Irradiation induced field fluctuations in graphite

Abstract

In irradiated porous medium, the presence of voids drastically reduces the electrical and mechanical strength of the system, as strong load enhancements occur following charge accumulation near the voids, leading to field emission or electric breakdown. The present work examines the charge accumulation and electric field distribution throughout charged particles irradiated porous matrix. Our objective is to show in a simple, but a quantitative manner, how hot spots develop in flawed sample with a possibility for coupling the heat enhancement produced under conditions where static electric fields are present back to problems of a safety concern such as the sudden release of the energy stored in neutron irradiated graphite. Spatial fluctuations of the local electric fields developed in graphite, following particle irradiation, are studied numerically using suitable Monte Carlo calculations. The present method is different from the conventionally used methods to realistically describe electric breakdown formation through charge inhomogeneities that we believe to be the most important physical implications. It is shown that the spatial distributions of the fields exhibit sharp peaks and strong fluctuations. Compared to unflawed material, field intensity enhancement reaches several orders of magnitude. The irradiated graphite seems to develop configurations typical of percolating composite materials where excess fields develop nonlinear susceptibilities that lead to new physical effects.