Candidate Low-Temperature Glass Waste Forms for Technetium-99 Recovered from Hanford Effluent Management Facility Evaporator Concentrate

Abstract

Alternative treatment and disposition options may exist for technetium-99 (99 Tc) in secondary liquid waste from the Hanford Direct-Feed Low-Activity Waste (DFLAW) process. One approach includes development of an alternate glass waste form that is suitable for on-site disposition of technetium, including salts and other species recovered by ion exchange or precipitation from the EMF evaporator concentrate. By recovering the Tc content from the stream, and not recycling the treated concentrate, the DFLAW process can potentially be operated in a more efficient manner that lowers the cost to the Department of Energy. This report provides a survey of candidate glass formulations and glass-making processes that can potentially incorporate technetium at temperatures <700 °C to avoid volatilization. Three candidate technetium feed streams are considered: (1) dilute sodium pertechnetate loaded on a non-elutable ion exchange resin; (2) dilute sodium-bearing aqueous eluent from ion exchange recovery of pertechnetate, or (3) technetium(IV) oxide precipitate containing Sn and Cr solids in an aqueous slurry. From the technical literature, promising candidate glasses are identified based on their processing temperatures and chemical durability data. The suitability and technical risk of three low-temperature glass processing routes (vitrification, encapsulation by sintering into a glass composite material, and sol-gel chemical condensation) for the three waste streams was assessed, based on available low-temperature glass data. For a subset of candidate glasses, their long-term thermodynamic behavior with exposure to water and oxygen was modeled using Geochemist's Workbench, with and without addition of reducing stannous ion.

Evaluation of Immobilizing Secondary Waste from a Proposed Treatment Process for Hanford WTP LAW Melter Condensate

“…Another option is to generate a Tc-specific glass waste form for this slurry as was previously evaluated by Los Alamos National Laboratory. 12 While this approach is potentially optimal in the long term because the waste form could be tailored to retain Tc and minimize volume, development of such a waste form is likely years away and very costly. Other alternative disposal paths, including tank farm storage options, will be pursued in the future if LAW glass disposal is not practical.…”