Epsilon metal: A waste form for noble metals from used nuclear fuel

JOURNAL OF NUCLEAR MATERIALS

卷:532

Article

Strachan, Denis¹  Crum, Jarrod, V¹  Bovaird, Chase C.²  Windisch, Charles³  Zumhoff, Mac¹  McIntosh, Brian⁴  Guo, Xiaolei⁵  Frankel, Gerald S.⁵ 

[1] Pacific Northwest Natl Lab, POB 999 K6-24, Richland, WA 99354 USA

[2] Bovaird Supply LLC, 1636 E 6th St, Tulsa, OK 74120 USA

[3] Univ Cent Missouri, Coll Sci & Technol, Warrensburg, MO 64093 USA

[4] 2639 Stonecrest Ln NW, Olympia, WA 98502 USA

[5] Ohio State Univ, 2041 Coll Rd, Columbus, OH 43210 USA

关键词: Epsilon-metal;    Nuclear waste form;    Corrosion;    Single-pass flow-through test;    Dissolution;    Electrochemical analysis;   

DOI  :  10.1016/j.jnucmat.2020.152040

来源: Elsevier

【 摘 要 】

Epsilon metal (epsilon-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 epsilon-metal should be an excellent waste form for the immobilization of the long-lived isotopes Pd-107 (6.5 x 10(6) a) and Tc-99 (2.13 x 10(5) a), with Tc-99 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 epsilon-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. (C) 2020 Elsevier B.V. All rights reserved.

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