There are large amounts of heavy α-emitters in nuclear waste and nuclear materials inventories stored in various sites around the world. These include plutonium and minor actinides such as americium and curium. In preparation for geological disposal there is consensus that actinides that have been separated from spent nuclear fuel should be immobilized within mineral-based ceramics rather than glass because of their superior aqueous durability and lower risk of accidental criticality. However, in the long term, the α-decay taking place in these ceramics will severely disrupt their crystalline structure and reduce their durability. A fundamental property in predicting cumulative radiation damage is the number of atoms permanently displaced per α-decay. At present, this number is estimated to be 1,000-2,000 atoms/α in zircon. Here we report nuclear magnetic resonance, spin-counting experiments that measure close to 5,000 atoms/α in radiation-damaged natural zircons. New radiological nuclear magnetic resonance measurements on highly radioactive, ~(239)Pu zircon show damage similar to that caused by ~(238)U and ~(232)Th in mineral zircons at the same dose, indicating no significant effect of half-life or loading levels (dose rate). On the basis of these measurements, the initially crystalline structure of a 10 weight per cent ~(239)Pu zircon would be amorphous after only 1,400 years in a geological repository (desired immobilization timescales are of the order of 250,000 years). These measurements establish a basis for assessing the long-term structural durability of actinide-containing ceramics in terms of an atomistic understanding of the fundamental damage event.
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