IRSN (the French Institute of Radioprotection and Nuclear Safety) is in charge of reviewing the LL-HLW geological repository project managed by ANDRA (the French National Radioactive Waste Management Agency) in support of the nuclear safety authority (ASN). Amongst other IRSN paies particular attention to the performance of confinement of the nuclear wastes packages, to the release of the radionuclides from the wastes and the associated uncertainties. In order to better assess the degradation process of the nuclear waste packages, IRSN has developed an experimental program in collaboration with laboratories from the university, the ENSMSE (École nationale supérieure des mines de Saint-Étienne) and the CNRS (the French National Center for Scientific Research). The studies concern on the one hand the activated compacted wastes packages and on the other hand the spent fuel.Regarding compacted wastes packages, at the end of the light water reactors operation, the Zircaloy (zirconium alloy) cladding tubes had been activated and oxidised. After processing, these cladding tubes are compacted in a wafer form, placed into a steel container, and then into a concrete over-pack with a view to being disposed of in geological repository. These wastes are mostly composed of activated oxidized metal pieces which also contain traces of fission, activation products and actinides. In the repository, they are exposed to radioactivity in presence of resaturation water. The water radiolysis may accelerate the oxidised metal corrosion processes. By the way, the wastes degradation is mainly due to corrosion process. A fundamental study has thus been defined on the effects of water radiolysis on Zircaloy corrosion. The second study aims at better understanding the influence of the fuel matrix defects on the radiolytic degradation of spent fuel. As a matter of fact, fission products and actinides decay during storage may cause defects of the fuel matrix by changing its composition and microstructure. The study is performed in close collaboration with CNRS laboratory.