Micro-Hardness of Neutron Irradiated Uranium Dioxide at Room Temperature

Abstract

Knoop hardness tests were performed on irradiated UO₂ in the fission range of 10¹⁴-10¹⁸ fiss./cm³. Hardness values were obtained as a function of applied load (25-1, 000 g). Three different regions of load dependence on hardness [work hardening or plastic (25-70 g), plateau (70-100 g) and crack formation (over 100 g) regions] were observed in a similar way to those of non-irradiated ones. The elastic effect was not observed on the hardness values of specimens irradiated to a dose more than 7.8 x 10¹⁴ fiss./cm³ in the load around 25-30 g in contrast to those of non-irradiated ones.
Hardness change after irradiation was discussed on the basis of the variation of lattice strain, lattice volume and whole volume for the similar specimens at the same irradiation condition.
The hardness change in work hardening or plastic region and that in plateau region in-creased with dose up to 4.8 x 10¹⁷ fiss./cm³ and decreased above that dose, and correlated to the lattice volume change and lattice strain.