Interaction of Radiolytic Species with Noble Metal Particles in Used Nuclear Fuel
EMSL Project ID
46901
Abstract
Noble metal particles (NMP) in used nuclear fuel are nanometer to micron sized alloys of the fission product elements Mo, Tc, Rh, Ru, and Pd. These metals are largely incompatible with the surrounding uranium dioxide (UO2) fuel matrix leading, to the appearance of NMP embedded in fuel grains, along grain boundaries, or in void regions that form during the burn-up of fuel in a nuclear reactor. During the long-term storage of used nuclear fuel, it is of interest to maintain anoxic and reducing conditions to prevent the oxidative dissolution of the uranium dioxide fuel matrix. Although they comprise only a small volume of the overall used fuel, NMP are thought to play a significant role in consuming radiolytic oxidants (e.g,. H2O2) that can be generated in a reducing or anoxic environment. They have also been observed to lower the electrochemical potential of the surrounding fuel matrix (most likely via solid state electron transfer when H2 is reduced at the NMP surface), compared to cases when NMP are not present. The objective of the proposed work is use atomic-scale, quantum-mechanical modeling to gain a fundamental understanding of how molecular species, which are relevant to a geologic storage environment (e.g., H2O2, O2, H2, and H2O), interact with NMP surfaces as a function of composition and surface termination. Pure Tc and Ru will be used as analogues for the alloyed NMP since they have the same hexagonal-closest-packed structure as the actual particles themselves. Since the composition of NMP changes as a function of fuel burn-up in a reactor, it will be possible to determine how the catalytic activity of these particles changes as a function of composition. Adsorption energies and surface-mediated reaction rates will be calculated and compared with a similar suite of calculations involving UO2 surface terminations (being performed off-site). These results will indicate how competitive NMP surfaces are for the radiolytic oxidants and reductants compared to the surrounding UO2 matrix. Results from these studies also couple with electrochemical experiments on NMP being performed at another location. Ultimately, these results will improve our understanding of the ability of NMP to contribute to maintaining reducing or anoxic conditions in a geologic storage environment for used fuel. Modeling these surface reactions also has bearing on understanding the fate of NMP in the environment, such as Pt, Pd, and Ru which are deposited along roadsides world-wide by catalytic converters. The use of EMSL facilities for this research endeavor provides an opportunity to access world-class computing power and collaborate with PNNL scientists in different areas of the laboratory from our own.
Project Details
Project type
Exploratory Research
Start Date
2012-05-16
End Date
2013-05-19
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
A.R. Geanes, F.N. Smith, D. Mei, and E.C. Buck (2013) Modeling the interaction of radiolytic species with noble metal particles, in Proceedings of the 14th International High-Level Radioactive Waste Management Conference (IHLRWMC), April 28th-May 2nd, Albuquerque, NM.