• 전산구조공학
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• 제9권2호
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• pp.153-161
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• 1996

본 논문에서는 가압열충격의 파괴역학적 해석에 필요한 이론을 조사하였고 원자로용기의 구조건전성을 평가하기 위하여 해석과정을 전산화하였다. 우선 사고 transient에 대하여 원자로용기내의 압력과 주입되는 냉각재의 온도변화가 주어지면 이들로 부터 시간에 따른 용기에서의 온도와 응력분포를 구하고, 중성자 조사량과 용기 재질의 화학성분으로 부터 기준무연성천이온도의 분포가 구해지며 이로부터 파괴인성치 K/sub IA/와 K/sub IC/의 분포가 얻어진다. 또한 응력분포로 부터 균열의 크기 및 형상에 따라 응력확대계수 K/sub I/이 구해지므로 이를 K/sub IA/및 K/sub IC/와 비교함으로써 균열의 성장거동을 예측할 수 있다. 지금까지 보고된 가압열충격을 유발할 수 있는 대표적인 사고 transient가 국내 발전소에 발생할 경우를 가정하여 해석을 수행하였고 그 결과에 대하여 검토하였다.

• 대한기계학회논문집A
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• 제29권10호
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• pp.1361-1368
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• 2005

The structural and leakage integrity of steam generator tubes should be sustained all postulated loads with appropriate margin even if a crack is present. During the past three decades, for effective integrity evaluation, several limit load solutions have been used world-widely. However, to predict accurately load carrying capacities of specific components under different conditions, the solutions have to be modified by using lots of experimental data. The purpose of this paper is to propose a new burst pressure estimation scheme based on fracture mechanics analyses for steam generator tube with an axial or circumferential through-wall crack. A series of three dimensional elastic-plastic finite element analyses were carried out and, then, closed-form estimation equations with respect to both J-integral and crack opening displacement were derived through reference stress method. The developed engineering equations were utilized for structural integrity evaluation and the resulting data were compared to the corresponding ones fiom experiments as well as limit load solutions. Thereafter, since the effectiveness was proven by promising results, it is believed that the proposed estimation scheme can be used as an efficient tool for integrity evaluation of cracked steam generator tubes.

• 한국안전학회지
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• 제16권4호
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• pp.29-38
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• 2001

The purpose of this paper is to evaluate the structural integrity of a reactor pressure vessel subjected to the pressurized thermal shock(PTS) during the transient events, such as main steam line break(MSLB) and small break loss of coolant accident(SBLOCA). For postulated surface or subsurface cracks, variation curves of stress intensity factor are obtained by using the three different methods, including ASME section XI code anlysis, the finite element alternating method and the finite element method. From the stress intensity factor curves, the maximum allowable nil-ductility transition temperatures(RT/NDT/) are determined by the tangent criterion and the maximum criterion for various crack configurations and two initial transient events. As a result of the analysis, it is noted that axial cracks have smaller maximum allowable RT$_{NDT}$ values than same-sized circumferential cracks for both the transient events in the case of the tangent criterion. Axial cracks have smaller RT$_{NDT}$ values than same-sized circumferential cracks for MSLB and circumferential cracks have smaller values than axial cracks for SBLOCA in the case of the maximum criterion.

• 한국건축시공학회지
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• 제23권5호
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• pp.547-558
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• 2023

초고강도 콘크리트의 강도와 유동성 확보를 위해 실리카흄(SF)를 사용하는 전통적인 방식에서 벗어나 산화 그래핀 나노플레이트릿(Oxidized graphene nanoplatelet, GO)와 유공유리분말( Hollow glass powder, HGP)를 사용한 초고강도 콘크리트를 개발하였고 본 연구에서는 자기수축 특성에 대해 검토하였다. 그 결과 SF를 사용한 Ref 배합보다 SF를 사용하지 않고 cGO(C사의 GO)와 HGP를 사용한 NewMix 배합의 자기수축이 13% 정도 감소하였다. NewMix의 자기수축에 의한 균열발생은 Ref 보다 1일 정도 지연되었고 균열발생 시의 인장응력은 가장 높았다. cGO의 높은 비표면적과 우수한 분산성으로 콘크리트 내의 공극들이 충전 되어 자기수축이 감소하고 cGO에 의한 균열저항 성능이 증가하여 초고강도 콘크리트의 자기수축 균열 제어에 효과가 있을 것으로 판단된다.

• 대한기계학회논문집A
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• 제37권1호
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• pp.47-54
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• 2013

본 논문에서는 Alloy 82/182를 용접재로 이용한 원자로 배관 이종금속 맞대기 용접부(Dissimilar Metal Butt Weld)에서의 PWSCC에 의한 균열성장 거동을 평가하였다. 이를 위해 먼저 유한요소 응력해석을 수행하여 이종금속용접부에서의 응력분포를 결정하였으며, 이때 이종금속용접 및 동종금속용접에 의한 용접잔류응력 외에 수압시험과 정상운전 조건도 고려하여 기계적 하중에 의한 응력 재분배를 고려하였다. 최종적으로 이와 같이 구한 응력 분포를 바탕으로 PWSCC에 의한 축방향 및 원주방향 가상 균열의 균열성장 거동을 평가하여 PWSCC 균열 성장량을 계산하였다. 본 논문의 결과는 향후 PWSCC에 의한 원자로 배관 이종금속 맞대기 용접부의 균열성장 거동 예측에 적용될 수 있다.

• Structural Engineering and Mechanics
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• 제10권6호
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• pp.589-601
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• 2000

A simplified analysis procedure utilizing the strut-tie modeling technique is developed to take a close look into the post-elastic deformation capacity of beam-column connections in ductile reinforced concrete frame structures. Particular emphasis is given to the effect of concrete strength decay and quantity and arrangement of joint shear steel. For this a fan-shaped crack pattern is postulated through the joints. A series of hypothetical rigid nodes are assumed through which struts, ties and boundaries are connected to each other. The equilibrium consideration enables all forces in struts, ties and boundaries to be related through the nodes. The boundary condition surrounding the joints is obtained by the mechanism analysis of the frame structures. In order to avoid a complexity from the indeterminacy of the truss model, it is assumed that all shear steel yielded. It is noted from the previous research that the capacity of struts is limited by the principal tensile strain of the joint panel for which the strain of the transverse diagonal is taken. The post-yield deformation of joint steel is taken to be the only source of the joint shear deformation beyond the elastic range. Both deformations are related by the energy consideration. The analysis is then performed by iteration for a given shear strain. The analysis results indicate that concentrating most of the joint steel near the center of the joint along with higher strength concrete may enhance the post-elastic joint performance.

• Corrosion Science and Technology
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• 제3권5호
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• pp.198-208
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• 2004

Although there has been no general agreement on the mechanism of primary water stress corrosion cracking (PWSCC) as one of major degradation modes of Ni-base alloys in pressurized water reactors (PWR's), common postulation derived from previous studies is that the damage to the alloy substrate can be related to mass transport characteristics and/or repair properties of overlaid oxide film. Recently, it was shown that the oxide film structure and PWSCC initiation time as well as crack growth rate were systematically varied as a function of dissolved hydrogen concentration in high temperature water, supporting the postulation. In order to understand how the oxide film composition can vary with water chemistry, this study was conducted to characterize oxide films on Alloy 600 by an in-situ Raman spectroscopy. Based on both experimental and thermodynamic prediction results, Ni/NiO thermodynamic equilibrium condition was defined as a function of electrochemical potential and temperature. The results agree well with Attanasio et al.'s data by contact electrical resistance measurements. The anomalously high PWSCC growth rate consistently observed in the vicinity of Ni/NiO equilibrium is then attributed to weak thermodynamic stability of NiO. Redox-induced phase transition between Ni metal and NiO may undermine the integrity of NiO and enhance presumably the percolation of oxidizing environment through the oxide film, especially along grain boundaries. The redox-induced grain boundary oxide degradation mechanism has been postulated and will be tested by using the in-situ Raman facility.