PNNL

Abstract

Getters are most commonly inorganic materials that selectively adsorb radionuclide and metallic contaminants. Typically, these materials have been deployed in two different modes to immobilize and retard contaminant release from monolithic waste forms. One mode is to first use getters to selectively scavenge the radionuclide of interest from a liquid waste stream, and then incorporate the radionuclide-loaded getters in cementitious or other monolithic waste forms. The other mode consists of mixing getters and liquid waste together during formulation of monolithic waste forms. Desirable characteristics for a getter material include, 1) specific adsorption of radionuclide of interest and very high selectivity toward radionuclides of concern in concentrations that would be several orders of magnitude less than the concentrations of competing anions and cations, 2) adsorption capacity that should be sufficient for the mass and volume of the material that will be deployed to be within practicable limits, 3) long-term adsorption and retention of radionuclide, 4) sufficient physical and chemical stability that its radionuclide retention performance will not degrade significantly during the designed life span of the waste form, 5) chemical stability under the range of Eh, pH, and solution conditions that exist in the waste form environment, and 6) should not adversely affect chemical and physical integrity of waste forms. We conducted a literature review to identify getters that are suitable for effectively sequestering 99Tc in monolithic waste forms that are being evaluated for stabilizing secondary liquid waste streams resulting from treatment and vitrification of radioactive tank wastes at Hanford. As a result of this review, we identified a set of getters that warrant further evaluation for this specific application.