Development of a stress intensity factor solution for circumferential through-wall cracks in cylinders with large radius-to-thickness ratio

矢田 浩基 ; 高屋 茂  ; 町田 秀夫*

Yada, Hiroki; Takaya, Shigeru; Machida, Hideo*

ASME Boiler and Pressure Vessel Code Case N-875 and Fitness-for-service code (Section XI, Division 2) provide a rational in-service inspection approach for liquid-metal cooled reactors. In this approach, fracture mechanics is essential. Not only part-through-wall cracks but also through-wall cracks need to be evaluated, for example, to determine the maximum allowable size of flaws in reactor internal components and investigate the applicability of continuous leakage monitoring to flaws in sodium-retaining components. The demonstration sodium-cooled fast reactor currently under development in Japan is expected to be designed with thin wall and large diameter to reduce the thermal stress. For some components, the ratio of radius to thickness is expected to exceed 100. There are currently no generalized Stress Intensity Factors (SIFs), which are required for fracture mechanics, applicable to components with such a large ratio of radius to thickness. In this study, as a part of the development of a flaw evaluation method applicable to components with large ratio of radius to thickness, the conservatism of applying the SIF solutions for through-wall cracks in plates to circumferential through-wall cracks in cylinders with large ratio of radius to thickness was discussed. As a result, it was clarified that the SIF solutions for plates should not be used for circumferential through-wall cracks. Therefore, a new SIF solution of circumferential through-wall cracks in cylinders was developed by using Finite Element Analysis.