Overview
ISO 9279:1992 specifies a mercury displacement (pycnometer) method for determining the density and total porosity of sintered uranium dioxide (UO2) pellets. The standard describes the principle, required apparatus, detailed procedure, calculation of results and required test-report contents. It also notes applicability to related fuels (e.g., UO2–PuO2, UO2–Gd2O3) and to irradiated material handled in hot cells.
Key topics and technical requirements
- Principle: Pellet volume is determined by mercury displacement; mercury does not enter open pores because of surface tension. Density and total porosity are calculated from measured mass differences and mercury density at the test temperature.
- Apparatus:
- Mercury pycnometer with two chambers and a mercury receiver (glass components sealed with vacuum grease).
- Vacuum installation capable of about 1 Pa.
- Analytical balance with precision of ±0.1 mg.
- Thermometer accurate to 0.1 K.
- High‑purity mercury (≥ 99.99%).
- Sample preparation:
- Clean in acetone then ethanol.
- Dry for 1 hour under ~10 Pa vacuum.
- Minimum sample mass guidance: not less than about 1 g for handling; for accuracy the standard notes sample mass > 5 g and the pellet should occupy at least 10% of the pycnometer chamber volume.
- Procedure controls:
- Calibrate/verify balance per laboratory control plan.
- Determine empty chamber volume before each measurement (procedure uses controlled valve operations, evacuation and transfer of mercury).
- Measure mercury temperature (must not vary by more than ±0.5 K during measurement) and obtain mercury density from the provided table.
- Repeat measurements at least three times and report mean values.
- Accuracy:
- Relative standard deviation for density: about ±0.5%.
- Absolute standard deviation for total porosity: about ±0.3% (V/V) within a density range of 90–98% of theoretical UO2 density.
- Reporting: Report must reference ISO 9279, identify the sample, state the method and results, note any departures from the standard and any incidents affecting results. The theoretical density of UO2 used by the standard is 10.96 g/cm3.
Applications and users
- Who uses it: nuclear fuel manufacturers, quality control and metrology laboratories, research institutions, hot‑cell facilities and regulatory bodies involved in fuel acceptance and characterization.
- Practical value:
- Quality control of sintered UO2 pellet manufacture (sintering consistency, density specifications).
- Determination of total porosity affecting thermal conductivity, fission gas behavior and mechanical performance of fuel pellets.
- Comparative testing for process optimization, material development and irradiation experiments.
Related keywords
ISO 9279, uranium dioxide pellets, UO2 density measurement, total porosity, mercury pycnometer, pycnometry, nuclear fuel quality control, mercury displacement method.
Open preview (PDF)Uranium dioxide pellets — Determination of density and total porosity — Mercury displacement method
