ISO 22765:2025

Nuclear fuel technology — Sintered (U,Pu)O2 pellets — Guidance for ceramographic preparation for microstructure examination

Scope

This document is applied to fuel fabrication. It describes the ceramographic procedure used to prepare sintered (U,Pu)O2 pellets for qualitative and quantitative examination of the (U,Pu)O2 pellet microstructure.
The examinations are performed
a)       before any treatment or any etching, and
b)       after thermal treatment or after chemical or ion etching.
They allow
—     observation of any cracks, intra- and intergranular pores or inclusions, and
—     measurement of the grain size, porosity and plutonium homogeneity distribution.
The mean grain diameter is measured by one of the classic methods: counting (intercept method), comparison with standard grids or typical images, etc.[2]. The measurement of individual grain sizes requires uniform development of the microstructure over the entire specimen.
The plutonium cluster and pore distribution and localization are generally analysed by automatic image analysis systems. The plutonium distribution is usually revealed by chemical etching or by alpha autoradiography. A scanning electron microscope (SEM) or a microprobe can also be used. In this case an additional preparation can be needed depending on the equipment used. This preparation is not in the scope of this standard.