Evaluation of material degradation of light water reactor structure using a miniaturized specimen sampled from actual components

The authors have proposed a miniaturized specimen method to evaluate the degree of sensitization for IASCC (irradiation assisted stress corrosion cracking), and fracture toughness using a small fragment sample from an actual component. This technique consists of two processes. The first process entails the sampling of a small fragment from the surface layer of the component by electric discharged machining (EDM). For this process a specially designed sampling electrode and technique have been developed. The results showed that the extraordinary layer was shallower than 300E m. This shallow extraordinary layer does not affect the evaluation of the material properties, because the surface layer of the sampled small fragment deeper than 300E m is removed when the test pieces are machined from the sampled fragment. The second process is a fracture toughness test using a miniaturized center cracked tension (CCT) specimen. The fracture toughness was evaluated by the stretch zone width (SZW) on the fracture surface. SZWs obtained in 1 mm thick CCT specimen well agreed with those in 1TCT specimen. However, SZW measured in 0.3 mm thick CCT specimen was about one fourth that of 1 TCT specimen, because SZW formation seems to be restricted by the deformation due to the plane stress condition on both sides of the CCT specimen. Accordingly, the macroscopic fracture toughness can be evaluated by measuring the SZW in a miniaturized CCT specimen with at least 1 mm thickness