Overview
ISO 12799:2015 defines a standardized method for the determination of total nitrogen content in sintered nuclear fuel pellets of UO2, (U,Gd)O2 and (U,Pu)O2 using an inert gas extraction technique combined with conductivity detection. The method measures nitrogen released at high temperature while excluding nitrogen compounds that decompose above 2 200 °C (notably Pu and U nitrides).
This procedure supports reliable fuel quality control, traceability, and inter-laboratory consistency for nuclear fuel manufacturing and research.
Key Topics
- Principle: Samples are heated in a degassed graphite crucible under helium carrier gas. Nitrogen liberated during high-temperature decomposition passes through oxidation and absorption traps and is quantified in a thermal conductivity cell.
- Temperatures: Samples are heated to ≥1 770 °C for determination; crucibles are degassed near 2 200 °C prior to loading.
- Carrier and calibration gases:
- Helium carrier gas with purity ≥99.995 % (volume fraction).
- Calibration nitrogen (if used) with purity ≥99.998 % (volume fraction) or certified reference materials (CRMs).
- Sample preparation: Pellets are crushed; fragments >1 mm are selected. Typical sample mass: 1.0 g to 1.5 g.
- Interferences: Avoid heating above 2 200 °C to prevent reaction between fuel and graphite and excessive CO/CO2 release that would bias conductivity measurements.
- Calibration and checks:
- Blank tests to verify column integrity and leak tightness.
- Calibration with gas injections or weighed certified standards.
- Verification using metal standards with certified nitrogen content.
- Precision: For 1–2 g samples at 10 µg/g nitrogen, repeatability standard deviation around 20 % (relative) can be expected; values for stainless steel standards are reported in the standard.
Applications
- Quality control (QC) of sintered nuclear fuel pellets (UO2, Gd-doped and Pu-bearing fuels).
- Process monitoring during fuel production and sintering.
- Verification and traceability of nitrogen contamination levels that can affect fuel performance and mechanical properties.
- Laboratory intercomparisons and method validation using CRMs.
Related Standards
- ISO/IEC Guide 98-3 (GUM) for expression of measurement uncertainty - referenced for uncertainty evaluation.
Practical notes
- Report results as nitrogen mass fraction in µg/g using: w_N2 = m_N2 / m_sample, where m_N2 is mass of nitrogen released (µg) and m_sample is sample mass (g).
- Include in the test report: sample identification, reference to ISO 12799, results and units, deviations, unusual observations, test location/date, and detection limit.
This method emphasizes traceable calibration, controlled high-temperature extraction, and mitigation of interferences to deliver reproducible nitrogen measurements for nuclear fuel quality assurance.
Open preview (PDF)Nuclear energy — Determination of nitrogen content in UO2, (U,Gd)O2 and (U,Pu)O2 sintered pellets — Inert gas extraction and conductivity detection method
