JPH0651089A - Recirculation pump installed in nuclear reactor - Google Patents

Abstract

PURPOSE:To keep resolutions even in case a pump loses its driving force and relieve the core stability and the transient characteristics by using a rolling bearing to a bearing means which supports a shaft in the thrust direction. CONSTITUTION:A rolling bearing A consisting of rolling elements 24, inner and outer rings 25, 26, and a retainer 27 is furnished on the undersurface of a thrust disc 20 at the bottom of a shaft 10. The inner ring 25 rotates together with the disc 20, while the outer ring 26 fixed to the upper part of a motor cover 8 is at a standstill even while a pump is in opeeation. A raceway 28, 28 where the rolling elements 24 are in contact is formed in the circumferential direction on the mating surface of each ring 25, 26, and the rolling elements 24 are held by the retainer 27 on the outer ring 26 so that they can rotate freely while their positions remain unchanged. Thereby the thrust force applied to the shaft 10 is received by the bearing A, so that the rotational resistance is reduced to a great extent, and revolutions of the pump are kept with the voluntary circulation force as the drive motive. Accordingly the flow resistance of the impeller part is reduced to lead to enhancement of the rate of flow in natural circulation, which permits relieving of the core safety and transient characteristics when the pump loses its driving force.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nuclear reactor built-in recirculation pump (also referred to as an internal pump) used in a boiling water reactor, and more particularly to a thrust direction of a shaft connecting a pump part and a motor part. The present invention relates to a recirculation pump with a built-in reactor for reducing bearing resistance.

[0002]

2. Description of the Related Art Reactor built-in recirculation pumps are used to forcibly circulate coolant in a reactor pressure vessel.
As shown in FIG. 7, a plurality of reactor pressure vessels 1 are installed around the lower end plate 1a.

This reactor built-in type recirculation pump is composed of a water immersion motor section 2 and a pump section 3.
Is provided above the attachment nozzle 4 fixed to the lower end plate 1a of the reactor pressure vessel 1. The upper portion of the motor casing 5 is inserted into the mounting nozzle 4 and fixed by welding 5a.

The water immersion motor section 2 in the motor casing 5 comprises a stator 6 and a rotor 7. The lower portion of the water immersion motor section 2 is sealed by a motor cover 8. In the motor casing 5, the cooling water warmed in the motor unit 2 is led out to the outside from the motor unit cooling outlet pipe 9a and becomes a low temperature by heat exchange, and then is returned to the motor unit 2 again from the motor unit cooling inlet pipe 9b. It is being introduced.

A shaft 10 is inserted into and integrated with the rotor 7, a pump impeller 11 is detachably attached to the upper end of the shaft 10, and the pump impeller 11 rotates as the shaft 10 rotates. To be done.
The pump impeller 11 is inserted into a diffuser 13 attached to a gap (downcomer portion) between the inner wall of the reactor pressure vessel 1 and the shroud 12, and the diffuser 13 is attached by a stretch tube 14 and a stretch tube nut 15. It is fixed to the tip of the nozzle 4. Therefore, at the time of maintenance and inspection, the pump impeller 11 and the shaft 10 can be integrally taken out of the reactor pressure vessel 1.

The motor unit 2 and the interior of the reactor pressure vessel 1 are spatially communicated with each other, and purge water driven by a CRD pump 17 is constantly supplied from a purge water pipe 16 attached to an upper portion of the motor casing 5. Inflowing, this purge water flows upward on the surface of the shaft 10,
Water quality is completely separated so that the reactor water in the reactor pressure vessel 1 does not leak out.

A secondary seal 18 is provided on the upper portion of the motor casing 5. When the motor unit 2 is removed, pressurized water is supplied to the secondary seal 18 via a pressurized water supply pipe 19. By expanding the secondary seal 8 and bringing it into close contact with the outer peripheral surface of the shaft 10, the reactor water is prevented from leaking out.

A thrust disc 20 is provided below the shaft 10, and the pump impeller 11 and the shaft 1 are provided.
0, the rotor 7, and the thrust disk 20 rotate together, and an upper thrust bearing 21 is installed on the upper side of the thrust disk 20 and a lower thrust bearing 22 is installed on the lower side thereof. The upper thrust bearing 21 and the lower thrust bearing 22 are both thrust bearings.

Therefore, the lower thrust bearing 22 is supported by the lower thrust bearing 22 via the thrust disk 20 when the rotating body composed of the pump impeller 11, the shaft 10, the rotor 7, and the thrust disk 20 is stopped and at low speed rotation. Further, at the time of high speed rotation, the rotating body floats up due to the reaction force of the fluid in the pump impeller 11 section, so that the upper thrust bearing 21 supports it. The lateral direction of the rotating body is supported by the upper radial bearing 23a and the lower radial bearing 23b.

[0010]

However, in the case where the internal reactor recirculation pump loses power due to some factor during normal operation, the internal reactor recirculation pump loses its driving force and its rotational speed gradually decreases. As a result, the contact resistance between the lower thrust bearing 22 and the thrust disk 20 increases.

On the other hand, heat is still generated in the core portion, and this heat generation heats the coolant inside the shroud 12, which causes a difference in density with the coolant outside the shroud 12 (downcomer portion). With this density difference as a driving force, the coolant inside the shroud 12 moves upward, and the shroud 12
The coolant on the outer side of the is naturally circulated so as to flow downward. That is, even when the internal reactor recirculation pump is stopped, a certain amount of core flow can be obtained by natural circulation of the coolant. The core flow rate obtained by this natural circulation is determined by the balance between the driving force due to the density difference and the flow resistance when circulating in the reactor.

With this natural circulation flow, the pump impeller 11
Drive force is obtained in the rotation direction, and the drive force by this natural circulation flow and the thrust disk 20 and the lower thrust bearing 22
The rotational speed of the pump during natural circulation is determined by the balance of the resistance with the. However, according to the conventional lower thrust bearing 22, the resistance rapidly increases in the low rotational speed region and exceeds the driving force due to the natural circulation force. Therefore, the recirculation pump with built-in reactor stops rotating. When the rotation of the pump is stopped in this manner, the flow resistance of the pump unit 2 is increased by about 14 times as compared with the case where the pump is kept rotating, and as a result, the natural circulation flow rate is reduced, so that the pump is rotated. The core stability and transient characteristics are worse than when maintained.

The present invention has been made in view of the above points, and has a structure capable of maintaining rotation even when the internal reactor recirculation pump loses the driving force, and increasing the natural circulation flow rate. Therefore, it is an object of the present invention to provide a reactor built-in type recirculation pump capable of achieving core stability and mitigation of transient characteristics.

[0014]

In order to solve the above problems, a reactor built-in type recirculation pump according to the present invention comprises a pump installed on the bottom surface of a reactor pressure vessel, and a motor unit for driving the pump. In a nuclear reactor built-in recirculation pump having a shaft connecting the pump and a motor part and a bearing means for supporting the shaft in a thrust direction, a rolling or non-contact bearing is used as the bearing means.

[0015]

[Effect] Even if the recirculation pump with built-in reactor loses power due to some cause, the resistance of the bearing means that supports the thrust direction of the shaft is minimized, and the pump is rotated using the natural circulation force as the driving force. Sustained and the flow resistance of the impeller is greatly reduced, so that the natural circulation flow rate can be improved, which alleviates the core stability and transient characteristics when the driving force of the internal reactor recirculation pump is lost. .

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 shows an entire longitudinal section of a first embodiment of the present invention, and FIG. 2 shows an enlarged section of thrust bearing means.
In this embodiment, the rolling element 24, the inner ring 25, and the outer ring 2 are provided on the lower surface of the thrust disk 20 at the lower end of the shaft 10.
A rolling bearing A composed of 6 and a cage 27 is installed. The inner ring 25 is immersed in the thrust disc 20 and is rotated together with the thrust disc 20. Further, the outer ring 26 is submerged in the upper portion of the motor cover 8 so that the outer ring 26 remains stationary even when the pump is in operation. On the respective facing surfaces of the inner ring 25 and the outer ring 26, raceways 28 with which the rolling elements 24 come into contact are formed in the circumferential direction, and the rolling elements 24, as shown in FIG.
It is held by the outer ring 26 so that its position can be freely rotated by 7.

Since the motor part 2 of the recirculation pump with built-in reactor is submerged, if oil or grease generally used as a lubricant for the bearing part is used, these may leak into water. . Therefore, these lubricants cannot be used, and water cannot help being used as a lubricant. Therefore, if a metal-based material is used for the inner ring 25, the outer ring 26, and the rolling elements 24, the wear becomes large and the durability becomes low.

According to this embodiment, since the thrust force applied to the shaft 10 is received by the rolling bearing A, the rotational resistance is remarkably reduced, and the rotation of the pump is sufficiently maintained by using the natural circulation force as a driving force.

FIG. 4 shows the entire longitudinal section of the second embodiment of the present invention, and FIG. 5 shows the enlarged section of the thrust bearing means.
In this embodiment, a hydrostatic bearing B including a lower thrust bearing 22 having a pocket 29 on the lower surface of the thrust disk 20 and a purge water pipe 16 for allowing purge water to flow into the pocket 29 is installed. There is.

The purge water pipe 16 is connected to the motor casing 5
Is attached to the lower portion of the lower thrust bearing 22, and the purge water is guided to the pocket 29 of the lower thrust bearing 22 through the flow path passing through the motor cover 8. Therefore, the high pressure purge water constantly flows into the pocket 29 so that the pocket 2
The pressure inside 9 becomes high, a vertical force acts on the thrust disk 20, and the contact resistance between the thrust disk 20 and the lower thrust bearing 22 is suppressed low.

In consideration of a power failure, as shown in FIG. 4, an auxiliary purge water system including an uninterruptible power supply 30, an auxiliary purge water pump 31 using the power supply 30 as a drive source, and a purge water water source 32 is provided. it can. Check valve 3 in the purge water pipe
3a and 33b are interposed to prevent backflow of purge water. The purge water pipe 16 is provided with shutoff valves 34a and 34b. During normal operation, the shutoff valve 34a is closed and the shutoff valve 34b is opened, so that the purge water flows from the lower portion of the motor casing 5. When the motor unit 2 is removed for maintenance or the like, the shutoff valve 34a is opened and the shutoff valve 34b is closed, and purge water is injected from the upper portion of the secondary seal 18.

Also in this embodiment, since the thrust force applied to the shaft 10 is received by the hydrostatic bearing B, the rotational resistance is remarkably reduced, the natural circulation force is used as the driving force to maintain the rotation of the pump, and the hydrostatic bearing B is also used. Does not lose its function even during a power outage.

FIG. 6 shows an overall longitudinal section of a third embodiment of the present invention, in which a permanent magnet 35 is installed above the rotor 7 and an electromagnet 36 is installed below the upper radial bearing 23a. The electromagnet 36 uses the uninterruptible power supply 37 as a drive source, senses that the drive source of the recirculation pump with built-in reactor has been lost, and instantly starts up so that an attractive force acts between the electromagnet 36 and the permanent magnet 35. Made of The suction force at this time is the shaft 10, the impeller 11, and the thrust disc 2.
0, the rotor 7, and the permanent magnet 35 are not enough to pull up the rotor, but the force is sufficient to sufficiently reduce the contact resistance between the lower thrust bearing 22 and the thrust disk 20.

Therefore, also in this embodiment, the rotation resistance is reduced, and the rotation using the natural circulation force can be continued.

[0026]

As described above, according to the present invention, the rotational resistance of the bearing means that receives the thrust force of the shaft becomes small even if the power supply to the recirculation pump with built-in nuclear reactor is lost due to some factor. Therefore, it is possible to continue the rotation of the pump using the natural circulation force as the driving force, and as a result, the flow resistance of the impeller can be greatly reduced, which improves the natural circulation flow rate. It is possible to secure core stability and alleviate transient characteristics when the driving force is lost.

[Brief description of drawings]

FIG. 1 is an overall vertical sectional view showing a first embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view of a main part of FIG.

3 is a perspective view of a half portion of the rolling bearing of FIG.

FIG. 4 is an overall vertical sectional view showing a second embodiment of the present invention.

5 is an enlarged cross-sectional view of the main part of FIG.

FIG. 6 is an overall vertical sectional view showing a third embodiment of the present invention.

FIG. 7 is an overall vertical cross-sectional view of a conventional nuclear reactor built-in recirculation pump.

FIG. 8 is an enlarged sectional view of a conventional thrust bearing.

[Explanation of symbols]

 1 Reactor Pressure Vessel 2 Water Immersion Motor Section 3 Pump Section 5 Motor Casing 6 Stator 7 Rotor 8 Motor Cover 10 Shaft 11 Impeller 12 Shroud 13 Diffuser 14 Stretch Tube 16 Purge Water Piping 17 CRD Pump 18 Secondary Seal 10 Pressure Water Supply Pipe 20 Thrust Disc 21 Upper Thrust Bearing 22 Lower Thrust Bearing 24 Rolling Element 25 Inner Ring 26 Outer Ring 27 Cage 29 Pocket 30 Uninterruptible Power Supply 31 Auxiliary Purge Water Pump 32 Purge Water Source 35 Permanent Magnet 36 Electromagnet 37 Uninterruptible Power Supply A Rolling Bearing B B Blade pressure bearing

Claims (1)

[Claims] 1. A pump installed on the bottom surface of a reactor pressure vessel, a motor section for driving the pump, a shaft connecting the pump and the motor section, and bearing means for supporting the shaft in the thrust direction. A built-in-reactor recirculation pump, wherein a rolling or non-contact bearing is used as the bearing means.