Subsurface Analysis of Localized Corrosion in Plutonium-bearing Nested Storage Containers by Scanning Electron Microscopy - Focused Ion Beam Tomography

Abstract The Integrated Surveillance Program, under the Department of Energy, is responsible for the periodic surveillance of storage containers containing plutonium-bearing materials. The container package consists of a stainless-steel three-layered structure with a convenience can that confines the material, and seal-welded inner and outer cans designed to isolate the materials for up to 50 years with minimal surveillance. The inner-can represents the first layer of containment. It was designed with the expectation that it would not be breached. Monitoring is carried by random and engineering-judgment selections where container-packages are selected for destructive examination. During sampling, degradation due to corrosion has been identified in the convenience- and inner-cans in some of the harvested packages. Chloride salts and water impurities from the stored materials have been implicated with the production of the corrosive environment. Earlier investigations for the characterizations of corrosion events relied solely on optical microscopy methods, which limited analyses to surface characterizations. More recently, electron microscopy techniques have been adopted to document the surfaces in greater detail to gain a better understanding of the corrosion processes at play. Herein, characterizations of subsurface of corrosion features are discussed.