Indentation creep of UO2 before and after irradiation

Measurements of creep by the indentation with Knoop indenter were performed for sintered UO2 pellets before and after irradiation and a non-irradiated single crystal with an applied load of 50 g. Room temperature creep of non-irradiated sinters included grain boundary sliding. The creep at the lowest dose (7.8 x 1014 fiss./cm3) also involved the grain boundary sliding, while no creep was observed after irradiation of 2.9 x 1015 fiss./cm3. Irradiated sinters at a dose between 1.4 x 1016 and 1 x 1018 fiss./cm3 yielded not only primary creep without the grain boundary sliding but also secondary creep, in which cracks were formed when a dose was less than 4.8 x 1017 fiss./cm3. At a dose of 1 x 1018 fiss./cm3 the enhanced secondary creep independent of the temperature between 100 and 1500C was observed. (author)