**Acknowledgements**

We acknowledge Olga A. Maslova for the mapping and analysis of UO2 ceramics. R. Augier, F. Choulet, D. DoCouto and F. Rull for the samples from Sierra Alhamilla, Morocco and Autun, la Sioule and Tenerife, respectively. We also acknowledge P. Bost for his help in sampling at Chéniers.
