Abstract: Provision is made for a container which stores and shields radioactive material. Included in the container is an enclosure defining a hollow chamber in which radioactive material is storable. A closure assembly cooperates with the enclosure in such a manner that an internal plug thereof effects a preselected gas-impervious sealing engagement. The closure assembly includes a lug which is rotatable to urge the assembly into sealing engagement and which torsionally fails following achievement of the desired sealing engagement of the closure plug to thereby prevent the lug from being subsequently used to open the container. The container and closure members provides desired radioactive shielding.