Inhomogeneous plastic deformation and its relevance to iodine stress corrosion cracking susceptibility in irradiated Zircaloy-2 tubing

Evidence from tensile tests on specimens derived from Zircaloy-2 tubing of current 8x8 BWR type design and irradiated to 3.2 x 1019 and 3.0 x 1020 n/cm2 (E > 1 MeV) showed that inhomogeneous plastic deformation occurred in the temperature range 300-3500C for the higher neutron fluence, but not for the lower one. Dislocation channelings were also identified by transmission electron microscopy for the specimen irradiated to the higher fluence and strained at around 3200C, but not for the lower fluence. On the basis of the results, an attempt was made to explain the influence of neutron irradiation on the iodine stress corrosion cracking (SCC) susceptibility of Zircaloy tubing, suggesting that a drastic increase of SCC susceptibility at neutron fluences above 1020 n/cm2, hypothesized by Lunde and Videm, could be successfully interpreted in terms of the occurrence of dislocation channels. (orig.)