HELIUM RELEASE ANDα-DAMAGE EFFECTS ON THE PROPERTIES OF UO_2 AND INERT MATRIX MATERIALS CONTAINING ACTINIDES

摘要

The effects due to the accumulation of He andα-decay damage on the microstructure and on some properties of several ceramic matrices, representing existing or proposed materials to be irradiated in nuclear reactors, have been investigated. Knudsen cell measurements performed on the nuclear fuel UO_2 containing a short-livedα-emitter (namely, ~(238)Pu) showed that He release occurred between ～ 950 and ～ 1950 K. TEM examination revealed a relatively high concentration of dislocation loops, while no large He-bubbles were visible. The results were compared to similar studies performed on candidate materials to be used as inert matrices, or U-free fuels (e.g. MgAl_2O_4 spinel and ZrO_2 implanted with He-ions of 100, 260 and 2000 keV energy at various fluences). The He release from spinel occurred between ～ 850 and ～ 1400 K. Rutherford Backscattering Spectroscopy in Channelling mode (RBS/C) showed only limited amounts of damage at the range depth of the implanted ions, indicating a good resistance against ion impact. The results were compared to previous findings for He-implanted MgAl_2O_4, which had shown formation of blisters as well as of bubbles upon annealing. Preliminary results from the ZrO_2 investigations show no macroscopic signs of alteration and confirm the high resistance of this material against radiation damage. These results are part of ongoing work to extend the available knowledge on the behaviour of He in fuels.