Microstructural modifications in ion-irradiated nuclear materials: characteristic features of fluorite-structured oxides
- PDF / 557,945 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 79 Downloads / 229 Views
1265-AA08-07-BB07-07
Microstructural modifications in ion-irradiated nuclear materials: characteristic features of fluorite-structured oxides A. Debelle, F. Garrido, L. Thomé Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse (CSNSM, UMR 8609) CNRS-IN2P3-Univ. Paris-Sud, Bat. 108, 91405 Orsay Cedex, France ABSTRACT The behavior of two nuclear materials, namely cubic zirconia and urania, is investigated under different irradiation conditions in the low and medium ion energy range (tens of keV to a few MeV). In each case, these materials display a multi-step damage build-up, as revealed by both RBS/C and XRD measurements. It is demonstrated that each step exhibits characteristic features such as damage fraction, elastic strain, nature of defects, and thus presents a specific microstructure. The transition from one step to the following involves radiation defect reorganization which arises to lower the energy of the system. INTRODUCTION Materials for nuclear applications are inherently submitted to harsh irradiation environments. In particular, they must face irradiation with various types of ions in a broad energy range, from low-energy heavy recoil nuclei arising from the alpha decay of actinides, to swift fission fragments. In the majority of cases, ion irradiation induces damage in the material, which may be deleterious for its relevant physical and chemical properties. In the case of lowand medium-energy (tens of keV to a few MeV) ion irradiation, it is now well known that the damage build-up can occur, for different classes of materials, in several steps as a function of the accumulated ion fluence [see e.g. Refs 1-2]. Therefore, the ability to monitor these steps, the determination of the key parameters that trigger them, and the understanding of the underlying fundamental mechanisms definitely appear as mandatory issues for a comprehensive knowledge of the behavior of nuclear materials under irradiation. In the present paper, it is demonstrated that each damage step exhibits characteristic features (damage level, elastic strain) and microstructure. For this purpose, two test-case nuclear materials, namely cubic zirconia (YSZ, yttria-stabilized ZrO2) and urania (UO2), are studied upon three different irradiation conditions. For a better understanding of the results, a description of the strain/stress state of these irradiated materials is previously given in the first section. EXPERIMENTAL DETAILS Both YSZ and UO2 specimens used in this study are (100)-oriented single crystals. They were irradiated at room temperature (RT) over a large fluence range with different ions: 300-keV Cs ions or 4-MeV Au ions for YSZ crystals, 20-keV He ions for UO2 samples. The ion flux was kept low (few 1011 to few 1012 cm-2.s-1) in order to avoid high-dose rate effects and significant temperature increase. The damage doses expressed in displacement per atom (dpa) have been calculated at the maximum of the SRIM-predicted [] damage distributions [see Refs. 2-5,6]. Irradiations and Rutherford backscattering spectrometry in
Data Loading...
