Control rod displacement

Claim 1

In a nuclear reactor including a core, a plurality of cylindrical control rods, a single support means supporting said plurality of control rods from their upper ends in spaced apart positions and movable for displacing said control rods in their longitudinal direction between a first end position in which said control rods are fully inserted into said core and a second end position in which said control rods are retracted from said core, and guide means contacting discrete regions of the outer surface of each said control rod at least when said control rods are in the vicinity of the second end position, said control rods being supported by said support means for longitudinal movement without rotation into and out of said core relative to the guide means to thereby cause the outer surface of said control rods to experience wear as a result of sliding contact with the guide means, said support means being so arranged with respect to said core and said guide means that it is incapable of rotation relative to said guide means, the improvement comprising a plurality of displacement means each of said plurality of displacement means being operatively coupled to a respective one of said control rods for periodically rotating said control rod in a single angular direction through an angle selected to change the locations on the outer surfaces of said control rods at which said control rods are contacted by said guide means during subsequent longitudinal movement of said control rods.