Overview
EN ISO 16793:2021 - "Nuclear fuel technology - Guidelines for ceramographic preparation of UO2 sintered pellets for microstructure examination" provides harmonized, practical guidance for preparing uranium dioxide (UO2) sintered fuel pellets for both qualitative and quantitative microstructural analysis. The standard covers sample sectioning, mounting options, grinding, polishing, dismounting, and both chemical and thermal etching to reveal grains, pores, fissures and inclusions for microscopy and image analysis.
Key topics and requirements
- Scope of examination: Observations of fissures, inter- and intra-granular pores, inclusions; measurement of pore and grain sizes and distributions.
- Preparation procedures: Three principal workflows - unmounted samples, mounted samples that remain mounted, and mounted samples that require later dismounting.
- Sectioning & equipment: Use of a metallographic sectioning machine with a diamond wheel and water inlet; manual or automatic polishing machines; ultrasonic cleaning; vacuum impregnation; thermal etching furnace; mechanical gripping devices and optical microscopes.
- Polishing & consumables: Abrasive papers (P60–P2500), diamond polish suspensions (0.25–15 µm), aqueous alumina/silica suspensions (0.05–1 µm), and various polishing cloths.
- Etching methods: Guidance on chemical etching and thermal etching (thermal etching requires unmounted samples and is recommended when image analysis is used to measure grain-size distributions to ensure uniform grain revelation). Thermal etching is performed under an oxidizing CO2 atmosphere.
- Measurement techniques: Average grain-size measurement may follow classical counting/intercept procedures as per ISO 2624 or ASTM E112. Pore-size distributions are commonly measured with automatic image analysers.
- Safety & reagents: Lists hazardous reagents used (e.g., hydrogen peroxide, concentrated sulfuric acid, hydrofluoric acid, chromium (VI) oxide) and the need for appropriate PPE and ventilation (fume hood) when handling them.
Applications and users
EN ISO 16793:2021 is intended for:
- Nuclear fuel manufacturers and fabrication quality-control laboratories
- Materials scientists and metallographers working on UO2 pellet microstructure
- Research institutions studying sintering, porosity, grain growth and failure mechanisms
- Regulatory and certification bodies assessing fuel microstructure for safety and performance
The standard supports routine production inspection, failure analysis, research characterization, and image-analysis workflows for assessing grain size and pore distributions in nuclear fuel pellets.
Related standards
- ISO 2624 - grain-size measurement methods (classical counting/intercept)
- ASTM E112 - standard for determining average grain size
- ISO 3696 - demineralized water quality (referenced for consumables)
Keywords: EN ISO 16793:2021, ceramographic preparation, UO2 sintered pellets, microstructure examination, thermal etching, chemical etching, grain size, pore-size distribution, image analyser.