Control rod drive system for nuclear reactor

A control rod drive system for a nuclear reactor vessel, the system comprising:

• a vertically oriented drive rod mechanically coupled to a control rod drive mechanism operable to raise and lower the drive rod through a plurality of axial positions;
• a rod cluster control assembly comprising a plurality of control rods configured for removable insertion into a nuclear fuel core;
• a drive rod extension extending axially between the rod cluster control assembly and the drive rod, the drive rod extension having a bottom end releasably coupled to the rod cluster control assembly;
• a drive rod extension grapple assembly connected to the drive rod,
• the grapple assembly releasably coupled to a top end of the drive rod extension;
• the grapple assembly including:
• a body defining a downwardly open chamber configured to movably receive the top end of the drive rod extension therein,
• the body including a plurality of spring-biased radially retractable lifting pins engageable with the drive rod extension and slideably movable in a linear manner between
• a radial inward position projected into the chamber,
• and a radial outward position retracted from the chamber,
• the drive rod extension including:
• a longitudinally-extending actuating tube and an actuating shaft slideably disposed in the actuating tube,
• the actuating shaft operably coupled to the grapple assembly for upward and downward movement with the drive rod relative to the actuating;
• a lifting head coupled to a first end of a lifting head sleeve tube,
• a second end of the lifting head sleeve coupled to the actuator tube;
• a diametrically enlarged bobbin slideably disposed and axially movable on the lifting head sleeve,
• the bobbin operable to selectively engage the lifting head and enter the downwardly open chamber of the grapple assembly;
• wherein the lifting head is configured to engage and force the lifting pins to the outward position when the lifting head enters the chamber of the grapple assembly;
• wherein the bobbin is movable in an upwards direction with the lifting head sleeve to engage and retract the lifting pins of the grapple assembly independently of the lifting head;
• wherein raising and lowering the drive rod raises and lowers the rod cluster control assembly.