Examination Of Aluminum Containers For Extended Wet Storage Of Non-Aluminum-Clad Spent Nuclear Fuel

Approximately 20 MTHM comprising 2000 elements of non-aluminum-clad spent nuclear fuel (NASNF) is owned by the U.S. Department of Energy and is managed in wet storage in the L Basin at the Savannah River Site. The NASNF claddings are primarily zirconium/zircaloy or stainless steel. These fuel elements are stored in one of the following configurations: i) directly within a thin-wall (0.052”-thick) aluminum tube with a 5” diameter, and either 12’ or 14’ in length, or within a square tube of 0.125”-thick aluminum in a 5” square, 12’ in length; ii) within small aluminum cans that are stacked and stored in the tubes; or iii) direct fuel or fuel within the small cans that are placed in thick (0.148”) aluminum oversize storage canisters (OSCs) 8” in diameter. These fuel containers must remain intact for safe handling and to maintain configuration for criticality control. This storage configuration could cause inside-out corrosion attack due to galvanic couples or sediment-induced corrosion. To verify the condition of the fuel containers under long-term storage, container interrogation using non-destructive examination (NDE) methods is being performed under the Augmented Monitoring and Condition Assessment Program (AMCAP) at Savannah River Site. The NDE methods selected to provide the condition assessment are visual testing (VT) and ultrasonic testing (UT) that are adapted to tooling for remote underwater examination of the containers. The VT examination was readied in a mockup to demonstrate the video recording cameras were capable and robust for in-situ deployment with tubes in the Vertical Tube Storage (VTS) racks to examine 90% or more of surfaces of the tubes. This required that the camera withstand water and radiation exposure, and that the camera deployment mast would fit within the narrow gap between the tube and rack. The cameras were tested at various dose rates and ultimately to failure in the SRNL 60Co irradiator. Five vulnerable bundles have been visually examined. The engineering development for the inspection and the inspection results are reported in this paper. An outline of the development of the UT method and deployment platform for the next phase of the condition assessment inspections are also described.