Waste Treatment

Introduction

The Department of Energy’s (DOE) Waste Management program directs the storage, treatment, and disposal of waste generated by DOE’s activities. In support of this mission, the Waste Management program uses a variety of treatment technologies to change the characteristics of the waste so that it may be more easily managed.



What Is Waste Treatment?



Waste treatment techniques are used to change the physical, chemical, or biological character of the waste, to reduce its volume and/or toxicity, and to make the waste safer for disposal. Waste treatment may be required for radioactive, hazardous, and other DOE wastes. However, DOE does not treat all of its wastes. Some solid sanitary waste does not require treatment prior to disposal, and hazardous wastes are treated by commercial treatment facilities. Mixed wastes (which contain both hazardous and radioactive components) pose special management challenges since they are difficult to treat with existing treatment technologies. These wastes are prohibited from disposal unless they have been treated to specific standards. DOE has worked with its state and Federal regulators and the public to identify and develop appropriate treatment strategies for mixed waste, and is now implementing the site treatment plans developed under the Federal Facility Compliance Act.



How Is Waste Treated?



Treatment methods are selected based on the composition, quantity, and form of the waste material. Some waste treatment methods are prescribed by regulations and DOE Orders; other treatment methods are being developed for specific wastes. Waste treatment methods being used today include solidification (e.g., calcining and vitrification) and volume reduction (e.g., incineration, compaction, and sizing).



Solidification



Solidification processes such as calcining and vitrification can be used to treat non-solid radioactive waste. DOE processing plants take liquid waste or semi-solid sludge and convert it to a solid waste form that can be safely disposed in a geologic repository.



For example, liquid waste can be solidified by a calcining process, such as that being used at DOE’s New Waste Calcining Facility (NCWF) at the Idaho National Engineering Laboratory (INEL). NCWF uses evaporation to solidify liquid high-level waste generated during past spent nuclear fuel processing operations at INEL.



The fluidized bed system is the heart of the calcining facility. Radioactive liquid waste droplets are sprayed into the calcining vessel where they solidify quickly on the hot fluidized beds. The end products are water vapor and small radioactive waste grains that are continuously withdrawn and transported through pipes to stainless steel bins for long-term storage pending disposal. These bins, which have a life span of hundreds of years, are encased in concrete vaults.



Vitrification is a solidification process that combines semi-liquid waste with glass, resulting in a stable glass form. In this process, highly radioactive liquid and sludge is mixed with glass particles and heated to very high temperatures to produce a molten glass. This molten glass is then poured into stainless steel canisters. When the mixture cools, it hardens into a stable glass that traps the radioactive elements and prevents them from moving through the air or water into the environment. DOE is currently operating vitrification plants at the Savannah River Site in South Carolina and the West Valley Demonstration Project in New York.



Solid Waste Reduction



By reducing the volume of waste that requires disposal, DOE can use the existing storage and disposal sites for a longer period of time. Solid waste reduction includes treatment methods that reduce the volume of solid waste such as incineration, compaction, and sizing.



Incineration can be used to treat and destroy combustible materials in transuranic, low-level, and