Stress Corrosion Cracking of Candidate Material for Nuclear Waste Containers

Types 304L (UNS⁽¹⁾ S30403) and 316L (UNS S31603) stainless steel (SS), lncoloy⁽²⁾ 825 (UNS N08825), Cu, Cu-30%Ni, and Cu-7%Al have been selected as candidate materials for the containment of high-level nuclear waste at the proposed Yucca Mountain site in Nevada. Susceptibility of these materials to stress corrosion cracking has been investigated by slow strain rate tests (SSRTs) in water simulating that from well J-13, which provides representative groundwater at the Yucca Mountain site. The slow strain rate tests were performed on specimens exposed to simulated J-13 water at 93°C and at a strain rate of 10^-7 and 10^-8 s^-1 under crevice and noncrevice conditions. All the tests were interrupted after nominal elongation strains of 1 to 4 percent. Scanning electron microscopy revealed some crack initiation in virtually all specimens. Optical microscopy of metallographically prepared transverse sections of type 304L SS suggests that the crack depths are small (<10 μm). Differences in cracking susceptibility for the six materials are evaluated and discussed in terms of a stress ratio, which is defined as the ratio of the increase in stress after local yielding in the environment to the corresponding stress increase in an identical test in air, both computed at the same strain.