September 12, 2024 [Nuclear Engineering International]- The US Department of Energy (DOE) Office of Environmental Management (EM) is deploying drones for the first time to undertake internal inspections of the radioactive liquid waste tanks at the Savannah River Site (SRS) in South Carolina.

The radioactive liquid waste generated by the SRS chemical separations processes is stored in the Tank Farms in both solid and liquid forms. About 160m gallons of radioactive waste has been generated and concentrated by evaporation to a current volume of approximately 35m gallons. SRS has a total of 51 waste tanks built in the Site’s F and H Areas; eight of those tanks have been operationally closed. Several of the remaining 43 waste tanks are in various stages of the waste removal, cleaning, and operational closure process.

Since 1954, SRS waste tanks have provided safe and environmentally sound storage for nuclear waste. All of SRS’s high-level waste tanks are below ground with only the tank tops exposed for access. These tanks include four designs.

Until now, the SRS Liquid Waste programme had used wall-crawling robots that cling to the tank walls using magnets. The drones provide more flexibility and capability, as they can cover more area more quickly than a magnetic crawler. Additionally, the drones are equipped with 3D-scanning light detection and ranging equipment, which can generate precise 3D scans of the tank and its waste.

Initially, the inspections will be of the annulus space in the tanks. The annulus provides secondary containment and protection for these tanks in the event of a leak. The drones were implemented for inspections late last month.

Before the work can begin with the drones, all administrative and regulatory requirements must be satisfied. Pilots are required to be trained on drone operations, followed by advanced training on successfully navigating the environment of a waste tank and learning best practices for planning flights for optimal results.

The remote-controlled aircraft, the Flyability Elios 3, is a 19-inch diameter drone with four helicopter-like propellers, a high-definition camera, thermal camera, and additional features that will benefit the tank inspection programme. The drones also have advanced stability features that make them easier to manoeuvre in flight. Four drones have been purchased for the project, and all are designed to fly in confined spaces, thanks to a protective cage that shields the propellors and cameras from potential collisions with a tank wall.

The Elios 3 model drone has undergone extensive radiation exposure testing at the Idaho National Laboratory. The lab determined the level of radiation exposure the drone could withstand before experiencing a failure. That level was judged to be adequate for the needs of the liquid waste programme.

“These drones are an important step in our ability to perform inspections of the tanks,” said Savannah River Mission Complete Chief Operations Officer Wyatt Clark. “The drones will help us determine the effectiveness of our cleaning efforts.”

Jim Folk, DOE-Savannah River Operations Office assistant manager for waste disposition, said this new use of technology is a safe and effective method to continue to protect people and the environment. “DOE wants to ensure we can ultimately close the remaining 43 liquid waste tanks at SRS in a safe manner,” Folk said. “With the help of drones, we can advance our work to complete the liquid waste mission by 2037.”