Control rod drive mechanism with separate latch and drive coils

A control rod drive mechanism for use in a nuclear reactor including a reactor core disposed in a pressure vessel, comprising:

• a control rod configured for insertion into the reactor core;
• a lead screw having a top end and a bottom end, the control rod being secured to the bottom end of the lead screw;
• a drive mechanism including:
• a torque tube having a top end and a bottom end,
• a pair of segment arms, each segment arm including a top end and a bottom end and being pivotably mounted to the torque tube,
• a pair of roller nuts, each roller nut being rotatably secured to the bottom end of a respective segment arm, and
• a drive motor including a stator and a rotor, the rotor secured to the top end of the torque tube and including a plurality of permanent magnets embedded therein, wherein the stator defines a central bore and the rotor is disposed within the central bore of the stator;
• and
• a latch coil assembly including a latch coil and a hold coil, wherein the latch coil assembly defines a central bore and the top ends of the segment arms are disposed within the central bore of the latch coil assembly radially-inwardly of the latch coil and the hold coil,
• wherein the latch coil and the hold coil are independently energizable and configured so that when the hold coil is energized and the latch coil is de-energized, the roller nuts are engaged with the lead screw.