【国外标准】 Standard Practice for Ceramographic Preparation of UO2 and Mixed Oxide (U,Pu)O2 Pellets for Microstructural Analysis

5.1 The ceramographic examination of the nuclear fuel pellet is mandatory to ensure that the microstructural characteristics are in compliance with the fuel specifications relative to performance in reactor, particularly concerning thermo-mechanical behavior and fission gas release.5.2 This practice is applicable for sintered UO2 pellets with any 235U concentration and (U,Pu)O2 pellets containing up to 15 weight % PuO2 with less than 10 % porosity.1.1 This practice describes the procedure for preparing nuclear-grade uranium dioxide (UO2) or mixed uranium-plutonium dioxide (MOX or (U,Pu)O2)), sintered and non-irradiated pellets for subsequent microstructural analysis (hereafter referred to as ceramographic examination).1.2 The ceramographic examination is performed to confirm that the microstructure of the sintered pellet is in compliance with the fuel specification, for example as defined in Specifications C776 and C833, as a function of the initial raw material properties and manufacturing process parameters.1.3 The microstructure of a ceramic pellet includes: grain size, porosity size and distribution, and phase distribution for (U,Pu)O2 pellets, that is, Pu-rich cluster size and distribution.21.4 The microstructural characteristics of the pellet are accessible after preparation which involves: sawing, mounting in a resin, surface polishing, and chemical etching, thermal etching, or both.1.5 This practice describes the preparation processes mentioned in 1.4; it does not discuss the associated sampling practices (for example, Practice E105) or ceramographic examination methods (for example, the methods for determining average grain size are covered in Test Method E112).1.6 Due to the radiotoxicity associated with these nuclear materials, all operations described in this practice should be performed in glovebox for (U,Pu)O2 pellets and in a hood for UO2 pellets.1.7 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.1.9 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.