3013 Container Inner Surface Changes After Exposure in Boiling Magnesium Chloride Solution

Abstract The 3013-container package is used to store plutonium-bearing materials at the Savannah River Site. The package consists of three nested containers: outer, inner, and convenience. The inner container, which is made from flow-formed 304L stainless steel and is welded shut around the lid, has been considered susceptible to stress corrosion cracking (SCC) or other types of localized corrosion. The possibility of through-wall damage is considered to be a major concern since it could cause the release of radioactive material. In this work, a worst-case scenario of chloride exposure to induce cracking was performed to analyze how it affects the surfaces of an inner container. To do this, a sample of 3013 container inner container closure weld region (ICCWR) was immersed in a boiling magnesium chloride (MgCl2) solution. Surface images were taken using a Laser Confocal Microscope (LCM) prior to exposure and after several predetermined exposure times to see how the surface changed after each immersion. The surfaces were then compared to those of other 304L stainless steel samples that underwent the same treatment, including samples under tension. The ICCWR sample showed a crack after 3 hours of immersion in boiling MgCl2, crossing the zone 2 and zone 3 interface. Two additional cracks developed across this interface after a total of 6 hours of immersion. It appears that the welding process may cause the zone 2 – zone 3 interface of the ICCWR to act as a preferential spot for cracks to form and it suggests that it is the region most susceptible to cracking.