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Title: Epsilon Metal: A Waste Form for Noble Metals from Used Nuclear Fuel

Abstract

Epsilon metal (e-metal) is the metallic phase that forms as inclusions at the grain boundaries in the UO2 fuel during reactor operation. This metal is composed of Pd, Mo, Rh, Ru, and Tc. These metallic inclusions are insoluble in strong acid and remnants of these metallic inclusions have been found in the UO2 matrix that remains from the natural reactors in Gabon that were active 1.8 billion years ago, therefore e-metal should be an excellent waste form for the immobilization of the long-lived isotopes 107Pd (6.5 ? 106 a) and 99Tc (2.13 ? 105 a), with 99Tc being the isotope of interest for repository performance. Therefore, the chemical durability of this potential waste form is assessed in this study. Typically, corrosion rates for metallic materials are measured electrochemically because they are quick, inexpensive, and can reveal the mechanism by which a metal corrodes, at least initially. However, in a repository the waste form would be subjected to slowly flowing water without an applied electrical potential over long time periods. Therefore, the corrosion rates of e-metal specimens were measured with both electrochemical tests and the single-pass flow-through test (SPFT). Potentiodynamic and potentiostatic polarization results suggest that a thin passive film existsmore » on the alloy surface, which seems to be responsible for its high corrosion resistance. Additionally, X-Ray photoelectron spectroscopic results suggest that Pd oxides are significantly enriched in the passive film Results from the SPFT show that the dissolution rates were weakly dependent on pH. Only Mo and Re were found in solution and were used for the calculation of the dissolution rates. In general, the electrochemically determined corrosion rates agree reasonably well with the initial dissolution rate measured with the SPFT test, but they are about one or two orders of magnitude higher than the steady state rates. The causes for this discrepancy are discussed.« less

Authors:
 [1];  [2];  [2];  [3];  [4];  [5];  [6];  [7]
  1. DM Strachan LLc
  2. BATTELLE (PACIFIC NW LAB)
  3. WASHINGTON RIVER PROTECTION SOLUTIONS
  4. MULTIPLE CONTRACTORS
  5. Private consultant
  6. Ohio State University
  7. OHIO STATE UNIVERSITY
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1604990
Report Number(s):
PNNL-SA-147059
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Journal of Nuclear Materials
Additional Journal Information:
Journal Volume: 532
Country of Publication:
United States
Language:
English
Subject:
epsilon-metal, nuclear waste form, corrosion, single-pass flow-through test, Dissolution, electrochemical analysis

Citation Formats

Strachan, Denis M., Crum, Jarrod V., Bovaird, Chase C., Windisch, Charles F., Zumhoff, Mac R., McIntosh, Brian, Guo, Xiaolei, and Frankel, Gerald S. Epsilon Metal: A Waste Form for Noble Metals from Used Nuclear Fuel. United States: N. p., 2020. Web. doi:10.1016/j.jnucmat.2020.152040.
Strachan, Denis M., Crum, Jarrod V., Bovaird, Chase C., Windisch, Charles F., Zumhoff, Mac R., McIntosh, Brian, Guo, Xiaolei, & Frankel, Gerald S. Epsilon Metal: A Waste Form for Noble Metals from Used Nuclear Fuel. United States. doi:10.1016/j.jnucmat.2020.152040.
Strachan, Denis M., Crum, Jarrod V., Bovaird, Chase C., Windisch, Charles F., Zumhoff, Mac R., McIntosh, Brian, Guo, Xiaolei, and Frankel, Gerald S. Wed . "Epsilon Metal: A Waste Form for Noble Metals from Used Nuclear Fuel". United States. doi:10.1016/j.jnucmat.2020.152040.
@article{osti_1604990,
title = {Epsilon Metal: A Waste Form for Noble Metals from Used Nuclear Fuel},
author = {Strachan, Denis M. and Crum, Jarrod V. and Bovaird, Chase C. and Windisch, Charles F. and Zumhoff, Mac R. and McIntosh, Brian and Guo, Xiaolei and Frankel, Gerald S.},
abstractNote = {Epsilon metal (e-metal) is the metallic phase that forms as inclusions at the grain boundaries in the UO2 fuel during reactor operation. This metal is composed of Pd, Mo, Rh, Ru, and Tc. These metallic inclusions are insoluble in strong acid and remnants of these metallic inclusions have been found in the UO2 matrix that remains from the natural reactors in Gabon that were active 1.8 billion years ago, therefore e-metal should be an excellent waste form for the immobilization of the long-lived isotopes 107Pd (6.5 ? 106 a) and 99Tc (2.13 ? 105 a), with 99Tc being the isotope of interest for repository performance. Therefore, the chemical durability of this potential waste form is assessed in this study. Typically, corrosion rates for metallic materials are measured electrochemically because they are quick, inexpensive, and can reveal the mechanism by which a metal corrodes, at least initially. However, in a repository the waste form would be subjected to slowly flowing water without an applied electrical potential over long time periods. Therefore, the corrosion rates of e-metal specimens were measured with both electrochemical tests and the single-pass flow-through test (SPFT). Potentiodynamic and potentiostatic polarization results suggest that a thin passive film exists on the alloy surface, which seems to be responsible for its high corrosion resistance. Additionally, X-Ray photoelectron spectroscopic results suggest that Pd oxides are significantly enriched in the passive film Results from the SPFT show that the dissolution rates were weakly dependent on pH. Only Mo and Re were found in solution and were used for the calculation of the dissolution rates. In general, the electrochemically determined corrosion rates agree reasonably well with the initial dissolution rate measured with the SPFT test, but they are about one or two orders of magnitude higher than the steady state rates. The causes for this discrepancy are discussed.},
doi = {10.1016/j.jnucmat.2020.152040},
journal = {Journal of Nuclear Materials},
number = ,
volume = 532,
place = {United States},
year = {2020},
month = {4}
}