Remote-Controlled System That Permanently Closes Waste Packages of Spent Nuclear Fuel

The U.S. Department of Energy's Idaho National Engineering and Environmental Laboratory is designing a prototype remote-controlled system that will permanently close the waste packages of spent nuclear fuel before final disposal in the proposed federal repository being studied at Yucca Mountain in Nevada. The INEEL will also build and test the system at the Idaho laboratory.

Federal law designated Yucca Mountain as the site to be studied for licensing as the national repository for commercial and government spent nuclear fuel and high-level waste. If the repository is licensed, INEEL's Waste Package Closure System will be a key element of the facility's operation.

The INEEL-designed closure system will be used to demonstrate the operations and equipment, and may be used in the operator training facility. The prototype will be constructed and operated at the INEEL.

Philip Wheatley, Yucca Mountain relationship manager, said the project takes advantage of INEEL's established expertise. "The INEEL has been designated as the DOE lead lab for Nuclear Energy Technology. We have a proven history of spent fuel canister welding process development. This expertise will help the Yucca Mountain Project and help meet the nation's need for the safe storage of nuclear waste," Wheatley said.

Wheatley added that other areas of expertise -- in particular, robotics, hot cell operations and design, systems engineering and automated welding developed by the Laboratory in receiving, handling, storing and transporting spent nuclear fuel -- made the INEEL attractive to the Yucca Mountain Project team.

In developing the waste package system, INEEL engineers faced a number of technical challenges. The waste package is two containers, one nested within the other, with three lids. The package can be various diameters and heights. INEEL engineers are integrating off-the-shelf equipment in the design of the closure system. However, the team has had to develop new or modified equipment for some parts of the operation, for instance, a tool to remotely purge and fill the inner container with helium.

The task becomes more challenging and complex because the high radiation fields require the entire operation to be done remotely.

As designed, a cart will move a waste package into the processing cell where all the operations occur. Three separate lids will be installed and welded onto the container using two weld torches rotating around the container on tracks. All the welds undergo one or more inspections visually, ultrasonically, with eddy current, or by a combination of these methods. The inner container will be filled with helium (to prevent corrosion), sealed and leak tested. Stress mitigation on the welds will be performed on the outer lid followed by another set of inspections. Once the waste package closure is complete, it is ready for placement in the repository.

Wheatley noted the INEEL is working on a number of other repository-related projects, including support in preparing the license application, analysis of criticality events, surface facility design, verification and validation of software for modeling the repository and preparing a corrective management plan for systems.

"The waste package closure project will be a significant piece of work for the next three or four years," Wheatley said. "This work allows the INEEL to apply some of our core competencies to help meet the nation's nuclear technology development mission. Engineering and other capabilities used for Yucca Mountain will contribute to future reactor development work."

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