1. Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, UK
2. Pacific Northwest National Laboratory, Richland, Washington 99352, USA

Correspondence to: Ian Farnan¹ Correspondence and requests for materials should be addressed to I.F. (Email: ifarnan@esc.cam.ac.uk).

There are large amounts of heavy -emitters in nuclear waste and nuclear materials inventories stored in various sites around the world¹. These include plutonium and minor actinides such as americium and curium. In preparation for geological disposal there is consensus² that actinides that have been separated from spent nuclear fuel should be immobilized within mineral-based ceramics rather than glass^{2, 3, 4} because of their superior aqueous durability and lower risk of accidental criticality. However, in the long term, the -decay taking place in these ceramics will severely disrupt their crystalline structure^{2, 3, 4} and reduce their durability^{5, 6}. A fundamental property in predicting cumulative radiation damage is the number of atoms permanently displaced per -decay. At present, this number is estimated to be 1,000–2,000 atoms/ in zircon⁴. Here we report nuclear magnetic resonance, spin-counting experiments that measure close to 5,000 atoms/ in radiation-damaged natural zircons. New radiological nuclear magnetic resonance measurements on highly radioactive, ²³⁹Pu zircon show damage similar to that caused by ²³⁸U and ²³²Th 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 ²³⁹Pu 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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