Review of the Expected Behavior of Alpha Titanium Alloys Under Yucca Mountain Conditions, TDR-EBS-MD-000015 REV 00

Enclosure 2 DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, nor any of their contractors, subcontractors or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or any third party's use or the results of such use of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof or its contractors or subcontractors. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. EXECUTIVE SUMMARY The use of titanium (ri) alloys in two different waste package designs has been reviewed under the conditions anticipated in the potential monitored geologic repository at Yucca Mountain for disposal of spent nuclear fuel and high-level nuclear waste. In the first design, they are considered as one of three barrier materials incorporated into the waste package design, and potentially in galvanic contact with the other two waste package materials, 316NG stainless steel and Alloy 22. In the second design, the Ti alloy is considered as a drip shield placed over, and not in contact with, a dual-wall waste package fabricated from the other two materials. The possible failure processes-crevice corrosion, pitting, and hydrogen-induced cracking (HIC)-have been reviewed for the candidate titanium alloys (Ti-12, Ti-16, and Ti-7). Both pitting and crevice corrosion are very remote possibilities under repository conditions. For Ti-12, a limited amount of crevice corrosion is possible, but repassivation will occur before substantial damage is sustained. When Ti is considered as part of the triple-wall waste package, hydrogen absorption leading to HIC, within an acidified but passive crevice, is the most likely failure mechanism. When the Ti alloy is utilized in the form of a drip shield, then hydrogen absorption under potentially alkaline conditions is the major failure mechanism. Both Ti-12 and Ti-16 have been shown capable of tolerating substantial amounts of hydrogen (-400 .tg-gl for Ti-12, and > 1000 itg'gT' for Ti-16) without having any effect on the materials …