Abstract: A tool is insertable in the narrow annular access space between the cylindrical core barrel and the thermal shield of a nuclear reactor for testing and removing a plug from a flow hole in the core barrel. The tool includes two hydraulically driven jaws which have gripping flanges receivable in a peripheral groove in the plug head for gripping same. The jaws are thin plate-like members and each carries two short pistons having a length less than the thickness of the jaws and hydraulically extendable into engagement with the core barrel for exerting on the jaws and the gripped plug a predetermined force in a plug-removing direction. The jaws are preferably substantially coplanar and carried by a flat arm with the plane of the jaws disposed at a slight angle to the plane of the arm, which angle is selectively variable. Means are provided for pivotally moving the arm about an axis substantially parallel to the axis of the plug.