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Type 347 stainless steel moderator circuit branch piping in a pressurized hot water reactor was experiencing frequent leakage. Investigation of the problem involved failure analysis of leaking pipe specimens, analytical stress analysis, and determination of “leak-before-break” conditions using fracture mechanics and thermal fatigue simulation tests. Failure analysis indicated that cracking had been initiated by thermal fatigue. Data from the analysis were used in making the leak-before-break predictions. It was determined that the cracks could grow to two-thirds of the circumferential length of the pipe without catastrophic failure. A thin stainless steel sleeve was inserted in the branch pipe to resolve the problem.

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Antonio Florio, Juan C. Crespi, Failure Analysis of the Moderator Branch Pipe of a Pressurized Hot Water Reactor, Handbook of Case Histories in Failure Analysis, Vol 1, Edited By Khlefa A. Esaklul, ASM International, 1992, p 153–156,

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