Molecular dynamics study of self-radiation damage in mineral matrices

Resumo

Mechanisms of radiation damages in minerals promising for the utilization of highly active radioactive waste (zircon ZrSiO₄, monazite LaPO₄, orthophosphate YbPO₄, lakargiite CaZr_0,8Sn_0,1Ti_0,1O, 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 CaZr_0.8Sn_0.1Ti_0.1O₃ makes it possible to propose them as a possible matrix for the utilization of highly active radioactive waste.