Small angle neutron scattering studies of MgO dispersions in UO2 at high temperatures

Three samples of magnesia-doped uranium dioxide have been studied using small-angle neutron scattering. This technique was used in situ at temperatures up to 16000C, with an ambient pressure of approx.= 5 x 10-3 Pa. The aim of these experiments was to characterise any temperature-dependent changes in the size and volume fraction of the inhomogeneities present. These inhomogeneities have been taken to consist of spherical fine 'particles' of uncertain composition. Our results show that these 'particles' exist in the size (dia.) range approx.= 5 to 8 nm (being monodisperse for a given sample) and low volume fractions ( a few %). As the temperature was raised a small increase in 'particle' size, with an associated large decrease in volume fraction occurred in one sample; but in the other samples no significant changes occurred. (orig.)