Novel Functionalized Ceramic Getter Materials for Adsorption of Radioiodine.
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Novel Functionalized Ceramic Getter Materials for Adsorption of Radioiodine. Shas V. Mattigod, Glen Fryxell, Kent Parker, and Dan Kaplan* Pacific Northwest National Laboratory, Richland, WA 99352 *Westinghouse Savannah River Company, Aiken, SC 29808
ABSTRACT A new class of getter materials has been synthesized for immobilization of long-lived radionuclides such as 129I. These novel materials consist of nanoporous ceramic substrates with tailored pore sizes ranging from 2 – 20 nm. These high surface area (~1000 m2/g) ceramic substrates have been functionalized with self-assembled monolayers consisting of soft cationcapped thiol-functionality. The resulting getter materials exhibit highly dense binding sites, and excellent selectivity for iodide. The effectiveness of these novel getter materials was evaluated using radioiodide-spiked samples of surface water and concrete leachate and adsorption performance was compared with natural sulfide mineral getter materials. The data indicated that the novel getter materials have very high affinity for radioiodide (Kd: 4 x 104 – 3 x 105 ml/g and 6 x 105 ml/g in surface and concrete leachate respectively). Comparatively, the radioiodide Kd values for natural mineral getters were typically two to three orders magnitude less than the novel getters. The results indicated that the synthetic getter materials have the potential to immobilize and therefore retard the migration of 129I in the subsurface environment. Additional studies are being conducted to evaluate the long-term stability of these materials in waste disposal environments.
INTRODUCTION A low-level radioactive waste site located at Savannah River Site (SRS) in South Carolina has been used to store and dispose waste generated over the last 20 years. A recent performance assessment (PA) modeling of this waste site indicated that 129I is the primary risk driver [1] and to allow additional wastes to be disposed at this site would require the deployment of a suitable getter material to immobilize this long lived radionuclide. During the last several decades, considerable research effort has been expended to identify suitable "getter" materials that can immobilize or delay the transport of radioiodine that would be released from waste repository environments. Metallic Cu and its oxides [2], sulfide minerals [3 –11], cementitious forms [12], various types of clay and oxide minerals [6, 12-16], modified zeolites [17], and organophilic clays [18-23] have been tested and evaluated for their getter properties for radioiodine.
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According to the criteria enumerated by Viani [24], successful getter materials 1) should have at least moderate adsorption/immobilization properties, 2) be stable for a long time in the post-closure environment, 3) should not adversely affect water chemistry, and 4) should not be prohibitively expensive. The objective of this study was to evaluate novel adsorbent materials that were developed at the Pacific Northwest National Laboratory (PNNL) as getters for radioiodine and to compare th
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