QUANTIFICATION BY EPMA OF GLASS FOR NUCLEAR APPLICATION

摘要

The confinement of high-level radioactive waste from spent nuclear fuel reprocessing is a key issue in the nuclear fuel cycle. In France, the waste storage strategy is based on four containment barriers including, respectively, a glass matrix for radioactive waste immobilisation, a primary stainless steel canister, a thick carbon steel overpack and finally a host rock. Substantial research is carried out on nuclear glass to improve the properties of the confinement material. Depending on the glass composition and process parameters crystals can appear in the glass matrix. The characterisation of these phases (micrometre size) and of the glass matrix surrounding them is of great importance for a proper understanding of the glass properties and its long term performance. The composition of these phases can be characterised by means of electron microprobe (CAMECA SX100) with a standard resolution electron beam. In order to improve the quantification of such small dimension inclusions, the use of a FEG-EPMA CAMECA SXFiveFE, which is well adapted to micrometre-range analysis, has been tested to determine their chemical composition. The improved analytical resolution obtained with the FEG-EPMA made it possible to optimise the analysis of the micro particles, and to determine their chemical composition. The nature of the crystal phases was confirmed by electron backscatter diffraction (EBSD) analysis coupled with SEM and confirmed the crystalline phases of apatite and cerianite measured by EPMA. To study the glass matrix near the crystals in a more precise way, thin lamellas were prepared by focussed FIB ion beam milling. A microstructural analysis by TEM was performed to characterise the glass matrix and the inclusions and their chemical composition was determined by EDS quantification. These thin lamella were also analysed by EPMA in transmission with the CAMECA SX 100 to get a more complete analysis of elements, including especially some light elements such as boron. TEM-EDS and EPMA analyses confirm a peculiar Zr enrichment in the glass matrix just around the inclusions.