April 29, 2003
Conference Paper

Microstructural Characterization of Stress Corrosion Cracks in an Irradiated Austenitic Steel Core Component from a BWR

Abstract

Intergranular stress-corrosion cracks in an austenitic stainless steel core component from a boiling-water reactor have been characterized by high-resolution analytical transmission electron microscopy. The goal of this work was to gain insights into the mechanistic causes of cracking produced during reactor operation. Cross-sectioned cracks were examined in a sample removed from a top guide after 26 years in service and an irradiation dose of approximately 0.7 dpa. The Type 304SS material showed no evidence of initial sensitization or cold work, but did develop a high density of small radiation-induced dislocation loops and measurable grain boundary segregation. Examinations revealed highly branched stress-corrosion cracks along high-angle grain boundaries. The cracks contained bi-layered oxide films consisting of epitaxial Cr-rich spinel along the crack walls and large grained magnetite at the centers, and were completely oxide-filled near the tips. Crack tips in the sample exhibited unique configurations with finger-like porosity and highly Ni-rich metal attributed to selective dissolution of Fe and Cr depletion ahead of the oxide. Crack and crack-tip characteristics in the BWR top guide are compared to those previously identified in a cold-worked Type 316SS PWR baffle bolt.

Revised: July 27, 2010 | Published: April 29, 2003

Citation

Thomas L.E., and S.M. Bruemmer. 2003. Microstructural Characterization of Stress Corrosion Cracks in an Irradiated Austenitic Steel Core Component from a BWR. In Proceedings of the 11th International Symposium on Environmental Degradation of Materials in Nuclear Power Systems Water Reactors, 133. La Grange, Illinois:American Nuclear Society. PNWD-SA-6018.