectivity measurement.