Karen Wright

Profile Information

Name: Ms Karen Wright
Institution: Idaho National Laboratory
Position: Instrument Scientist
Affiliation: Microanalysis Society
h-Index: 11
ORCID: 0000-0003-4504-929X
Biography: Karen Wright is a graduate of Idaho State University, with a Master’s degree in Geoscience.  For the past seven years she has been working in the Nuclear Energy division at Idaho National Laboratory to set up facilities and methods to analyze irradiated nuclear fuel using the first modern shielded electron probe microanalyzer available to the scientific community in the United States.  To date, her work has focused on the fission product distribution of tristructural isotropic (TRISO) nuclear fuels and component migration and secondary phase formation in metallic transmutation fuels.  Ms Wright has served as a visiting scientist at the Institute for Transuranium Elements in Karlsruhe, Germany and is now the lead EPMA instrument scientist at Idaho National Lab.
Expertise: Electron Probe Microanalysis (EPMA)

Publications:

		"Characterization of Metallic Fission Products in 13.7% FIMA MOX Fuel using Electron Microscopy Techniques " Karen Wright, Journal of Nuclear Materials Vol. 524 2019 67-79 Link This work utilizes electron microscopy-based techniques to examine the radial behavior of solid fission products in plutonium (Pu) bearing mixed oxide (MOX) fuel irradiated to a burnup of 13.7% fissions per initial metal atom (FIMA). Metallic precipitates primarily consist of five fission products: ruthenium (Ru), rhodium (Rh), technetium (Tc), molybdenum (Mo), and palladium (Pd). The five metal precipitates (FMPs) examined in this work have low concentrations of Pd and Mo, with no major compositional differences along the fuel radius. A secondary Pd–Te metallic phase forms in cooler regions of the pellet, likely due to the diffusion of gaseous species away from the central void. X-ray chemical maps indicate that the Pd–Te phase can nucleate on the surface of FMPs before precipitating into separate particles. These particles were also found to alloy with iron (Fe) near the surface of the fuel pellet due to interdiffusion with the stainless-steel cladding. The insoluble perovskite oxide phase was found to form near the central void and at intermediate radial positions, but not at the fuel edge. These findings suggest that solid fission product phases form at varying counts and compositions along the fuel pellet radius, and thus should be considered when describing the thermal behavior of the fuel.
		"Characterization of solid fission products in 13.7% FIMA MOX fuel using electron microscopy techniques" Riley Parrish, Karen Wright, Alexander Winston, Jason Harp, Casey McKinney, Assel Aitkaliyeva, Journal of Nuclear Materials Vol. 524 2019 67-79 Link This work utilizes electron microscopy-based techniques to examine the radial behavior of solid fission products in plutonium (Pu) bearing mixed oxide (MOX) fuel irradiated to a burnup of 13.7% fissions per initial metal atom (FIMA). Metallic precipitates primarily consist of five fission products: ruthenium (Ru), rhodium (Rh), technetium (Tc), molybdenum (Mo), and palladium (Pd). The five metal precipitates (FMPs) examined in this work have low concentrations of Pd and Mo, with no major compositional differences along the fuel radius. A secondary Pd–Te metallic phase forms in cooler regions of the pellet, likely due to the diffusion of gaseous species away from the central void. X-ray chemical maps indicate that the Pd–Te phase can nucleate on the surface of FMPs before precipitating into separate particles. These particles were also found to alloy with iron (Fe) near the surface of the fuel pellet due to interdiffusion with the stainless-steel cladding. The insoluble perovskite oxide phase was found to form near the central void and at intermediate radial positions, but not at the fuel edge. These findings suggest that solid fission product phases form at varying counts and compositions along the fuel pellet radius, and thus should be considered when describing the thermal behavior of the fuel.
		"Electron Probe Microanalysis of Irradiated FUTURIX-FTA U-Pu-Zr Alloy with Added Minor Actinides" Karen Wright, Journal of Nuclear Materials Vol. 526 [unknown] Link Electron microprobe examinations were performed to characterize the chemical features of a full cross section of irradiated nuclear fuel from the FUTURIX-FTA experiment. This experiment investigated the nuclear fuel performance of a candidate fuel alloy intended for the transmutation of long-lived minor actinides in a fast neutron spectrum. The irradiated fuel, designated FUTURIX-FTA DOE1, was composed of 34.1U-28.3Pu-3.8Am-2.1Np-31.7Zr (where the preceding numbers indicate concentrations in weight %). The fuel was irradiated in the Phénix sodium fast reactor in France to a measured burnup of 9.5% fissions per initial heavy metal atom (FIMA), and experienced a peak cladding temperature of 550 °C. Microprobe analysis showed elemental redistribution of Zr and U where Zr has increased in concentration in the fuel center from an initially fabricated content of 31.7 wt % to 41.5 wt%, and U decreased from 34.1 wt% to 24.8 wt%. From the center of the fuel extending out radially approximately 1 mm, the fuel represented dominantly a single phase. Beyond this region to the fuel periphery, the fuel separated into two major phases, descibed by their composition as a (U, Np, Pu) Zr2-like phase and a high uranium content-low zirconium content phase. From the outer radius of the fuel extending approximately 1.7 mm radially into the fuel, americium, lanthanide elements, and actinide elements precipitated in a phase whose chemical analysis resembles Nd7(Pd, Rh)3. In addition, americium occurred as a dissolved species in the major fuel phases. Sm and Am penetrated up to 15 μm into the cladding along presumed grain boundaries, while major cladding elements Fe, Ni, and Cr penetrated at least 30 μm into the fuel. No phase formation between cladding elements and fuel elements was observed as the result of cladding element diffusion into the fuel.
		"Exploring constituent redistribution in irradiated U-19Pu-14Zr fuel via Electron Probe Microanalysis" Karen Wright, Journal of Nuclear Materials Vol. 603 2025 Link The phenomena of constituent redistribution, wherein a previously homogeneous metallic fuel forms discrete, radially concentric compositional zones upon irradiation was investigated by examining an irradiated U-19Pu14Zr fuel (where numbers represent wt. %) with a burnup of 11.5 at.% with electron probe microanalysis (EPMA) and quadruple inductively coupled plasma mass spectroscopy (Q-ICP-MS). EPMA-generated U, Pu, and Zr compositional data obtained from a diameter traverse of the sample was converted to mass and was used to: 1) compare the overall fuel element analysis results between the two methods, 2) determine the number of compositionally distinct zones forming as a result of constituent redistribution; and 3) quantify the post-irradiation loss or gain of U, Pu, and Zr atoms in each distinct compositional zone. Weight percent concentrations of U, Pu, and Zr for the overall cross section compare favorably between the two analytical methods, suggesting that the spatially resolved EPMA analysis complements bulk chemical analysis. Among the four identified compositional zones, post-irradiation quantification of U, Pu, and Zr elemental atom content changes shows that the quantity of U atoms lost from the innermost zone is slightly less than the quantity of U atoms gained by the middle two zones, and the quantity of Zr atoms lost from the high-U third zone is slightly less than is gained by the two innermost zones. Pu is lost from all four zones, although the innermost zone and the high-U third zone lose a significantly higher percentage (> 22 %) of their initial Pu atoms than the other two zones. For all three elements, EPMA cannot distinguish between atoms lost due to transport to a different zone from atoms lost due to nuclear processes; however, the insight gained from using this process can be used to experiment with new modeling techniques to predict constituent redistribution in U-Pu-Zr fuels.

Presentations:

	"Investigation of Constituent Redistribution in a 12 at.% Burn-up Annular U-10Zr Fuel Using EPMA and TEM" Mary Meyer, Karen Wright, Daniele Salvato, Fei Xu, Tiankai Yao, Assel Aitkaliyeva, ANS Annual Meeting June 15-18, (2025)

NSUF Articles:

DOE Awards 37 RTE Proposals - Awarded projects total nearly $1.4M in access awards Tuesday, July 14, 2020 - News Release, Calls and Awards

Additional Publications:

Accomplishments

NSUF Reviewer

Reviewed an RTE Proposal

NSUF Supported Research

Secondary Phase Formation in Irradiated Metallic Fuels: Understanding Phase Structure, Chemistry and Light-Element Stabilization - FY 2020 RTE 2nd Call, #20-4163

NSUF Research Collaborations

Understanding Early Redistribution Dynamics in U-20Pu-10Zr Fuels Through EPMA - FY 2025 RTE 1st Call, #25-5253

Quantification of Radial Constituent Redistribution in Annular U-10Zr Irradiated Fuel Using EPMA - FY 2024 RTE 3rd Call, #24-5135

Characterization of U8Pu10Zr fluff sample - FY 2024 Super RTE Call, #24-5097

Quantification of Zr Redistribution in Irradiated U-Zr Annular Fuel using EPMA - FY 2024 RTE 2nd Call, #24-4979

An Assessment of Radial Compositional Variations of the Grey Phase in FBR MOX Fuel Using EPMA - FY 2022 RTE 1st Call, #22-4388

Electron Probe Microanalysis of Localized Phases in Irradiated U-10 wt%Zr Alloy Fuel - FY 2022 RTE 1st Call, #22-4425

Study of minor actinides redistribution and fission products in high burnup MOX using Electron Probe Micro Analysis (EPMA) - FY 2021 RTE 1st Call, #21-4265

Electron Probe Microanalysis (EPMA) of a metallic fuel transmutation alloy for fast reactor: A Microchemical Comparison between Fast Reactor and Simulated Fast Reactor Irradiation - FY 2020 RTE 2nd Call, #20-3096

EPMA and TEM Characterization of a UO2 fuel pellet and cladding interaction layer - FY 2019 RTE 2nd Call, #19-1796

Karen Wright

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