• 대한기계학회논문집A
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• 제20권6호
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• pp.1862-1871
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• 1996

The puopose of this paper is sto modify the current LBB criteria. The validity of current LBB criteria and current standard LBB analysis mehtod are evaluated using linear elastic fracture mechanics and elastic-plastic fracture mechanics. The results of evaluation demonstrate that the current LBB driteria are very conservative and some level of margins already exist in the standard LBB analysis method. Thus, the margin on load .root. and margin on crack size 2 can be eliminated to extend LBB application for the samller diameter pipe.

• 대한기계학회논문집
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• 제19권5호
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• pp.1182-1189
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• 1995

Several methods have been developed to predict the creep rupture time of the steam pipes in thermal power plant. However, existing creep life prediction methods give very conservative value at operating stress of power plant and creep rupture strain cannot be well estimated. Therefore, in this study, creep rupture time and strain prediction method accounting for material damage and grain boundary sliding is newly proposed and compared with the existing experimental data. The creep damage evolves by continuous cavity nucleation and constrained cavity growth. The results showed good correlation between the theoretically predicted creep rupture time and the experimental data. And creep rupture strain may be well estimated by using the proposed method.

• 대한기계학회논문집A
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• 제20권6호
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• pp.1872-1881
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• 1996

LBB(Leak-Before-Break) analysis is performed for the highest stress location of each different type of mateerials in the nuclear piping line. In most cases, the highest stress occurs in the pipe and nozzle interface location. i.e. terminal end. The current finite element analysis approach utilizes the symmetry condition both for locations near the nozzle and for locationa away from the nozzle to minimize the size of the finite element model and to make analysis simple when calculating the J-integral values at the crack tip. In other words, the nozzle is not included in the finite element model. However, in reality, the symmetric condition is not applicable for the pipe-nozzle interface location. Because the pipe-nozzle interface location is asymmetric due to different stiffenss of the pipe and nozzle(both material and dimensions). The simplified analysis approach for pipe-nozzle interface locaiton is too conservative for a smaller diameter piping. In tlhis paper, various analyses are performed for the range of materials and crack sizes to evaluate the nozzle effect for a LBB anlaysis. This paper presents methodology for developing the piping evaluaiton diagram at the pipe-nozzle interface location.

• 에너지공학
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• 제21권1호
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• pp.75-80
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• 2012

본 논문은 원자력발전소의 대형탱크 또는 배관파단에 따른 격실의 침수분석을 수행함에 있어 최적평가방법을 개발하여 원전에 실제로 적용하는 방법에 관한 논문을 작성하는데 목적이 있다. 주급수관파단사고 분석을 위해 RETRAN 전산코드를 사용하였다. 유출수 질량유량을 계산하는데 있어서 주급수제어밸브가 계통설계에 의거 원자로정지 후 5.0초 만에 닫히는 것으로 모델링하여 분석하였다. 출력 70% 운전시 방출유량이 가장 높은 것으로 나타났다. 방출 질량유량을 가지고 침수위를 계산한 결과 주급수관 격실의 최대 침수위는 1.43m로서 이는 안전성기기가 설치된 위치보다 낮아 원전의 안전정지에 미치는 영향이 없는 것으로 나타났다.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1998년도 춘계학술발표회논문집(2)
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• pp.48-53
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• 1998

원자력 발전소 배관계통에 파단전 누설 (LBB) 설계개념의 적용을 위해서는 원자로 가동온도에서의 재료의 파괴저항성 평가가 필수적이다. 본 연구에서는 국내 원자로의 1차 냉각계통배관의 엘보우 소재로 사용되는 SA516-Gr.70 강의 파괴저항성에 미치는 DSA (Dynamic Strain Aging, 동적변형시효) 영향을 고찰하였다. 파괴저항성 평가를 위해 원자로 가동온도를 포함한 상온~50$0^{\circ}C$ 온도영역에서 준정적 하중에서부터 지진 하중 정도의 동적 하중까지 하중속도를 달리하여 직류전위차법 (DCPD) 이용하여 J-R 시험을 행하였다. J-R 시험결과, SA516-Gr.70 강은 특정한 온도와 하중속도의 조합에서 파괴저항성이 크게 떨어지는 양상을 보였으며, 낮은 파괴저항성을 나타내는 온도는 하중속도가 증가함에 따라 높은 온도쪽으로 이동하는 전형적인 DSA 감수성을 보였다. 인장시험을 통해서도 큰 폭의 serration 이 관찰되었으며 SA516-Gr.70 강에서 파괴저항성의 변화와 DSA 현상과의 연관성을 고찰하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.357-362
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• 2001

The pipe fracture tests were performed on 102mm-Sch.80 carbon steel pipe with various local wall thinning shapes, in order to understand failure behavior of thinned pipe. Pipe specimens were subjected to monotonic bending moment, using 4-points loading system, under internally pressurized condition. From the results of experiment, the failure mode, load carrying capacity, and deformability of local wall thinning pipe were investigated. Failure mode of thinned pipe depended on magnitude of internal pressure and thinning length as well as loading direction and thinning depth and angle. The variation in load carrying capacity and deformability of thinned pipe with length of thinned area was determined by stress type appled to thinning region and circumferential thinning angle. Also, the effect of internal pressure on failure behavior was dependent on failure mode of thinned pipe, and it promoted crack occurrence and mitigated local buckling at thinned area.

• Korean Chemical Engineering Research
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• 제56권3호
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• pp.388-403
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• 2018

본 연구는 소듐냉각고속로 원형로 소듐-물 반응 압력완화계통의 소듐, 물, 가스 배출배관 설계에 필요한 요건 도출을 목적으로 한다. 증기발생기의 전열관 파단에 의한 대규모 물 누출 사고 발생 시, 증기발생기 전열관 측의 물과 전열관 외측의 소듐 및 반응생성물을 물배출조와 소듐배출조로 신속하게 배출하기 위해 증기발생기의 소듐 배출배관 파열판 면적, 소듐배출조의 가스 방출배관 직경, 물배출조의 기체 방출배관 직경, 증기발생기의 물 배출배관 직경 등을 설정하기 위한 계산을 수행하였다. 이를 바탕으로 대규모 물 누출 사고 발생 시 증기발생기 내 유체 배출 소요시간 및 압력거동 해석을 수행하였고, 증기발생기 물 배출배관 격리밸브의 차단 설정압력 등의 설계인자를 도출하였다. 본 연구에서 도출된 설계인자들은 소듐냉각고속로 원형로 소듐-물 반응 압력완화계통 설계에 기초자료로 활용할 예정이다.

• 한국압력기기공학회 논문집
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• 제9권1호
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• pp.70-76
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• 2013

Several finite element models for the leak-before-break (LBB) assessment of overlay dissimilar metal weldment were constructed and analyzed to develop a simple finite element modeling method. The J-integral, crack opening displacement (COD) and J-integral distribution along the crack front in thickness direction due to the applied moment were obtained from the analysis results of the constructed finite element models, and studied compared to the previous literatures. It is concluded that the modeling with base material only is simple and produces a slightly conservative results compared to the complex modeling composed with weld metal and base metal in the calculation of J-integrals and COD values which are used for the calculation of fracture toughness and postulated leakage crack length respectively.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집A
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• pp.80-86
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• 2001

An engineering estimation equation for the crack opening displacement (COD) is proposed for a complex cracked pipe, based on the reference stress approach. To define the reference stress, a simple plastic limit load analysis for the complex cracked pipe subjected to combined bending and tension is performed considering the crack closure effect in the compressive-stressed region. Comparison with ten published test data and the results from existing method shows that the present method not only reduces non-conservatism associated with the existing method, but also provides consistent and overall satisfactory results.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집A
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• pp.67-72
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• 2001

The LBB behavior and the crack opening displacement after a crack penetrated wall thickness of statically indeterminate piping system were investigated in this study, compared with statically determinate piping system. The reduction of ultimate strength caused by a crack was relatively small in the statically indeterminate piping system. The statically indeterminate piping system has more safety margin for LBB behavior than the statically determinate piping system. The crack opening displacement could be evaluated by using the plastic rotation angle proposed to evaluate the crack opening displacement after crack penetration in pipe with a non-penetrating crack.