AgCl proves effective in reducing Savannah River’s I-129 contamination

April 30, 2021, 12:00PMRadwaste Solutions
SRNS subcontractors Donald Miles and Richard Mooney drill for soil samples as part of a project to immobilize I-129 in the groundwater and soil at the Savannah River Site. Photo: DOE/SRNS

A silver chloride–based cleanup technology is expected to reduce radioactive iodine-129 contamination found in soil and groundwater near the center of the Department of Energy’s Savannah River Site in South Carolina to levels well below regulatory limits. The I-129 was created during the production of plutonium and tritium at the site throughout the Cold War era.

Developed by DOE cleanup contractor Savannah River Nuclear Solutions (SRNS) and in use at SRS since 2019, the process uses the conventional industrial product silver chloride to immobilize I-129. On April 29, SRNS announced that extensive studies confirm that injecting silver chloride beneath a portion of the site reduced I-129 by up to 50 percent during pilot program field tests.

“The silver can capture and lock into place a high percentage of the iodine nuclides, reducing the amount of contamination in the groundwater,” said Jeff Thibault, an SRNS cleanup projects engineer.

The process: Ultra-fine particles of silver chloride are specially milled by an off-site vendor to create highly irregular edges, which greatly increases the surface area of the particles. The material is mixed with water and injected into the water table 30 to 60 feet below the surface. Workers have injected a total of 240,000 gallons of water and 165 gallons of silver chloride.

A passive system, the cleanup technology does not generate waste and requires no power.

Stopping the plume: Working with Savannah River National Laboratory scientists, SRNS is striving to prevent I-129 contamination from moving into nearby wetlands in large quantities. The current method relies on the silver chloride and soil to work together to bind the iodine to sub-surface sediment before it reaches the wetlands.

“Once this plume fully enters the marsh, treatment, much less immobilization of the iodine, becomes much more difficult,” Thibault said. “There’s no sediment. We’ve gone from mud-like sediment to working with organic material and the water of the marsh.”

SRNL Geochemist Hansell Gonzalez-Raymat said that workers have completed shallow drilling for soil samples in the affected wetlands. “The data collected from the samples will help us to determine how the iodine will interact with the organic matter and surface water found within SRS wetlands,” he said. “This is part of a larger project within the site’s F Area that is partially funded by the [DOE Office of Environmental Management] Office of Technology Development.”

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