• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.3
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• pp.174-180
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• 2006

Steam generator (SG) tubes are expanded inside tubesheet holes by using explosive or hydraulic methods to be fixed in a tubesheet. In the tube expansion process, it is important to minimize the crevice gap between expanded tube and tube sheet. In this paper, absolute and differential signals are computed by a numerical method for several different locations of tube expansion inside and outside a tubesheet and signal variations due to tubesheet, tube expansion and operating frequencies are observed. Results show that low frequency is good for detecting tubesheet location in both types of signals and high frequency is suitable for sizing of tube diameter as well as the detection of transition region. Also learned is that the absolute signal is good for measuring tube diameter, while the differential signal is good for locating the top of tubesheet and both ends of the transition region. In the case of mingled anomaly with tube expansion and tubesheet, low frequency inspection is found to be useful to analyze the mixed signal.

• Journal of the Korean Society for Nondestructive Testing
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• v.7 no.2
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• pp.16-26
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• 1988

In the in-service inspections for the steam generator tubing of the nuclear power plants by the Eddy Current Testing, the ECT signals are evaluated by their phase. If oxidized copper sludge is piled up in the secondary side, however, big sludge signals occur in large quantities which originate from copper layers forming in the sludge piles due to the pitting mechanism of the steam generator tubing by $Cu^{2+}$, and modulate the defect signals, causing the difficulty in the defect detection. In this research, sludge specimens were prepared considering the formations of the sludge signal sources and multi-frequency ECT mixing experiments by different choices of the mixing standards were performed. The results were found to be 5 to 30% of the tube wall thickness over-estimated. Experiments using the ring-type mixing standards showed the least errors of all, while those with the mixing standards nearing the sludge conditions brought larger errors as a result of the influence of the interference between the defect and the copper layers.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.24 no.3
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• pp.294-301
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• 2015

Oil filters for vehicular parts are used under high and low temperatures as the engine is cooled, and defects can be generated with repeated changes in the operating environment and with changes in the shape, such as very high internal losses for the bolts. Visually checking for defects inside a bolt is impossible. Nondestructive evaluation methods such as eddy current testing (ECT) are recommended as a more effective way to examine inside a bolt and detect surface defects in a short amount of time. In this study, the fit bobbin coil eddy current probe was applied to checking the bolts. The bolt parameters were calculated by using a COMSOL analysis program to obtain parameters for professional interior design and fault diagnosis.

• The KSFM Journal of Fluid Machinery
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• v.19 no.2
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• pp.49-54
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• 2016

A conceptual study of an air-cooled heat exchanger is conducted to achieve the long-term passive cooling of an integral reactor. A newly designed air-cooled heat exchanger is introduced in the present study and preliminary thermal sizing is demonstrated. This study mainly focuses on feasibility of an innovative air-cooled heat exchanger to extend the cooling period of the passive residual heat removal system(PRHRS) only in passive manners. A vertical shell-and-tube air-cooled heat exchanger is installed at the top of the emergency cooldown tank(ECT) to collect evaporated steam into condensate, which enables water inventory of the ECT to be kept. Finally, thermal sizing of an air-cooled heat exchanger is presented. The length and the number of tubes required, and also the height of a stack are calculated to remove the designated heat duty. The present study will contribute to an enhancement of the passive safety system of an integral reactor.

• Journal of Korean society of Dental Hygiene
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• v.9 no.3
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• pp.294-305
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• 2009

Objectives : The purpose of this study was to conduct a survey on the senses of employment so that it could provide a basic reference required for good human resources specializing in oral health with responsibility as professional. Methods : To meet these goals, a self-administrated questionnaire survey was conducted to dental hygiene college students in Gwang-ju. Results : 1. It was found that 30.7% respondents wanted to be employed as government officials of oral health. Most respondents 37.4% answered that faithfulness is the highest value as prerequisite for employment in hospital. 2. It was found that interpersonal relationships among employees had most significant effects 4.58 score on selection of employment, which was followed by in-house welfare benefit (hospital size, rest room, ect; 4.31). 3. The survey on respondents' occupational sense was represented by hospital/clinic management and dental management support 25.2%, oral health education 22.7%, oral disease prevention 19.7% respectively. Conclusion : For future social awareness about dental hygienists as occupation, desirable training courses as a part of qualification for professional dental hygienists were represented by case management (services, manners, ect; 25.0%), implant (22.8%), esthetics 14.7% and so on. As for working years, it was noted that 13.2% respondents would keep working as dental hygienists as long as they could.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.14 no.5
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• pp.41-48
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• 2005

The Rotating transmission is made up of belts, mass disks and gears. This transmission is controlled electro-mechanically by the motor and operation program. The control strategy of the system can be to change belts' stiffness and the masses of mass disk and gear. This system can be modeled as a rigid body, and also finds broad application in such diverse fields as machine tools, the cruise control system In automobiles, and control in the attitude and gimbals of spacecraft. This Transmission proves the necessity and effect of a closed loop control. The study of the Rotating Transmission excited by its base motion is able not only to predict the rotational performance, but to obtain the fundamental data for vibration isolation. In this research, we compared the response characteristics of the two controllers by means of the experiments on PD controller and PID controller added on integral action. Furthermore, we studied the response abilities such as steady state error, overshoot, and ect. and the response velocities such as rising time, settling time, and ect. in the rotating transmission.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.7 no.4
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• pp.19-25
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• 2011

Steam Generator(SG) tube is an important component of Nuclear Power Plant(NPP), which is the pressure boundary between the primary and secondary systems. The integrity of SG tube has been confirmed by the eddy current test every outage. The eddy current technique adopting bobbin probe is currently the primary technique for the steam generator tubing integrity assesment. The bobbin probe is one of the essential components which consist of the whole ECT examination system and provides us a decisive data for the evaluation of tube integrity. Until now, all of the ECT bobbin probes in Korea which is necessary to carry out inspection are imported from overseas. However, KHNP has recently developed the bobbin probe design technology and transferred it to domestic manufacturers to fabricate the probes. This study has been conducted to establish technical requirements applicable to the steam generator tube inspection using the bobbin probes fabricated by the domestic manufactures. The results have been compared with the results obtained by using foreign probe to identify the availability to the steam generator tube inspection. As a result, it is confirmed that the domestic bobbin probe is generally applicable to SG tube inspection in the NPPs.

• Imaging Science in Dentistry
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• v.36 no.3
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• pp.163-168
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• 2006

A 60-year-old female, who complained of delayed healing and swelling after extraction of left lower second molar during chemotherapy, visited our department. She had a history of a resection surgery of breast cancer and postoperative radiotherapy. The conventional radiographs showed diffuse permeative bone destruction in posterior mandibular body, which gave the first radiologic impression of osteonecrosis associated with radiotherapy or chemotherapy. And bone metastasis from the breast cancer was also considered in the differential diagnosis. On the enhanced computed tomography (ECT) the posterior mandibular body was occupied by a large expansile lesion showing central low attenuation with peripheral rim enhancement. Magnetic resonance images revealed that the low attenuated area on ECT did not show as high signal intensity as water on T2 weighted image and indicated solid component of a tumor. The final diagnosis was central squamous cell carcinoma. We present the diagnostic imaging features of the patient with special emphasis on the differential diagnosis.

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.1008-1010
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• 2005

In the examination of steam generator(SG) tube in nuclear power plant, eddy current testing probes play an important role in detecting the defects. Bobbin probe and MRPC probe is usually used for the inspection of SG tube. Bobbin probe is good at high speed inspection, but ability of detection of circumferential defect is very weak. On the contrary MRPC probe, which moves for inspection in the direction of axial and circumferential simultaneously, has very slow inspection speed, but it has excellent detection capability for small cracks, which is hardly detected by bobbin probe. In this paper, for the accurate analysis of experimental ECT signals, construction of MRPC probe signals database according to the variation of defect size is the main purpose. Using 3-D finite element method, ECT signals are analyzed, and signals analysis add according to frequency ingredient. The results, which are analysis and characteristics ion of electromagnetism simulation signals, is databased.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.715-720
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• 2005

The rotating transmission is made up of belts, mass disks and gears. This precise piece of equipment is controlled electro-mechanically by the mote. and operation program. The control strategy and the transmission can be changed by belts' stiffness and change of the mass and gear. This transmission can be modeled as a rigid body, and also finds broad application in such diverse fields as machine tools, the cruise control system in automobiles, and control in the attitude and gimbals of spacecraft. The study of the rotating transmission excited by its base motion is not only able to predict the rotational performance, but obtain the fundamental data for vibration isolation. In this thesis, we studied the response abilities such as steady overshoot, undershoot and ect. and the response velocities such as rising time, settling time, and ect. in the rotating transmission through PD control experiment.