Abstract: A control rod cluster assembly of a nuclear reactor is repeatedly repositioned in a guide tube assembly above a fuel assembly in the reactor core in single steps at separate times during a single fuel cycle. For instance, the single-step repositioning can be repeated once every month or every four months in a twelve month fuel cycle.

Abstract: A latch and linkage arrangement in a nuclear reactor control rod drive mechanism includes a latch having an elongated body with opposite ends and opposite side edges and multiple latch teeth defined along one of body side edges between the opposite ends. The arrangement also includes a plurality of links. A first link pivotally connects with the latch body adjacent one end and is pivotally connected to an electromagnetic armature for applying a motive force to the latch body through the first link. Second and third links are pivotally connected to the latch body and to a support tube in parallel relationship to one another so as to define a parallelogram therewith such that when the motive force is applied to the body via the first link the latch body and thereby the latch teeth undergo curvilinear movement toward and away from a latching position.