While the scientific understanding of the dissolution of standard spent uranium oxide fuel has reached a certain mature state, new types of fuels with additives (“doped fuels”) have been developed. These fuels are already in use in some reactors, and their use is foreseen to be expanded. Dissolution data is now required to confirm that the dissolution behaviour of such fuels in a geological repository environment is similar to that of standard fuel. Similarly, there is a dearth of dissolution data from MOX fuels, which are also currently in use in several reactors. This project is therefore targeting oxide fuels containing additives, including Cr, Gd and Pu, in order to ensure that relevant characteristics are understood to a level commensurate with standard fuels. This project aims to expand the database on spent fuel dissolution with results from dissolution studies performed in truly reducing conditions, with hydrogen present. The effects of dopants will be investigated through experiments using both spent nuclear fuel and synthetic materials specifically designed for the project. In addition, chemical modelling will be employed to improve the understanding and description of the dissolution process relevant to the expected chemical conditions inside a failed waste container in a deep geological repository environment.