Assessment of Corrosion-Based Failure in Stainless Steel Containers Used for the Long-Term Storage of Plutonium-Based Salts

This paper summarizes our efforts to assess corrosion-related failure in stainless steel long-term storage containers bearing plutonium oxides and electrorefining salts. Pitting corrosion of the internal can wall is believed to occur when these salt particles deliquesce forming the electrolyte necessary for corrosion-electrochemistry. Extrapolation of pit depths from coupon studies using generalized extreme value (GEV) statistics found that the probability of a through-wall corrosion pit is finite; the maximum pit depth after 50 years would be on the order of 1.7 mm where the container wall is only 1.6 mm thick. To assess susceptibility to environmental cracking fracture toughness (J1C), experiments were used in conjunction with a J-integral diagram constructed using the GE/EPRI method for linear elastic-plastic materials. As a part of this analysis, the residual stress associated with the weld was measured using the laser contour method. The hoop stress in the weld region was found to be on the order of 135 MPa to 180 MPa. Assuming that the axial stress that results from the weld is equal to one half of the hoop stress (σax = σh/2) and our laboratory measurement of J1C is accurate, one would conclude there is sufficient energy associated with the weld to propagate a crack in the container.