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Workers poured an initial mud mat to serve as a solid surface for the Saltstone Disposal Unit 6.
Workers poured an initial mud mat to serve as a solid surface for the Saltstone Disposal Unit 6.

AIKEN, S.C. – Workers completed construction of a massive disposal unit for the Savannah River Site’s (SRS) saltstone waste more than $25 million under budget and more than a year ahead of when it’ll be needed for cleanup. 

   The 32.8-million gallon Saltstone Disposal Unit 6 (SDU 6), designed and built by SRS liquid waste contractor Savannah River Remediation (SRR), is more than 10 times larger than the six previously constructed SDUs. The SDU 6 is designed for the larger decontaminated salt solution stream to be produced by the site’s Salt Waste Processing Facility, scheduled to begin operating in December 2018.

   “Construction of SDU 6 is significant for the SRS liquid waste mission and underscores the Department of Energy's continued commitment to furthering progress on tank closure and risk reduction,” Savannah River Operations Office Manager Jack Craig said. 

   SRR completed construction of SDU 6 in late April at a cost of about $118 million — more than $25 million under the budget of $143.2 million — and 16 months ahead of the originally established completion date of November 2018.

 

Saltstone Disposal Unit 6 at the halfway point in construction.
Saltstone Disposal Unit 6 at the halfway point in construction.
Savannah River Remediation successfully completed its first mega-volume Saltstone Disposal Unit on a 2-1/2 acre site.
Savannah River Remediation successfully completed its first mega-volume Saltstone Disposal Unit on a 2-1/2 acre site.

 

 

 

 

 

 

 

 

 

 

   “The cost savings of these SDUs is significant to all of us,” SRR President and Project Manager Tom Foster said. “The Saltstone Disposal Units have proven to be very successful in the dispositioning of decontaminated salt solution, which is key to achieving our mission here at SRS.”

   Salt waste makes up about 90 percent of the waste volume in SRS tanks. The Saltstone facility receives decontaminated salt solution after highly radioactive isotopes — primarily cesium — are removed and transferred to the Defense Waste Processing Facility to be turned to glass and stored at SRS awaiting permanent disposal. 

   The SDU 6 design differs from the previous six SDUs, each holding roughly 3 million gallons of saltstone. Built with more than 13,000 cubic yards of concrete, SDU 6 measures 43 feet high and 375 feet in diameter. Its tank walls are wrapped in 289 miles of pre-tensioned wire strand. They were designed to expand outward as the tank is filled, and the wire strand maintain the structural integrity of the tank walls while waste is added to the tank.

   The larger design, which mirrors those for commercial water applications, allows for cost savings because it requires less infrastructure and materials to design and build. 

   SRS will need only seven of the larger units to meet mission needs — equivalent to 80 of the smaller units — and DOE has approved the concept of replicating the efficient SDU 6 design for all remaining SDUs. Work has begun on SDU 7, and initial approvals are slated for the remaining SDUs in 2017.

   “This change will result in a significant life-cycle cost savings of over $500 million over the life of the program, given economies of scale, layout, design and construction processes,” SDU 6 Project Manager Jon Lunn said.