• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.1
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• pp.47-54
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• 2013

This study investigates the crack growth behavior due to primary water stress corrosion cracking (PWSCC) in the dissimilar metal butt weld of a reactor piping using Alloy 82/182. First, detailed finite element stress analyses were performed to predict the stress distribution of the dissimilar metal butt weld in which the hydrostatic and the normal operating loads as well as the weld residual stresses were considered to evaluate the stress redistribution due to mechanical loadings. Based on the stress distributions along the wall thickness of the dissimilar metal butt weld, the crack growth behavior of the postulated axial and circumferential cracks were predicted, from which the crack growth diagram due to PWSCC was proposed. The present results can be applied to predict the crack growth rate in the dissimilar metal butt weld of reactor piping due to PWSCC.

• Journal of Korean Society of Steel Construction
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• v.12 no.3 s.46
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• pp.269-279
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• 2000

It is much expected that steel bridges, which have been damaged by increase of vehicle load and corrosion, need repair or strengthening. In this paper, the stress generated by repair welding under loading are analyzed by three dimensional elasto-plastic analyses. The longer and deeper repair weld line bocemes, the larger the magnitude of transient stress becomes. The magnitude of transient stress generated by repair welding under loading $({\sigma}_y/3,\;{\sigma}_a)$ is similar to summation of stresses generated by repair welding and loading. The longer repair weld line ratio(1/b) becomes, the larger the magnitude of transient stress generated by repair welding under loading bocomes. And, the longer repair weld line ratio(1/b) becomes, the larger the magnitude of in-plane displacement generated by repair welding under loading$({\sigma}_y/3,\;{\sigma}_a)$.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.108-113
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• 2007

In this report, stress corrosion cracking generation due to pipe material degradation in the primary stage of the nuclear power plant was investigated. Firstly, after artificially degrading the CF8A steel during 2, 4, and 6 months in actual temperature, $400^{\circ}C,$ assessed corrosion susceptibility of the degraded material following ASTM G5 standard. And next, the S.C.C. tests for the degraded material were conducted under the condition of $60^{\circ}C,$ 2wt.% H2BO3+Li70H solution, 0.8 oy. From the results, Corrosion rates linearly increased with degradation period and solution temperature increase. And both the raw material and the degraded materials were not failed in the S.C.C. test condition. In spite of long time test (about 3,900 hrs) under S.C.C. condition, surface pits or surface corrosion by the electro chemical reaction were not observed. And also, even though the nondestructive DCPD and ACPD methods were applied to on-line monitor the S.C.C. failure processes it was impossible because the surface pits and cracks were not generated.

• CORROSION AND PROTECTION
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• v.12 no.1
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• pp.24-29
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• 2013

원자력 발전소의 설계 수명이 늘어나고 기존의 가동 원전 또한 장기 운전을 목표로함에 따라, 원자로 압력용기, 가압기, 증기발생기, 배관 등의 주요 구조재료의 장기 열화에 따른 재료 건전성을 유지하는 것이 매우 중요하다. 특히, 응력부식균열 현상은 장기 열화에 의해 일어날수 있는 구조재료에서의 심각한 취화 문제들중의 하나로써, 이 현상을 예방하거나 지연시키기 위해서는 현상의 근본원인과 작동기구를 규명하는 것은 원전의 안전성 유지를 위해 매우 중요하다. 이를 위해서 구조재료 표면의 원전 운전 조건에서의 산화막 특성과 그 형성 거동을 분석하는 것은 매우 중요하게 되는데, 원전 운전 조건은 고온고압의 수화학 환경으로 일반 환경에서 사용가능한 다양한 분석 방법들을 적용하기에 많은 제약을 받게 된다. 그러나, 라만 분광법은 가동 원전의 운전 조건인 고온/고압수 환경 하에서도 실시간으로 산화막 분석이 가능한 기법으로, 본 논문에서는 지금까지의 라만 분광법을 이용하여 고온고압수 환경에서의 주요 구조용 금속 및 합금 표면에 생성된 산화막에 대한 분석 연구 결과에 대하여 소개하고, 앞으로 이를 이용한 구조재료의 열화 현상을 분석 및 열화기구 규명을 위한 연구개발 방향을 제시하고자 한다.

• Journal of the Korea Concrete Institute
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• v.14 no.6
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• pp.851-863
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• 2002

Corrosion products of reinforcement in concrete induce pressure to the adjacent concrete due to the expansion of steel. This expansion causes tensile stresses around the reinforcing bar and eventually induces cracking through the concrete cover The cracking of concrete cover will adversely affect the safety as well as the service life of concrete structures. The purpose of the this study is to examine the critical corrosion amount which causes the cracking of concrete cover. To this end, a comprehensive experimental and theoretical study has been conducted. Major test variables include concrete strength and cover thickness. The strains at the surface of concrete cover have been measured according to the amount of steel corrosion. The corrosion products which penetrate into the pores and cracks around the steel bar have been considered in the calculation of expansive pressure due to steel corrosion. The present study indicates that the critical amount of corrosion, which causes the initiation of cracking, increases with an increase of compressive strength. A realistic relation between the expansive pressure and average strain of corrosion product layer in the corrosion region has been derived and the representative stiffness of corrosion layer was determined. A concept of pressure-free strain of corrosion product layer was introduced to explain the relation between the expansive pressure and corrosion strain. The proposed theory agrees well with experimental data and may be a good base for the realistic durability design of concrete structures.

• Fire Science and Engineering
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• v.27 no.5
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• pp.26-31
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• 2013

In nuclear power plant, anchor bolts for pressurizer supports are sufficiently used in terms of safety reason, but field inspections have reported that some bolts exceed the limit of their allowable hardness. Because the high level of hardness may lead to failures due to the stress corrosion or fracture toughness, a regular inspection is required for the bolts in nuclear power plant. Thus, this research measures the hardness of bolts currently used in pressurizer supports and then estimates maximum allowable stresses preventing failures by stress corrosion and fracture toughness. Using the ANSYS program, the stresses of the bolts in the regular condition and accidental condition have been calculated, and the possible maximum stress has been compared with the estimated allowable stresses. From the results, the stresses of bolts in the accidental condition satisfy the allowable safety stress from the stress corrosion failure. However, in the future, it shall be needed to consider the reflection of the structure assembling method on the assembling procedure to ensure the pressurizer integrity during maintenance period time.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.2
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• pp.153-161
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• 2009

After several PWSCCs were found in Bugey(France), Ringhals(Sweden), Tihange(Belgium), Oconee, Arkansas, Crystal Fever, Davis-Basse, VC Summer(U.S.A.), Thuruga(Japan), USNRC and PNNL started the research on PWSCC, that is, PINC project. The aim of this project is to fabricate and obtain representative NDE mock-ups with flaws to simulate tight PWSCC cracks, to identify and quantitatively assess NDE methods for accurately detecting, sizing and characterizing tight cracks such as PWSCC, to document the range of locations and crack morphologies associated with PWSCC and observed responses and to incorporate findings from other ongoing PWSCC research programs, as appropriate. By participating in PINC project, Korean morphology technique about PWSCC and NDE technique have improved and become similar lever with other advanced country. Therefore, the evaluation technique of integrity for nickel alloy component has been improved by cooperation with university, research institute and industries.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.3
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• pp.23-30
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• 2012

For cracked concrete, it is obvious that cracks should be preferential channel for the penetration of aggressive substances such as chloride ions according to the previous researches. In order to extend the lifetime of cracked concrete, critical issues in the performance of the concrete is the risk of chloride-induced corrosion. Even though crack width can be reduced due to the high reinforcement ratio, the question is to which extend these cracks may jeopardize the durability of cracked concrete. If the size of crack is small, surface treatment system can be considered as one of the best options to extend the service life of concrete structures exposed to marine environment simply in terms of cost effectiveness versus durability performance. Thus, it should be decided to undertake an experimental study on the effect of surface coating system, which can be able to seal the concrete and the cracks to aggressive substances-induced corrosion in particular. In this study, it is excuted to examine the effect of surfaced treated systems on chloride penetration and carbonation through compressive stress induced cracks. Experimental results have showed conclusively that critical stress linked with deterioration, should be existed in compressive stress ratio 50 ~ 70% for chloride penetration and 70 ~ 80% for carbonation, respectively. When the critical stress is exceeded in concrete, a comparatively large deterioration was measured where the critical stress in concrete, the increase in the mass transportation is marginal in spite of the large increase in micro-cracks. As for the effect of surface coating system on crack-sealing, it can be seen conclusively that cracks can be healed.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.7-12
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• 2004

A lifetime prediction of holddown spring screw in nuclear fuel assembly was performed using fracture mechanics approach. The spring screw was designed such that it was capable of sustaining the loads imposed by the initial tensile preload and operational loads. In order to investigate the cause of failure and to predict the stress corrosion cracking life of the screw, a stress analysis of the top nozzle spring assembly was done using finite element analysis. The elastic-plastic finite element analysis showed that the local stresses at the critical regions of head-shank fillet and thread root significantly exceeded than the yield strength of the screw material, resulting in local plastic deformation. Normalized stress intensity factors for PWSCC life prediction was proposed. Primary water stress corrosion cracking life of the Inconel 600 screw was predicted by using integration of the Scott model and resulted in 1.78 years, which was fairly close to the actual service life of the holddown spring screw.

• Proceedings of the Korean Nuclear Society Conference
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• 1995.10a
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• pp.217-222
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• 1995

1994년 11월에 나타난 고리 1호기 증기발생기의 전열관 누설에 대한 원인 조사결과, 손상원인은 2차측 응력부식균열(ODSCC)로 밝혀졌으므로, 이에 따른 단기적인 손상완화대책으로 (1) TiO$_2$와 보론산을 첨가한 틈새 세정, (2) TiO$_2$를 첨가한 하이드라진 담금, (3) $Na^{+}$/Cl$^{-}$ 몰비 조절, (4) 용존산소 제거, (5) T$_{HOT}$ 감소 등을 선정하였다. 이와 같은 완화 대책을 적용한 경우의 ODSCC 손상진전율을 확률론적으로 분석한 결과, 증기발생기교체(1998년 예정) 이전까지 전열관 누설에 의한 운전정지 가능성은 매우 낮게 나타났다.