General Corrosion and Localized Corrosion of Waste Package Outer Barrier
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| ANL-EBS-MD-000003 REV 03 ADD 01DOC.20100310.0002.pdf (33.46 MB) | 33.46 MB |
The purpose and scope of this model report is to document models for general and localized corrosion of the waste package outer barrier (WPOB) to be used in evaluating long-term waste package performance in the total system performance assessment (TSPA). The waste package design for the license application is a double-wall waste package placed underneath a protective drip shield (SNL 2007 [DIRS 179394]; SNL 2007 [DIRS 179354]). The WPOB will be constructed of Alloy 22 (UNS N06022) (SNL 2007 [DIRS 179567], Section 4.1.1.6), a highly corrosion-resistant nickel-based alloy. The inner vessel of the waste package is constructed of Stainless Steel Type 316 (UNS S31600) (SNL 2007 [DIRS 179567], Section 4.1.1.6). The Alloy 22 WPOB prevents or substantially delays the time at which water contacts and begins to degrade the Stainless Steel Type 316 inner vessel, which provides additional structural stability to the thinner Alloy 22 WPOB. No corrosion performance credit is taken for the waste package inner vessel. This is a conservative treatment because, before it breaches, the waste package inner vessel would provide some performance for waste containment and potentially decrease the rate of radionuclide transport after it breaches. However, the performance of the inner vessel is expected to be less than that of the more corrosion-resistant Alloy 22 WPOB.
Treatment of seismic and igneous events and their consequences on WPOB performance are not specifically discussed because they are outside of the scope of this report, although the general and localized corrosion models developed in this report are suitable for use in these scenarios. The localized corrosion processes considered in this report include pitting corrosion and crevice corrosion. However, the latter process is treated as the most important form of localized corrosion under repository conditions. Stress corrosion cracking of the Alloy 22 WPOB is discussed in Stress Corrosion Cracking of Waste Package Outer Barrier and Drip Shield Materials (SNL 2007 [DIRS 177417]).
