Radiation stability of natural britholites

Britholite, Ca-REE silicate with apatite structure, is an actinide host phase occurred in vitreous borosilicate waste forms. Such glass-ceramics are considered as potential host phases for immobilization of actinide-containing high-level waste. Crystalline phases have to be radiation resistant for this application. Radiation stability of the britholites was mainly studied by either heavy ions irradiation or incorporation of Cm-244 or Pu-238 and 240. A wide range of critical doses (0.15-0.6 dpa at 25 degrees C) and temperatures have been obtained depending on the compositions of the samples. Natural analogue study of the waste forms allows to predict the behavior of actinide host phases for long periods after disposal. Britholites with age from 320 to 2600 millions years, ThO2+UO2 content from 1.0 to 12 wt.%, and cumulative doses from 0.6 x 10(19) to 7.7x10(19) alpha-decays/g have been studied. The britholite becomes amorphous at a dose of 1 dpa (0.9 x 10(19) alpha-decays/g) and higher. Critical doses for natural minerals are higher than those for synthetic samples, most likely due to re-crystallization during annealing.