In medium-level waste (MLW) and high-level waste (HLW), the wasteform undergoes self-irradiation due to enclosed radionuclides. This interaction results in the generation of gaseous products and at the same time the possible release of volatile radionuclides by the waste itself. Their accumulation could be a source of safety problems in the production stage and also during interim storage or final disposal. It is necessary to study these phenomena. The principle for monitoring, sampling, and instrumentation equipment for containers (Appareillage de Surveillance, de Prélèvement et d’Instrumentation pour Conteneurs), intended for study and the follow-up of gaseous products released by a waste package, is presented.