Direct observations of Pd–Te compound formation within noble metal inclusions in spent nuclear fuel

Sean H. Kessler; Timothy G. Lach; Kerry E. Garrett; Michele A. Conroy; David G. Abrecht; Jon M. Schwantes; Richard A. Clark

doi:10.1016/j.jnucmat.2020.152249

Direct observations of Pd–Te compound formation within noble metal inclusions in spent nuclear fuel

Sean H. Kessler, Timothy G. Lach, Kerry E. Garrett, Michele A. Conroy, David G. Abrecht, Jon M. Schwantes, Richard A. Clark

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3 Scopus citations

Abstract

Although the existence of a five-metal (Mo-Tc-Ru-Rh-Pd) phase – as nanoparticles observed in irradiated nuclear fuel – has been known for more than half a century, the chemical and physical mechanisms controlling the formation and behavior of such particles remain stubbornly elusive. We present in this work new evidence for the presence of a separate nonmetallic phase associated with the metallic particles and containing a significant fraction of Te in addition to Pd. While this new phase potentially complicates the thermodynamic picture of a mixed alloy in equilibrium with the surrounding fuel environment, it also provides new clues in the search for a chemical mechanism for Pd migration through the uranium dioxide matrix and the nucleation behavior of the particles. Fractionation between phases may subsequently affect the mechanical performance of fuels during irradiation and their interactions with the surrounding environment during long-term waste storage.

Original language	English
Article number	152249
Journal	Journal of Nuclear Materials
Volume	538
DOIs	https://doi.org/10.1016/j.jnucmat.2020.152249
State	Published - Sep 2020
Externally published	Yes

Funding

This work was funded by Pacific Northwest National Laboratory utilizing Laboratory Directed Research and Development (LDRD) funds with support from the Nuclear Process Science Initiative (NPSI) and was performed using PNNL Institutional Computing (PIC). Microscopy experiments were performed in the PNNL RPL Facility within the RPL Microscopy Quiet Suite, which is outfitted with a FEI Helios 660 FIM/SEM and a JEOL Grand ARM300 Aberration Corrected (AC) STEM/TEM. Additional TEM/STEM measurements were also collected on a JEOL ARM200 AC-STEM/TEM located in 3410, part of the Physical Sciences Facility. All of these instruments are part of PNNL’s Institutional Microscopy Tools. Pacific Northwest National Laboratory is operated by Battelle Memorial Institute for the United States Department of Energy under contract DE-AC05-76RL0-1830 . The particle labelled by point A in Fig. 1 is examined at higher magnification in Fig. 3, covering an area of approximately 100 nm on each side. Heterogeneity in the particle, evidenced by intensity variations in the Z-contrast HAADF image (Fig. 3a), is supported further by the elemental EDS maps. The Ru, Mo, Tc, and Rh distribution represented in Fig. 3 shows regions of high concentration toward the top-left and bottom areas, while the Pd distribution has the highest concentration along the left and right sides of the image connected by a strip elevated in Pd and Te. The latter case correlates with the Te map (Fig. 3d), which qualitatively replicates the features of the Pd map. The anticorrelation between Ru and Pd is also better illustrated by Fig. 3i, which overlays the two individual maps with very little direct overlap. Elemental maps of Mo, Tc, and Rh also match approximately the Ru distribution, albeit with a weaker overall signal. Because the observed trend is strongest among Ru, Pd, and Te, the remainder of the results described here will focus on these three elements.This work was funded by Pacific Northwest National Laboratory utilizing Laboratory Directed Research and Development (LDRD) funds with support from the Nuclear Process Science Initiative (NPSI) and was performed using PNNL Institutional Computing (PIC). Microscopy experiments were performed in the PNNL RPL Facility within the RPL Microscopy Quiet Suite, which is outfitted with a FEI Helios 660 FIM/SEM and a JEOL GrandARM300 Aberration Corrected (AC) STEM/TEM. Additional TEM/STEM measurements were also collected on a JEOL ARM200 AC-STEM/TEM located in 3410, part of the Physical Sciences Facility. All of these instruments are part of PNNL's Institutional Microscopy Tools. Pacific Northwest National Laboratory is operated by Battelle Memorial Institute for the United States Department of Energy under contract DE-AC05-76RL0-1830.

Funders	Funder number
Nuclear Process Science Initiative
Laboratory Directed Research and Development Program at Pacific Northwest National Laboratory
United States Department of Energy
U.S. Department of Energy	DE-AC05-76RL0-1830
Battelle
Laboratory Directed Research and Development
Pacific Northwest National Laboratory

Keywords

Noble metal phase particles
Nuclear reactor materials
Palladium telluride
Thermodynamic modeling
Transition metal alloys and compounds

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10.1016/j.jnucmat.2020.152249

Cite this

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title = "Direct observations of Pd–Te compound formation within noble metal inclusions in spent nuclear fuel",

abstract = "Although the existence of a five-metal (Mo-Tc-Ru-Rh-Pd) phase – as nanoparticles observed in irradiated nuclear fuel – has been known for more than half a century, the chemical and physical mechanisms controlling the formation and behavior of such particles remain stubbornly elusive. We present in this work new evidence for the presence of a separate nonmetallic phase associated with the metallic particles and containing a significant fraction of Te in addition to Pd. While this new phase potentially complicates the thermodynamic picture of a mixed alloy in equilibrium with the surrounding fuel environment, it also provides new clues in the search for a chemical mechanism for Pd migration through the uranium dioxide matrix and the nucleation behavior of the particles. Fractionation between phases may subsequently affect the mechanical performance of fuels during irradiation and their interactions with the surrounding environment during long-term waste storage.",

keywords = "Noble metal phase particles, Nuclear reactor materials, Palladium telluride, Thermodynamic modeling, Transition metal alloys and compounds",

author = "Kessler, {Sean H.} and Lach, {Timothy G.} and Garrett, {Kerry E.} and Conroy, {Michele A.} and Abrecht, {David G.} and Schwantes, {Jon M.} and Clark, {Richard A.}",

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doi = "10.1016/j.jnucmat.2020.152249",

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volume = "538",

journal = "Journal of Nuclear Materials",

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T1 - Direct observations of Pd–Te compound formation within noble metal inclusions in spent nuclear fuel

AU - Kessler, Sean H.

AU - Lach, Timothy G.

AU - Garrett, Kerry E.

AU - Conroy, Michele A.

AU - Abrecht, David G.

AU - Schwantes, Jon M.

AU - Clark, Richard A.

PY - 2020/9

Y1 - 2020/9

N2 - Although the existence of a five-metal (Mo-Tc-Ru-Rh-Pd) phase – as nanoparticles observed in irradiated nuclear fuel – has been known for more than half a century, the chemical and physical mechanisms controlling the formation and behavior of such particles remain stubbornly elusive. We present in this work new evidence for the presence of a separate nonmetallic phase associated with the metallic particles and containing a significant fraction of Te in addition to Pd. While this new phase potentially complicates the thermodynamic picture of a mixed alloy in equilibrium with the surrounding fuel environment, it also provides new clues in the search for a chemical mechanism for Pd migration through the uranium dioxide matrix and the nucleation behavior of the particles. Fractionation between phases may subsequently affect the mechanical performance of fuels during irradiation and their interactions with the surrounding environment during long-term waste storage.

AB - Although the existence of a five-metal (Mo-Tc-Ru-Rh-Pd) phase – as nanoparticles observed in irradiated nuclear fuel – has been known for more than half a century, the chemical and physical mechanisms controlling the formation and behavior of such particles remain stubbornly elusive. We present in this work new evidence for the presence of a separate nonmetallic phase associated with the metallic particles and containing a significant fraction of Te in addition to Pd. While this new phase potentially complicates the thermodynamic picture of a mixed alloy in equilibrium with the surrounding fuel environment, it also provides new clues in the search for a chemical mechanism for Pd migration through the uranium dioxide matrix and the nucleation behavior of the particles. Fractionation between phases may subsequently affect the mechanical performance of fuels during irradiation and their interactions with the surrounding environment during long-term waste storage.

KW - Noble metal phase particles

KW - Nuclear reactor materials

KW - Palladium telluride

KW - Thermodynamic modeling

KW - Transition metal alloys and compounds

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Direct observations of Pd–Te compound formation within noble metal inclusions in spent nuclear fuel

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Keywords

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