Abstract: A steam generator having a steam generator chamber, a tube plate bordering the chamber, tubes terminating in the tube plate being accessible through the steam generator chamber, a tubular column in the steam generator chamber having an end facing toward the tube plate, and a swivel arm extended from the tubular column being movable parallel to the tube plate for carrying a device for testing and/or repairing the steam generator tubes, includes a clamping element for positioning the tubular column relative to a tube of the tube plate, and a coupling being detachable from outside the steam generator chamber connecting the clamping element to the tubular column, the clamping element including a drive element disposed in the tubular column, an expansion plunger connected to the drive element for axially inserting the expansion plunger partially into a tube, an expansion sleeve formed of separate clamping jaws for engaging the tubes, the clamping jaws having ends being insertible into a tube, and a holding element