• Nuclear Engineering and Technology
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• 제46권6호
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• pp.869-874
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• 2014

It was discovered in a Korean PWR that an extensive number of very short and shallow cracks in the SG tubes were undetectable by eddy current in-service-inspection because of the masking effect of sludge deposits. Axial stress corrosion cracks at the outside diameter of the steam generator tubes near the line contacts with the tube support plates are the major concern among the six identical Korean nuclear power plants having CE-type steam generators with Alloy 600 high temperature mill annealed tubes, HU3&4 and HB3~6. The tubes in HB3&4 have a less susceptible microstructure so that the onset of ODSCC was substantially delayed compared to HU3&4 whose tubes are most susceptible to ODSCC among the six units. The numbers of cracks detected by the eddy current inspection jumped drastically after the steam generators of HB4 were chemically cleaned. The purpose of the chemical cleaning was to mitigate stress corrosion cracking by removing the heavy sludge deposit, since a corrosive environment is formed in the occluded region under the sludge deposit. SGCC also enhances the detection capability of the eddy current inspection at the same time. Measurement of the size of each crack using the motorized rotating pancake coil probe indicated that the cracks in HB4 were shorter and substantially shallower than the cracks in HU3&4. It is believed that the cracks were shorter and shallower because the microstructure of the tubes in HB4 is less susceptible to ODSCC. It was readily understood from the size distribution of the cracks and the quantitative information available on the probability of detection that most cracks in HB4 had been undetected until the steam generators were chemically cleaned.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 봄학술 발표회 논문집(II)
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• pp.477-480
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• 2005

The discharge of sewage sludge is rapidly increasing in Korea. But the most common sewage sludge disposal alternative is to incinerate and to deposit it in controlled landfills. However, space limitations on existing landfill sites, and increasing environmental concerns have prompted the investigation of alternative ash disposal routes. The utilization of sewage sludge ash would contribute to the elimination of an environmental problem and to the development of new high-performance materials. The purpose of this study is to apply to Alkali Activation into solidification of sewage sludge ash. It achieves leaching test, chemical composition and compressive strength test. As a result of tests, the sewage sludge ash has sufficient potential for use of pozzolanic raw material. However, it is judge to be available to construction material if research is continuously gone.

• 상하수도학회지
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• 제20권5호
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• pp.667-676
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• 2006

This study was conducted to evaluate the effect of longitudinal baffle on hydrodynamic behavior within a certain full-scale sedimentation basin (flow rate per basin; $1,000m^3/d$). Comparative experimental investigations have been carried out on the sediment removal efficiencies and the sludge deposit distribution in the baffled and un-baffled sedimentation basin, respectively. From the results derived in the baffled and un-baffled sedimentation, the turbidity removal rate in the baffled sedimentation basin is about 38% higher than that in un-baffled. Also, the height of sludge deposit in the baffled sedimentation basin is approximately 20% lower, and the sludge concentration is 10% higher than those in un-baffled sedimentation basin. In order to explain the experimental results and investigate the effect of longitudinal baffle in more detail, we conducted Computational Fluid Dynamics (CFD) simulation. From the results of CFD simulation, the flow, especially in the near of outlet orifice, was more stable in the case of longitudinal baffled sedimentation basin than that in un-baffled basin. Also, it could be concluded that the longitudinal baffle made a fully developed flow more effective for sedimentation.

• 한국물환경학회지
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• 제22권3호
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• pp.468-474
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• 2006

In the secondary settling tanks, three different types of settling phenomena occurs; i.e., zone settling for sludge thickening in the bottom part of settling tank, and discrete and flocculent settling for clarification in the upper part. In this paper, morphological parameters of the floc in sludge blanket layers along the length of a long rectangular tank were investigated. The plant used for this study had a serious bulking problem caused by Microthrix parvicella. Floc size decreased as the surface area of settling tank increases, which indicates that in the secondary settling tank where zone settling believed to be predominant, free or flocculent type of settling contributes to floc size distributions. Large floc particles deposit in the front zone of settling tank, but small and loose flocs mostly in the zone near its outlet. On the other hand, filament length contained in one gram of sludge blanket solid increases along the flow direction. Large flocs with less filaments settle faster, but small flocs having more filaments result in poor settling. These results support function of microorganism selection occurring in secondary settling tank. In addition, designing a long rectangluar settling tank with double hoppers might be one of the ways of bulking control, but this idea has to be verified with a further study.

• 한국수자원학회논문집
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• 제35권2호
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• pp.137-148
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• 2002

도시하천 하류부에서의 하상퇴적토 준설에 따른 수직개선효과를 검토하기 위해 유한차분법을 사용하여 목표년도 하수의 차집율에 따라 목표수질 달성에 대한 기여정도를 분석하였다. 도시를 관류하고 있는 11.2km의 하천구간내에 21개 지점을 선정하여 시추를 실시하였으며, 용출시험을 통한 하상퇴적토의 오염정도을 조사하였다. 하상퇴적토 준석에 따른 주요지점별 COD 변화를 갈수량, 저수량 및 평수량에 대해서 검토하였고, 그 결과 오염된 하상퇴적토의 준설이 수질개선에 미치는 효과가 비교적 큰 것으로 나타났다.

• 비파괴검사학회지
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• 제32권5호
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• pp.545-550
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• 2012

원자력발전소 증기발생기 세관은 방사성물질이 외부로 누출되지 않도록 압력경계 역할을 하는 주요부품이다. 설비 운전기간이 증가함에 따라 이차측에서 유입된 슬러지가 증기발생기 2차측 유체 흐름을 따라 상부로 이동하면서 유체비등과 난류에 의해 세관 외면에 스케일이 부착되어 세관열화, 유로홈 막힘 및 열전달을 감소시키는 파울링을 유발하는 원인으로 작용한다. 따라서, 원전 운영자는 세관 외면에 쌓인 스케일의 두께를 확인하여 일정시점이 되면 화학세정 등의 정비를 수행한다. 본 논문에서는 보빈코일 와전류신호를 이용하여 세관 외면에 부착된 스케일 두께를 정량적으로 평가하는 기술을 개발하고자 스케일 시험편을 제작하여 스케일 두께와 와전류신호 진폭 간의 상관관계를 분석하였고, 이를 바탕으로 스케일의 두께를 정량적으로 평가하는 기법과 대량의 와전류 데이터를 평가할 수 있는 프로그램을 개발하였다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 하계학술대회 논문집
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• pp.335-338
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• 2001

With the use of the electron microscopy and X-ray phase analysis the regularities of carbon deposit formation in process of methane and propane pyrolysis on the zeolites, Kazakhstan natural clays, chrome and bauxite sludge containing metal oxides of iron subgroup, have been studied. In process of over-carbonization the trivalent iron was reduced to metal form. In addition, the carbon tubes of divers morphology had been impregnated with ultra-dispersed metal particles. The kinetic parameters of carbon formation in process of methane decomposition on the zeolite CoO mixture surface were investigated by method of thermo-gravimetric analysis. The morphology and structure of formed carbon fibrils, with the metal particles fixed at their ends, have been investigated, the formation of branched carbon fibrils pattern, so called octopus, being found.

• Transactions on Electrical and Electronic Materials
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• 제2권2호
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• pp.5-15
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• 2001

The experiment established optimal conditions for over-carbonization. With the use of the electron microscopy and X-ray phase analysis the regularities of carbon deposit formation in process of methane and propane pyrolysis on the zeolites, Kazakhstan natural clays, chrome and bauxite sludge containing metal oxides of iron subgroup, have been studied. In process of over-carbonization the trivalent iron was reduced to metal form. In addition, the carbon tubes of divers morphology had been impregnated with ultra-dispersed metal particles. The kinetic parameters of carbon formation in process of methane decomposition on the zeolite - CoO mixture surface were investigated by method of thermo-gravimetric analysis. The morphology and structure of formed carbon fibrils, with the metal particles fixed at their ends, have been investigated, the formation of branched carbon fibrils pattern, so called octopus, being found. Also, the walnut shells and grape kernel carbonization, their immobilization by the cells of selective absorption of heavy metal and sulfur dioxide ions have been studied. The example of metal-carbon composites used as adsorbents for wastewater purification, C$_3$- C$_4$ hydrocarbon cracking catalysts and refractory materials with improved properties have been considered.

• 한국산학기술학회:학술대회논문집
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• 한국산학기술학회 2004년도 춘계학술대회
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• pp.258-260
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• 2004

암모니아 대신 에탄올아민은 원자력 발전소 2차계통수에서 pH를 증가시켜 철 부식을 억제하고, 중기 발생기 전열관의 건전성을 제고하기 위해 사용하고 있다. 에탄올아민은 암모니아와 물리화학적 성질이 다르므로, 증기발생기에 유입되는 부식생성물의 용해와 흡착, 이온성 불순물의 잠복현상에 미치는 영향이 다르다. 본 연구에서는 온도가 증가함에 따라 암모니아와 에탄올아민이 부식생성물에 대한 용해와 흡착, 이온성 불순물의 잠복현상에 미치는 영향을 조사하였다. 2차 계통수의 pH 제어제로서 에탄올 아민은 암모니아보다 증기발생기 슬러지의 철산화물에 많이 흡착되어 철산화물의 용해도를 증가시키므로 퇴적된 슬러지의 양을 감소시키며, 또한 슬러지에 흡착된 불순물의 양을 감소시켜 잠복 현상을 억제할 것으로 판단된다.

• 에너지공학
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• 제12권3호
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• pp.223-230
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• 2003

본 연구에서는 제철소의 슬러지 소각로 배가스의 냉각을 위한 열교환기에서의 가스측 파울링 현상의 측정 및 분석에 대한 연구를 수행하였다. 소각로 배가스는 열교환기의 수직 전열관을 통과하면서 냉각되며 동시에 연소용 공기를 예열한다. 이러한 열교환기의 파울링은 주로 열교환기 입구에 발생하여, 본 연구에서는 열교환기의 입구 형태와 비슷한 형상의 오염다공판을 사용하여 슬러지 소각로 배가스의 파울링 현상을 측정하였으며, 부착분진에 대한 특성분석을 수행하였다. 분석 결과, 분진 부착율은 온도와 분진성분 및 분진크기에 영향을 받으며, 또한 오염다공판의 위치에 따라 부착형태가 다르게 나타났다. 또한 전산 해석을 통하여 오염다공판의 구멍 크기에 따라 분진부착율이 변하는 것을 알 수 있었다. 그리고 오염다공판을 사용하여 다관식 원통형 열교환기의 입구에서의 파울링 특성을 측정할 수 있음을 확인하였다.