• Nuclear Engineering and Technology
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• 제54권12호
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• pp.4522-4533
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• 2022

For severe accident assessment of reactor pressure vessel (RPV), it is important to develop an accurate model that can predict transient thermo-mechanical behavior of the RPV lower head under the given condition. The present study revisits the lower head failure with two- and three-dimensional finite element models. In particular, we aim to give clear insight regarding the effect of the three-dimensionality present in the distribution of the thickness and thermal load of the lower head. For a rigorous validation of the result, both the OLHF-1 and the OLHF-2 tests are considered in this study. The result suggests that the three-dimensional effect is not negligible as far as the failure location is concerned. The non-uniformity of the thickness distribution is found to affect the failure location and time. The thermal load, which may not be axisymmetric in general, has the most significant effect on the failure assessment. We also observe that the creep property can affect the global deformation of the lower head, depending on the applied mechanical load.

• Nuclear Engineering and Technology
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• 제32권4호
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• pp.299-308
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• 2000

A safety assessment of reactor vessel lower head integrity under in-vessel vapor explosion loads has been performed. The core melt relocation parameters were chosen within the ranges of physically realizable bounds. The premixing and explosion calculations were performed using TRACER-II code. Using the calculated explosion pressures imposed on the lower head inner wall, strain calculations were peformed using ANSYS code. Then, the calculated strain results and the established failure criteria were used in determining the failure probability of the lower head, In the explosion analyses, it is shown that the explosion impulses are not altered significantly by the uncertain parameters of triggering location and time, fuel and vapor volume fractions in uniform premixture bounding calculations. Strain analyses show that the vapor explosion-induced lower head failure is not possible under the present framework of assessment. The result of static analysis using the conservative explosion-end pressure of 50 MPa also supports the conclusion. It is recommended, however, that an assessment of fracture mechanics for preexisting cracks be also considered to obtain a more concrete conclusion.

• Nuclear Engineering and Technology
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• 제55권11호
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• pp.4134-4145
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• 2023

This paper proposes strain-based failure model of A533B1 pressure vessel steel to simulate failure, followed by application to OECD lower head failure (OLHF) test simulation for experimental validation. The proposed strain-based failure model uses simple constant and linear functions based on physical failure modes with the critical strain value determined either using the lower bound of true fracture strain or using the average value of total elongation depending on the temperature. Application to OECD Lower Head Failure (OLHF) tests shows that progressive deformation, failure time and failure location can be well predicted.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2001년도 추계학술대회 논문집
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• pp.144-149
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• 2001

The failure at the head section of rubble-mound detached breakwaters is more important than other failure modes. because this initial failures will occur the failure of the trunk section and lead to the instability of the structure. The three-dimensional failure modes are discussed using the experimental data with multi-directional waves considering the failure modes occurring around the head of the rubble-mound detached breakwater. The spacial characteristics of failure mode around the rubble-mound structures can be summarized as follows: 1) It was clarified that the failure modes at the round head of a detached breakwater are classified as failure by plunging breaker on the slope, failure by direct incident wave force and failure by scouring at the toe of the detached breakwater. 2) The failure mode was found in the lower wave height than the design wave by the breaker depth effects. It is clarified that the structure monitored was safely designed for the design wave but the failure was occurred by the reason of breaker waves and scouring processes at the toe 3) It was observed that scouring at the toe developed in the region where steady stream due to vorticity was generated and the spatial variation of scour at the toe of the round head was predominated by incident wave direction.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2004년도 학술대회지
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• pp.303-308
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• 2004

The failure at the head section of rubble mound breakwaters is more important than other failure modes. because this initial failures will occur the failure of the trunk section and lead to the instability of the structure. The three-dimensional failure modes are discussed using the experimental data with multi-directional waves considering the failure modes. It was occurred by the topographical characteristics around the head of rubble mound breakwater. The spacial characteristics of failure mode around the rubble-mound structures can be summarized as follows: 1) It was clarified that the failure modes at the round head of a detached breakwater are classified as failure by plunging breaker on the slope, failure by direct incident wave force and failure at the rubble mound breakwaters. 2) The failure mode was found in the lower wave height than the design wave by the breaker depth effects and topography around structures. It is clarified that the structure was monitored safely designed for the design wave but the failure was occurred by the reason of breaker waves.

• 대한기계학회논문집A
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• 제24권11호
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• pp.2866-2874
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• 2000

This paper is concerned with the optimum design for external reinforcement of a nuclear reactor pressure vessel(RPV) in a severe accident. During the severe reactor accident of molten core, the temperature and the pressure in the nuclear reactor rise to a certain level depending on the initial and subsequent condition of a severs accident. The reis of the temperature and the internal pressure cause deterioration of the load carrying capacity and could cause failure of the RPV lower head. The deterioration of failure can be mitigated by the external cooling or the reinforcement of the lower head with additional structures. While the external cooling forces the temperature of an RPV to drop to the desired level, the reinforcement of the lower head can attain both the increase of the load carrying capacity and the temperature drop. The reinforcement of the lower head can be optimized to have the maximum effect on the collapse pressure and the temperature at the inner wall. Optimization results are compared to both the result without the reinforcement and the result with the designated reinforcement.

• Journal of Mechanical Science and Technology
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• 제14권7호
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• pp.744-751
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• 2000

To achieve lower flying height for high areal recording density, the laser zone texturing of the disk needs to be designed to reduce glide height. One problem of the laser bump design is that the regular laser bump pattern often produces glide resonance phenomenon, which leads to failure of the glide height test. However, it was found in this study that glide resonance is an intrinsic problem of the glide head used and resonance phenomenon depends on the type of the head slider, that is, the natural frequency of the slider body. Therefore, higher glide height or glide failure caused by glide resonance does not lead to head/media interface problem in the real drive operating conditions in which the data head is used. Pseudo-random bump pattern greatly reduces the glide resonance. Smaller bump pitch will also help to reduce the glide resonance. However, as bump spacing becomes smaller, glide height will be increased due to increased air pressure developed around the bumps. Lowering bump height is the most effect way to reduce glide avalanche.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2003년도 추계학술대회 논문집
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• pp.317-322
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• 2003

The Sectional and Spatial failure modes are discussed using the experimental data with long crest wave and multi-directional waves considering the failure modes occurring around the rubble-mound breakwater. The spatial & sectional stability and failure mode around the rubble-mound structures with construction progress can be summarized as follows: 1) The rubble mound structures at basic construction step was occurred serious failures when ${\xi}$ was about 6.5. 2) It was clarified that the failure modes at the round head of detached breakwater are classified as failure by plunging breaking on the slope, failure by direct incident wave force and failure by scouring at the toe of the detached break water. 3) The failure mode was found in the lower wave height than the design wave by the breaker depth effect. 4) The failure on the slope were also developed at the lee side of the round head because diffracted wave propagated into the behind area by grouping effect of multi-directional irregular wave.

• 한국전산구조공학회논문집
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• 제27권3호
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• pp.191-198
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• 2014

본 논문에서는 노심용융사고 시 관통노즐이 제거된 원자로용기 하부헤드의 구조 건전성 평가를 수행하였다. 열응력, 노심용융물의 질량 그리고 내압조건의 해석결과를 고려할 때, 하부헤드의 열응력에 의한 영향이 가장 크게 나타났다. 손상 가능성은 파손기준에 따라 평가하였으며, 등가소성변형률이 임계변형률 파손기준보다 낮은 수준으로 평가되었다. 열-구조물 연성해석 결과 하부헤드의 두께 중간층에서 항복강도보다 낮은 응력이 발생한 탄성영역 구간을 확인하였다. 내압이 커지면서 탄성영역 범위가 점차 좁아지면서 탄성영역이 내벽으로 이동하는 결과를 확인하였고, 노심용융사고 시 구조적 건전성을 만족하는 것으로 평가되었다.

• Archives of Reconstructive Microsurgery
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• 제8권1호
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• pp.35-43
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• 1999

저자들은 1988년부터 1998년까지 시행한 252예의 유리피판술 중 9예에서 미세혈관 문합부의 혈전 등의 이유로 실패하였으며, 이들 중 두경부 및 하지의 7예에서는 첫 수술 4-16일 사이에 제 2의 유리피판술을 성공적으로 시행하여 환부를 치유시키고, 처음에 계획하였던 수술적 목표를 달성하였다. 수부의 2예는 환자 및 보호자와 충분한 상의하여 원거리 피판과 피부이식 등 고식적인 치료 방법을 선택하였다. 수부의 경우는 다른 부위보다 고식적 치료 방법이 덜 부담되었던 것으로 생각되었으며, 두경부와 하지는 환부의 특성상 제 2의 유리 피판술이 최선의 선택으로 생각되었다. 유리 피판술이 실패한 환부에서 계속된 제 2의 유리 피판술을 시행하는 것은, 처음의 수술보다 면밀한 술전 계획과 준비, 완벽한 수술, 수술후의 철저한 환자 관리가 요구되었으나, 이들 환부의 처치에 매우 효과적이고 환자의 기대에 부응할 수 있는 방법이라고 생각된다.