Secondary Waste Form Testing - Engineering-scale demonstration for production of Ceramicrete and DuraLith materials.

Background
The Hanford Site in southeast Washington State has 54 million gallons of radioactive and chemically hazardous wastes stored in 177 underground tanks. The US Department of Energy, Office of River Protection (ORP), through its contractors, is constructing the Hanford Tank Waste Treatment and Immobilization Plant (WTP) to convert the radioactive and hazardous wastes into stable glass waste forms for disposal. Within the WTP, the pretreatment facility will receive the retrieved waste from the tank farms and separate it into two treated process streams. The pretreated high-level waste (HLW) mixture will be sent to the HLW Vitrification Facility, and the pretreated low-activity waste (LAW) stream will be sent to the LAW Vitrification Facility. The two WTP vitrification facilities will convert these process streams into glass, which is poured directly into stainless steel canisters. The immobilized HLW (IHLW) canisters will ultimately be disposed of at an offsite federal repository. The immobilized LAW (ILAW) canisters will be disposed of onsite in the Integrated Disposal Facility (IDF).

In addition to the primary IHLW and ILAW glass waste forms, the processing of the tank wastes will generate secondary wastes, including routine solid wastes and liquid process effluents. Liquid wastes may include process condensates and scrubber/off gas treatment liquids from the thermal waste treatment processes. The liquid-effluent secondary wastes will be sent to the Effluent Treatment Facility (ETF) for further treatment and solidification before disposal at the IDF.

MSE and PNNL Engineers working on Secondary Waste Form Testing for Ceramicrete
and DuraLith materials at the MSE Facility

Washington River Protection Solutions (WRPS) has been chartered to move forward with the design and construction of the STU for ETF. The ETF upgrades need to be operational by 2018 to receive secondary liquid wastes from the WTP. There will be a formal decision on the waste form for the secondary liquid wastes including agreement with the Washington State Department of Ecology (Ecology) by 2012.

The current baseline calls for solidification of the ETF evaporator concentrate in a cement-based waste form. However, alternative secondary waste forms are being considered. In 2006, Pacific Northwest National Laboratory (PNNL) completed for DOE an evaluation of three low-temperature technologies for the immobilization of mixed radioactive and hazardous waste. That testing program showed that the DuraLith alkali-aluminosilicate geopolymer and the Ceramicrete phosphate bonded ceramic showed potential as a waste form for the liquid secondary waste stream from WTP based on TCLP, compressive strength, and sodium leachability index requirements.

To support the selection of a waste form for the liquid secondary wastes from WTP, WRPS has initiated secondary waste form testing work at PNNL. In 2009, preliminary screening of waste forms was conducted to assess the viability of each for the solidification of the liquid secondary wastes. Additional testing is underway in 2010 to further develop and optimize Cast Stone, DuraLith, and Ceramicrete for the projected liquid secondary waste compositions.

Of the three waste forms, Cast Stone is a mature technology from a waste processing perspective. Its counterpart cementitious waste form at Savannah River, Saltstone, has been successfully produced for a number of years in treating their low-level wastes. Ceramicrete phosphate bonded ceramic and DuraLith alumino-silicate geopolymer are much less mature from a processing perspective. Ceramicrete has been demonstrated on the drum scale and DuraLith has been demonstrated at the bench scale with a 6-inch by 12-inch cylinder.

MSE. To support a final down selection, an engineering-scale demonstration was conducted for the production of Ceramicrete and DuraLith materials at the MSE test facility in Butte, Montana. The engineering-scale demonstration evaluated 1) the mixing steps in which the dry materials and liquid wastes were blended, 2) the pourability of the resulting slurry, 3) heat generation during curing, 4) voids and layering in the final product, and 5) any residual free liquids. Cores were collected from the waste forms and PNNL will perform leachability and compressive strength testing and those tests are currently being performed.