Thermal Conductivity and Electrical Resistivity of Simulated Fuel Elements
It is well-known that important changes may occur in the physical properties of bonded fuel rods during their lifetime within a reactor. These changes are caused by the high temperatures, environment, and lastly (and probably most importantly) by the high neutron fluxes. Neutrons have a strong effect in reducing the thermal conductivity, λ, by introducing defects such as vacancies and dislocations into the basal planes of graphitic material. The reduction of λ raises the operating temperature which lowers the lifetime of the graphite. Although the quantitative effects of neutron irradiation on the λ of polycrystalline graphites have been extensively studied, they have not been studied for carbonaceous material nor for carbonaceous material containing various quantities of spherical fuel particles which are envisioned for use in a high-temperature gas-cooled reactor (HTGR). The primary purpose of this experiment, therefore, was to measure the thermal conductivity of simulated fuel elements consisting of inert particles suspended in a carbonaceous matrix as a function of temperature, T, volume percent particle loading, and neutron fluence.