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Waste Solidification

The two primary facilities operated within the Waste Solidification program are Saltstone and the Defense Waste Processing Facility (DWPF).

Each DWPF canister is 10 feet tall and 2 feet in diameter, and typically takes a little over a day to fill.
Each DWPF canister is 10 feet tall and 2 feet in diameter, and typically takes a little over a day to fill.

The largest radioactive waste glassification plant in the world, DWPF converts the high-level liquid nuclear waste currently stored at the Savannah River Site (SRS) into a solid glass form suitable for long-term storage and disposal.

Scientists have long considered this glassification process, called “vitrification,” as the preferred option for immobilizing high-level radioactive liquids into a more stable, manageable form until a federal repository is ready. About 36 million gallons of high-level liquid wastes are now stored in 49 underground carbon-steel tanks at SRS. This waste has about 425 million curies of radioactivity, and requires permanent isolation from the environment.

Construction began in late 1983 on the plant, and it was completed at a capital cost of $1.276 billion and start-up operating costs totaling $1.2 billion. Changing environmental requirements and major safety upgrades and process modifications to the facility, in addition to implementing an enhanced operator training program and a “waste qualification” test phase to demonstrate that the glass form meets all environmental and operational requirements for long-term storage, were required before system testing began in 1990. That was followed by cold chemical tests with non-radioactive simulated waste that were completed in 1993.

Employees perform operations remotely, from outside shielded windows.

Employees perform operations remotely, from outside shielded windows.

DWPF successfully completed its waste qualification testing in late 1995, filling 70 canisters with a nonradioactive glass form that met all environmental and operational requirements. Nonradioactive chemicals simulated the properties and constituents of the waste.

DWPF began radioactive operations in March 1996. The projected production to vitrify all high-level waste currently stored at SRS is approximately 6,000 canisters over the next 20-25 years. Under an accelerated risk reduction and closure plan, the number of canisters could be reduced to 5,000 as a result of a program that will complete high level waste processing years earlier and at much lower cost.

The Saltstone Facility safely treats and disposes of low-level liquid radioactive wastes produced and stored at the Savannah River Site.

Soluble salts, primarily sodium nitrate (similar to fertilizer), make up about 93 percent of the 37 million gallons of material in the radioactive waste storage tanks in the High Level Waste (HLW) storage tanks at the site. Pretreatment of this HLW will separate soluble salts from insoluble sludge to generate about 100-120 million gallons of salt solution. This salt solution will be treated to remove cesium and strontium. These two contaminants are sent to the Defense Waste Processing Facility, where they are combined with the sludge, turned into glass and poured into canisters.

Removal of the cesium and strontium converts the majority of the salt solution to low-activity waste containing less than 0.01 percent of the total radioactivity now present in the waste. This salt solution is sent to the Saltstone Facility for immobilization.

A portion of the Saltstone facilities
A portion of the Saltstone facilities

In addition to receiving low-level waste from the tank farms, Saltstone also receives a similar waste stream from the Effluent Treatment Facility. This facility processes other waste from the tank farms as well as from the site's two chemical separation facilities.

After the waste is received at Saltstone, the salt solution is mixed with cement, fly ash and blast furnace slag to form grout. The grout is then pumped into large concrete vaults divided into sections (called cells); here, it cures into stable concrete (called "saltstone"). Each cell is 100 feet long, 100 feet wide and 25 feet tall. Currently two vaults exist at the facility, one with 12 cells and one with six cells (each vault is partially full). After filling, the vault will be capped with clean concrete to isolate it from the environment. Final closure of the area will consist of covering the vaults with a clay cap and backfilling with earth.

Extensive testing shows that any waste constituents leached from the saltstone will remain within Environmental Protection Agency drinking water standards. Wells near the edge of the disposal site are used to monitor groundwater to ensure that it meets standards established by the South Carolina Department of Health and Environmental Control.

The Saltstone control room.

Two Saltstone employees run the mixing and transfer system from the Saltstone control room.

Construction was completed of the Saltstone Facility and the first two vaults between February 1986 and July 1988 at a cost of $45 million. The Saltstone Facility started radioactive operations June 12, 1990, and to date has processed approximately 3.1 million gallons of low-activity waste. The facility was recently modified to process higher curie levels of material, and is now waiting permission from DHEC to start up.



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