Computational and Experimental Investigations of the Structure of Halite Nanoparticles

Salt repositories are currently being considered for the disposal of high-level waste. One issue that has yet to be resolved is the effect of radiation damage on halite. Radiolysis of halite could cause changes in the chemical interactions between the host rock and the waste. Observing the impact of e-beam damage on halite in the TEM is a simple in situ method of investigating the effects of heating and radiolysis on halite crystallography, texture, and chemistry. These effects are critical for creating improved, integrated versions of the process models describing the macroscale thermal and mechanical response of halite to stresses arising from emplacement of high-level waste.

Recently, we have developed techniques for preparing and halite samples using Transmission Electron Microscopy. These techniques preserve orientation, fluid inclusion geometry, and texture. While imaging halite samples in the TEM we have observed large (200 nm) truncated-octahedral halite nano-particles, formed as the result of TEM e-beam damage. While surface-energy versus lattice-strain competition resulting in non-cubic particles has been observed many times before for metals, these particles are unusual because they are ionic crystals that feature large truncated octahedra. Using molecular dynamics simulations of salt systems comprising thousands of atoms, we will study the observed structure formation as a function of system size and initial conditions. This work will add fundamental knowledge to the behavior of salt under radiation, which will be essential for predicting the performance of nuclear waste repositories in halite.