[en] In the Federal Republic of Germany it is intended to dispose of radioactive waste with negligible heat impact on the host rock in the former Konrad iron ore mine. The waste packages will be disposed of in emplacement rooms which, once completely filled, will be sealed by closing-off structures. The requirements to be imposed on the closing-off structures are derived by a safety analysis for the operational phase. Referring to different levels of requirements two concepts of closing-off structures are introduced. The feasibility of the almost tight closing-off structure is shown in situ. (orig.)