The Joint European Torus (JET) Active Gas Handling System (AGHS) will store and process the tritium required for the active phase operation of JET. Numerous types of secondary containments are used to house the process components necessary for this processing and storage. Secondary containments are a key safety feature of the plant's design and provide a defence-in-depth against the release of tritium. The secondary containment designs, features, operating conditions and integrity monitoring and the role that they play in mitigating releases from the AGHS are discussed.