Direct Compositional Characterization of (U,Th)O2 Powders, Microspheres, and Pellets Using TXRF

Area of Science:

• Nuclear Chemistry
• Analytical Chemistry
• Materials Science

Background:

• Accurate compositional analysis of nuclear fuel materials like (U,Th)O2 is critical for fuel cycle management and safety.
• Traditional methods often require sample dissolution, which is complex and hazardous for radioactive materials.
• Developing direct, non-destructive analytical techniques is essential for efficient characterization of nuclear fuels.

Purpose of the Study:

• To develop and validate a novel total reflection X-ray fluorescence (TXRF) method for direct compositional analysis of (U,Th)O2.
• To enable characterization of sintered and green (U,Th)O2 in various forms (pellets, powders, microspheres) without sample dissolution.
• To establish a reliable method for determining uranium content relative to thorium in solid solutions.

Main Methods:

• Developed a TXRF methodology involving minimal sample transfer (nanograms) onto a support, forming a thin film.
• Utilized gentle rubbing or slurry preparation in collodion for sample transfer, minimizing matrix effects.
• Determined uranium content using thorium as an internal standard in TXRF spectral analysis.

Main Results:

• Achieved direct compositional characterization of (U,Th)O2 samples with an average precision of 2.6% (RSD, 2σ, n=8).
• TXRF-determined uranium values showed deviations within 5% of expected values and good agreement with biamperometry.
• Demonstrated a strong correlation between lattice parameters (from XRD) and TXRF-determined U at%, validating the compositional analysis.

Conclusions:

• The developed TXRF method provides direct, rapid, and accurate analysis of (U,Th)O2, suitable for radioactive samples with minimal preparation.
• The technique minimizes matrix effects and is effective for a wide range of uranium compositions (0-100 at%).
• The method shows potential for extension to other nuclear fuel materials like nitrides and carbides.