Remaining life prediction on jointed elements; in FBRs based on evaluation of creep fractures

This study aims to intend upgrading of precision on evaluation of structural integrity at abnormality and incident, to establish a base of remaining life prediction on jointed elements at middle and later period of life on FBR, and to contribute to upgrading of safety, by quantifying time-dependent type creep fractures accumulated at jointed portions of reactor vessels and primary pipings, under normal operation condition of FBRs. And, this study were carried out on long-time creep tests at objects of welded joints on austenitic stainless steels (SUS-304, and -316FR) and ferrite heat resistant steels (2.25Cr-1Mo) of structural elements for FBRs. As a result, it was found that on SUS-304 steels, shapes of creep rate-time curve at a diagram with both logarithmic scales were dependent upon magnitude of stress, which was based on changes of transition infrastructures and deposition conditions of carbides M23C6 with elapsed creep times, that by investigating possibility of detection of creep fractures by using ultra-sonic waves for SUS-304 steels change of sonic rates and ultra-sonic wave propagation energy losses showed good agreement with a process of creep fractures, and so on. (G.K.)