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Evaluating the Potential for Atmospheric Corrosion of 304 Stainless Steel Used for Dry Storage of Spent Nuclear Fuel

Weirich, Timothy Douglas

Abstract Details

2019, Master of Science, Ohio State University, Materials Science and Engineering.
Spent dry nuclear fuel (SNF) in the United States is stored in a welded 304/316 stainless steel (SS) shell surrounded by a vented concrete overpack on-site at the commercial reactor where it is generated. The ambient air used to cool the SNF can contain corrosive aerosols (i.e. Cl-) that have been shown to deposit on the outside surface of the SS canister. At sufficiently high humidity levels and temperatures below ~80°C, these deposits can absorb moisture from the air leading to atmospheric corrosion concerns. While most research has focused on the initial stages of atmospheric corrosion ranging from 1 day to 1 week under singular microliter-sized droplets, there is a gap in understanding the effect of atmospheric exposure on pitting corrosion under nano to microscale aerosol droplets for longer periods of time. The current research aims to understand the effect of time, humidity, salt loading density, and surface roughness on the corrosion morphology and pitting damage distribution of 304 SS in atmospheric environments under aerosol size ASTM D1141-98 seawater droplets. Two salt loading densities, 10 and 300µg/cm2, were deposited on ground and polished coupons via printing then exposed to 40 and 76% RH at 35°C for interval times up to 1 year. The distribution and morphology of corrosion damage was characterized using a combination of optical profilometry, electron microscopy, and focused ion beam milling. Low pit counts (< 1 pit/cm2) or no corrosion was found on samples with a polished surface or low salt loading density (10 µg/cm2) after one year of atmospheric exposure. Conversely, ground surfaces loaded with 300 µg/cm2 of sea salt loading density showed pitting damage as early as one week, and the degree of damage was directly related to humidity. Ground surfaces exposed to 40% RH resulted in irregularly-shaped pits with rough surfaces due to selective dissolution of slip bands associated with the deformed, ground steel surface. At 76% RH, pits were characteristically hemispherical with relatively smooth, but faceted surfaces. Additionally, small cracks were found to emanate from pit edges only when exposed at 40% RH. Higher pit number densities were observed at 40% RH due to the discrete droplets that remain intact during the exposure time, which allows for a higher number of pit initiation sites. The limited volume of electrolyte and area coverage, as well as the concentrated brine chemistry (indicative of deliquesced electrolytes), is used to explain the mechanisms leading to limited corrosion damage on polished surfaces and at low salt loading densities as well as the unique morphologies and cracking observed on ground surfaces.
Jenifer Locke, PhD (Advisor)
Jerry Frankel, PhD (Committee Member)
114 p.

Recommended Citations

Citations

  • Weirich, T. D. (2019). Evaluating the Potential for Atmospheric Corrosion of 304 Stainless Steel Used for Dry Storage of Spent Nuclear Fuel [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1557098372186951

    APA Style (7th edition)

  • Weirich, Timothy. Evaluating the Potential for Atmospheric Corrosion of 304 Stainless Steel Used for Dry Storage of Spent Nuclear Fuel. 2019. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1557098372186951.

    MLA Style (8th edition)

  • Weirich, Timothy. "Evaluating the Potential for Atmospheric Corrosion of 304 Stainless Steel Used for Dry Storage of Spent Nuclear Fuel." Master's thesis, Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1557098372186951

    Chicago Manual of Style (17th edition)