Overview
ISO 16795:2024 - "Nuclear energy - Determination of Gd2O3 content in pellets containing uranium oxide by X‑ray fluorescence spectrometry" - specifies a validated method to determine gadolinium oxide (Gd2O3) mass fraction in UO2 fuel pellets. The document describes an X‑ray fluorescence (XRF) approach (WD‑XRF is specified using the Gd Lα‑line, although ED‑XRF is noted as applicable) and has been tested for Gd2O3 mass fractions from 2 % to 10 %.
Key topics and requirements
- Technique: Wave‑dispersive X‑ray fluorescence (WD‑XRF) using the Gd Lα line (ED‑XRF also applicable).
- Sample preparation:
- Standard pellets of (U,Gd)O2 prepared by blending UO2 and Gd2O3 powders.
- Powders dried at 110 °C for 2 h, blended (shaken) for ≥4 h for homogeneity.
- Pressing into pellets with the same size as production fuel pellets; sintered under production conditions (furnace up to ~1 800 °C).
- Polishing of the pellet face with 800‑grit SiC paper and cleaning prior to analysis.
- Instrumentation & calibration:
- Sequential X‑ray spectrometer with precision goniometer, LiF 200 analyser crystal, multi‑channel analyser, and appropriate detectors.
- Mandatory calibration steps: angle calibration, pulse‑height distribution, background correction, and stability (sensitivity) check (drift monitor).
- Linear calibration curve is generated from standard pellets covering 2 %–10 % Gd2O3 (Y = net count rate; X = mass fraction).
- Typical measurement parameters (as given): 40 kV voltage, 60 mA current, Gd Lα at 6.056 keV, 2θ ≈ 61.115°, counting time ~200 s, background correction ±1.20°.
- Quality and reporting:
- Precision/accuracy examples: RMS of calibration curve ~0.014 %; coefficient of variation in tests ranged up to ~0.98 %.
- Test report must identify the sample, reference ISO 16795:2024, list method, results, any deviations, calibration standard reference, and buoyancy correction status.
Applications and users
- Practical for nuclear fuel manufacturers, fuel quality control laboratories, and irradiation testing facilities requiring routine or acceptance testing of Gd2O3 doped UO2 fuel pellets.
- Useful where non‑destructive, high‑throughput compositional checks are needed during pellet production, calibration of process controls, or verification of burnable poison loading.
- Also applicable to laboratories preparing metrologically traceable working standards in accordance with ISO 17034 or ASTM C1128.
Related standards
Keywords: ISO 16795:2024, Gd2O3, UO2 pellets, X‑ray fluorescence, WD‑XRF, Gd Lα‑line, calibration curve, fuel fabrication, nuclear fuel quality control.
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