• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.5
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• pp.464-474
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• 2003

Ultrasonic imaging of 3-D structures for nondestructive evaluation must provide readily recognizable images with enough details to clearly show various flaws that may or may not be present. Typical flaws that need to be detected are miniature cracks, for instance, in metal pipes having aged over years of operation in nuclear power plants; and these sub-millimeter cracks or flaws must be depicted in the final 3-D image for a meaningful evaluation. As a step towards improving conspicuity and thus detection of flaws, we propose a pulse-echo ultrasonic imaging technique to generate various 3-D views of the 3-D object under evaluation through strategic scanning and processing of the pulse-echo data. We employ a 2-D Wiener filter that filters the pulse-echo data along the plane orthogonal to the beam propagation so that ultrasonic beams can be sharpened. This three-dimensional processing and display coupled with 3-D manipulation capabilities by which users are able to pan and rotate the 3-D structure improve conspicuity of flaws. Providing such manipulation operations allow a clear depiction of the size and the location of various flaws in 3-D.

• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.4
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• pp.361-367
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• 2013

Many of the nuclear power plant pipe is used in high temperature and high pressure environment. Wall thinning frequently caused by the corrosion. These wall thinning in pipe is expected gradually increase as nuclear power become superannuated. Therefore there is need to evaluate wall thinning in pipe and corrosion defect by non-destructive method to prevent the accident of the nuclear power facility due to pipe corrosion. Especially for real-time assessment of the wall thinning that occurs in nuclear power plant pipe, the laser ultrasonic technology can be measured even in hard-to-reach areas, beyond the limits of earlier existing contact methods. In this study, the optical method using laser was applied for non-destructive and non-contact evaluation. Ultrasonic signals was acquired through generating ultrasonic by pulse laser and using laser interferometer. First the ultrasonic signal was detected in no wall thinning in pipe, then a longitudinal wave velocity was measured inside of pipe. Artificial wall thinning specimen compared to 20, 30, 40 and 50% of thickness of the pipe was produced and the longitudinal wave velocity was measured. It was possible to evaluate quantitatively the wall thinning area(internal defect depth) cause it was able to calculate the thickness of each specimen using measured longitudinal wave velocity.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.6
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• pp.1405-1410
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• 2015

In this study we designed the radiation-hardened sensor signal processing modules that can be commonly used for a variety of sensors during normal operation and even in high-radiation environments caused by an accident. First development module was designed to receive the change of the R and C value from the sensors and to process the signal as a PWM modulation scheme. This module was assessed to have ± 10% error to the Full-Scale in the radiation test in the range of 12 kGy TID. The main cause of the error was analyzed as the annealing of the common circuit in the switching element and the consequent increase in the duty ratio of the pulse width modulation circuit according to the radiation dose increasement. The redesigned module for higher radiation resistivity with Stub transistor circuit was found to have less than 5% error to the Full-scale from the radiation test results for 20.7 kGy TID range.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.1
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• pp.12-17
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• 2006

A steam generator of nuclear power plant has thousands of thin tubes. These tubes play an important role in maintaining the pressure boundary between the primary and secondary side of nuclear power plant. The steam generator tube is easy to be damaged because of the severe operating conditions such as the high temperature and pressure. Therefore, tremendous efforts are made to assess the structural integrity of the steam generator tubes. The eddy current test is the most popular non-destructive test to assess the integrity of the tubes. However, the eddy current test has the limitation to size the flaw accurately because the eddy current signal behavior depends on the total volume of flaw. This paper shows the possibility that the ultrasonic test method can be applied to detect the flaws in the steam generator tubes and to measure them quantitatively. From the test results, it is expected that if the ultrasonic test is put to practical use in the steam generator tube inspection, the inspection results will be improved.

• Journal of Radiation Protection and Research
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• v.46 no.4
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• pp.194-203
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• 2021

Background: Surface soil radiation monitoring around nuclear facilities is important to classify and characterize the contaminated areas. A scanning and direct measurement technique can survey the sites rapidly before starting sampling analysis. Materials and Methods: Regarding this, we test and suggest a measurement technique for gross alpha/beta and ⁹⁰Sr activities in surface soil based on a mobile ZnS(Ag)/PVT (polyvinyltoluene) array and a handheld PVT rod, respectively. To detect ⁹⁰Sr selectively in soil mixed with naturally occurring radioactive materials, chosen energy channel counts from the multichannel analyzers were used instead of whole channel counts. Soil samples contaminated with exempt liquid ⁹⁰Sr with 1 Bq·g^-1, 3 Bq·g^-1, and 10 Bq·g^-1 were prepared and hardened by flocculation. Results and Discussion: The mobile ZnS(Ag)/PVT array could discriminate gross alpha, gross beta, and gamma radiation by the different pulse-shaped signal features of each sensor material. If the array is deployed on a vehicle, the scan minimum detectable concentration (MDC) range will be about 0.11-0.17 Bq·g^-1 at 18 km·h^-1 speed, highly sensitive to actual sites. The handheld PVT rod with 12 mm (Φ) × 20 mm (H) size can directly measure ⁹⁰Sr selectively if channels on which energies are from 1,470 and 2,279 keV are gated, minimizing crossdetection of other radionuclides. These methods were verified by measuring soil samples fabricated with homogeneous ⁹⁰Sr concentrations, showing static MDC of 2.16 Bq·g^-1 at a measurement time of 300 seconds. Conclusion: Based on the results, comprehensive procedures using these detectors are suggested to optimize soil sites survey.

• Nuclear Engineering and Technology
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• v.20 no.3
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• pp.170-178
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• 1988

An automated ultrasonic flaw detection system was developed for thin-walled and short tubes such as Zircaloy-4 tubes used for cladding heavy-water reactor fuel. The system was based on the two channels immersion pulse-echo technique using 14 MHz shear wave and the specially developed helical scanning technique, in which the tube to be tested is only rotated and the small water tank with spherical focus ultrasonic transducers is translated along the tube length. The optimum angle of incidence of ultrasonic beam was 26 degrees, at which the inside and outside surface defects with the same size and direction could be detected with the same sensitivity. The maximum permissible defects in the Zircaloy-4 tubes, i.e., the longitudinal and circumferential v notches with the length of 0.76mm and 0.38mm, respectively and the depth of 0.04 mm on the inside and outside surface, could be easily detected by the system with the inspection speed of about 1 m/min and the very excellent reproducibility. The ratio of signal to noise was greater than 20 dB for the longitudinal defects and 12 dB for the circumferential defects.

• The Journal of the Acoustical Society of Korea
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• v.17 no.1E
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• pp.44-53
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• 1998

Bolt degradation has become a major issue in the nuclear industry since the 1980's due to failure during operation. If small cracks in stud bolt are not detected early enough, they grow rapidly and cause catastrophic disasters. Their detection, despite its importance, is known to be a very difficult problem due to the complicated structures of the stud bolts. This paper presents a method of detecting and sizing a small crack in the root between two adjacent crests in threads. The key idea is from the fact that the Rayleigh wave propagates slowly along a crack from the tip to the opening and is reflected from the opening mouth. When there exists a crack, a small delayed pulse due to the Rayleigh wave is detected between large regularly spaced pulses from the thread. The delay time is the same as the propagation delay time of the slow Rayleigh wave and is proportional to the size of the crack. To efficiently detect the slow Rayleigh wave, three methods based on digital signal processing are proposed : modified wave shaping, dynamic predictive deconvolution, and dynamic predictive deconvolution combined with wave shaping.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.5
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• pp.426-431
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• 2007

When a high-energy ultrasound propagates through a solid body that contains a crack or a delamination, the two faces of the defect do not ordinarily vibrate in unison, and dissipative phenomena such as friction, rubbing and clapping between the faces will convert some of the vibrational energy to heat. By combining this heating effect with infrared imaging, one can detect a subsurface defect in material in real time. In this paper a realtime detection of the brazing defect of thin Inconel plates using the UIR (ultrasonic infrared imaging) technology is described. A low frequency (23 kHz) ultrasonic transducer was used to infuse the welded Inconel plates with a short pulse of sound for 280 ms. The ultrasonic source has a maximum power of 2 kW. The surface temperature of the area under inspection is imaged by an infrared camera that is coupled to a fast frame grabber in a computer. The hot spots, which are a small area around the bound between the two faces of the Inconel plates near the defective brazing point and heated up highly, are observed. And the weak thermal signal is observed at the defect position of brazed plate also. Using the image processing technology such as background subtraction average and image enhancement using histogram equalization, the position of defective brazing regions in the thin Inconel plates can be located certainly.

• Journal of Sensor Science and Technology
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• v.5 no.5
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• pp.11-20
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• 1996

In this paper, the characteristics of therapy radiation diode sensors have been studied by using therapy radiation from the MM22 microtron accelerator. The linearity, reproducibility and error ratio were measured for feasibility as a radiation detector. Energy dependence, sensitivity change after a amount of irradiation and output value according to a number of diodes were also measured for same purpose. We have formed pulse shaping of diode signal with nuclear instruments for portal image reconstruction. The percent depth dose ratio according to field size and depth was compared with that of the detector of a ion chamber. Using thirteen silicon diodes, we can directly read diode outputs on a computer monitor after A/D conversion with 16 channels analog to digital conversion board with 12 bit resolution. The possibility for portal image with diodes has been suggested from output comparison between output value with a human phantom and that without a human phantom.

• Journal of the Korea Society for Simulation
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• v.30 no.2
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• pp.33-40
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• 2021

The situation of high-altitude electromagnetic pulses (HEMP) arises from high-altitude nuclear explosions. The HEMP situation can be simulated through the threat level investigation (TLI). In this paper, the induced voltage according to the antenna type of the tactical mobile radio communication system was measured and analyzed by TLI. Under the influence of HEMP, electronic equipment can be paralyzed or damaged. HEMP protection filters are commercially available for power lines and signal lines. However, commercialization of HEMP filters for antennas is insufficient, and even some of them exist for lightning protection. In order to make an appropriate HEMP protection filter according to the frequency and type of the antenna, the induced voltage was measured and the maximum induced voltage was analyzed through extrapolation. It was found that the measured induced voltage decreased as the frequency increased, such as in the HF, VHF and UHF bands of the measurement results.