The effect of impurities and radiation damage on the glass network-caesium loaded iron phosphate molecular dynamics case study

The use of iron phosphate glass as a wasteform is contingent both on its response to the addition of waste products and on its evolution in response to radiation emitted by these waste products. We perform molecular dynamics simulations of high-energy radiation damage in caesium iron phosphate glasses to study the mobility of caesium, a nuclear decay product, in vitreous wasteforms and their effect on the glass network. We simulate overlapping 70 keV cascades and examine the structural and topological effects that caesium has on the iron phosphate glasses before and after these cascades. We find that the glass network is substantially altered by the presence of caesium as a potent network modifier and that radiation cascades produce qualitatively different effects from those in pure iron phosphate glasses. Overlapping cascades produce minimal effects on the mobility of caesium at low loading. At higher loading, the glass network accommodates caesium atoms less well, particularly after irradiation. We explain this in terms of caesium's role as an excluded network modifier in comparison to iron, which is tightly incorporated into the glass network.