The Department of Energy’s Office of Environmental Management (EM) is managing the release of tritiated water using a 62-acre plantation of pine trees and other natural resources to limit radioactively contaminated groundwater from reaching waterways on the Savannah River Site in South Carolina.
According to the DOE, in the 20 years the system has been in operation, approximately 190 million gallons of water containing nearly 7,000 curies of tritium that otherwise would have entered the Savannah River has been harmlessly sprayed throughout thousands of loblolly pine trees.
In the trees: The trees effectively act like a forest of tall hydraulic pumps, each drawing up irrigated water containing tritium pumped from a nearby holding pond and harmlessly released into the atmosphere through photosynthesis. SRS produced tritium for use in the manufacture of nuclear weapons from the site’s inception in the early 1950s until the end of the Cold War.
“With this project, we learned a lot about harnessing nature to continually move toward passive, low-energy, and sustainable cleanup technology with minimal cost,” said Philip Prater, senior physical scientist with DOE-Savannah River. “And it’s accomplished effectively without the generation of any waste.”
A super soaker: Using an extensive irrigation system of pipes and sprinkler heads, the tritiated water is evenly spread over the forest floor debris. Large-scale evaporation also takes place during this process, releasing additional tritium into the atmosphere.
“We knew that capturing and containing the contaminated groundwater seeping to the surface and into a manmade pond would greatly limit this flow from eventually reaching the Savannah River,” said Jeff Thibault, an engineer with Savannah River Nuclear Solutions, the site’s management and operations contractor. “However, the challenge was, how do you keep it from overflowing? We do so through the pine plantation’s irrigation system, which is extremely effective.”
Sampling and testing demonstrate that nearly 90 percent of the tritium in the water applied to the pine plantation is evaporated, according to Christina Logan, of the Savannah River Ecology Laboratory. Logan collects samples and analyzes tritium levels in the irrigated soil.
According to the DOE, U.S. Forest Service–Savannah River (USFS-SR) researchers and engineers with the EM program began designing this interim treatment in 1999 with the goal of reducing the amount of tritium reaching a creek known as Four-Mile Branch by 25 percent. Treatment began in 2001.
The savings: “Traditional remediation costs associated with this level of tritium removal would be close to $220 million over a 20-year period,” said Marsue Lloyd, USFS-SR civil engineer. “Our costs over that same span of time for this project are approximately $12 million.”
Costs associated with phytoremediation are lower because only a few operators are needed, and the contaminated groundwater flows naturally to the surface without a need for mechanized pumping. In addition, the process, which includes 51 irrigation zones, is largely computerized for optimal evaporation efficiency.
The safety: Thibault noted that public concerns about managing contaminated water at SRS are understandable. “However, test results validate that the level of tritium found within the plants and animals affected by this process are so low as to be insignificant,” he said. “The fact is, optimal water levels are being maintained in the pond, while the evaporated tritium becomes virtually immeasurable beyond the irrigated section of the forest, much less at the site boundary.”
Thibault added that officials with the South Carolina Department of Health and Environmental Control have verified data supporting the effectiveness of the system.
Lesson for Fukushima: While the SRS system demonstrates that tritium can be safely released to the environment, antinuclear activists, along with neighboring governments, are opposing the release of tritiated water from Japan’s Fukushima Daiichi site.
TEPCO is currently storing more than 300 million gallons of water containing around 23,000 curies of tritium at Fukushima in hundreds of on-site tanks. Continued storage of the water is hampering efforts to safely decommission the disabled reactors.
Under an agreement with the Japanese government, TEPCO plans to begin releasing water from Fukushima in 2023. The process of releasing the water, which will be heavily diluted with seawater before being sent into the ocean, is expected to take decades.