Hostname: page-component-7bb8b95d7b-qxsvm Total loading time: 0 Render date: 2024-09-20T18:45:02.038Z Has data issue: false hasContentIssue false
  • English
  • Français

Chemical Effects at the Reaction Front in Corroding Spent Nuclear Fuel

Published online by Cambridge University Press:  19 October 2011

Jeffrey A. Fortner ,
A. Jeremy Kropf ,
James L. Jerden  and
James C. Cunnane
Jeffrey A. Fortner
Affiliation:
fortner@cmt.anl.gov, Argonne National Laboratory, Chemical Engineering, CMT/205, 9700 S. Cass Avenue, Argonne, IL, 60439, United States, 630-252-5594
A. Jeremy Kropf
Affiliation:
kropf@cmt.anl.gov, Argonne National Laboratory, Chemical Engineering, CMT/205, 9700 S. Cass Avenue, Argonne, IL, 60439, United States
James L. Jerden
Affiliation:
jerden@cmt.anl.gov, Argonne National Laboratory, Chemical Engineering, CMT/205, 9700 S. Cass Avenue, Argonne, IL, 60439, United States
James C. Cunnane
Affiliation:
cunnane@cmt.anl.gov, Argonne National Laboratory, Chemical Engineering, CMT/205, 9700 S. Cass Avenue, Argonne, IL, 60439, United States
Get access

Abstract

Performance assessment models of the U. S. repository at Yucca Mountain, Nevada suggest that neptunium from spent nuclear fuel is a potentially important dose contributor. A scientific understanding of how the UO2 matrix of spent nuclear fuel impacts the oxidative dissolution and reductive precipitation of Np is needed to predict the behavior of Np at the fuel surface during aqueous corrosion. Neptunium would most likely be transported as aqueous Np(V) species, but for this to occur it must first be oxidized from the Np(IV) state found within the parent spent nuclear fuel. In this paper we present synchrotron x-ray absorption spectroscopy and microscopy findings that illuminate the resultant local chemistry of neptunium and plutonium within uranium oxide spent nuclear fuel before and after corrosive alteration in an air-saturated aqueous environment. We find the Pu and Np in unaltered spent fuel to have a +4 oxidation state and an environment consistent with solid-solution in the UO2 matrix. During corrosion in an air-saturated aqueous environment, the uranium matrix is converted to uranyl (UO22+) mineral assemblage that is depleted in Np and Pu relative to the parent fuel. The transition from U(IV) in the fuel to a fully U(VI) character across the corrosion front is not sharp, but occurs over a transition zone of ∼ 50 micrometers. We find evidence of a thin (∼ 20 micrometer) layer that is enriched in Pu and Np within a predominantly U(IV) environment on the fuel side of the transition zone. These experimental observations are consistent with available data for the standard reduction potentials for NpO2+/Np4+ and UO22+/U4+ couples, which indicate that Np(IV) may not be effectively oxidized to Np(V) at the corrosion potential of uranium dioxide spent nuclear fuel in air-saturated aqueous solutions.

Keywords

actinideextended x-ray absorption fine structure(EXAFS)corrosion
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 985: Symposium NN – Scientific Basis for Nuclear Waste Management XXX , 2006 , 0985-NN01-03
Copyright
Copyright © Materials Research Society 2007

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

REFERENCES

1. Finch, R. J., Buck, E. C., Finn, P. A., and Bates, J. K., “Oxidative Corrosion of Spent UO2 Fuel in Vapor and Dripping Groundwater at 90°C.” Scientific Basis for Nuclear Waste Management XXII, MRS Symp. Proc. Vol.556. Wronkiewicz, D. J., and Lee, J. H., eds., 431–438. Warrendale, Pennsylvania: Materials Research Society (1999).Google Scholar
2. Dehaudt, P., “State of the Art of the Oxidation of Spent Nuclear Fuel.” Section 7.2 of Synthesis on the Long Term Behavior of the Spent Nuclear Fuel. Poinssot, C., ed. CEA-R- 5958(E). Volume II. Paris, France: Commissariat à l'Énergie Atomique (2001).Google Scholar
3. Kropf, A. J., Fortner, J. A., Finch, R. J., Cunnane, J. C., and Karanfil, C.. “A Bent Silicon Crystal in the Laue Geometry to Resolve X-ray Fluorescence for X-ray Absorption Spectroscopy,”; Phys. Scripta Vol. T115, 998–1000 (2005).Google Scholar
4. Fortner, J. A., Finch, R. J., Kropf, A. J., and Cunnane, J. C., “Re-evaluating Neptunium in Uranyl Alteration Phases from Corroded Spent Fuel,” Nucl. Technol. 148(2) 174–180 (2004).Google Scholar
5. Guenther, R. J., Blahnik, D. E., Campbell, T. K., Jenquin, U. P., Mendel, J. E., and Thornhill, C. K., “Characterization of Spent Fuel Approved Testing Material–ATM-106.” PNL- 5109-106. Richland, Washington: Pacific Northwest Laboratory (1988).Google Scholar
6. See, for example, Putnis, A., “Mineral replacement reactions: from macroscopic observations to microscopic mechanisms,” Mineral. Mag., August 2002, Vol.66(4), pp. 689–708.Google Scholar
7. Conradson, S. D., “Application of X-ray Absorption Fine Structure Spectroscopy to Materials and Environmental Science,” App. Spectros. 52 (7) 252A–279A (1998).Google Scholar
8 L. Soderholm,, Mark Antonio, R., Williams, Clayton, and Wasserman, S. R., “XANES Spectroelectrochemistry: A New for Determining Formal Potentials.” Anal. Chem. 71, 4622–4628 (1999).Google Scholar
9. Sassani, D. C., Luik, A. Van and Summerson, J., “Neptunium Solubility in the Near-Field Environment of a Proposed Yucca Mountain Repository,”; Scientific Basis for Nuclear Waste Management XXIX, MRS Symp. Proc. Vol.932. P. Van, Iseghem, ed., 991–998. Warrendale, Pennsylvania: Materials Research Society (2006).Google Scholar
10. Burns, P. C., Ewing, R. C., and Miller, M. L., “Incorporation Mechanisms of Actinide Elements Into The Structures of U6+ Phases Formed During the Oxidation of Spent Nuclear Fuel.” J. Nucl. Mater. 245 1–9 (1997).Google Scholar
11. Burns, P. C., Deely, K. M., and Skanthakumar, S., “Neptunium incorporation into uranyl compounds that form as alteration products of spent nuclear fuel: Implications for geologic repository performance,” Radiochim. Acta 92 151–159 (2004).Google Scholar
12. Finch, R. J., “Precipitation of Crystalline NpO2 During Oxidative Corrosion of Neptunium- Bearing Uranium Oxides.” Scientific Basis for Nuclear Waste Management XXV, MRS Symp. Proc. Vol.713. McGrail, B. P. and Cragnolino, G. A., editors, pp. 639–646 Warrendale, Pennsylvania: Materials Research Society (2002).Google Scholar