Characterization of the Local Structure and Chemistry of 99Tc in Simulated Nuclear Waste Glasses and its Effect on Chemical Leaching
EMSL Project ID
48294
Abstract
A priority goal of the United States Department of Energy is to dispose of nuclear wastes accumulated in underground tanks at the Hanford Nuclear Reservation in Richland, WA. Incorporation and stability of technetium (Tc-99) into vitrified waste forms is a concern to the waste glass community and DOE due to its long half-life (2.1?105 y) and its high mobility in the subsurface environment under oxidizing conditions. We intend to utilize the world-class facilities in the EMSL Radiochemistry Annex to enable first-of-a-kind chemical structure determination of poorly understood, environmentally relevant, technetium compounds such as Na3TcO5, Na5TcO6, Na2TcO3 and Na4TcO4. Knowledge of structure and spectral signature of these compounds will aid in refining the understanding of Tc-99 incorporation into and release from oxide nuclear waste glasses. Through investigation of model alkali Tc-99 compounds and Tc-99-containing oxide glasses we intend to provide key data on glass structure around Tc-99, the stability of the glass, its corrosion in water, and the subsequent Tc-99 chemistry in the presence of near-field iron-bearing minerals. This work provides much needed data for improvement of performance assessment models of Tc-99 release in waste repositories. Our primary objective is to develop a clear understanding of Tc-99 local structure in oxide glass produced under various conditions, including those anticipated for processing of Low Activity Waste at Hanford. Secondly, knowledge of the effect of the local structure of Tc-99 on the leaching and dissolution behavior of glass is needed. Our team will synthesize new model compounds of Na-Tc(IV and VI)-O, and measure first-of-a-kind spectroscopic and structural data (Raman, XANES, XANES, XRD, NMR, and EPR) to support the understanding of mesoscale ordering of Tc-99 in glass. Furthermore, we will study Tc-99-containing glasses using EPR (for Tc(IV), and Fe), NMR (for Tc(VII), Na, and glass formers), TEM, and Electron Microprobe (for crystalline inclusions). After leaching the glasses under various conditions for 9 months, dissolved constituents will be measured with ICP-MS, and corroded surfaces will be investigated with XPS to ascertain Tc-99 oxidation state and chemistry of corroded layers.
In parallel we will perform advanced electronic structure calculations of the molecular Na-Tc-O compounds. Relativistic density functional theory (DFT) will be employed to optimize geometries and study the relative stability of compounds having the same Tc-99 oxidation state. Computations supporting direct comparison with experimental Raman vibrational frequencies, XANES electronic transitions, and NMR/EPR parameters (anisotropic shielding tensors, g-tensors, and hyperfine coupling constants) will be performed to aid in the scientific interpretation of local chemistry and structure.
This project is relevant to BER's mission "... to provide innovative solutions to the nation's environmental and energy production challenges [...] in subsurface science"?. Furthermore, Tc-99, an environmentally significant component in nuclear waste, is of particular importance for DOE/BER. The state-of-the-art equipment available at EMSL is essential for the success of this project, and the fundamental understanding of glass and Tc-99 geochemical behavior. The geographical proximity of Washington State University to EMSL/PNNL will facilitate the successful completion of this work. It is expected that high-impact publications will result from this work.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2014-07-01
End Date
2016-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Co-Investigator(s)
Team Members
Related Publications
Marcial J., J. Kabel, M. Saleh, N.M. Washton, Y. Shaharyar, A. Goel, and J.S. Mccloy. 2018. "Structural dependence of crystallization in glasses along the nepheline (NaAlSiO4) - eucryptite (LiAlSiO4) join." American Ceramic Society Bulletin 101, no. 7:2840-2855. PNNL-SA-132244. doi:10.1111/jace.15439
Nienhuis E.T., M. Saleh, J. Marcial, K. Kriegsman, J.M. Lonergan, A.S. Lipton, and X. Guo, et al. 2019. "Structural characterization of ZnSO4-K2SO4-NaCl glasses." Journal of Non-crystalline Solids 524. PNNL-SA-146862. doi:10.1016/j.pnucene.2019.103059
Weaver JL, CZ Soderquist, NM Washton, AS Lipton, PL Gassman, WW Lukens, AA Kruger, N Wall, and JS Mccloy. 2017. "Chemical Trends in Solid Alkali Pertechnetates." Journal of the American Chemical Society 56(5):2533–2544. doi:10.1021/acs.inorgchem.6b02694
Weaver J.L., C.Z. Soderquist, N.M. Washton, P.L. Gassman, E.D. Walter, M.E. Bowden, and W.W. Lukens, et al. 2018. "Challenges and Solutions for Handling and Characterizing Alkali-Tc-Oxide Salts." MRS Advances 3, no. 21:1191-1200. PNNL-SA-130916. doi:10.1557/adv.2018.165
Weaver J L,Soderquist C Z,Gassman P L,Walter E D,Lukens W W,McCloy J S 2017. "Synthesis and Characterization of 5- and 6- Coordinated Alkali Pertechnetates" MRS Advances