Microstructural Changes and Chemical Analysis of Fission Products in Irradiated Uranium-7 wt.% Molybdenum Metallic Fuel Using Atom Probe Tomography

Mukesh Bachhav,Brandon Miller,Ann Leenaers,S Van Den Berghe,Jian Gan,Mitchell K Meyer,Dennis Keiser

doi:10.3390/app11156905

Mukesh Bachhav, Brandon Miller + Show 5 more

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https://doi.org/10.3390/app11156905

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Abstract

Understanding the microstructural and phase changes occurring during irradiation and their impact on metallic fuel behavior is integral to research and development of nuclear fuel programs. This paper reports systematic analysis of as-fabricated and irradiated low-enriched U-Mo (uranium-molybdenum metal alloy) fuel using atom probe tomography (APT). This study is carried out on U-7 wt.% Mo fuel particles coated with a ZrN layer contained within an Al matrix during irradiation. The dispersion fuel plates from which the fuel samples were extracted are irradiated at Belgian Nuclear Research Centre (SCK CEN) with burn-up of 52% and 66% in the framework of the SELENIUM (Surface Engineering of Low ENrIched Uranium-Molybdenum) project. The APT studies on U-Mo particles from as-fabricated fuel plates enriched to 19.8% revealed predominantly γ-phase U-Mo, along with a network of the cell boundary decorated with α-U, γ’-U2Mo, and UC precipitates along the grain boundaries. The corresponding APT characterization of irradiated fuel samples showed formation of fission gas bubbles enriched with solid fission products. The intermediate burnup sample showed a uniform distribution of the typical bubble superlattice with a radius of 2 nm arranged in a regular lattice, while the high burnup sample showed a non-uniform distribution of bubbles in grain-refined regions. There was no evidence of remnant α-U, γ’-U2Mo, and UC phases in the irradiated U-7 wt.% Mo samples.

Highlights

IntroductionMaintaining reactor performance with the use of low-enriched uranium (LEU) dispersion fuels requires an increase in uranium (U) densities in the dispersed fuel particles
Scanning electron microscopy (SEM) images shown in Figure 1 provide an overview of the fuel particles dispersed in the aluminum fuel plate matrix (Figure 1a) and the particle microstructure and coating (Figure 1b) showing lamellar-like features (Figure 1c) distributed non-uniformly across the sample
Irradiation led to predominantly Moenriched γ-U-Mo phase with the presence of the bubble superlattice structures enriched with fission products

Summary

Introduction

Maintaining reactor performance with the use of LEU dispersion fuels requires an increase in uranium (U) densities in the dispersed fuel particles. Pure metallic U provides the highest U density, it exhibits anisotropic irradiation growth during irradiation [7], resulting in unacceptable performance relevant to irradiation behavior studies. Alloying U with molybdenum (Mo) results in a metastable body-centered cubic structure that exhibits stable swelling behavior and eliminates anisotropic growth. The fuel particles studied here incorporate a ZrN coating to limit the detrimental effect of the U-Mo interaction with the Al dispersion fuel matrix [11,12,13,14,15]

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