Patent Number: 052326560
Section: description

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 illustrates a layout scheme of a fast acting nuclear reactor control device 10. The device 10 controls a safety control rod 12 within or without the core 14 of a nuclear reactor. The safety control rod's position is indicated by an encoder system 16. A primary safety control rod drive means, or drive shaft, 18 is operatively connected to the safety control rod 12, for driving and positioning the safety control rod within or without the reactor core 14. More specifically, the control rod 12 is a typical nuclear reactor control rod as described previously that includes a neutron absorber (poison), shown as the shaded portion 13. The position of the control rod 12 shown in FIG. 1 is half withdrawn (or half inserted). Rotation of the shaft 18 to raise the control rod 12 will position the poison portion 13 in the full "out" position for full reactor power. Lowering the assembly will place the poison 13 within the core 14. As shown, the safety control rod 12 is oriented in a substantially vertical position in a reactor of downward coolant flow to allow the safety control rod to fall into the reactor core under the influence of gravity and water pressure during shutdown of the reactor. The drive shaft 18 is also operatively connected to a hydraulic pump 20. The operation of the drive shaft 18 drives and positions the safety control rod 12 within or without the reactor core 14, while simultaneously operating the hydraulic pump 20 such that hydraulic fluid is forced into a pressurized accumulator 22. This fills or charges the accumulator 22 with oil while under pressure of compressed gas which provides storage of potential energy, the us of which will be explained below. A high pressure gas supply 23 supplies gas for pressurizing the accumulator. An electromagnetic clutch 26 is coaxial with the drive shaft 18. The drive shaft 18 is powered by an electric gearmotor 28. The gearmotor has a double worm gear reducer 29 and is self locking. The gear motor 28 driving through the electrically engaged clutch 26 will thus position the safety control rod 12 in the run position. To eliminate constant pressure on the hydraulic pump 20, which would tend to cause the shaft to rotate in the rod-insertion direction, a solenoid operated valve 24 can be interposed between the hydraulic pump 20 and the accumulator 22. This solenoid operated valve is a normally open valve, remaining open except when electrical power is applied to its solenoid. Power is applied to close the valve 24 only when the safety control rod 12 is out of the reactor core 14 for reactor operation. Should electrical power fail or a signal be received from the encoder system 16 calling for rapid insertion of the safety control rod, the solenoid valve 24 will open to release the potential energy in the accumulator to provide primary motive force to drive the safety control rod. The electromagnetic clutch 26 will also release allowing the shaft 18 to rotate. More specifically, the opening of the solenoid valve releases the hydraulic oil, pressurized by compressed gas in the accumulator 22 and forces the hydraulic fluid to flow back through the hydraulic pump, thereby converting the hydraulic pump 20 to a hydraulic motor, rotating the shaft 18, and inserting the safety control rod 12. This hydraulic drive accelerates the safety control rod 12 and maintains a drive force torque via the high pressure gas of the accumulator 22. The insertion of the safety control rod 12 is now powered by the combined effects of high pressure gas, gravity, and differential hydraulic pressure. The compressed gas provides the energy necessary for full length and high speed insertion of the safety control rod 12. The maximum driving force can be easily adjusted by adjusting the gas pressure in the accumulator (up to the maximum pressure that the safety control rod drive motor is able to provide) and can be increased above this level while the reactor is operating in preparation for fast SCRAM. Once the safety control rod is withdrawn the solenoid valve 24 can close and the current to the clutch 26 can automatically drop to a lower level, and thus reduce the clutch release time. With the solenoid valve closed only the safety control rod's torque can pass through the clutch. The safety control rod 12 is also connected to a rack gear 34, and the safety control rod drive shaft 18 has a pinion gear 36 in contact with the rack for allowing the safety control rod to be positioned within or without the reactor core. The novel features of the invention described herein are functional regardless of whether the rack 34 is above the poison 13 and core 14, or below the poison and core. However, for the gravity assisted SCRAM feature, the poison 13 must be above the core 14 as is shown in FIG. 1. Other mechanisms for positioning the safety control rod within or without the reactor core are also possible. In addition, an overrunning clutch 30 can be coaxial with the drive shaft 18, located intermediate the hydraulic motor 20 and the electromagnetic clutch 26. The overrunning clutch 30 is capable of allowing the speed of the drive shaft 18 to rotate at a speed greater than the speed of the hydraulic motor during shutdown of the reactor to provide for rapid insertion of the safety control rod into the reactor core in the event of partial drive system failure. The overrunning clutch 30 will allow the safety control rod 12 to move back down into the reactor core, due to gravity and pressure drop across the safety control rod, caused by coolant flow through the reactor even if the SCRAM system (whether it is the currently utilized cocked-spring system or the disclosed hydraulic system) has failed and locked the SCRAM system. The overrunning clutch also will not allow the SCRAM system to hinder safety control rod insertion speed if the SCRAM shaft is turning slower than the main safety rod shaft. Additionally, a reservoir of hydraulic fluid 32 is connected to the hydraulic pump 20 for pump supply. The electric motor 28, driving through the electrically engaged clutch 26 will position the safety control rod 12 in the run position, while also driving, via the overrunning clutch 30, the hydraulic pump 20, which thus transfers hydraulic fluid from the reservoir 32 to the accumulator 22. The clutch 26 will operate at high current during cocking until the solenoid valve 24 closes. With the hydraulic power now contained, the current may drop to low levels, reducing a release lug in the clutch during a SCRAM. The foregoing description of a preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiment was chosen and described to best explain the principles of the invention and its practical application and thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as ar suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.