Andra, the French national radioactive waste management agency, is in charge of studying the disposal of high-level and long-lived intermediate-level waste (HLW and ILW-LL) in a deep geological repository (aka Cigéo). After a brief description of HLW disposal package models, their main functions are presented (handling purposes, containment of radioactive substances, criticality hazard control, delaying water contact with vitrified matrix, etc.). The horizontal steel cased disposal cell (0.7m ID micro-tunnel) inside which the disposal packages will be stored is also presented. The design options and the manufacturing processes of the disposal package are then described in order to show how the best technologies have been selected to ensure that the leak and gas tightness of the overpack is maintained as long as possible (and at least 500 years).

The following part of the paper is then focused on a description of the numerical simulations and corrosion tests (general corrosion, pitting and crevice corrosion, stress corrosion cracking with influence of the evolution of the water chemistry, temperature and radiolysis) performed in order to evaluate the mechanical behavior and durability of the disposal package. The mechanical studies focus on the behavior of a confined API5LX65MS steel casing (the disposal cell liner) submitted to general corrosion which governs the long term mechanical loading of the overpack. First numerical simulations performed to determine the ductile damage of a low alloy steel overpack subjected to both, general corrosion and localized mechanical loads are also presented.