Effect of natural irradiation in fluorites: possible implications for nuclear waste management?

Samples of naturally irradiated fluorite have been analyzed by means of X-ray powder diffraction analysis (XRPD), differential scanning calorimetry (DSC) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The diffraction patterns of all irradiated samples show peak broadening caused by micro-strain, which was evaluated by Williamson-Hall method, and an increase in the unit cell parameter. The DSC analysis showed an exothermic peak at 273 C corresponding to enthalpy change about 16 kJ.mol-1. This value is an order of magnitude higher than calculated change due to unit cell volume increase that is only 2 kJ.mol-1. The LA-ICP-MS did not show any significant substitutions, which might account for observed unit-cell parameter increase. The results have shown that high radiation doses lead to formation of defect clusters.