F.N. Speller Award Lecture:: Corrosion considerations related to permanent disposal of high-level radioactive waste

The designated site for a high-level radioactive waste geologic repository at Yucca Mountain is located approximately 100 miles northwest of Las Vegas, Nevada, on the western boundary of the U.S. Department of Energy (DOE) Nevada Test Site in a sparsely populated rural desert area. A crucial element of the potential repository is to contain the radioactive waste and keep it dry within emplaced waste packages for a sufficient time so that the resultant annual dose for a reasonably maximally exposed individual remains below the regulatory limit for at least 10, 000 years. Since the metal alloy waste packages are a primary engineered barrier they must retain high corrosion resistance for an unprecedented time period. The current cylindrical waste packages have a weld-sealed Alloy 22 (UNS N06022) outer corrosion-resistant barrier and are located beneath titanium Grade 7 (UNS R52400) drip shields that divert potential seepage water and rock-fall impingement. An extensive U.S. DOE-sponsored corrosion evaluation and modeling program has been underway for several years. The objective is to provide a technical basis to support the expected long-term corrosion performance under a broad range of relevant as well as accelerated chloride-containing brine environments that include a range of temperatures and pH values. Degradation modes considered include general and localized corrosion, stress corrosion cracking (SCC), hydrogen-induced cracking (HIC), and microbiologically influenced corrosion (MIC).