Molecular dynamics study of self-radiation damage in mineral matrices

Abstract

Mechanisms of radiation damages in minerals promising for the utilization of highly active radioactive waste (zircon ZrSiO4, monazite LaPO4, orthophosphate YbPO4, lakargiite CaZr0,8Sn0,1Ti0,1O, and Gd2Zr2O7 and Gd2Ti2O7 compounds with the pyrochlore structure) are studied by the computer simulation using the molecular dynamics method. The formation of a damaged region in the structures under study is considered along with the recovery (relaxation) processes in these structures. The number of Frenkel pairs and antistructural defects that form in the structure of these minerals after the pass of the knocked out thorium atom is calculated by the molecular dynamics method. A parameter is proposed that characterizes the mineral tendency to amorphization under the effect of the radiation damage. The obtained results show that one of the main factors determining the radiation stability of minerals is the crystal structure type, compounds with the monazite structure being more radiationally stable than compounds with the zircon structure. It is found that the Gd2Zr2O7 compound and lakargiite have a weaker tendency to amorphization than other minerals such as zircon, monazite, and orthophosphate YbPO4. A high radiation stability of the studied Gd2Zr2O7 compound as well as a solid solution of the composition CaZr0.8Sn0.1Ti0.1O3 makes it possible to propose them as a possible matrix for the utilization of highly active radioactive waste.