Overview of corrosion issues for the Yucca Mountain waste container

Abstract

Alloy 22, a Ni-Cr-Mo alloy, is the primary candidate for the outer container of the Yucca Mountain (YM) container. An inner container of Type 316 stainless steel is also planned but there is no consideration of the inner container providing any long-term corrosion protection of the buried waste. Therefore, Alloy 22 is the primary barrier between the contents of the container and the environment. The primary corrosion issues that are being investigated to qualify the YM container and repository are: uniform corrosion; localized corrosion; and stress corrosion cracking (SCC). Metallurgical stability is also being evaluated and modeled by the program. Alloy 22 is shown to be very resistant to SCC in environments expected in the YM repository. SCC requires three conditions to occur: an environment that polarizes the metal surface to a critical cracking potential; a microstructure and microchemistry that is susceptible to cracking; and a tensile stress. The YM program has no control over the environment but the selection of a SCC resistant alloy and modification of the surface stresses will help mitigate the possibility that SCC will occur during the lifetime of the repository.