Vitrification of Low-Activity Radioactive Waste Streams and a High-Level Radioactive Waste Stream in Support of the Hanford River Protection Program

摘要

Hanford tank waste consists of about 190 million curies in 54 million gallons of highly radioactivernand mixed hazardous waste stored in underground storage tanks at the Hanford Site in Washington State. Therntank waste includes solids (sludge), liquids (supernatant), and salt cake (dried salts that dissolve in water to formrnsupernatant). The tank waste will be remediated through treatment and immobilization to protect the environmentrnand meet regulatory requirements. The U.S. Department of Energy’s (DOE’s) preferred alternative to remediaternthe Hanford tank waste is to pretreat the waste by separating it into low-activity waste (LAW) and high-level wastern(HLW), followed by immobilization of the LAW for on-site disposal and immobilization of the HLW for ultimaterndisposal in a national repository.rnThe Savannah River Technology Center (SRTC) at the Savannah River Site (SRS) in Aiken, South Carolina, hasrnbeen involved in research and testing with actual radioactive Hanford tank samples to demonstrate and verify thernconceptual design of the waste treatment and immobilization plant (WTP) processes. This paper describes the crucible-rnscale vitrification and associated wasteform product tests in support of the WTP at Hanford. The two differentrnLAW glasses produced in this study were from pretreated Envelope A (Tank 241-AN-103) and Envelope Crn(Tank 241-AN-102) waste. The HLW glass was produced from Tank C-106 HLW sludge and the HLW radionuclidernproducts separated from Hanford Site tank samples AN-103, AN-102 and AZ-102. Pretreatment of thesernthree supernates consisted of characterization, strontium and transuranics removal by precipitation and filtration,rnand final Cs-137 and Tc-99 removal by ion exchange (IX). The glasses were produced from formulations suppliedrnby Vitreous State Laboratory of the Catholic University of America (CUA). Formulations were based on previousrnsurrogate testing and the actual characterization data from the radioactive feed streams. Crucible-scale vitrificationsrnwere performed in platinum/gold crucibles in a custom-designed furnace fit with an offgas containment system.rnBoth LAW and HLW melter feed slurries were evaporated, calcined, and then melted at 1150oC. The LAWrnand HLW glasses were heat-treated per a modeled centerline cooling curve for the LAW canister and HLW canister,rnrespectively.rnAll glasses were analyzed for chemical and radionuclide content and examined for crystalline phase identification.rnThe glasses were also durability tested using the ASTM Product Consistency Test (PCT) procedure and wererntested by the U.S. Environmental Protection Agency’s Toxicity Characteristic Leaching Procedure. The LAWrnglasses were also analyzed for regulatory analyses by Babcock and Wilcox Technology (BWXT) Services, Inc. perrnU.S. EPA SW-846 protocol. These analyses included cyanide, ignitability, RCRA metals to the Universal TreatmentrnStandard (UTS), volatile and semivolatile organic compounds, dioxins and furans, pesticides, and polychlorinatedrnbiphenyls (PCBs).