CODE ACCEPTANCE OF A NEW JOINING TECHNOLOGY FOR STORAGE CONTAINMENTS [REISSUE]

One of the activities associated with cleanup throughout the Department of Energy (DOE) complex is packaging radioactive materials into storage containers. Much of this work will be performed in high-radiation environments requiring fully remote operations, for which existing, proven systems do not currently exist. These conditions require a process that is capable of producing acceptable (defect-free) welds on a consistent basis; the need to perform weld repair, under fully-remote operations, can be extremely costly and time consuming. Current closure-welding technologies (fusion welding) are not well suited for this application and will present risk to cleanup cost and schedule. To address this risk, Fluor and the Pacific Northwest National Laboratory (PNNL) are proposing that a new and emerging joining technology, Friction Stir Welding (FSW), be considered for this work. FSW technology has been demonstrated in other industries (aerospace and marine) to produce near flaw-free welds on a consistent basis. FSW is judged capable of providing the needed performance for fully-remote closure welding of containers for radioactive materials for the following reasons: FSW is a solid-state process; material is not melted. FSW does not produce the type of defects associated with fusion welding, e.g., solidification-induced porosity, cracking, and distortion due to weld shrinkage. In addition, because FSW is a low-heat input process, material properties (mechanical, corrosion and environmental) experience less degradation in the heat affected zones than do fusion welds. When compared to fusion processes, FSW produces extremely high weld quality. FSW is performed using machine-tool technology. The equipment is simple and robust and well-suited for high radiation, fully-remote operations compared to the relatively complex equipment associated with fusion-welding processes. Additionally, for standard wall thicknesses of radioactive materials containers, the FSW process can perform the final closure in a single pass (GTAW requires multiple passes) resulting in increased productivity. The performance characteristics of FSW, Le., high weld quality, simple machine-tool equipment and increased welding efficiency, suggest that this new technology should be considered for radioactive materials packaging campaigns. FSW technology will require some development, adaptation for this application, along with several activities needed for commercialization. One of these activities will be to obtain approval from the governing construction code to use the FSW technology. The American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME B&PVC) will govern this work; however, rules for the use of FSW are not currently addressed. A code case will be required, defining appropriate process variables within prescribed limits, and submitted to the Code for review/approval and incorporation