ISO 9278:2008

Overview

ISO 9278:2008 specifies a standardized laboratory method for determining the bulk density and the volume fraction of open and closed porosity of sintered uranium dioxide (UO2) pellets. The method is applicable to UO2‑PuO2, UO2‑Gd2O3 and other similar pellet types (including green pellets) used in nuclear fuel production. Results are based on measurements of dry mass, saturated mass and immersed mass after liquid impregnation.

Key topics and technical requirements

• Principle: Porosity and bulk density are derived from the pellet geometric volume and pore volumes calculated using the dry, saturated and immersed masses together with the density of the impregnation liquid.
• Ethanol impregnation method (recommended):
  • Vacuum impregnation to fill open pores with ethanol.
  • Measurement sequence: dry mass → vacuum impregnation → saturated mass (in air) → immersed mass (in liquid) → re‑dry.
• Apparatus:
  • Precision balance (accuracy 0.1 mg).
  • Oven capable of 100 °C (vacuum drying oven recommended for high open‑porosity samples).
  • Weighing/immersion device and suitable container.
  • Vacuum impregnation apparatus and a test ball (radius 5–10 mm, known to ±0.5 µm) for determining liquid density.
• Alternative penetration liquids: water, cyclohexane, toluene may be used if they do not react with the material, can be fully removed, and are analytical grade. Surfactant addition is recommended if water is used to reduce surface tension effects.
• Calculation:
  • Density of the immersion liquid is determined using the test ball method.
  • Geometric volume, open‑pore and closed‑pore volumes, bulk density and porosity percentages are computed from measured masses and the theoretical UO2 density (ρth = 10.96 g·cm−3 for UO2).
• Precision:
  • Relative standard deviation of bulk density ≈ ±0.05%.
  • Absolute standard deviation of open and closed porosity fractions ≈ ±0.03%.

Applications and users

ISO 9278:2008 is intended for:

• Nuclear fuel manufacturers performing quality control on sintered UO2 pellets.
• Analytical and metrology laboratories validating pellet microstructure and density.
• R&D teams developing fuel formulations (e.g., UO2‑PuO2, UO2‑Gd2O3) and process optimisation.
• Regulatory bodies and auditors assessing conformance to fuel fabrication specifications.

Practical uses include acceptance testing, batch release, process troubleshooting (sintering/green‑density issues) and comparative studies of additive effects on porosity and density.

Related standards

• Prepared by ISO/TC 85 (Nuclear energy), Subcommittee SC 5 (Nuclear fuel technology). For broader context, refer to other ISO nuclear fuel characterization standards and ISO/TC 85 guidance documents for fuel fabrication and testing practices.

Keywords: ISO 9278:2008, UO2 pellets, bulk density, open porosity, closed porosity, ethanol impregnation, vacuum impregnation, nuclear fuel quality control.