In situ thermal conductivity measurement of ceramics in a fast neutron environment

A temperature controlled instrumented capsule has been irradiated in the RB* position of the high flux isotope reactor (HFIR) at the Oak Ridge National Laboratory in order to perform in situ thermal conductivity measurements of monolithic ceramics and composite materials during neutron irradiation. This determination of thermal conductivity utilizes a temperature gradient technique whereby two thermocouples measure the absolute temperature along a cylindrical sample which is constrained to one-dimensional thermal conduction. The heat source is the intrinsic gamma heating of the core region of the HFIR. This paper provides an overview of the experiment and gives preliminary results on the degradation in thermal conductivity of a few ceramic specimens measured as a function of irradiation temperature (200-700 °C) and fast neutron fluence up to approximately 3.4×10²⁵ n/m² (E>0.1 MeV).