quantification by epma of glass for nuclear application
Résumé
The confinement of high-level radioactive waste from spent nuclear fuel reprocessing is a key issue in the nuclear fuel cycle. In France, waste storage concept is based on four containment barriers including respectively glass matrix for radioactive waste immobilization, a primary stainless steel canister, a thick carbon steel overpack and finally a host rock. Numerous researches are carried out on nuclear glass to improve the properties of the confinement material. Depending on glass composition and process parameters crystals can appear in the matrix (Fig. 1). The characterization of these phases (range of micrometer size) and of the glass 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 characterized by means of electron microprobe (CAMECA SX 100) with a standard resolution electron beam. In order to improve the quantification of such small dimension inclusions, the use of FEG-EPMA CAMECA SX FiveFE has been tested to determine their chemical composition which is well adapted to micrometer range analysis. The improved analytical resolution obtained with the FEG-EPMA made it possible to optimize the analysis of the micro particles, and to determine their chemical composition. The nature of the crystal phases was confirmed by EBSD electronic diffraction analysis coupled with SEM and approved the crystalline phases of apatite and cerianite measured by EPMA. To study in a more precise way the glass matrix near crystals, thin lamellas were prepared by ionic cut by FIB (Fig. 2). A microstructural analysis by TEM was performed to characterize the glass matrix and the inclusions and the chemical composition was settled by EDS quantification. This thin lamella were analyzed by EPMA in transmission with the microprobe CAMECA SX 100 to get a more complete analysis of elements, including especially some light elements such as Boron. The results of TEM EDS and EPMA analyses in transmission are self-consistent and confirm a peculiar enrichment in Zr of the glass matrix near crystals.