Nondestructive Analysis of SAVY Containers: Application of Nondestructive Testing to Assess Corrosion Damage

Stainless-steel SAVY containers are widely used at the Los Alamos National Laboratory (LANL) Technical Area TA-55 for long-term storage of nuclear materials. Recent surveillance activities completed have shown that these SAVY containers are prone to interior corrosion while in use due to a number of factors, such as decomposition of the poly-vinyl chloride bag-out bags and radiolytic hydrogen chloride gas generation. There is a strong need to develop nonintrusive inspection techniques that can monitor these corrosion processes in real time and in situ. Nondestructive testing (NDT) and procedures for assessing corrosion within SAVY containers are being developed to augment current destructive container monitoring and testing procedures. An earlier trade study completed at LANL narrowed down the choices to ultrasonic testing (UT) and eddy current array (ECA) testing. The two NDT methods were validated for SAVY container surveillance through controlled corrosion experiments and simulated pit creation. Pitting corrosion has been observed during the surveillance of SAVY containers and is a form of extremely localized corrosion that takes the form of cavities. The results have shown that UT and ECA testing complement each other and can be used to determine corrosion on the interior surface as well as pitting. UT can accurately detect changes in wall thicknesses due to corrosion processes. The wall thickness measurements completed on the sides and base of the corroded containers using UT were within 6.3% of those measured using a contour measurement machine (CMM). These results are significant because they demonstrate that UT can be used in lieu of the CMM measurements, which are extremely accurate but time consuming and which require opening the containers prior to use. In addition, ECA can be used to determine pitting and cracking within the containers. The smallest detectable pit depth on a SAVY container was repeatably measured at 0.0762 mm (even though the detection limit of the technique is lower). Building on the UT and ECA in this study, an automated inspection system combining the two systems is being developed and can be used to generate color-coded contour and damage plots of the interior of each SAVY container