• Nuclear Engineering and Technology
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• v.39 no.3
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• pp.231-236
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• 2007

Due to the occasional occurrences of stress corrosion cracking(SCC) in steam generator tubing(Alloy 600), degraded tubes are removed from service by plugging or are repaired for re-use. Since electrodeposition inside a tube does not entail parent tube deformation, residual stress in the tube can be minimized. In this work, tube restoration via electrodeposition inside a steam generator tubing was performed after developing the following: an anode probe to be installed inside a tube, a degreasing condition to remove dirt and grease, an activation condition for surface oxide elimination, a tightly adhered strike layer forming condition between the electro forming layer and the Alloy 600 tube, and the condition for an electroforming layer. The reliability of the electrodeposited material, with a variation of material properties, was evaluated as a function of the electrodeposit position in the vertical direction of a tube using the developed anode. It has been noted that the variation of the material properties along the electrodeposit length was acceptable in a process margin. To improve the reliability of a material property, the causes of the variation occurrence were presumed, and an attempt to minimize the variation has been made. A Ni alloy electrodeposition process is suggested as a primary water stress corrosion cracking(PWSCC) mitigation method for various components, including steam generator tubes. The Ni alloy electrodeposit formed inside a tube by using the installed assembly shows proper material properties as well as an excellent SCC resistance.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.6 no.1
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• pp.65-71
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• 2010

The plugging rate of reheater tubes of Wolsung unit 1 nuclear power plant has been increased by corrosion and erosion since 1990. As the dimensions of the new first stage reheater bundle tubes which were supplied by Hanjung company to replace were different from old one, numerical calculations are carried out for flow and heat transfer in the reheater bundle tubes of the N.P.P. Numerical calculations consists of thermal performance, drain line pressure drop, flow change by pressure drop of line, stress analysis of finned tubes and analysis of flow induced vibration. Computational analysis using heat transfer research institute program is adopted to verify the results of the numerical calculations. It contains the evalution of performance in the system with view to location of the new reheater bundle and it shows the differences between the numerical calculation results and heat transfer research institute program output.

• Nuclear Engineering and Technology
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• v.36 no.4
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• pp.316-326
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• 2004

The $40\%$ of wall criterion, which is generally used for the plugging of steam generator tubes, is applied only to a single crack. In a previous study, a total number of 9 failure models were proposed to estimate the local failure of the ligament between cracks, and the optimum coalescence model of multiple collinear cracks was determined among these models. It is, however known that parallel axial cracks are more frequently detected than collinear axial cracks during an in-service inspection. The objective of this study is to determine the plastic collapse model that can be applied to steam generator tubes containing two parallel axial through-wall cracks. Three previously proposed local failure models were selected as the candidates. Subsequently, the interaction effects between two adjacent cracks were evaluated to screen them. Plastic collapse tests for the plate with two parallel through-wall cracks and finite element analyses were performed to determine the optimum plastic collapse model. By comparing the test results with the prediction results obtained from the candidate models, a COD base model was selected as an optimum model.

• Journal of the Korean Applied Science and Technology
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• v.27 no.1
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• pp.70-75
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• 2010

Scale generation in the inside of a pipe IS restricted by reduction and oxidation(REDOX) reaction of alloyed metal of Cu-Zn. To measure the scale generating rate in the 1.67 mm of inside diameter of stainless steel tube, 300 ppm of $CaCO_3$ solution is circulated in the REDOX reactor and stainless steel tube in the order. In the case of $CaCO_3$ solution treated by REDOX reactor, flowing is maintained without plugging in the stainless steel tube, and the concentration of Cu and Zn in the circulating solution showed less than 1 ppm, which is equal to that of untreated by REDOX reactor. The crystal type of $CaCO_3$ generated by crystalline nucleus of Cu or Zn, mostly showed aragonite type.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.8 s.239
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• pp.1070-1077
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• 2005

The $40\%$ of wall thickness criterion which has been used as a plugging rule is applicable only to a single cracked steam generator tubes. In the previous studies performed by authors, several failure prediction models were introduced to estimate the plastic collapse pressures of steam generator tubes containing collinear or parallel two adjacent axial through-wall cracks. The objective of this study is to examine the failure prediction models and propose optimum ones for non-aligned two axial through-wall cracks in steam generator tubes. In order to determine the optimum ones, a series of plastic collapse tests and finite element analyses were carried out for steam generator tubes with two machined non-aligned axial through-wall cracks. Thereby, either the plastic zone contact model or COD based model was selected as the optimum one according to axial distance between two clacks. Finally, the optimum failure prediction model was used to demonstrate the conservatism of flaw characterization rules for various multiple flaws according to ASME code.

• Geotechnical Engineering
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• v.11 no.4
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• pp.75-86
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• 1995

After open -ended model pipe pile, which was composed of inner tube and outer tube was driven by different installation methods, degradation in open -ended pipe pile capacity was studied during simulated horizontal seismic shaking, which was modeled by records of actual earthquake. Drgradation in ultimate capacity of open -ended pipe pile during simulated earthquake was about 20% in impact pile and was approached up to about 40% in vibratal pile. Most of degradation in ultimate pile capacity was occured in the outer shaft surface and degradations in outer skin friction, toe resistance of steel, and plugging force were about 80%, 10%, 10%, respectively. out of ultimate pile capacity. It appeared that this trend did not depend upon the different installation methods of pile.

• Journal of Energy Engineering
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• v.28 no.3
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• pp.1-9
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• 2019

A major stress determining the remaining life of the tube in feedwater heater of fossil fuel power plant is hoop stress by the internal pressure. However, thermal stress due to temperature difference across the wall thickness also contributed to reduce the remaining life of the tube. Therefore, thermal loading must be considered even though the contribution of internal pressure loading to the stresses of the tube was known to be much higher than that of the thermal loading. In this study, thermal stress of the tubes in the de-superheating zone was estimated, which was generated due to the temperature difference across the tube thickness. Analytic equations were shown for determining the hoop stress and the radial stress of the tube with uniform thinning and for the temperature across the tube thickness. Accuracy and effectiveness of the analytic equations for the stresses were verified by comparing the results obtained by the analytic equations with those obtained from finite element analysis. Using finite element analysis, the stresses for eccentric thinning were also determined. The effect of heat transfer coefficient on thermal stress was investigated using series of finite element analyses with various values of heat transfer coefficient for both inner and outer surface of the tube. It was shown that the effect of heat transfer coefficient at outer surface was larger than that of heat transfer coefficient at inner surface on the thermal stress of the tube. Also, the hoop stress was larger than the radial stress for both cases of uniformly and eccentrically thinned tubes when the thermal loading was only considered without internal pressure loading.

• Journal of Korean Neurosurgical Society
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• v.57 no.4
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• pp.311-313
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• 2015

Chiari type I malformation is a tonsillar herniation more than 3 mm from the level of foramen magnum, with or without concurrent syringomyelia. Different surgical treatments have been developed for syringomyelia secondary to Chiari's malformations: craniovertebral decompression with or without plugging of the obex, syringo-subarachnoid, syringo-peritoneal, and theco-peritoneal shunt placement. Shunt placement procedures are useful for neurologically symptomatic large-sized syrinx. In this paper, authors define the first successful treatment of a patient with syringomyelia due to Chiari type I malformation using a pre-defined new technique of syringo-subarachnoid-peritoneal shunt with T-tube system.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.40 no.2
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• pp.155-160
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• 2004

Water jet trajectories and velocity deficits from a high pressurize nozzles were experimentally observed. In this article, several parameters affecting plugging and erosion onto the steam generator tube were quantitatively analyzed. Visualization, velocity distribution, and spray growth rate with different nozzle configurations have been mainly focused using a 2-D PDPA (Phase Doppler Particle Analyzer) system. The results indicated that trajectories along the centerline regardless of their momentum has its potential core region. However, the phenomena from the peripheral part need to be meticulosly considered. Accordingly, it is evident that quantitative velocity deficits at the outer region are outstanding due to the aerodynamical drag and entrainment.

• Proceedings of the Korean Nuclear Society Conference
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• 1995.05a
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• pp.961-966
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• 1995

국내 상업적으로 운용증인 경수로 원자력 발전소중, 중기발생기의 건전성 유지를 위하여 보수 유지에 많은 비용을 소비하고 있다 특히 중기발생기 전열관으로 사용되는 inconel 600 재질에 많은 문제점이 발생되었다. 전열관 파손에 대한 보수 및 방지기술은 plugging, sleeving, shot penning, Ni-plating 등이 있다. 특히 최근에 개발된 고출력 Nd:YAG 레이저를 이용한 sleeving 보수 기술이 개발되었다. Nd:YAG 레이저를 이용한 보수 방식은 미국의 WH 및 일본의 MHI 등이 선정하여 실용화 단계에 있으며, 이는 광섬유로 전송이 가능한 Nd:YAG 레이저를 이용하여 원격으로 가공할 수 있는 기술이다. 현재 한국 원자력 연구소에서는 전열관 레이저 보수 용접에 대한 개념을 확립하고 장비 및 기구를 개발하였으며, 고리 1 호기 전열관규격에(7/8") 3/4" sleeve tube를 삽입하여 약 50 m 떨어진 곳으로부터 원격 레이저 용접을 실험실적 규모로 실증 하였다.모로 실증 하였다.