First synthesis of U18O2 pellets

For the first time, a wet synthesis of U¹⁸O₂ pellets has been carried out as part of Aurélien Perrot's thesis (PRECCI project). The aim of this synthesis is to develop a material whose solid oxygen atoms can be used as tracers. This will enable us to deepen our understanding of fuel weathering mechanisms in the context of underwater storage with a ruptured rod.

The synthesis involved producing an ammonia-saturated solution in H₂¹⁸O-labeled water, and attacking uranium metal with hydrochloric acid diluted in HCl + H₂¹⁸O-labeled water. Following preparation of the precursors, hydroxide precipitation took place and various heat treatments resulted in the production of a labeled oxide. This was then pelletized and sintered to produce UO₂ pellets enriched in oxygen 18, with a density of 91%. Despite all the heat treatments, including sintering at 1600°C, their isotopies remained predominantly ¹⁸O, with 61% oxygen 18.

^{Credit: S. Szenknect / ICSM}

These results demonstrate the feasibility of synthesizing UO₂ pellets with a high oxygen-18 enrichment, and open up new avenues of research, such as studies into the weathering and oxidation mechanisms of UO₂ fuel.

One of the pellets has been transported to the Atalante facility to carry out an underwater alteration experiment in the presence of gamma irradiation. The experiment will take place at the Laboratoire d'études des Matériaux et Procédés Actifs (LMPA) on the C18/C19 shielded chain. In parallel, complementary leaching experiments in the presence of H₂¹⁶O₂ or H₂¹⁸O₂ have been carried out at ICSM on other samples.

All this work required the involvement of a large number of LIME laboratory members, as well as many people from ICSM.