EPMA and EBSD observations of unirradiated MIMAS-MOX fuels for the study of fission gas release and thermal conductivity

Abstract

ABSTRACT MOX fuel fabricated through the micronized master blend process (MIMAS) is used in light water reactors. The MIMAS-MOX fuel is characterized by a non-uniform plutonium distribution with plutonium-rich agglomerates. The distributions of plutonium and crystal grains can respectively influence the fuel properties and behaviors during irradiation. However, it was difficult to examine the correlation between the distributions of plutonium and crystal grains in an unirradiated MIMAS-MOX fuel because chemical etching for the grain boundary had little effect on the plutonium-rich agglomerates. In this study, the analytical techniques of electron probe micro analyzer and electron backscattered diffraction were applied to the observation of unirradiated MIMAS-MOX fuels. The observation using the two analytical techniques revealed crystal grain distributions in the phases with different concentrations of plutonium, including plutonium-rich agglomerates. In addition to the observation, the fission product gas release and thermal conductivity of MIMAS-MOX fuels were briefly discussed as initial approaches aiming to model them based on the results of the observation using the techniques of electron probe micro analyzer and electron backscattered diffraction.