[en] Inspection shafts which are annular and lead from the top to the bottom are arranged in the annular space between the pressure vessel of the sodium-cooled FBR and a wall surrounding it. Television cameras, lighting and test heads can be taken along the pressure vessel surface at the head of a chain-driven trolley. The trolley chain is securely guided by a guide rail system, while its drive is situated in a storage container outsider or above the annular space. The opening through the vessel lid, through which the trolley chain runs, can be sealed so that the device can be transferred from one opening to another. (orig./PW)