K validity criterion of neutron irradiated type 316L stainless steel CT specimen for SCC growth test

In order to evaluate SCC growth rate of BWR core shroud by test results with compact tension (CT) specimens, the validity of neutron irradiated small CT specimen was verified on the basis of FEM and the deformation mark observations. As for the same stress intensity factor (K), the plastic zone size differs depending on the combination of the specimen size and the irradiation hardening. The deformation marks near the crack tip of the SUS316L CT specimens irradiated in JMTR were observed by optical microscope and compared with the plastic strain distributions in FEM. The adequate K value of CT specimen was discussed on the basis of comparison with plastic strain distribution near the crack tip of the core shroud model in FEM. For plastic strain comparison, appropriate K in CT specimen is at least 30 MPa√m for 11.4 mm thickness in 5 x 1024 n/m2 and 1 x 1025 n/m2 and for 5.8 mm thickness in 3 x 1025 n/m2. (author)