Development of non-destructive evaluation methods for degradation of HTGR graphite components

Shibata, Taiju ; Sumita, Junya ; Tada, Tatsuya; Sawa, Kazuhiro

To develop the non-destructive evaluation methods for degradation of HTGR graphite components, the applicability of the micro-indentation method to detect the residual stress was studied. The IG-110 and IG-430 graphites were used. (1) The residual stress in a graphite block at the HTTR in-core condition was analyzed. For the components in the VHTR which would be used at much severer condition, the development of lifetime extension methods was suggested as an important subject. (2) Micro-indentation behavior at stress free condition was investigated with some indenters. The spherical indenter R0.5 mm with indentation load of 5 and 10 N was selected to detect the specimen surface condition sensitively. (3) The relationship between the average indentation depth and compressive stress of the specimen was expressed by an empirical formula. It would be possible to evaluate the residual stress by the indentation. It is necessary to assess the data with statistic method in the future study.