A new disposal unit for low-level radioactive, nonhazardous salt waste materials at the Savannah River Site is working so well, according to Savannah River Remediation, the construction of two additional and similar disposal units are under way.

The units provide on-site permanent disposal of decontaminated salt solution taken from inside underground waste storage tanks.

The new disposal unit, called Saltstone Disposal Unit 2, comprises two separate cells that are circular in design. Each cell will hold approximately 2.9 million gallons of nonhazardous cement grout, which is a mixture of the decontaminated salt solution with Portland, fly ash and slag cement powders. The first cell put into service is nearly full.

Dave Olson, SRR president and project manager, said the new design has been used in industrial applications for more than 20 years and has many enhanced features that will improve SRR’s ability to safely and permanently dispose of the waste in its final nonhazardous waste form.

“The improved design incorporates lessons learned from the first disposal units and meets or exceeds regulatory requirements set forth in the S.C. Department of Health and Environmental Control permit,” Olson said. “The design has been proven in other industrial applications and is proving successful for us.”

The new disposal unit cells have a watertight design and a cylindrical shape, unlike the Site’s current disposal unit, which has a rectangular shape. The cylindrical design reduces wall stresses found in the rectangular units. It also includes an engineered concrete and steel shell, a wall-to-floor joint design and high-density polyethylene and Geosynthetic-clay barriers below the unit.

SDU 2 began accepting low-level, nonhazardous cement grout in one of its two cells in October 2012. Once filled, the second cell will continue accepting the cement mix.

In the meantime, construction is continuing on two additional SDUs, each with two individual disposal cells. Together, these four cells will hold approximately 11.6 million gallons of the cement grout, which will provide enough disposal capacity until mid-2015.

Terrel Spears, assistant manager for the Waste Disposition Project, DOE-SR Office, called the implementation of SDUs another step toward safe waste disposal at SRS.

“Since 1990 when the Saltstone Disposal Facility became operational, we have learned a great deal about safe waste disposal,” Spears said. “While the current disposal unit has done a good job of allowing us to safely disposition waste, the new facility takes additional steps to further enhance the safety of the environment, workers and the public.”