CREEP PROPERTIES OF OXIDE AND CARBIDE FUELS UNDER IRRADIATION

Abstract

The creep behaviour of uranium dioxide and uranium carbide has been examined in both bend and compression experiments in DIDO Materials Test Reactor. In UO2 no significant variation in creep rate with dose and temperature occured above ~1025 fissions m−3between 450°C and 1230°C, the high strain rates measured in compression at low doses being largely attributable to pore sintering. Both a linear rating and stress dependence were observed up to 40 MNm−2 and creep rates were found to be independent of grain size. At higher doses (>6 × 1026 fissions m−3) transient strains were incurred on varying stress and temperature due to the development of grain boundary gas bubbles. This also resulted in a six fold increase in the radiation creep constant between 6 × 1026 and 1.2 × 1027 fissions m−3. A similar pattern of behaviour with respect to rating and stress was observed in hyperstoichiometric UC between 450 and 800°C up to 1 × 1027 fissions m−3. However the nominally steady state creep rate was a factor 8 lower than in UO2 irradiated under the same conditions. The experimental results also suggest that the primary creep contribution to the initial strain in compression is much higher than in UO2. There was no evidence of either transient strain on changing stress or of an increasing creep rate at high doses. The experimental observations are reported and discussed in relation to models for irradiation induced low temperature creep in ceramic fuels.