Annealing of Irradiation‐Induced Thermal Conductivity Changes in ThO ₂ ‐1.3 wt% UO ₂

Abstract

The thermal conductivities of sintered pellets of ThO 2 ‐1.3 wt% U0 2 were measured at 60°C before and after irradiation. The irradiation temperature was below 156°C, and the exposures varied from 3.1 × 10 14 to 4.7 × lo L7 fissions/cm 3 . Each fission fragment damaged a region of 2.2 × 10 ‐16 cm 3 with the reduction in conductivity saturating by about 10 17 fissions/cm 3 . Samples having exposures from 10 15 to 10 16 fissions/cm 3 were annealed isothermally at 651 °C or isochronally from 300° to 1200° C to study the annealing of damage. Most of the annealing occurred between 500° and 900°C. The width of this interval plus the slow isothermal annealing suggest that the damage is annealed by a number of single order processes with a spectrum of activation energies from 1.8 to 3.9 eV or, less probably, by a high order process with an activation energy of 3.55 ± 0.4 eV.