• Nuclear Engineering and Technology
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• 제45권4호
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• pp.513-522
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• 2013

The ODSCC detected in the TSP position of Ulchin 3&4 SGs are typical ODSCC of Alloy 600MA tubes. The causative chemical environment is formed by concentration of impurities inside the occluded region formed by the tube surface, egg crate strips, and sludge deposit there. Most cracks are detected at or near the line contacts between the tube surface and the egg crate strips. The region of dense crack population, as defined as between $4^{th}$ and $9^{th}$ TSPs, and near the center of hot leg hemisphere plane, coincided well with the region of preferential sludge deposition as defined by thermal hydraulics calculation using SGAP computer code. The cracks developed homogeneously in a wide range of SGs, so that the number of cracks detected each outage increased very rapidly since the first detection in the $8^{th}$ refueling outage. The root cause assessment focused on investigation of the difference in microstructure and manufacturing residual stress in order to reveal the cause of different susceptibilities to ODSCC among identical six units. The manufacturing residual stress as measured by XRD on OD surface and by split tube method indicated that the high residual stress of Alloy 600MA tube played a critical role in developing ODSCC. The level of residual stress showed substantial variations among the six units depending on details of straightening and OD grinding processes. Youngwang 3&4 tubes are less susceptible to ODSCC than U3 and U4 tubes because semi-continuous coarse chromium carbides are formed along the grain boundary of Y3&4 tubes, while there are finer less continuous chromium carbides in U3 and U4. The different carbide morphology is caused by the difference in cooling rate after mill anneal. There is a possibility that high chromium content in the Y3&4 tubes, still within the allowable range of Alloy 600, has made some contribution to the improved resistance to ODSCC. It is anticipated that ODSCC in Y5&6 SGs will be retarded more considerably than U3 SGs since the manufacturing residual stress in Y5&6 tubes is substantially lower than in U3 tubes, while the microstructure is similar with each other.

• 생명과학회지
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• 제14권6호
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• pp.906-912
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• 2004

한국에서 분리한 Helicobacter pylori 균주가 위암 세포주에서 IL-8를 유도하는 유도능을 관찰하고자 하였으며, 특히 4형 분비구조의 주요 구성체인 cagE 유전자의 다형성에 따라 IL-8 유도능의 차이 및 각 질환에서 분리한 균주에서의 차이가 있는지 검토하고자 하였다. 강남성모병원 내시경검사를 받은 환자들 중 H. pylori 감염 양성으로 확인된 위암 23명 $(31.0\%)$, 위염 24명$(32.6\%)$, 십이지장궤양27명$(36.4\%)$ 총 74명을 대상으로 하여 H. pylori를 분리한 후 PCR-RFLP방법을 이용하여 cagE 다형성을 확인하였으며, PCR 및 Real-time PCR을 이용하여 ragA TPMs를 결정하였다, 또한 분리된 균주를 위암세포주에 감염시켜 상등액을 취하여 ELISA방법으로 IL-8을 정량화 하였다. 전체 74개의 분리 균주 중 59개의 균주$(79.7\%)$에서 IL-8 유도능이 있는 것으로 확인되었으며, cagE 다형성 중에서 가장 높은 빈도로 관찰되는 형태는 MboI/NlaIII B-C, A-C 및 C-C 타입 이었으며, 이중 A-C와 B-C 형태가 C-C 형태에 비해 유의적으로 높은 IL-8 유도능을 나타냈다. 그러나 cagA TPMs의 분류 및 vacA m-아형 분류와 IL-8 유도능과는 연관성이 없었다. 비록 본 연구에서 cagE 다형성과 IL-8 유도능과 아주 밀접한 연관성이 나타나지는 않았지만 vacA m-아형이나 cagA TPMs 보다는 cagE 다형성이 IL-8 유도능과 연관성이 클 것으로 생각된다.