Tritium Aging Effects on Fracture Toughness of Stainless Steel Weldments

Journal Article · Fri Apr 24 00:00:00 EDT 2020 · Fusion Science and Technology

DOI:https://doi.org/10.1080/15361055.2019.1704138· OSTI ID:1616263

Morgan, Michael J. ^[1]; Hitchcock, Dale A. ^[1]; Krentz, Timothy M.  ^[1]; West, Scott L. ^[1]

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1. Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL)

The long-term embrittlement effects of tritium and decay helium on the structural properties of stainless steels have been studied for years at Savannah River to provide required data for establishing safe operating conditions and lifetimes of pressure vessels used to contain tritium gas. In this study, the fracture toughness properties of the longest-aged tritium-precharged stainless-steel base metals and weldments tested at Savannah River were measured and compared to earlier results. The fracture toughness values were the lowest recorded here for tritium-exposed stainless steel. As-forged and as-welded specimens were thermally precharging with tritium gas at 34.5 MPa and 623 K, then aged for up to 17 years to buildin decay helium prior to testing. ASTM J-Integral fracture mechanics analyses, transmission electron microscopy (TEM), and small angle neutron scattering (SANS) examinations were conducted to characterize the effects of tritium and its radioactive decay product, helium-3. Results show that the fracture toughness values were reduced to less than 2-4% of the as-forged values for specimens with more than 1300 appm helium from tritium decay. The trend of decreasing fracture toughness values with increasing helium content was consistent with earlier observations, and the data show that Type 304L stainless steel is more resistant to tritium-induced cracking than Type 21-6-9 stainless at similar decay helium levels. The fracture toughness properties of long-aged weldments were also affected, but the reductions were not as severe over time because weldments did not retain as much tritium as did the base metals. TEM observations were used to characterize the effects of decay helium bubbles on the deformation substructures, but nanometer-sized helium bubbles were not easily resolved because of high dislocation densities within the forged microstructures. SANS results are presented that suggest the technique can provide information on decay helium bubble size, spacing, and distribution in these steels.

• Research Organization: Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL)
• Sponsoring Organization: USDOE Office of Environmental Management (EM)
• Grant/Contract Number: AC09-08SR22470
• OSTI ID: 1616263
• Report Number(s): SRNL-STI-2019-00249; TRN: US2106429
• Journal Information: Fusion Science and Technology, Vol. 76, Issue 3; ISSN 1536-1055
• Publisher: American Nuclear Society
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE