Introduction
The U.S. Department of Energy (DOE) sponsors research and development (R&D) in advanced radiochemical separations to reduce the volume of high-level waste (HLW) that must be disposed in deep geological repositories, and to cut the toxicity and volume of low- level waste (LLW) acceptable for near-surface disposal. These R&D activities are sponsored through the DOE Office of Technology Development Efficient Separations and Processing Integrated Program (ESPIP). ESPIP also develops separation processes to extract high-value materials and non-radioactive hazardous components from nuclear waste and will transfer separations processing to commercial markets.
Technical Focus
ESPIP R&D activities are designed to remove radionuclides and hazardous materials and chemicals from radioactive defense wastes. Radionuclides and other materials under consideration for separation include transuranic (TRU) elements such as neptunium, plutonium, americium, and cerium, highly radioactive elements (Sr-99 and Cs-137), and long-lived soluble fission products including technetium-99 and iodine-129. Separation processes will also be developed to extract the long-lived soluble activation product carbon-14; aluminum, phosphorous, and chromium, the elements that degrade borosilicate glass waste forms; the strategic metals rhodium, palladium, and ruthenium; and Resource Conservation and Recovery Act elements and compounds.
The program oversees efficient separations R&D for DOE sites. Current priorities are the cleanup of high-level wastes (HLW) in underground storage tanks at Hanford Production Operations, Hanford, WA, and the cleanup of HLW at Idaho National Engineering Laboratory (INEL), Idaho Falls, ID. Many of the technologies developed for HLW will be applicable to other waste streams throughout the DOE Complex and ESPIP will transfer technologies as appropriate.
Hanford High Level Waste
The acidic liquid HLW from reprocessing defense reactor fuels for plutonium, which began in 1944, was made alkaline (pH 14) by adding caustic soda and was stored in underground concrete storage tanks lined with carbon steel. Over the years, 149 of these single-shell tanks (SST) were built and eventually some began to leak. Today, 66 SSTs are known to be or suspected of leaking, posing a threat to contaminate the groundwater. The 149 SSTs contain 165,500 cubic meters of waste, all of which is currently treated as HLW, approximately 2.5 x 10^8 kg. The maximum migration of these SST wastes into the ground is estimated to be 75 meters. When the SSTs began to leak, new underground double-shell tanks (DST) were built, and there are now 28 DSTs, none of which have leaked. These tanks contain 79,300 cubic meters of HLW, approximately 100,000 Mg.
Idaho High-Level Waste
Most INEL HLW is reprocessed naval reactor fuel. Acidic liquid waste is stored in underground stainless steel tanks that are housed inside concrete vaults. The waste is then converted into a calcine powder and stored retrievably in stainless steel bins inside reinforced concrete vaults. There are 3,500 cubic meters of HLW stored as calcine, containing 90 percent of the radioactivity, and 8,500 cubic meters of liquid HLW containing ten percent of the radioactivity. The INEL waste is uniform and well characterized, but will not meet Land Disposal Requirements (LDRs).
Economic Benefits
Currently the preferred waste form for permanent disposal of HLW is vitrified borosilicate glass inside a stainless steel canister. Approximately 25 to 30 volume percent of the vitrified glass is HLW and the balance is glass frit, unless the HLW contains aluminum, phosphorous, or chromium.
Recent estimates for the Hanford SST and DST HLW disposal indicate that sludge wash of the waste, primarily to rid the waste of sodium nitrate and other soluble compounds without further separations and processing, would require 40,000 canisters. If advanced separations are implemented to separate TRU elements, cesium, strontium, and technetium, from the non-radioactive chemicals, the number of canisters is expected to be reduced to 2,000. Less than 10 cubic meters are radionuclides.
The sludge wash and advanced separations is expected to generate 940,000 cubic meters of aqueous LLW, which will be disposed of as 1,600,000 cubic meters of cement grout in 300 near-surface concrete vaults. The cost of LLW disposal is projected to be $5,800 per cubic meter of liquid or $3,400 per cubic meter of grout. The cost of vitrification and disposal of a cubic meter of HLW, which requires six canisters, is about $6M; or over 1000 times the cost of disposal of a cubic meter of LLW.
Since the INEL HLW is in calcine form, processing the waste with aqueous solvent extraction would require dissolving the calcine in nitric acid, which would generate a large volume of aqueous LLW. As an alternative, ESPIP is exploring a glass-ceramic waste form and the possibility of pyrochemical processing. The glass-ceramic waste form would reduce the number of logs from 9,500 to 3,770. If pyrochemical processing was used with a glass waste form, the number of logs generated would be less than 900.
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Selected Past Accomplishments
Prepared glass-ceramic waste forms with leach rates comparable to borosilicate glass.
Completed systems total-mass-balance analysis model for Hanford underground storage tanks and evaluated TRans Uranic EXtraction (TRUEX) option.
Demonstrated utility of molecular mechanics in designing highly specific sequestering agents.
1993 Accomplishments/Objectives
Define and test candidate radiochemical separations processes on high-level waste (HLW) and transuranic (TRU) wastes at Hanford.
Complete preliminary feasibility laboratory tests for pyrochemical treatment of Idaho high-level waste (HLW) calcine.
Complete Phase I of industrial contracts to develop cesium and strontium removal techniques, evaluate potential of developing technologies.
Start Phase II-test of promising industrial-contract materials on high-level waste.
Initiate new industrial contracts in separations or sludge treatment technologies.
Begin R&D on treatment processes for high-level waste (HLW) sludges present in underground storage tanks at Hanford and Oak Ridge.
Continue international dialogue and technical exchanges on separations technologies; sponsor high-level waste (HLW) treatment R&D in Russia.
1994 Objectives
Begin extension of new technologies developed for High-level waste (HLW) to contaminated soil and groundwater cleanup via selective extraction and separation of transuranics (TRUs) and toxic metals.
Continue international dialogue and technical exchanges on separations technologies.
Initiate separations needs assessment for low-level and mixed wastes.
Transfer an industrial cesium/strontium removal technology to customer (EM- 30).
Initiate sludge treatment testing on actual waste.
Continue studies of pyrochemical processing and equipment feasibility tests; make go/no-go decision on whether to further pursue pyroprocessing/transfer to EM-30 if go decision.
Begin development of separations technologies for extraction of heavy metals and technetium from high-level waste and low-level waste as needed.
Begin R&D on noble metal separation/recovery from high-level waste to insure vitrification reliability and glass quality and for possible monetary value.
Begin evaluation of separation methods developed for high-level waste for treating mixed wastes, soils, groundwater, and toxic wastes.
Initiate collaborative industrial/DOE laboratory efforts to develop methods for toxic and noble metal removal from contaminated waters such as the Berkeley Pit with a molecular recognition technology.
1995 Planned Objectives
Initiate/continue R&D for processing of mixed and low-level wastes. Particular emphasis on adaptation of technologies developed for high-level waste treatment to these needs.
Continue work on sludge treatment processes and testing on actual wastes. Develop database on results for range of actual waste compositions to provide input for treatment of dissolved sludges.
Expand work on industrial cesium/strontium removal technologies completed in FY 94 to other waste streams and radionuclides.
Continue development of technology selection tool for Idaho National Engineering Laboratory and Rocky Flats.
Continue work on advance processing schemes, incorporating data on new technologies and sludge treatment studies developed in program.
Initiate/continue study of separations/processing methods for removing radioactive materials and toxic metals from soils/groundwater.
Begin studies of selective leaching of example mixed-waste sludges.
Continue development of technologies for technetium and heavy metal extraction.
Continue R&D on noble metal separations from high-level waste; assess needs other than high-level waste.
Continue extension of new processing technologies developed for high-level waste to other waste streams, such as decontamination and decommissioning streams, heavy metal removal from wastewaters and groundwaters/streams, etc.
Initiate expansion/modification of industrial technologies for high-level waste to other waste streams.
Initiate development of technologies of removal treatment of tritium, carbon-14, and radioactive iodine.
Complete assessment of organic/nitrate destruction technologies and make recommendation to EM-30.
Transfer one or more generally applicable separations technologies to industry.
Develop database on sludge treatment based on results of testing actual wastes/make recommendations for treatment of dissolved sludge.
Assess needs for recovering contaminants from decontamination fluids and recycling of reagents.
Initiate studies of selecting chelating leach materials for removing contaminants from metal surfaces.
Assess separations/processing opportunities for increasing the acceptable waste loading of conventional waste forms.
Begin studies of new waste forms, particularly forms that can handle concentrated contaminants that are not retained effectively by conventional waste forms.
Complete development of polymer-based sequestering agents for transuranic removal of Rocky Flats Plant and transfer results to underground storage tanks and EM-50.