CH2M HILL’s Waste Treatment
242-Evaporator
CH2M HILL operates the 242-A Evaporator in the 200 East Area near the center of the 586-square-mile Hanford Site. The evaporator concentrates radioactive liquid tank waste from Hanford’s double-shell tanks to reduce the waste volume and reduce the number of tanks required to store waste. By removing water from the waste CH2M HILL is able to make additional storage space available for continued retrieval of aging waste in Hanford’s 149 single-shell tanks.
Prior to processing waste through the evaporator, the waste is extensively analyzed to determine its key constituents. If acceptable for processing, the candidate waste is pumped into the evaporator from nearby double-shell tanks via double-encased underground transfer lines. It goes into a sealed vessel in a highly-shielded enclosure where atmospheric pressure is reduced and steam heat is applied, allowing the waste to boil at a much lower temperature than would be required under normal pressure conditions. When the waste reaches a designated thickness, called specific gravity, the waste is transferred to a compatible double-shell tank for storage.
The evaporator is able to achieve a significant reduction in waste volume, which increases available tank storage space. This reduction in volume helps avoid the high cost of building and eventually disposing of new storage tanks. The evaporator operates under strict environmental regulations and stringent operational controls; the facility requires extensive maintenance and operator training to maintain it in a fully operable condition.
Supplemental Treatment Solutions
Bulk Vitrification
The process of Bulk Vitrification involves mixing waste with Hanford’s silica-rich soil and surrounding it with sand and insulation in a large steel box (50 cubic yards). Two large electrodes heat the mixture to about 2,400 degrees Fahrenheit. The mixture melts and then cools to a large brick of black glass, resembling, but more durable than, natural volcanic obsidian. The hazardous material is immobilized in the glass and the entire container, including the electrodes, is suitable for disposal in an on-site burial ground.
CH2M HILL is evaluating a technology with the potential to expedite production-scale treatment of tank waste at the Hanford site. Bulk Vitrification was selected as the primary technology for pilot testing and demonstration after evaluating 22 different technologies. It may be used to supplement the immobilization of mixed low-activity tank waste, thus augmenting the processing capacity of the Waste Treatment Plant.
Fractional Crystallization test apparatus in a hot cell in CH2M HILL’s 222-S Laboratory.
Fractional Crystalization
The Fractional Crystallization process separates dissolved materials based on how readily they turn to crystals. As water evaporates, non-radioactive salts in the solution form crystals. As these crystals form, they leave behind the radioactive contaminants in the solution. The technology is promising because much of the Hanford tank waste includes sodium nitrate, sodium nitrite, and a variety of other salts. Using fractional crystallization, such materials as sodium nitrate, sodium carbonate sulfate, and sodium fluoride phosphate can be separated from the radioactive materials such as cesium nitrate.
Fractional Crystallization is a familiar and well understood technology that is used to purify table salt. Now it is being explored to determine if it can be used effectively to treat some of the radioactive waste in Hanford’s underground storage tanks. If successful, this technology could reduce the volume of waste that must be sent through the Waste Treatment Plant.