Development of in-pile SCC test technique and crack initiation behavior using pre-irradiated austenitic stainless steel at JMTR

Irradiation assisted stress corrosion cracking (IASCC) is one of the critical concerns when stainless steel components have been in service in light water reactors (LWRs). In general, IASCC can be reproduced on the materials irradiated over a certain threshold fluence level of fast neutron by the post-irradiation examinations (PIEs). It is, however, considered that the reproduced IASCC by PIEs must be carefully distinguished from the actual IASCC in nuclear power plants, because the actual IASCC occurs in the core under simultaneous effects of radiation, stress and high temperature water environment. Hence, we have embarked on a development of the test technique for the in-pile IASCC testing. We adopted the uniaxial constant load (UCL) tensile test method with small tensile specimens for in-pile SCC initiation test, and tried to evaluate the crack initiation behavior as the detection of specimen rupture or detailed observation of surface of loaded specimens. In this paper, we described the techniques for in-pile crack initiation test and the results of evaluation for crack initiation behavior comparing results from in-pile and out-of-pile tests on type 304 stainless steel. As a result of this study, it was inferred that an acceleration effect of in-pile environment for SCC initiation behavior was not observed under the test condition of this study. (author)