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Report No.
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Development of Advanced Methodology for Defect Assessment in FBR Power Plants (Phase II)

Meshii, Toshiyuki*; Watashi, Katsumi; Doi, Motoo; Hashimoto, Takashi

Based on the results of the Phase I of the titled research, we started Phase II scheduled to reach conclusion (develop basic methods necessary for FBR post-construction code) in three years. The following results were obtained. (1) Development of assessment procedure for multiple defects due to creep damage: We first confirmed that multiple surface cracks in axial and circumferential direction inside a cylinder can be evaluated independently by investigating multiple flaws found in a cylinder due to cyclic thermal shock. Then we developed a method to evaluate the stress intensity factors (SIFs) of the multiple circumferential cracks in a finite legth cylinder under axisymmetric loads. (2) Improving creep-fatigue crack grown (C-FCG) assessment pfodedure: We reviewed the French code A16 for flaw assessment and compared it with the JNC proposal. Since the fundamenfal philosophy for both was to evaluate the C-FCG by estimating elastic-plastic fracture mechanics parameter from the SIF, we developed a "3D crack finite element analysis system that can specify the target error in SIF." (3) Crack propagation assessment under thermal stresses (fatigue crack grown (FCG) resistace for small load): To improve accuracy of FCG assesment for components in FBR power plants (designed to minimize thermal stresses) under thermal cycles, we obtained near threshold FCG data for S55C, SUS304, HT60, SS400, 2.25Cr-1Mo, SUS316, SUS321, T91, Inconel718 by Kmax = constant test method. The results showed that FCG curves in the JSME post construction code (which is an extrapolation of the curves in ASME PVP code sec. XI) are valid in general. However, precise review of S55C, HT60's data suggested that the JSME FCG, evaluation curve may not have enough safety margin. In addition, we proposed a method to predict the decrease in the threshold SIF range DeltaKth due to high Kmax and showed its validity.

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