In-Reactor Measurement of Operating Temperature in ThO2-UO2 Fuel: Effect of Pellet Microstructure

Abstract

We have measured central operating temperatures in three types of Zircaloy-clad, ThO₂-UO₂ fuels, in-reactor, at linear power ratings up to 70 kW/m as part of a program to assess the thermal conductivities of ThO₂-UO₂ Our results showed that fuel whose microstructures comprised granules, introduced during pre-pressing and granulating, operated at higher temperatures than fuel with a uniformly dense microstructure. Although ThO₂-UO₂ should have a higher thermal conductivity than UO₂, one of the ThO₂-UO₂ fuels, possessing a granular microstructure, operated at temperatures similar to those predicted for an equivalent UO₂ element.