Stored energy in natural zirconolite and its synthetic counterpart after alpha recoil self-irradiation damage

Abstract

Zirconolite (nominally CaZrTi 2O 7) was fully substituted with 238Pu, resulting in the composition CaPuTi 2O 7. The effects of self-irradiation due to alpha decay were monitored at room temperature for times as long as 1198 days and doses as high as 1.6 × 10 26 α/m 3, using differential thermal analysis. As storage time increased, the temperature of recovery from the damaged to the crystalline state increased and the recovery step became more abrupt. Stored energy reached a maximum of 100 J/g at 2.1 × 10 25 α/m 3 and then decreased to half this value with further damage. Results for synthetic samples were compared with those for naturally-occurring zirconolites that had attained a damage dose of ≈ 4.8 × 10 26 α/m 3 as a result of their high Th and U contents. At high alpha decay doses the synthetic and natural materials behaved similarly, indicating the absence of major damage recovery or alteration effects for the natural mineral at ambient temperature. It is concluded that actinide-doped zirconolite and natural mineral analogues can both be used to study alpha decay damage under nuclear waste storage conditions after the initial cooling-off period.