Stress intensity factor solutions for circumferential through-wall cracks applicable to pool type sodium cooled fast reactors

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

ASME Code Case N-875 provides a rational in-service inspection (ISI) approach for liquid-metal cooled reactors. This is a risk informed approach and ISI requirements including acceptance criteria are established by considering features of respective plants in terms of the effects of flaws on the plant safety. 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 basic procedure of the Code Case has also been incorporated in Fitness-for-service code (Section XI, Div. 2) in ASME, which provides requirements for Reliability and Integrity Management programs for nuclear power plants, including advanced reactors. The demonstration sodium-cooled fast reactor currently under development in Japan is expected to be designed with thin wall and large diameter. For some components, the ratio of radius to thickness (R/t) 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 R/t ratio. In this study, as a part of the development of a flaw evaluation method applicable to components with large R/t ratio, the conservatism of applying the SIF solutions for a through-wall crack in a plate to a circumferential through-wall crack in a cylinder with large R/t ratio was discussed. As a result, it was clarified that the SIF solution for a plate should not be used for circumferential through-wall cracks. Then, a new SIF solution of a circumferential through-wall crack in a cylinder was developed.