Studtite under pressure: implication for a geological repository

The generation of electricity by nuclear power has generated, and will continue to do so, highly radioactive waste and safe stewardship for hundreds of thousands of years is a socially important but technically challenging prospect. Current thinking is that spent nuclear fuels (SNF) will be buried in engineered geological repositories. Under certain conditions UO2, the major component of spent nuclear fuel, can oxidise to form studtite [UO2(O2)(H2O)2].2H2O that has unusual thermal behaviour. At ca. 200 oC this decomposes to what is suggested to be U2O7 that can react with water generating O2. This pressure buildup constitutes a safety hazard. At the depths of the repository, the pressures will change the chemistry and herein we aim to observe what happens to studtite upto 6 GPa to shed light on the stability of these phases. This work feeds into safety cases for worldwide repositories.