Stress Corrosion Cracking of Waste Package Outer Barrier and Drip Shield Materials

Stress corrosion cracking (SCC) is one of the most common corrosion-related causes for premature breach of metal structural components. SCC is the initiation and propagation of cracks in structural components due to three factors that must be present simultaneously (Jones 1992 [DIRS 169906], Section 8.1): metallurgical susceptibility, critical environment, and sustained tensile stresses. The purpose of this report is to provide an evaluation of the potential for SCC of the Engineered Barrier System (EBS) components (i.e., the waste package outer barrier and drip shield) under repository relevant exposure conditions. For the waste package outer barrier and drip shield, the critical environment is taken as any aqueous environment contacting the metal surfaces. This is conservative because SCC usually requires an aqueous environment that is corrosive to the the waste package and drip shield materials.
The waste package outer barrier contributes to waste isolation by keeping water away from the waste for its lifetime and, when breached, by reducing both the contact of water with the waste and the radionuclide release rate from the waste. The drip shield barrier contributes to waste isolation by keeping seepage waters and falling rocks away from the waste package for its lifetime and, when breached by SCC, by reducing the contact of water with the waste package.