Determination of the defect creation mechanism in the mono-silicated fluoroapatite. Disorder modeling under repository conditions

Amorphization resulting from α-decay events can strongly reduce the chemical durability of nuclear waste matrices. The creation rate of defects produced by α recoils in mono-silicated fluoroapatite was determined using a transmission electron microscope (TEM) on line with an ion implanter and compared to previous results obtained in fully phosphated fluoroapatite. In both materials, the defect creation is controlled at room temperature, by the amorphization process directly in the cascade. Furthermore, it has been shown previously that in mono-silicated fluoroapatite, the disorder recovery proceeds mainly via α-annealing. Taking into account our already published data and new results on the defect creation in the mono-silicated fluoroapatite, we have modeled the amorphization level evolution versus time under repository conditions. The main conclusion is the following: thanks to α-annealing, mono-silicated fluoroapatite loaded with 244Cm, will maintain a disorder at a level low enough to prevent the total amorphization of the host lattice during the long-term disposal.