JP5666793B2 - Internal pump and boiling water reactor - Google Patents

Description

  The present invention relates to an internal pump and a boiling water reactor.

  In an improved boiling water reactor (ABWR), a plurality of internal pumps are provided at the bottom of the reactor pressure vessel. An internal pump impeller is disposed in an annular downcomer formed between the reactor pressure vessel and a core shroud installed in the reactor pressure vessel. A core loaded with a plurality of fuel assemblies is disposed inside the core shroud.

  The internal pump has a motor casing, a motor, a shaft, and an impeller (see Japanese Patent Application Laid-Open No. 64-11837). A motor casing is provided at the bottom of the reactor pressure vessel and extends downward. A motor is installed in the motor casing, a shaft rotated by the motor extends upward and reaches the reactor pressure vessel, and an impeller is attached to the upper end portion of the shaft. The lower end of the shaft is supported by the lower radial bearing, and the center is supported by the upper radial bearing. These bearings suppress vibration in the radial direction of the shaft during rotation.

  In order to prevent high-temperature cooling water in the reactor pressure vessel from flowing into the motor casing during operation of the reactor, purge water is supplied from a purge water supply pipe connected to the motor casing above the upper end of the motor. It is fed into the motor casing. This purge water rises through an annular passage formed between the shaft and the stretch tube surrounding the shaft, and is guided into the reactor pressure vessel.

  A labyrinth is provided on the inner surface of the stretch tube. This labyrinth has a function of slowing the flow of purge water and increasing the temperature of purge water. For this reason, the purge water whose temperature has risen sufficiently is introduced into the reactor pressure vessel, so the temperature of the purge water that is in contact with the lower part of the shaft of the internal pump and the purge water that is in contact with the upper part of the shaft The temperature gradient of the temperature can be made gentle. Thereby, the thermal fatigue of a shaft can be reduced.

  In order to increase the temperature of the purge water, it is proposed in Japanese Patent Laid-Open No. 1-210897 to form a spiral groove on the inner surface of the stretch tube. For the same purpose, Japanese Patent Laid-Open No. 1-182597 proposes forming a spiral groove on the outer surface of the shaft.

Japanese Unexamined Patent Publication No. 64-11837 Japanese Patent Laid-Open No. 1-210897 JP-A-1-182597

  Since the internal pump is not provided with a radial bearing at the upper part of the shaft, the upper part of the rotary body of the internal pump is likely to overhang. For this reason, in order to increase the critical speed of the rotating body, the internal pump employs a structure in which the mass of the lower part of the rotating body is increased.

  In such an internal pump, when the impeller is enlarged in order to increase the capacity of the internal pump, it is necessary to increase the mass of the lower part of the rotating body. For this reason, the whole internal pump will be enlarged.

  An object of the present invention is to provide an internal pump and a boiling water reactor capable of increasing the critical speed.

The features of the present invention that achieve the above-described objects are: a motor installed in a motor casing; a shaft disposed in the motor casing and rotated by the motor; an impeller attached to the shaft outside the motor casing; A cylindrical stretch tube disposed between the motor casing and the shaft and surrounding the shaft;
Purge water supplied into the internal pump is led to the end of the stretch tube on the impeller side, and an underwater bearing for supporting the shaft is provided.

  The shaft is supported by the underwater bearing at the end of the stretch tube on the impeller side by providing an underwater bearing to which the purge water supplied into the internal pump is guided at the end of the stretch tube on the impeller side. Therefore, the eccentricity of the shaft at the end portion on the impeller side can be suppressed. For this reason, the critical speed of the internal pump can be increased.

  According to the present invention, the critical speed of the internal pump can be increased.

It is a longitudinal cross-sectional view of the internal pump of Example 1 which is one suitable Example of this invention. It is an enlarged view of the II section of FIG. FIG. 3 is a sectional view taken along line III-III in FIG. 2. It is IV-IV sectional drawing of FIG. It is explanatory drawing which shows the state in which the shaft of the internal pump of Example 1 was eccentric. It is a longitudinal cross-sectional view of the shaft upper end part vicinity of the internal pump in Example 2 which is another Example of this invention. It is VII-VII sectional drawing of FIG.

  Examples of the present invention will be described below.

  An internal pump which is a preferred embodiment of the present invention will be described with reference to FIGS. 1, 2, 3 and 4. The internal pump 4 of this embodiment is applied to ABWR and includes a motor casing 5, a motor 6, a shaft 7, and an impeller 8.

  The motor casing 5 is attached to the bottom of the reactor pressure vessel 1 via a nozzle 11 and extends downward from the reactor pressure vessel 1. A motor 6 is installed in the motor casing 5. A shaft 7 rotated by a motor 6 extends upward and penetrates the bottom of the reactor pressure vessel 1. A diffuser 9 is disposed in an annular downcomer 3 formed between the reactor pressure vessel 1 and a core shroud 2 installed in the reactor pressure vessel 1. The impeller 8 is disposed in the diffuser 9 and attached to the upper end portion of the shaft 7. A stretch tube 10 surrounds the shaft 7 and is disposed between the shaft 7 and the motor casing 5. The stretch tube 10 has a function of fixing the diffuser 9 to the reactor pressure vessel 1, directly to the nozzle 11.

  The lower end of the shaft 7 is supported by the lower radial bearing 12 and the center is supported by the upper radial bearing 13. A purge water supply pipe 14 is connected to the motor casing 5 above the upper radial bearing 13.

  A cylindrical bearing member 16 is disposed between the upper end portion of the stretch tube 10 and the shaft 7, and the upper end portion of the bearing member 16 is installed on the stretch tube 10. The bearing member 16 surrounds the shaft 7. An underwater bearing 25 is disposed at the end of the stretch tube 10 on the impeller 8 side, and is provided on the bearing member 16. Since the bearing member 16 is provided in the stretch tube 10, it can be said that the underwater bearing 25 is provided in the stretch tube 10. The underwater bearing 25 has a plurality of pocket portions 17 and a plurality of through holes 15 and 18, respectively. Four pocket portions 17 that are recessed portions face the inner surface of the shaft 7, and four pocket portions 17 are formed on the inner surface of the bearing member 16 at 90 ° intervals in the circumferential direction of the bearing member 16. Four through holes 18 are formed in the bearing member 16 in the radial direction, and each through hole 18 communicates with each pocket portion 17 separately. Four through-holes 15 are formed in the stretch tube 10 at 90 ° intervals in the circumferential direction of the stretch tube 10. Each through hole 15 communicates with each through hole 18 separately. An annular gap 20 communicated with the purge water supply pipe 14 is formed between the inner surfaces of the nozzle 6 and the motor casing 5 and the outer surface of the stretch tube 10.

  The stretch tube 10 has a stepped portion 22 at the upper end. For this reason, the inner diameters of the stretch tube 10 and the bearing member 16 can be made substantially the same, and the bearing member 16 can be accommodated in the stretch tube 10. The lower end of the bearing member 16 contacts the upper surface of the step portion 22. The thickness of the stretch tube 10 above the step portion 22 is thicker than its thickness below the step portion 22.

  An annular gap 21 is formed between the inner surfaces of the bearing member 16 and the stretch tube 10 and the outer surface of the shaft 7. Each pocket portion 17 is opened to the annular gap 21. Four grooves 19 are formed on the inner surfaces of the bearing member 16 and the stretch tube 10 in the circumferential direction of the shaft 7 and extend in the axial direction of the shaft 7. These grooves 19 are arranged between the pocket portions 17 in the circumferential direction of the shaft 7. The upper ends of the groove 19 and the annular gap 21 are communicated with the reactor pressure vessel 1.

  A labyrinth 23 is formed on the inner surface of the stretch tube 10 at the lower end of the stretch tube 10 (see FIG. 4). A through-hole 24 is formed in the stretch tube 10 below the labyrinth portion 23 in the circumferential direction of the stretch tube 10. The through holes 24 communicate with the purge water supply pipe 14 through the annular gap 20 and the groove 19. In order to increase the flow resistance of the annular gap 20 so that most of the purge water supplied from the purge water supply pipe 14 flows through the through hole 24, the annular gap 20 is throttled above the through hole 24. Yes. A purge water supply pipe 14 communicates with the annular gap 20.

  A plurality of control rod drive mechanism housings (hereinafter referred to as CRD housings) (not shown) pass through the bottom of the reactor pressure vessel 1 and are installed in the reactor pressure vessel 1. A control rod drive mechanism (hereinafter referred to as CRD) (not shown) is installed in each CRD housing. The CRD is connected to a control rod (not shown) that is disposed in the reactor pressure vessel 1 and controls the reactor power. In order to prevent the high-temperature cooling water in the reactor pressure vessel 1 from flowing into the CRD housing and coming into contact with the CRD, ABWR includes a CRD purge water system (not shown) for supplying purge water into the CRD housing. ing. The CRD purge water system has a purge water pipe (not shown) for guiding the purge water, and this purge water pipe is connected to the CRD housing. The purge water supply pipe 14 is connected to the purge water pipe of the CRD purge water system.

  During the operation of ABWR, the internal pump 4 is driven. That is, the motor 6 is driven, the shaft 7 rotates, and the impeller 8 rotates. The cooling water in the downcomer 3 is boosted by the rotation of the impeller 8, discharged from the diffuser 9, and guided into the core shroud 2. This cooling water is supplied to a core surrounded by the core shroud 2 and loaded with a plurality of fuel assemblies. The cooling water is heated by heat generated by fission of nuclear fuel material existing in the fuel assembly, and a part thereof becomes steam. The gas-liquid two-phase flow containing the steam discharged from the core is guided to the steam separator in the reactor pressure vessel 1 to separate the steam. The separated steam is exhausted from the reactor pressure vessel 1 and supplied to a turbine (not shown). Among the gas-liquid two-phase flow, the separated cooling water descends the downcomer 3 together with the water supplied to the reactor pressure vessel 1 and is pressurized by the internal pump 4.

  While the internal pump 4 is being driven, the purge water supplied into the CRD housing is guided into the CRD housing by the purge water piping of the CRD purge water system. Since the purge water supplied into the CRD housing is discharged into the reactor pressure vessel 1, this purge water is supplied to the reactor pressure vessel by a pump (not shown) provided in the purge water piping of the CRD purge water system. The pressure is raised to a pressure higher than the pressure of the cooling water in 1. A part of the purge water flowing in the purge water pipe of the CRD purge water system is supplied into the annular gap 20 from the purge water supply pipe 14 as purge water for the internal pump 4. This purge water is a part of the purge water supplied into a CRD housing (not shown) provided at the bottom of the reactor pressure vessel. Most of the purge water supplied into the annular gap 20 is guided into the groove 19 through the through hole 24. The purge water rises through the grooves 19 and the annular gap 21 and flows into the reactor pressure vessel 1. The flow rate of the purge water that rises in each groove 19 and the annular gap 21 is decelerated in the labyrinth portion 23, and the purge water rise rate decreases. The purge water rises in temperature while passing through the labyrinth portion 23, and as described above, thermal fatigue of the shaft 7 can be reduced. The purge water that rises in each groove 19 and the annular gap 21 functions as seal water that prevents high-temperature cooling water in the reactor pressure vessel 1 from flowing into the motor casing 5.

  A part of the purge water supplied into the annular gap 20 rises in the annular gap 20 and is guided to the pocket portions 17 through the respective through holes 15 and 18. The through holes 15 and 18 are purge water supply passages for supplying purge water to the pocket portion 17.

  When the axis of the shaft 7 coincides with the axis of each of the stretch tube 10 and the bearing member 16, the shaft 7 of the annular gap 21 formed between the outer surface of the shaft 7 and the inner surface of the bearing member 16 is used. The width in the radial direction is the same in the circumferential direction of the shaft 7. For this reason, the flow rates of the purge water supplied from the through holes 15 and 18 corresponding to the four pocket portions 17 existing in the circumferential direction of the shaft 7 and the pressures of the pocket portions 17 become equal.

  However, as shown in FIG. 5, when the rotating shaft 7 is eccentric in the direction of the arrow A, the shaft 7 moves from the pocket portion 17b to the pocket portion 17a. The width of the gap between the outer surface of the shaft 7 and the inner surface of the bearing member 16 on the pocket portion 17a side is narrower than the width of the gap between the outer surface of the shaft 7 and the inner surface of the bearing member 16 on the pocket portion 17b side. . For this reason, the flow rate of the purge water supplied from the corresponding through holes 15 and 18 into the pocket portion 17a decreases, and the pressure in the pocket portion 17a increases. The flow rate of the purge water supplied from the corresponding through holes 15 and 18 into the pocket portion 17b increases, and the pressure in the pocket portion 17b decreases. As the pressure in the pocket portion 17a increases and the pressure in the pocket portion 17b decreases, the pressure in the pocket portion 17a becomes higher than the pressure in the pocket portion 17b. These pressure differences cause the eccentric shaft 7 to move in the direction opposite to the arrow A, that is, toward the pocket portion 17b where the pressure is low. The movement of the shaft 7 in the direction opposite to the arrow A stops at a position where the pressure in the pocket portion 17a is equal to the pressure in the pocket portion 17b.

  As described above, when the shaft 7 is eccentric, the pressure in one of the two pocket portions 17 that are opposed to each other across the shaft 7 is lower than the pressure in the other pocket portion 17. The shaft 7 moves toward the pocket portion 17 where the pressure is low, and the eccentricity of the shaft 7 is suppressed. Since the shaft 7 is supported by the underwater bearing 25 at the position of the upper end portion of the stretch tube 10 of the shaft 7, eccentricity at the upper end portion of the shaft 7 can be suppressed. Thereby, the critical speed of the internal pump 4 can be increased.

  In this embodiment, the bearing member 16 having four pocket portions 17 formed on the inner surface in the circumferential direction is disposed in the vicinity of the nozzle 11 to which the motor casing 5 is attached. Shaking is performed. For this reason, the internal pump 4 does not need to increase the mass of the lower part of a rotary body, and can be reduced in size.

  In the present embodiment, the underwater bearing 25 that supports the upper end portion of the shaft 7 includes a plurality of pocket portions 17 and through holes 15 and 18 that supply part of the purge water to the pocket portions 17. Since the shaft 7 does not contact the stretch tube 10 and the bearing member 16 by configuring the bearing having the plurality of pocket portions 17, the frequency of replacement of these members due to wear can be reduced.

  The purge water supplied to each pocket portion 17 is purge water supplied into the CRD housing as described above. For this reason, the purge water is boosted to a pressure higher than the pressure of the cooling water in the reactor pressure vessel 1 by a pump provided in the purge water piping of the CRD purge system. A part of the high-pressure purge water supplied into the CRD housing can be supplied to the pocket portion 17 through the purge water supply pipe 14 and the annular gap 20 and through the through holes 15 and 18. In this embodiment, a plurality of pocket portions 17 and a plurality of through holes 18 are formed in the bearing member 16, and further, the through holes 15 are formed in the stretch tube 10. An underwater bearing 25 that supports the upper end can be provided. Since the underwater bearing 25 having such a simple configuration can be formed in the internal pump 4 in the vicinity of the upper end portion of the shaft 7, the configuration of the upper end portion of the internal pump 4 can be simplified.

  If the purge water is not supplied to the pocket portions 17, it is also conceivable to supply the cooling water pressurized by the impeller 8 to the respective pocket portions 17. In this case, it is necessary to form in the internal pump 4 a passage for guiding the cooling water pressurized by the impeller 8 to the pocket without intersecting the groove 19 and the gaps 20 and 21. Such a passage is difficult to form. When such a passage can be formed, the shape of the upper end portion of the internal pump becomes complicated. In addition, the temperature of the cooling water boosted by the impeller 8 is significantly higher than the temperature of the purge water. Supplying such high-temperature cooling water to the pocket portion 17 to approach the motor 6 This will increase the amount of heat input to. In this embodiment, since a part of the purge water supplied into the CRD housing is supplied to the pocket 17, the purge water is prevented from flowing into the motor casing 5 by the purge water. In addition, the amount of heat input to the motor 6 can be significantly reduced.

  It is also conceivable to support the upper end portion of the shaft 7 by a radial bearing that supports the lower end portion of the shaft 7. When a radial bearing is disposed at a position where the pocket portion 17 is disposed instead of forming the pocket portion 17 or the like of the underwater bearing 25, the following problems occur. (1) Since the formation position of the pocket portion 17 is close to the reactor pressure vessel 1, (a) it is necessary to lower the temperature around the radial bearing to a temperature that the radial bearing can withstand, and (b) around the radial bearing. When the temperature of the purge water supplied between the shaft 7 and the stretch tube 10 is lowered to lower the temperature, an abrupt temperature gradient is generated at the upper portion of the shaft 7 and the thermal fatigue potential of the shaft 7 increases. (2) Since the radial bearing is periodically replaced, it is not preferable to install the radial bearing in the vicinity of the reactor pressure vessel 1 having a high dose. On the other hand, since the underwater bearing 25 is not frequently replaced and has a high heat-resistant temperature, it is not necessary to lower the temperature around the underwater bearing 25.

  An internal pump according to another embodiment of the present invention will be described with reference to FIGS. The internal pump 4A of the present embodiment has a configuration in which the bearing member 16 is deleted from the internal pump 4 of the first embodiment, the stretch tube 10 is replaced with the stretch tube 10A, and the underwater bearing 25 is replaced with the underwater bearing 25A. The other structure of the internal pump 4A is the same as that of the internal pump 4. The internal pump 4A is also applied to ABWR. A description will be given focusing on a portion of the internal pump 4A different from the internal pump 4, that is, an underwater bearing.

  The underwater bearing 25A is provided in the stretch tube 10A. The underwater bearing 25 </ b> A has a plurality of pocket portions 17 and a plurality of through holes 15. Four pocket portions 17 face the outer surface of the shaft 7 and are formed on the inner surface of the stretch tube 10A. The four pocket portions 17 are arranged at intervals of 90 ° in the circumferential direction of the stretch tube 10A as in the first embodiment. Each through hole 15 communicated with each pocket portion 17 is communicated with an annular gap 20. In the present embodiment, the stretch tube 10 </ b> A also has the function of the bearing member 16 of the internal pump 4 of the first embodiment.

  During the operation of ABWR, the internal pump 4 is driven. Purge water rising in the annular gap 20 is supplied into the respective pocket portions 17 through the respective through holes 15. Also in this embodiment, as shown in FIG. 5, when the shaft 7 is eccentric, the pressure of the pocket portion 17a becomes higher than the pressure of the pocket portion 17b. Can be suppressed.

  In the present embodiment, each effect produced in the first embodiment can be obtained. Furthermore, since the bearing member 16 does not need to be installed in this embodiment, the structure of the internal pump can be simplified as compared with the first embodiment.

  The present invention can be applied to a boiling water reactor.

  DESCRIPTION OF SYMBOLS 1 ... Reactor pressure vessel, 4 and 4A ... Internal pump, 5 ... Motor casing, 6 ... Motor, 7 ... Shaft, 8 ... Impeller, 10 ... Stretch tube, 15, 18, 24 ... Through-hole (purge water supply passage) ), 16 ... bearing member, 17 ... pocket part, 20, 21 ... annular gap, 23 ... labyrinth part, 25, 25A ... underwater bearing.

Claims (3)

A motor casing; a motor installed in the motor casing; a shaft disposed in the motor casing and rotated by the motor; an impeller attached to the shaft outside the motor casing; and the motor casing And a cylindrical stretch tube disposed between the shafts and surrounding the shafts,
Purging water supplied into the internal pump is guided to an end of the stretch tube on the impeller side, and an underwater bearing that supports the shaft is provided.
An annular gap is formed between the inner surface of the stretch tube and the shaft;
The underwater bearing includes a plurality of indentations formed on an inner surface of the stretch tube and disposed in a circumferential direction, open to the annular gap and facing the outer surface of the shaft;
A first purge water supply passage connected to the barge water supply pipe for supplying the purge water connected to the motor casing passes through the stretch tube below the recess and is connected to the annular gap. And
The submersible bearing is formed between the motor casing and the stretch tube to communicate the gap through which the purge water flows and the recess, and the first purge water supply passage formed in the stretch tube internal pump, characterized in that it includes another second purge water supply passage. A motor casing; a motor installed in the motor casing; a shaft disposed in the motor casing and rotated by the motor; an impeller attached to the shaft outside the motor casing; and the motor casing A cylindrical stretch tube disposed between the shaft and surrounding the shaft; and disposed between the stretch tube and the shaft so as to surround the shaft; and provided at an end of the stretch tube on the impeller side A cylindrical bearing member formed,
Purging water supplied into the internal pump is guided to an end of the stretch tube on the impeller side, and an underwater bearing that supports the shaft is provided.
An annular gap is formed between each of the inner surface of the stretch tube and the inner surface of the bearing member and the shaft;
The underwater bearing includes a plurality of indentations formed on an inner surface of the bearing member and disposed in a circumferential direction, open to the annular gap and facing the outer surface of the shaft;
A first purge water supply passage connected to the barge water supply pipe for supplying the purge water connected to the motor casing passes through the stretch tube below the recess and is connected to the annular gap. And
The submersible bearing is formed between the motor casing and the stretch tube to communicate the gap through which the purge water flows and the recess, and the first purge water is formed in the stretch tube and the bearing member. internal pump, characterized in that it includes another second purge water supply passage and the supply passage. A reactor pressure vessel, an internal pump provided at the bottom of the reactor pressure vessel, and a control rod drive mechanism provided in a plurality of control rod drive mechanism housings provided at the bottom of the reactor pressure vessel; A cooling water pipe that communicates with the control rod drive mechanism housing and guides cooling water supplied into the control rod drive mechanism housing;
The internal pump is an internal pump according to claim 1 or 2 ,
A boiling water reactor, wherein a purge water supply pipe connected to the cooling water pipe and guiding the purge water as the cooling water is connected to the motor casing.

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