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Post-irradiation annealing studies indicate small detect clusters may be a potential contributor to IASCC. In this study, small defect clusters and their behavior during annealing are examined. A CP-304 SS alloy was irradiated with 3.2 McV protons to 0.17 dpa at <75° C. The increase in hardness after 0.17 dpa at <75° C was greater than that after 0.55 dpa at 360° C, but dropped significantly after annealing at 350°C for short times, although, no dislocation damage was observed using transmission electron microscopy (TEM). For samples irradiated in a previous study at 360°C, the smallest dislocation loops and clusters were removed preferentially during annealing at 500° C for 45 minutes. Computer simulations of the annealing behavior were performed for the data from both sets of experiments in order to gain further insight into the nature of small clusters. [ABSTRACT FROM AUTHOR]

Irradiation has a profound effect on the stress corrosion cracking propensity of austenitic alloys in high-temperature water. Irradiation-assisted stress corrosion cracking (IASCC) has been well documented both in the laboratory and in service over the past two decades. Numerous studies have shown that the degree of intergranular stress corrosion cracking increases with dose. However, the microstructure is simultaneously changing in several ways (dislocation loops, voids, segregation and hardening) and, not surprisingly, they all simultaneous increased cracking susceptibility. As a consequence of their simultaneous development, the attribution of IASCC to one or more of these features has been difficult to establish. Mechanisms based on each of the principal effects of irradiation in the alloy are considered. Arguments can be made in support of any one of these features as the cause of IASCC, but substantial evidence exists to refute a first order correlation. The mechanism of IASCC is more likely due to a combination of factors, or second order effects not yet considered. One such mechanism that is considered is based on the change in the deformation mode caused by the irradiated microstructure and the interaction of localized deformation bands with grain boundaries. [ABSTRACT FROM AUTHOR]

Proton irradiation at temperatures of 310 and 350° C has been explored as a method of studying radiation effects in Zircaloy 4 under power-reactor conditions. The dislocation-loop and hardness evolution are similar to those observed under neutron irradiation. Amorphization and Fe loss at Zr(Cr,Fe)2 precipitates are observed. Energy-filtered images indicate Fe accumulation in the matrix near the precipitate, a phenomenon not reported in neutron-irradiated alloys. [ABSTRACT FROM AUTHOR]