Irradiation effects on graphite foam

Abstract

The solid state reactor is an advanced reactor concept that takes advantage of newly developed materials with enhanced heat transfer characteristics to provide an inherently safe, self-regulated heat source. High conductivity graphite foam, developed and produced at Oak Ridge National Laboratory, is being evaluated as a candidate material for the core of basic heat source modules. Irradiation studies at the Oak Ridge National Laboratory High Flux Isotope Reactor were conducted to obtain preliminary data on the effects of neutron damage on the thermal properties and volume change behavior of the graphite foam as a function of neutron dose up to 2.6 displacements per atom at an irradiation temperature of ∼740 °C. Samples were characterized for dimensional and structural changes, and thermal transport as a function of dose. Following the initial effects of the irradiation, the samples were annealed at 1000 and 1200 °C and the thermal diffusivity measured as a function of temperature. A simple microstructural model was developed for graphite foam and, by coupling this model to the known single crystal and polycrystalline irradiation behavior of graphite; a mechanism by which the irradiation-induced volume and dimensional changes in graphite foam may be explained is postulated.