Multiple voltage electron probe microanalysis of fission gas bubbles in irradiated nuclear fuel

The accurate analysis of locally retained fission gas in nuclear fuel is inherently difficult since the physical form under which it is stored varies from an atomic dispersion to bubbles with a diameter of several hundreds of nanometers. One of the techniques that has been applied since more than 20 yr is electron probe microanalysis (EPMA). This technique, however, is difficult to apply in a quantitative manner if the studied materials are inhomogeneous at the scale of the electron-solid interaction volume. In this paper, a method is developed to analyze a system of gas bubbles distributed in a solid matrix. It is based on the geometric modelling of a gas bubble dispersion and the assessment of its influence on the emitted X-ray intensity. The calculation exploits experimental results acquired at different accelerating voltages. The resulting more accurate analysis of gas retained in nuclear fuel may lead to a better insight in the gas release mechanisms.