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The chemical speciation, ionic plus particulate forms, of long-lived isotopes of Pu, Am, Cm, Cs, Sr, Ni, I, and Tc was determined in four contaminant plumes at the Chalk River Nuclear Laboratories. Comparative data were also determined for shorter-lived isotopes of Ce, Eu, Fe, Co, Ru, Zr and Sb. Anionic species were the predominant solution species, and hence the mobile form, for many of the elements. Complexation by organic ligands, both natural and synthetic, was postulated to be important in mobilizing Co, Ce, Cs, Eu, Sb, Zr, Fe, Ni, I, Pu and possibly Am. Thermodynamically-predicted aqueous speciation was consistent with our data for only four elements; Ru, Sr, I and Tc. The chemical speciation of Am was found to be particularly anomalous in the study sites. On the basis of our data we conclude that the predictions of Kd-based models for radionuclide mobility must be carefully evaluated with respect to the adequacy of the speciation assumptions of the Kd approach.

SummaryExperiments were conducted in fiscal year 1998 by Pacific Northwest National Laboratory' to evaluate potential incorporation of radionuclides in secondary mineral phases that form from weathering vitrified nuclear waste glasses. These experiments were conducted as part of the Immobilized LowActivity Waste-Performance Assessment (ILAW-PA) to generate data on radionuclide mobilization and transport in a near-field environment of disposed vitrified wastes.An initial experiment was conducted to identify the types of secondary minerals that form from two glass samples of differing compositions, LD6 and SRL202. Chemical weathering of LD6 glass at 90°C in contact with an aliquot of uncontaminated Hanford Site groundwater resulted in the formation of a crystalline zeolitic mineral, phillipsite. In contrast, similar chemical weathering of SRc202 glass at 90°C resulted in the formation of a microcrystalline smectitic mineral, nontronite.A second experiment was conducted at 90°C to assess the degree to which key radionuclides would be sequestered in the structure of secondary crystalline minerals; namely, phillipsite and nontronite. Chemical weathering of LD6 in contact with radionuclide-spiked Hanford Site groundwater indicated that substantial &actions of the total activities were retained in the phillipsite structure.Similar chemical weathering of SRL202 at 90°C, also in contact with radionuclide-spiked Hanford Site groundwater, showed that significant fractions of the total activities were retained in the nontronite structure.These results have important implications regarding the radionuclide mobilization aspects of the ILAW-PA. Additional studies are required to c o n f i i the results and to develop an improved understanding of mechanisms of sequestration and attenuated release of radionuclides to help refine certain aspects of their mobilization. ~ ~~Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.

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