Patent Number: 
Section: claims

1. A control rod assembly for a nuclear reactor having a reactor core and a pressurized fluid source, comprising:a control rod disposed within a control rod sleeve;a piston disposed on the control rod;a lead screw that is selectively secured to the control rod;a pneumatically-operated trip latch that is secured to a bottom end of the lead screw, the trip latch being selectively securable to a top end of the control rod and movable between a closed position and an open position, wherein when the trip latch is in the open position the control rod is not secured to the lead screw;a control rod drive motor that is operably connected to the lead screw; anda gas valve that is configured to be in fluid communication with the pressurized fluid source of the nuclear reactor andwherein with the gas valve in fluid communication with the pressurized fluid source, the gas valve is movable betweena first position in which the pressurized fluid source is isolated from the control rod sleeve anda second position in which the pressurized fluid source is in fluid communication with the control rod sleeve;whereinin the first position of the gas valve the pressurized fluid source is isolated from the trip latch and the trip latch is in the closed position andin the second position of the gas valve the pressurized fluid source is in fluid communication with both the piston and the trip latch to trip the trip latch into the open position,wherein with the trip latch in the open position, pressurized fluid from the pressurized fluid source acts against the piston to drive the control rod. 2. The control rod assembly of claim 1, wherein when the trip latch is in the open position the control rod is released from the lead screw. 3. The control rod assembly of claim 2, wherein when the gas valve is in the second position the control rod is driven into the reactor core by the pressurized fluid source. 4. The control rod assembly of claim 1, wherein the pressurized fluid source is a pneumatic source. 5. The control rod assembly of claim 1, wherein the piston forms a gas-tight seal with the inner surface of the control rod sleeve. 6. A nuclear reactor comprising:a reactor core;a pressurized fluid source; anda control rod assembly comprising:a control rod disposed within a control rod sleeve;a piston disposed on the control rod;a lead screw that is selectively secured to the control rod;a pneumatically-operated trip latch that is secured to a bottom end of the lead screw, the trip latch being selectively securable to a top end of the control rod and movable between a closed position and an open position, wherein when the trip latch is in the open position the control rod is not secured to the lead screw;a control rod drive motor that is operably connected to the lead screw; anda gas valve that is in fluid communication with the pressurized fluid source of the nuclear reactor andwherein with the gas valve in fluid communication with the pressurized fluid source, the gas valve is movable betweena first position in which the pressurized fluid source is isolated from the control rod sleeve anda second position in which the pressurized fluid source is in fluid communication with the control rod sleeve;whereinin the first position of the gas valve the pressurized fluid source is isolated from the trip latch and the trip latch is in the closed position andin the second position of the gas valve the pressurized fluid source is in fluid communication with both the piston and the trip latch to trip the trip latch into the open position,wherein with the trip latch in the open position, pressurized fluid from the pressurized fluid source acts against the piston to drive the control rod. 7. The control rod assembly of claim 6, wherein when the trip latch is in the open position the control rod is released from the lead screw. 8. The control rod assembly of claim 7, wherein when the gas valve is in the second position the control rod is driven into the reactor core by the pressurized fluid source. 9. The control rod assembly of claim 6, wherein the nuclear reactor further comprises a nuclear thermal propulsion space reactor. 10. The control rod assembly of claim 6, wherein the pressurized fluid source is a pneumatic source. 11. The control rod assembly of claim 6, wherein the piston forms a gas-tight seal with the inner surface of the control rod sleeve.