Non-destructively detecting spinodal decomposition at a distance towards developing gigahertz ultrasonics for in-vessel inspection
Name
1281707326-MIT.pdf
Size
14.58 MB
Format
Adobe PDF
Checksum (MD5)
6c4c0ab1cb11c125c9b047f166c2796e
Author(s)
Al Dajani, Saleem AbdulFattah Ahmed.
Advisor(s)
Michael P. Short.
Date Issued
2020
Publisher
Massachusetts Institute of Technology
Abstract
Given the existential climate crisis faced by mankind and the world, the lifetime and sustainability of nuclear reactors as a carbon-free source of renewable energy depend on the susceptibility of their structural components to environmental degradation. In particular, critical components for light water reactors (LWRs) evolve over decades in service, losing ductility and toughness due to thermal and irradiation aging. Techniques to monitor their health cannot be easily applied in the field due to their destructive, expensive, or immobile nature. Thus, non-destructive evaluation (NDE) methods are sought to monitor and evaluate the health of major LWR components such as core barrels, steam generator tubes, or primary coolant pipes and are often required by policy, such as NRC policy 10-CFR-50.65. Here we demonstrate the use of gigahertz, non-contact ultrasonics to gauge the state of cast austenitic stainless steels (CASS), used in some of the largest components in LWR primary systems. We do so by linking changes in their surface acoustic wave (SAW) characteristics using transient grating spectroscopy (TGS) to transmission electron microscopy (TEM)-verified evidence of spinodal decomposition and G-phase precipitation. In this thesis, thermal aging is shown to induce SAW peak splitting in spinodally decomposed CASS alloys, correlated strongly with lowered toughness and decreased ductility. Furthermore, statistical testing on the number of SAW peak splits observed show that the second SAW peak significantly appears more frequently and is significantly different in frequency in comparison to counts and frequencies measured in unaged specimens. The ability of this technique to non-destructively detect microstructural degradation at a distance in a predictive manner in the case of CASS motivates extending gigahertz ultrasonics to detect other LWR material degradation modes as an in-vessel inspection technique, such as reactor pressure vessel (RPV) embrittlement. This allows for the greater use of NDE techniques for confident monitoring of LWR structural material health to 80 years and beyond, saving costs by minimizing structural replacements until needed and maximizing energy production by preventing early decommission until necessary.
Description
Thesis: S.M., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, February, 2020
Cataloged from the official PDF of thesis.
Includes bibliographical references (pages 107-116).
Subjects
Nuclear Science and Engineering.
MIT Department
Massachusetts Institute of Technology. Department of Nuclear Science and Engineering
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