Technitium Management at the Hanford Site

The Hanford tank waste contains -26,000 Ci of technetium-99 (Tc-99), the majority of which is in the supernate fraction. Tc-99 is a long-lived radionuclide with a half-life of -212,000 years and, in its predominant pertechnetate (TcO{sub 4}) fonn, is highly soluble and very mobile in the vadose zone and ultimately the groundwater. Tc-99 is identified as the major dose contributor (in groundwater) by past Hanford site performance assessments and therefore considered a key radionuclide of concern at Hanford. The United States Department of Energy (DOE) River Protection Project's (RPP) long-term Tc-99 management strategy is to immobitize the Tc-99 in a waste fonn that will retain the Tc-99 for many thousands of years. To achieve this, the RPP flowsheet will immobilize the majority of the Tc-99 as a vitrified low-activity waste product that will be ultimately disposed on site in the Integrated Disposal Facility. The Tc-99 will be released gradually from the glass at very low rates such that the groundwater concentrations at any point in time would be substantially below regulatory limits.The liquid secondary waste will be immobilized in a low-temperature matrix (cast stone) and the solid secondary waste will be stabilized using grout. Although the Tc-99 that is immobilized in glass will meet the release rate for disposal in IDF, a proportion is driven into the secondary waste stream that will not be vitrified and therefore presents a disposal risk. If a portion of the Tc-99 were to be removed from the Hanford waste inventory and disposed off-site, (e.g., as HLW), it could lessen a major constraint on LAW waste form performance, i.e., the requirement to retain Tc-99 over thousands of years and have a positive impact on the IDF Performance Assessment. There are several technologies available at various stages of technical maturity that can be employed for Tc-99 removal. The choice of technology and the associated efficacy of the technology are dependent on the chemical fonn of the technetium in the waste, the removal location in the tlowsheet. and the ultimate disposition path chosen for the technetium product. This paper will discuss the current plans for the management of the technetium present in the Hanford tank waste. It will present the risks associated with processing technetium in the current treatment tlowsheet and present potential mitigation opportunities, the status of available technetium removal technologies, the chemical speciation of technetium in the tank waste, and the available disposition paths and waste fonns for technetium containing streams