A waste disposal project at the Savannah River Site took another step forward recently when the facility’s liquid waste contractor conducted a successful leak tightness test for Saltstone Disposal Unit 6 (SDU 6). SDU 6 is the first 30-million gallon, megavolume salt waste disposal concrete unit constructed at the Department of Energy site in South Carolina. Once complete, it will be a permanent disposal receptacle for saltstone, a low radioactive salt waste found in the SRS storage tanks.
Site officials reported in May that the initial leak test had failed: The unit’s concrete cell had been constructed, but the water tightness test did not meet requirements. To pass the test, contractor Savannah River Remediation over the past three months installed an interior liner to protect the concrete shell from chemical degradation and achieve leak tightness. The new test began on Dec. 15 and ended Dec. 29.
The test required filling SDU 6 with 32 million gallons of water. A safe lime-green dye was mixed into the water to reveal any leaks. None were found.
The next step is to release the dyed water from the unit. That process began Dec. 29 and is expected to take 12 days. Once the unit is drained, final construction must be conducted, including welding, vent installation, and piping. The work should be completed by the end of January – roughly two months sooner than the March 2017 projection. DOE also expects that SDU 6 will be ready to use ahead of the project need date of February 2018, and that the unit will cost about $122 million – significantly less than the $143 million baseline budget.
SDU 6 and other disposal units at SRS are used for permanent diposal of the salt waste stored in the site’s aging waste tanks. The 36 million gallons of waste is a byproduct of Cold War nuclear weapons production. About 90 percent of the liquid waste stored in the tanks is salt waste. The salt waste is broken down by mixing it with a cement-like grout, which creates saltstone. It is then stored for final disposition on site.
The site’s saltstone disposal facilities also include Vaults 1 and 4, along with SDUs 2, 3, and 5. Each of the three units consists of two tanks, with each tank able to hold up to 2.9 million gallons. According to Revision 20 of the SRS Liquid Waste System Plan, another eight units will be required to complete the liquid waste mission, with SDU 7 projected to be needed by fiscal 2021.
Savannah River Remediation is a partnership of AECOM, Bechtel, BWX Technologies, and CH2M. Its roughly $4 billion contract expires on June 30, 2017.
