Control rod drive mechanism for a nuclear reactor

Claim 2

Drive apparatus which is mounted to a pressure vessel containing a nuclear core and is adapted to move a drive shaft and an attached control rod into and out of the core in a step-by-step manner including a housing, said drive shaft being disposed for axial movement within said housing, a pair of axially spaced gripper means pivotally mounted within said housing for engaging and disengaging said drive shaft, first electrically energized magnet coil means mounted to said housing for actuating said gripper means and for moving said drive shaft in said step-by-step manner, and locking means for preventing disengagement of said gripper means from said drive shaft upon interruption of electrical power to said first magnet coil means, said locking means including second electrically energized magnet coil means which is electrically independent of said first magnet coil means.

Claim 3

The drive apparatus of claim 1, wherein said drive shaft has a plurality of axially spaced teeth thereon, and each of said gripper means comprises at least one gripper member having a projection thereon for engaging with said teeth on said drive shaft, said gripper member being pivotally connected within said housing and being pivotally moved into and out of engagement with said drive shaft by said first magnet coil means.

Claim 4

The drive apparatus of claim 1, wherein said first magnet coil means includes a magnet coil which is attached to said housing in spaced concentric relationship with said drive shaft, a non-movable magnet pole and a movable magnet plunger axially spaced therefrom, said non-movable pole and said movable plunger each having an annular configuration and being interposed concentrically between said drive shaft and said magnet coil, said gripper means including a latch member which is pivotally connected at one end to said magnet pole and a link member which pivotally connects the other end of said latch member to said magnet plunger, said magnet coil serving to move said magnet plunger and thereby pivot said latch member into engagement with and out of engagement with said control rod drive shaft.

Claim 5

The drive apparatus of claim 1 wherein said locking means includes a locking member, and said second magnet coil means includes a magnet coil which is mounted on said housing in spaced concentric relationship with said drive shaft, a magnet pole and a magnet plunger axially spaced therefrom, said magnet pole and said magnet plunger being interposed concentrically between said drive shaft and said magnet coil, said locking member being fixedly connected to said magnet plunger such that activation of said magnet coil moves said magnet plunger and said locking member attached thereto into a position behind said gripping means to prevent disengagement of said gripper means from said control rod drive shaft.

Claim 6

The drive apparatus of claim 1, wherein said drive shaft has a plurality of axially spaced teeth thereon, and each of said gripper means includes a latch member having a projection thereon for engaging with said teeth on said drive shaft, said latch member being pivotally connected to a support member within said housing and being pivotally moved into and out of engagement with said drive shaft by said first magnet coil means, and said locking means includes a ring which is moved axially by said second magnet coil means, said ring being axially positioned with respect to said latch member such that when said second magnet coil means is activated a portion of said latch member extends through said ring to prevent pivoting of said latch member and thereby disengagement of said latch member from said drive shaft, and when said second magnet coil means is not activated said ring is axially displaced from said latch member thereby permitting pivoting of said latch member and its disengagement from said drive shaft.

Claim 7

The drive apparatus of claim 1 wherein said first magnet coil means is activated by first direct current voltage, and said second magnet coil means is activated by second direct current voltage, said second voltage being substantially higher than said first voltage such that said second magnet coil means cannot be activated by said first voltage.

Claim 8

The drive apparatus of claim 1, wherein said second magnet coil means is activated at approximately 250 Volts direct current, and is thermally insulated to be above 150° during reactor power operation, at which temperature the electrical resistance of said second magnet coil means is increased so that said activation voltage will be insufficient to activate said second magnet coil means.

Claim 9

The drive apparatus of claim 1, wherein a missile shield is located above said drive apparatus, said missile shield having to be removed in order to open said reactor vessel to expose said core, and said second magnet coil means has an electrical connector attached thereto for applying electricity to said second magnet coil means, said electrical connector being exposed only when said missile shield is removed such that connection of electrical power to said second magnet coil means is possible only when said missile shield is removed.