The PuMMA (Plutonium Management for More Agility) project brings together 20 partners from 12 European countries to address issues related to Generation IV reactors and the fuel cycle. To date, the dissolution of MOX fuel is fully qualified for Pu contents of up to 30%. One of the objectives of the PuMMA project is to acquire the experimental data needed to reach technological maturity around TRL-4 for fuels containing up to 45% Pu. To this end, work has been carried out at the CEA to conduct dissolution tests in medium and high activity on fuels with high Pu contents before and after irradiation.