Installation for welding fuel assembly top nozzles onto nuclear fuel rods comprising a device (D) for axially retaining said rod and for setting it in rotation and a welding chamber (C), said device (D) comprising a gripper and means for closing the gripper onto the fuel rod, said means comprising a push-rod (32) to apply an axial force to the gripper, a linear actuator (44) of axis (X2) parallel to the longitudinal axis of the device (X), a yoke (46) translationally secured to said push-rod and able to rotate about a fixed axis (Y) orthogonal to the longitudinal axis (X) which is not secant therewith, said yoke (46) being articulated with respect to the linear actuator (44) about an axis (Y1) parallel to the orthogonal axis (Y) such that the linear actuator (44) causes the yoke (46) to rotate about the first orthogonal axis (Y) and causes a translational movement of the push-rod, closing the gripper onto the fuel rod.