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Assessment of Initial Test Conditions for Experiments to Assess Irradiation Assisted Stress Corrosion Cracking Mechanisms

Irradiation-assisted stress corrosion cracking is a key materials degradation issue in today’s nuclear power reactor fleet and affects critical structural components within the reactor core. The effects of increased exposure to irradiation, stress, and/or coolant can substantially increase susceptibility to stress-corrosion cracking of austenitic steels in high-temperature water environments. Despite 30 years of experience, the underlying mechanisms of Irradiation Assisted Stress Corrosion Cracking (IASCC) are unknown. Extended service conditions will increase the exposure to irradiation, stress, and corrosive environments for all core internal components. The objective of this effort within the Light Water Reactor Sustainability (LWRS) program is to evaluate the response and mechanisms of IASCC in austenitic stainless steels with single variable experiments.

A group of high-value irradiated specimens has been acquired from international research programs, providing a valuable opportunity to examine the mechanisms of IASCC. This batch of irradiated specimens has been received and inventoried. In addition, visual examination and sample cleaning has been completed.

Microhardness testing has been performed on these specimens. All samples show evidence of hardening, as expected, although the degree of hardening has saturated and no trend with dose is observed. Further, the change in hardening can be converted to changes in mechanical properties. The calculated yield stress is consistent with previous data from light water reactor conditions.

In addition, some evidence of changes in deformation mode was identified via examination of the microhardness indents. This analysis may provide further insights into the deformation mode under larger scale tests.

Finally, swelling analysis was performed using immersion density methods. Most alloys showed some evidence of swelling, consistent with the expected trends for this class of alloy. The Hf-doped alloy showed densification rather than swelling. This observation may be related to the formation of second-phases under irradiation, although further examination is required.