an improved plugging system for plugging chamfered flow ports of small diameters in the core barrel of a pressurized water nuclear reactor is disclosed herein . the system is comprised of improved core barrel plugs that are telescopically contractible to facilitate installation , as well as a handling tool having a compact hydraulic ram and plug - holding cradle that is easily manipulable in the limited access space between the core barrel and thermal shield of the reactor for inserting and expanding the plugs into sealing engagement with the core barrel flow ports . the plugs of the system are formed from a generally cylindrical plug body that is radially expandible , and a retaining ring that is telescopically engaged around the plug body which allows it to be slid toward the middle of the plug prior to installation in order to minimize the overall length of the plug prior to the insertion operation . the retaining ring is also slidably installable around the plug body to allow different - sized retaining rings to be installed around plug bodies in order to accommodate different - size port chamfers . finally , both the hydraulic ram and the plug - holding cradle of the installation tool are movable within the frame of the tool , and co - act by way of a pivoting linkage to insert the plug completely into a selected flowport prior to the expansion of the plug within the port by the ram .