Potential SCC Initiation and Propagation of Titanium Alloys Under U.S. Nuclear Waste Repository Environmental Conditions

Abstract: The Yucca Mountain Project Nuclear Waste Repository design uses a two-layer cylindrical waste package with a highly corrosion resistant Ni-based Alloy 22 (UNS N06022) outer barrier surrounding a Type 316 stainless steel structural inner vessel. The emplaced waste package is covered by a self-supported inverted U‑shaped drip shield composed of Ti Grade 7 plate material welded with Ti Grade 28 composition filler metal to Ti Grade 29 structural supports.  The drip shield diverts potential seepage waters and potential tunnel degradation debris such as rock fall from contacting the waste package.
This paper provides a summary of data and analyses that can be used to assess the SCC performance of the titanium alloys.  The threshold stresses for SCC initiation, crack propagation rates and threshold stress intensity factors for Ti Grades 7, 28, and 29 under repository relevant environmental conditions are discussed..