• Nuclear Engineering and Technology
• /
• 제36권6호
• /
• pp.485-496
• /
• 2004

Typical probabilistic safety assessment (PSA) results were used to estimate the performance indicator (PI) thresholds of unplanned reactor scram (URS) and safety system unavailability (SSU) for Korean nuclear power plants (NPPs). The changes in core damage frequency (${\Delta}$CDFs) of $10^{-6}/yr$, $10^{-5}/yr$, and $10^{-4}/yr$ were adopted as the risk criteria in setting up the PI thresholds. The PI thresholds for the URS were estimated using information pertaining to the initiating event frequencies, the CDF, and the CDF contribution of each initiating event. The PI thresholds of the SSU were estimated using information on the unavailability, the Fussell-Vesely importance, and the CDF.

• Nuclear Engineering and Technology
• /
• 제44권5호
• /
• pp.437-452
• /
• 2012

The Tohoku earthquake (Mw9.0) occurred on March 11, 2011 and caused a large tsunami. The Fukushima Dai-ichi NPP (F1-NPP) were overwhelmed by the tsunami and core damage occurred. This paper describes the overview of F1-NPP accident and the usability of tsunami PRA at Tohoku earthquake. The paper makes reference to the following current issues: influence on seismic hazard of gigantic aftershocks and triggered earthquakes, concepts for evaluating core damage frequency considering common cause failure with correlation coefficient against seismic event at multi units and sites, and concepts of "seismic-tsunami PSA" considering a combination of seismic motion and tsunami effects.

• Nuclear Engineering and Technology
• /
• 제40권4호
• /
• pp.285-298
• /
• 2008

This study evaluates the performance of a coil spring-viscous damper system for the vibration and seismic isolation of an Emergency Diesel Generator (EDG) by measuring its operational vibration and seismic responses. The vibration performance of a coil spring-viscous damper system was evaluated by the vibration measurements for an identical EDG set with different base systems - one with an anchor bolt system and the other with a coil spring-viscous damper system. The seismic performance of the coil spring-viscous damper system was evaluated by seismic tests with a scaled model of a base-isolated EDG on a shaking table. The effects of EDG base isolation on the fragility curve and core damage frequency in a nuclear power plant were also investigated through a case study.

• 융합보안논문지
• /
• 제15권6_2호
• /
• pp.141-149
• /
• 2015

현대사회의 무한경쟁시대는 경제적 가치가 매우 큰 최첨단 과학기술을 확보 선점하는 것이 국가의 경쟁력에 상당한 영향력을 미치게 된다. 이러한 국가의 핵심기술이나 기업의 최첨단 기술을 탈취해가는 산업보안범죄는 국가의 경제안보에 위협적인 피해를 줄 수가 있고, 방위산업 분야의 경우 국가안보와 직결되어 있는 심각한 범죄에 해당한다. 한번 유출된 국가의 핵심기술과 기업의 영업비밀은 회수가 불가능하기 때문에 엄격한 처벌과 대책으로 산업보안 침해범죄를 미연에 방지해야 한다. 일부 선진외국에서도 국가의 경제 및 국가안보와 직결된 산업보안범죄에 대해서는 국가차원에서 관리 가능하도록 법과 제도들이 운영되고 있다. 최근 들어 국내에서도 국가핵심기술이 침해되는 사례가 급증하고 있으며, 아울러 기업의 핵심적인 산업기술을 유출시키는 방법도 과거 저장된 문서를 단순하게 복사하거나 출력해 나가는 수단이 아니라, 최첨단 IT기술 발달로 인해 그 유형과 행태도 다양해졌다. 따라서 국가의 핵심기술과 기업의 영업비밀을 침해하는 산업보안범죄에 대한 피해는 상당히 위협적이기 때문에 산업보안을 단순히 기술유출방지라는 시야가 아닌 산업과 관련된 모든 손실방지와 지적재산보호라는 넓은 범주에서 파악하는 것이 필요하다.

• Composites Research
• /
• 제12권5호
• /
• pp.54-64
• /
• 1999

본 연구에서는 낙하추 방식의 충격시험기를 이용하여 스티칭된 샌드위치 복합재의 저에너지 충격거동을 조사하였다. 스티칭된 샌드위치 복합재는 유리섬유직물의 면재와 우레탄 폼의 코아로 구성되어 있으며 위쪽 면재와 아래쪽 면재는 폴리에스터 보강섬유로 코아의 두께방향을 따라 스티칭하여 일체형으로 결합되어 있다. 이때 코아의 두께가 충격거동에 미치는 영향을 조사하기 위해 코아의 두께를 달리한 네 종류의 스티칭된 샌드위치 복합재를 고려하였다. 스티칭된 샌드위치 복합재에 작용되는 충격조건은 낙하추의 질량과 낙하추의 낙하높이를 조절함으로써 변화시켰다. 연구결과에 따르면 코아의 두께, 낙하추의 낙하높이, 그리고 낙하추의 질량 등의 변화는 스티칭된 샌드위치 복합재에서의 충격하중, 충격체와의 접촉시간, 면재에 형성된 변형율 등에 영향을 미침을 알 수 있었다. 또한 스티칭된 샌드위치 복합재는 스티칭부의 보강효과로 인해 손상을 억제시킬 분 아니라 손상이 발생한 경우에도 구조물로서 역할을 담당할 수 있다. 그러나 스티칭된 샌드위치 복합재를 효율적으로 기존의 구조물에 적용하기 위해서는 스티칭부에서의 수지함침성을 개선할 수 있는 제작공법의 연구가 필요하다.

• Steel and Composite Structures
• /
• 제38권5호
• /
• pp.477-496
• /
• 2021

The main objective of this paper is to study vibration of sandwich open cylindrical panel with damaged core and FG face sheets based on three-dimensional theory of elasticity. The structures are made of a damaged isotropic core and two external face sheets. These skins are strengthened at the nanoscale level by randomly oriented Carbon nanotubes (CNTs) and are reinforced at the microscale stage by oriented straight fibers. These reinforcing phases are included in a polymer matrix and a three-phase approach based on the Eshelby-Mori-Tanaka scheme and on the Halpin-Tsai approach, which is developed to compute the overall mechanical properties of the composite material. Three complicated equations of motion for the panel under consideration are semi-analytically solved by using 2-D differential quadrature method. Several parametric analyses are carried out to investigate the mechanical behavior of these multi-layered structures depending on the damage features, through-the-thickness distribution and boundary conditions. It is seen that for the large amount of power-law index "P", increasing this parameter does not have significant effect on the non-dimensional natural frequency parameters of the FG sandwich curved panel. Results indicate that by increasing the value of isotropic damage parameter "D" up to the unity (fully damaged core) the frequency would tend to become zero. One can dictate the fiber variation profile through the radial direction of the sandwich panel via the amount of "P", "b" and "c" parameters. It should be noticed that with increase of volume fraction of fibers, the frequency parameter of the panels does not increase necessarily, so by considering suitable amounts of power-law index "P" and the parameters "b" and "c", one can get dynamic characteristics similar or better than the isotropic limit case for laminated FG curved panels.

• Composites Research
• /
• 제27권2호
• /
• pp.77-81
• /
• 2014

본 연구에서는 전기체 복합재가 적용되어 설계된 소형 항공기의 손상 평가 및 유지 보수 연구를 수행하였다. 본 연구에서 개발 중인 항공기의 스킨 부위는 샌드위치 구조가 적용되었다. 본 연구에서는 노멕스 허니컴코어와 카본 면재가 적용된 샌드위치 복합재 구조에 대해 구멍 손상 이후의 잔류 강도 평가에 대한 연구를 수행하였다. 4점 굽힘 시험을 통해 시편의 굽힘 강도를 확인하고, 시편에 손상을 모사하기 위하여 시편의 중앙 부위에 구멍 손상을 가하였다. 손상된 시편을 손상 전 시편과 동일한 시험을 통해 손상 전의 강도와 비교하였다. 또한 손상된 복합재 구조는 손상 부위 제거 후 패치 수리 기법을 적용하고 손상된 시편과 보수된 시편의 굽힘 강도 시험결과를 비교하였다. 샌드위치 복합재 구조 시편의 유지 보수 후 굽힘 강도 시험 결과 손상 전 시편의 강도와 비교하여 강도의 95%까지 회복되는 것으로 분석되었다.

• 한국안전학회지
• /
• 제33권5호
• /
• pp.157-163
• /
• 2018

This paper describes design improvement to a research rector for safety enhancement using Probabilistic Safety Assessment (PSA). This PSA under reactor design was undertaken to assess the level of safety for the design of a research reactor and to evaluate whether it is probabilistically safe to operate and reliable to use. The scope of the PSA reported here is a Level 1 PSA, which addresses the risks associated with the core damage. The technical objectives of this study were to identify accident sequences leading to core damage and to derive design improvement from the dominant accident sequences through the sensitivity analysis. The AIMS-PSA and FTREX were used for the this PSA of the research reactor. The criterion for inclusion was all sequences with a point estimate frequency greater than a truncation value of 1.0E-14/yr. The final result indicates a point estimate of 6.79E-05/yr for the overall Core Damage Frequency (CDF) attributable to internal initiating events for the research reactor under design. Based on the dominant accident sequences from the PSA, the seven kinds of sensitivity analysis were performed and some design improvement items were derived. When the five methods to improve the safety were all applied to the reactor design and emergency operating procedure, its risk was reduced to about 1.21E-06/yr from 6.79E-05/yr. The contribution of LOCA and LOEP with high CDF were significantly reduced by the sensitivity analysis. The safety of the research reactor was well improved and the risk was reduced than before adapting the design improvement gotten from the sensitivity analysis. The present study indicated that the research reactor has the well-balanced safety in regard to each initiating event contribution to CDF. The PSA methodology is very effective to improve reactor safety in a conceptual design phase and especially, Risk-informed design(RID) is very nice way to find the deficiencies of research reactor under design and to improve the reactor safety by solving them.

• 한국복합재료학회:학술대회논문집
• /
• 한국복합재료학회 2004년도 춘계학술발표대회 논문집
• /
• pp.111-114
• /
• 2004

Using the embedded optical fiber sensor of totally-reflected extrinsic Fabry-Perot interferometer(TR-EFPI), longitudinal strains(Ex) of the core and skin layers in glass fiber reinforced plastic(GFRP) cross-ply composite laminates have been measured. Transmission optical microscopy was employed to study the damage formation around the TR-EFPI sensor. It was observed that values of ex in the interior of the skin layer and the core layer measured by embedded TR-EFPI sensor was significantly higher than that of the specimen surface measured by strain gauges. The experimental results agreed well with those from finite element analysis on the basis of uniform stress model. Large strains in the core layer led to the occurrence of transverse cracks which drastically reduced the strain at failure of optical fiber sensor embedded in the core layer.

• Earthquakes and Structures
• /
• 제21권5호
• /
• pp.515-530
• /
• 2021

In a tall reinforced concrete (RC) core wall system subjected to strong ground motions, inelastic behavior near the base as well as mid-height of the wall is possible. Generally, the formation of plastic hinge in a core wall system may lead to extensive damage and significant repairing cost. A new configuration of core structures consisting of buckling restrained braced frames (BRBFs) and RC walls is an interesting idea in tall building seismic design. This concept can be used in the plan configuration of tall core wall systems. In this study, tall buildings with different configurations of combined core systems were designed and analyzed. Nonlinear time history analysis at severe earthquake level was performed and the results were compared for different configurations. The results demonstrate that using enough BRBFs can reduce the large curvature ductility demand at the base and mid-height of RC core wall systems and also can reduce the maximum inter-story drift ratio. For a better investigation of the structural behavior, the probabilistic approach can lead to in-depth insight. Therefore, incremental dynamic analysis (IDA) curves were calculated to assess the performance. Fragility curves at different limit states were then extracted and compared. Mean IDA curves demonstrate better behavior for a combined system, compared with conventional RC core wall systems. Collapse margin ratio for a RC core wall only system and RC core with enough BRBFs were almost 1.05 and 1.92 respectively. Therefore, it appears that using one RC core wall combined with enough BRBF core is an effective idea to achieve more confidence against tall building collapse and the results demonstrated the potential of the proposed system.