DOE fills first 33-million-gallon Savannah River waste unit with grout

Saltstone Disposal Unit 6 at the Savannah River Site near Aiken, S.C., has been filled with grouted legacy tank waste, the Department of Energy said last week. It is the first of the site's seven mega-volume disposal units to fill completely. SDU 6, one of the mega-volume designs approved in 2012, accepted its first shipment of waste material in 2018. SDU 7 was listed as operational on DOE's website as of May 2026.

Waste sent to the units is low-level material that has undergone several stages of processing. Salt waste has gone to the site's Salt Waste Processing Facility since 2020, where radionuclides are removed and sent for vitrification, or immobilization in glass. The remaining decontaminated salt solution goes to the Saltstone Processing Facility, where it is combined with fly ash and slag to form a saltstone grout that hardens in an SDU. Before the SWPF came on line, SDU 6 received low-level waste from the Actinide Removal Process/Modular Caustic Side Solvent Extraction Unit and from the site's Tank Closure Cesium Removal demonstration project.

SDU 6 was the first mega-volume unit to be constructed and to begin operations, but smaller SDUs are also in use at the site. SDUs 1 and 4, rectangular units built in the mid-1980s, no longer receive waste. Construction of SDUs 2, 3 and 5 finished between September 2012 and September 2013; each cylindrical unit holds about 3 million gallons of saltstone grout. Units 6 through 12 each will hold an estimated 33 million gallons when filled.

SDUs 8, 9 and 10 have passed leak tightness tests and been deemed ready to operate. Concrete construction of SDU 11 was completed in July 2026, and initial construction work on SDU 12, including a multilayer foundation, recently was completed, according to the Savannah Business Journal.