Abstract: A tool for exchanging and transporting irradiation capsules of a nuclear reactor using water, which capsules contain samples experiencing, during the operation of the reactor, comparable irradiation to that experienced by the reactor vessel, between the vessel and the swimming pool and between several positions along the heat shield surrounding the core thereof, said tool comprises tongs comprising pivotable fingers pivotable between an inoperative position and an operative position for engaging a capsule, mounted in the region of the lower end of a vertical operating tube and controlled by first coaxial cam means mounted at the end of a vertical operating rod which is coaxial with the operating tube, said rod having a handle at its upper part and being movable vertically between a position in which said fingers are in the inoperative position and a position in which said fingers are in their operative position, means for exerting a downward thrust on a capsule by said operating tube comprising a double-actin