Historic disposal site at INL to close

May 26, 2021, 9:30AMRadwaste Solutions
Work crews prepare to place the final waste shipment into a vault at the Subsurface Disposal Area at the Idaho National Laboratory site. (Photo: DOE)

Work crews recently placed a final radioactive waste shipment into the Idaho National Laboratory site’s largest waste disposal area. The Department of Energy's Office of Environmental Management noted on May 25 that it would begin closing the facility, fulfilling its commitment to the state of Idaho.

Disposal: Workers from Fluor Idaho, the DOE’s INL site cleanup contractor, used a 55-ton cask to insert activated metals into a concrete-lined vault within a fenced section of the 97-acre disposal site, known as the Subsurface Disposal Area (SDA).

The metals are structural components of nuclear fuel assemblies that have been removed from reactors. The metal end pieces from the fuel assemblies are detached and disposed in one of the vaults at the site.

History: The SDA began receiving INL-generated radioactive and hazardous waste in 1952. Beginning in 1954, the landfill accepted Cold War weapons waste from the former Rocky Flats Plant in Colorado and other off-site generators.

Due to a policy change in 1970, the SDA stopped receiving transuranic and hazardous waste for disposal but continued to receive boxed low-level radioactive waste and, later, highly radioactive metal debris in specially designed vaults inside the SDA.

The DOE noted that the SDA is unique in that targeted waste is being removed under a federal regulation, while other waste, such as activated metals, has been disposed in the landfill vaults under a separate federal regulation.

The vaults: The disposal site's first set of 100 concrete vaults was constructed in 1993, and it received its first waste shipment in 1994. The second set, also of 100 concrete vaults, was constructed in 2003, with its first waste shipment in 2008. The last waste shipment to the second set of vaults was completed earlier this month.

Constructed of concrete sections resting on a base and capped with a concrete plug, the vaults are configured in honeycomb arrays. The vaults are surrounded by soil for additional shielding and protection from earthquakes, and the void spaces between the vaults in each array are filled with sand.

Next step: Following closure of the SDA, activated metals will be disposed in a facility managed by INL contractor Battelle Energy Alliance. That disposal facility is located near the Advanced Test Reactor Complex in the central portion of the 890-square-mile INL site.