  The changing thermal conductivity of an irradiated material is among the
principal design considerations for any nuclear reactor, but at present few
models are capable of predicting these changes starting from an arbitrary
atomistic model. Here we present a simple model for computing the thermal
diffusivity of tungsten, based on the conductivity of the perfect crystal and
resistivity per Frenkel pair, and dividing a simulation into perfect and
athermal regions statistically. This is applied to highly irradiated
microstructures simulated with Molecular Dynamics. A comparison to experiment
shows that simulations closely track observed thermal diffusivity over a range
of doses from the dilute limit of a few Frenkel pairs to the high dose
saturation limit at 3 displacements per atom (dpa).
