A control rod drive mechanism having a torque tube with an inner surface defining a central bore, a control rod assembly including a connecting rod including a cam extending radially-outwardly therefrom and an annular collar defining a key slot, an elongated key that is slidably receivable within the key slot, and a holdout collar disposed non-rotatably within the torque tube and defining a locking recess, wherein the connecting rod is axially-movable with respect to the torque tube between a first position in which the elongated key is disposed within the key slot so that the connecting rod is non-rotatable with respect to the torque tube, and a second position in which the elongated key is removed from the key slot and the connecting rod is rotatable with respect to the torque tube.