Abstract Fuel elements have been made by industrial methods from 2 uranium alloys containing Al, Fe, Si, Cr (Sicral F1 and Sicral F2) and from 3 uranium alloys containing Cr, Mo, Fe and Si (U-Cr 0,1%; U-Mo-Cr-Fe and U-Si-Cr) in various proportions. Information is presented about the structure mechanical strength creep resistance and pre-irradiation thermal conductivity of these fuel elements. The five alloys were each irradiated to two different neutron doses in the range 1300–4200 MWd tonne . The irradiation temperature was 250 °C at the tube surface and reached a maximum of 630 °C at the internal interface. During irradiation, the thermal conductivity of one of the alloys decreased by 35% at a dose of 5000 MWd/tonne; the density also decreased and we noted the appearance of a porous ring at temperatures slightly below 500°C. Substantial differences in the change of density consequence on irradiation were found between the five alloys, “Sicral f 1” being particularly good, uranium-chromium particularly bad. The possible explanations for these differences are discussed: mechanical strength and creep resistance do not have an important role in this connection.