Method and joint for sealing a bare hole in a nuclear heat exchanger tubesheet. The tubesheet has a plurality of holes formed therethrough, wherein at least one of the holes has been left vacant by a heat transfer tube removed from the hole. Such a hole is defined as a bare hole. One embodiment of the method of the invention comprises disposing a sleeve in the bare hole to protect the tubesheet material from the corrosive attack of the heat exchanger primary coolant and sealingly disposing a sleeve plug in the sleeve in order to seal the sleeve. A leak-tight joint is defined as the sleeve plug is sealingly disposed in the sleeve.