JPH0587969A - Boiling water type nuclear reactor - Google Patents

Abstract

PURPOSE:To obtain a boiling water type nuclear rotor which utilizes an internal space of a nuclear reactor pressure vessel very effectively as well as increases extent of inertia and pump efficiency of an internal pump, and enables keeping the pump performance at fully available level. CONSTITUTION:A boiling water type nuclear rotor is equipped with a nuclear rotor pressure vessel 32 in which a reactor core 40 is provided, and internal pumps 75 provided with pump impellers 76 which are arranged in the nuclear reactor pressure vessel 32. A reactor core shroud 66 which extends downwardly penetrating through a center part of the rotor core 40, is installed, and the pump impellers 76 of the internal pumps 75 are provided at a lower part of the reactor core shroud 66. On the other hand, an opening part 67 reaching to the reactor core shroud 66 is opened at a center part of a shroud head 55, covering an upper part of the reactor core 40, and therewith reactor core outlet flow from the rotor core and downward flow in the rotor core shroud are well separated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a boiling water reactor equipped with an internal pump, and more particularly to an internal structure of a boiling water reactor in which a shroud and an internal pump are arranged in a reactor pressure vessel.

[0002]

2. Description of the Related Art In a boiling water reactor as a light water reactor, as a method of forcibly recirculating the reactor coolant in the reactor pressure vessel, a reactor recirculation system of an external loop system is used. Some have a pump and some have an internal pump as a recirculation pump in the reactor. Of these, the boiling water reactor equipped with an internal pump is shown in Fig. 7.
And as shown in FIG.

In this reactor, a reactor pressure vessel 1 contains a core portion 3 surrounded by a core shroud 2. The core part 3 holds a large number of fuel assemblies 6 by means of a core support plate 4 and an upper lattice plate 5. Four fuel assemblies 6 form a set, and a control rod 7 having a cross-shaped cross section is arranged between the fuel assemblies 6 of each set. The control rod 7 is driven up and down by a control rod drive mechanism 8 to be taken in and out of the core portion 3 from below.
Reference numeral 9 is a control rod guide tube, and the control rod pulled out from the core 3 is guided and accommodated in the control rod guide tube 9.

On the other hand, the fuel assembly 6 loaded in the core 3
9 is configured as shown in FIG. 9, and a fuel bundle 11 is housed in a channel box 10 having a rectangular tube shape. The fuel bundle 11 includes a water rod 12 and a large number of fuel rods 1.
3 are bundled by the upper and lower tie plates 14 and 15, and the spacers 16 keep the mutual spacing. A cooling water (coolant) flow path 17 is formed in the channel box 10 of the fuel assembly 6, and the channel box 1
A bypass flow path 18 is formed outside the zero.

As shown in FIG. 7, the upper part of the core 3 is covered with a shroud head 20, and a large number of steam separators 21 are planted in the shroud head 20 in a forested state. The gas-liquid two-phase flow generated in the core 3 is separated into high temperature water and steam.

The steam separated by the steam separator 21 is guided to an upper steam dryer 22 where moisture is removed,
Dry steam is sent from the steam outlet nozzle 23 to a steam turbine (not shown).

The steam that has worked in the steam turbine is cooled by a condenser (not shown) and becomes condensate. This condensate passes through the reactor condensate / water supply system and enters the water supply nozzle 24 in the reactor pressure vessel 1. Is injected through the water supply sparger 25.

This water supply is mixed with the high temperature water separated by the steam separator 21 and guided to the downcomer section 26. The downcomer section 26 includes the reactor pressure vessel 1 and the core shroud 2.
It is formed in an annular space with. Below the downcomer unit 26, a plurality of reactor recirculation pumps, for example, 10 to 1
Two internal pumps 27 are arranged at appropriate intervals in the circumferential direction. The reactor water (reactor coolant) guided to the downcomer section 26 by the internal pump 27 is pumped up and sent to the lower core plenum 28.

The reactor water sent to the lower core plenum 28 is
Upper opening of control rod guide tube 9 and fuel support fitting (not shown)
Is sent to the core 3 through the coolant inlet (orifice). Specifically, the lower tie plate 15 of the fuel assembly 6
(Refer to FIG. 9) and is guided to the cooling water flow path 17 in the channel box 10 through the inside. Part of the reactor water is the lower plate 1
It is guided to the bypass flow path 18 from the leak hole provided in 5. The reactor water (cooling water) guided to the cooling water flow path 17 is boiled by the heat generation of each fuel rod 13, rises in the cooling water flow path 17 and is mixed with the bypass flow in the upper plenum 29.

In the conventional 1.1 million KW class boiling water reactor, 10 to 12 internal pumps 27 are arranged below the narrow downcomer portion 26 sandwiched between the reactor pressure vessel 1 and the core shroud 2. Therefore, the diameter of the pump impeller 27a cannot be made large, and the diameter of the pump impeller is about 50 cm, which is relatively small. Since the small-diameter pump impellers 27a are discretely arranged in the circumferential direction, a large space is formed between the pump impellers of the internal pumps 27. This space becomes a dead space and is a useless space for effectively using the internal space in the reactor pressure vessel 1.

On the other hand, in the boiling water reactor, as shown in FIG. 8, a reflector region 3a having a thickness of about 30 cm is provided on the outer peripheral portion of the core 3, and the reactor pressure vessel 1 is formed by the reflector region 3a. Irradiation with fast neutrons is reduced. In the nuclear reactor, it is preferable that as many fuel assemblies 6 as possible can be arranged in the reactor pressure vessel 1 even if the reflector region 3a is secured in the vicinity of the reactor pressure vessel 1. It is preferable to make effective use of the internal space.

Further, since the internal pump 27 is arranged in the narrow space of the downcomer portion 26, the diameter of the pump impeller 27a is made small.
When the diameter of 7a is reduced, the pump efficiency is low, but the inertial amount is also low, and there is a problem that the core flow rate drops too rapidly when the internal pump 27 is stopped. Furthermore, since the diameter of the pump impeller 27a is small, the gap between the impellers is small, which causes a reduction in the natural circulation capacity of the core as compared with a boiling water reactor that employs a conventional jet pump.

In consideration of these points, the boiling water reactor disclosed in Japanese Patent Laid-Open No. 63-70196 has one large internal pump arranged at the center of the bottom of the reactor pressure vessel, and a pump In addition to increasing efficiency and inertia, the internal space inside the reactor pressure vessel is effectively used.

In this boiling water reactor, a cylindrical member is arranged so as to vertically penetrate through the center of the core, and the reactor water descending in this cylindrical member is fed to the lower plenum by a large central internal pump. ing.

[0015]

Problems to be Solved by the Invention JP-A-63-7019
In the boiling water reactor disclosed in Japanese Patent No. 3 publication, the shroud head is not provided, and the reactor water inlet of the cylindrical member opens directly into the upper plenum above the core, so that it boils in the core to the upper plenum. The guided gas-liquid two-phase flow is mixed with the feed water and guided by the cylindrical member, and becomes a downward flow and is sent to the lower plenum by the internal pump.

For this reason, the temperature of the reactor water sucked into the internal pump becomes high and cavitation is likely to occur in the internal pump, which may adversely affect the pump performance and the pump life of the internal pump.

Further, in the conventional boiling water reactor shown in FIGS. 7 and 8, there is a problem in effectively utilizing the internal space in the reactor pressure vessel, and further, the internal pump 27
Since the diameter of the pump impeller 27a is small, the pump efficiency and the inertial amount are small, and the core flow rate may be rapidly reduced when the internal pump 27 is stopped.

Furthermore, since this boiling water reactor has the downcomer portion 26 formed on the outer peripheral portion of the core, the core shroud 2 which divides the downcomer portion 26 and the core portion 3 becomes a considerably large internal structural material. The core shroud 2 has a large diameter, and the tensile strength acts on the inner and outer pressures of the shroud, the strength required to support the load of the upper lattice plate 5, and the lateral load on the reactor pressure vessel 1. Due to the requirement of strength for transmitting, for example, it is a heavy product made of a cylindrical tube having a considerably large thickness of about 5 cm.

The present invention has been made in consideration of the above-mentioned circumstances, and while effectively utilizing the internal space of the reactor pressure vessel, the inertial amount of the internal pump and the pump efficiency are increased to ensure sufficient pump performance. It is to provide a boiling water reactor that can be maintained at

Another object of the present invention is to provide a boiling water reactor in which the reactor output can be increased without increasing the diameter of the reactor pressure vessel.

Still another object of the present invention is to provide a boiling water reactor capable of preventing cavitation in the internal pump and maintaining pump performance for a long period of time.

Another object of the present invention is to provide a core shroud with
It is an object of the present invention to provide a boiling water reactor capable of exerting a compressive stress by applying pressure from the outside to reduce the shroud diameter and thin the wall to significantly reduce the weight.

Still another object of the present invention is to provide a peripheral internal pump in addition to the central internal pump to provide a plurality of internal pumps, and ensure the core flow rate even if the central internal pump should fail. Then, the core is cooled to provide a boiling water reactor with improved reliability.

[0024]

In order to solve the above-mentioned problems, a boiling water nuclear reactor according to the present invention is provided with a reactor pressure vessel having a reactor core therein as described in claim 1, and In a boiling water reactor having an internal pump provided with a pump impeller arranged in a reactor pressure vessel, a core shroud is provided which vertically extends through a central portion of the core and extends downward, and the core shroud is installed. While the pump impeller of the internal pump is provided in the lower part of the core, an opening into the core shroud is opened in the central part of the shroud head that covers the upper part of the core, and the core outlet flow from the core and the downward flow in the core shroud are It is separated.

Further, in order to solve the above-mentioned problems, the boiling water reactor according to the present invention has, as described in claim 2, a plurality of reactors in the outer peripheral portion of the core close to the inner peripheral wall of the reactor pressure vessel. Shroud pipes are arranged discretely, and pump impellers for peripheral internal pumps are installed at the bottom of each shroud pipe.The peripheral internal pumps are made smaller than the central internal pumps arranged on the center side of the core. is there.

Further, in this boiling water nuclear reactor, a swirl preventing flow straightening plate may be provided in the pump suction side passage of the core shroud.

[0027]

In this boiling water reactor, a core shroud that vertically penetrates the central portion of the core housed in the reactor pressure vessel is provided, and the pump impeller of the internal pump is provided below the core shroud. It is possible to prevent the formation of dead space outside the core shroud, to effectively utilize the internal space of the reactor pressure vessel, and to mount it inside the reactor pressure vessel without increasing the diameter of the reactor pressure vessel. The number of loaded fuel assemblies can be increased, and the reactor output can be increased.

Further, since an opening into the core shroud is opened in the central part of the shroud head covering the upper part of the core to separate the core outlet flow from the core and the downflow in the core shroud, the downflow is prevented. It is possible to prevent the liquid two-phase flow from being mixed. Therefore, it is possible to effectively prevent the temperature of the downflow from becoming high, prevent cavitation from occurring in the internal pump effectively, and maintain the pump performance for a long period of time, while maintaining the reactor performance. It is possible to prevent deterioration of the steam generation efficiency.

Furthermore, since the internal pump is installed in the core shroud in the lower central part of the reactor pressure vessel, the internal pump can be upsized, the pump efficiency can be improved, and the inertial amount can be increased. The pressure acting on the core shroud is a pressure from the outside to the inside, and a compressive stress acts, so that the core shroud can be made thinner and the weight can be significantly reduced in combination with the reduction of the shroud diameter.

Furthermore, since a plurality of peripheral internal pumps are provided in the reactor pressure vessel in addition to the central internal pump to make a plurality of internal pumps, if the central internal pump should fail. Moreover, since the core flow rate can be secured and the core can be cooled, the reliability of the nuclear reactor can be improved.

Further, when a large internal pump is arranged on the center side of the core and a swirling flow preventing flow straightening plate is installed in the pump suction side flow passage of the core shroud, swirling flow due to Coriolis force is prevented from occurring and pump efficiency is improved. Can be prevented. Moreover, since the impeller gap of the pump impeller can be increased by enlarging the internal pump, the natural circulation capacity is improved.

[0032]

An embodiment of a boiling water reactor according to the present invention will be described below with reference to the accompanying drawings.

1 to 3 show a first embodiment of a boiling water reactor according to the present invention. FIG. 1 is a sectional view showing a reactor building containing a boiling water reactor, FIG. 2 is a vertical sectional view of the boiling water reactor, and FIG. 3 is a plan view of a core portion of the boiling water reactor.

Reactor building 30 containing a boiling water reactor
Is constructed with a concrete skeleton, and a reactor containment vessel 31 is housed in the reactor building 30. Primary containment vessel 3
A reactor pressure vessel 32 is stored in the unit 1. This reactor pressure vessel 32 is a reactor pressure vessel support pedestal (hereinafter,
It is called RPV pedestal. ) Supporting skirt 34 on 33
And is covered with a cylindrical blocking wall 35. The blocking wall 35 is integrally erected on the RPV pedestal 33.

On the other hand, the inside of the reactor containment vessel 31 is vertically divided into a dry well 36 and a suppression chamber 37, of which the suppression chamber 37 is formed outside the RPV pedestal 33 and contains the suppression pool water. On the other hand, the dry well 36 is divided into an upper dry well 36 a formed above the suppression chamber 37 and a lower dry well 36 b formed inside the RPV pedestal 33. Upper dry well 36
The dry well head 38 partitions a from the reactor well 39.

The reactor pressure vessel 32 housed in the reactor containment vessel 31 is constructed as shown in FIG. 2, and the reactor core 40 is housed in the reactor pressure vessel 32. The core 40 is loaded with a large number of four fuel assemblies 6 in groups between the core support plate 41 and the upper lattice plate 42, and a cross-shaped cross-shaped control is provided between the fuel assemblies 6 of each group. The rod 44 is housed so that it can be freely inserted and removed from below the core. The core support plate 41 is a core support flange 4 provided on the lower inner wall of the reactor pressure vessel 32.
While the load is supported by bolting to No. 5, a large amount of coolant is suppressed from directly leaking from the lower core plenum 46 to the bypass region of the core 40 by flange joining. The upper lattice plate 42 is supported by the support bracket 47.

The control rods 44 are driven by a control rod drive mechanism 49 provided in the lower portion of the reactor pressure vessel 32. When the control rods 44 are pulled out from the reactor core 40 by the drive of the control rod drive mechanism 49, the control rods 44 are Is stored in the control rod guide tube 50 below the core. Control rod guide tube 5
0 is supported by a control rod drive mechanism housing 51 attached to the bottom of the reactor pressure vessel 32.

A lower core plenum 46 is formed below the core 40, while an upper plenum 54 is formed above the core 40 and is covered with an annular shroud head 55 so as to define the upper plenum 54. The outer peripheral portion of the shroud head 55 is joined and supported by a flange portion 56 provided on the inner wall of the reactor pressure vessel 32.

The shroud head 55 is provided with a number of steam-water separators 58 in a forested state via stand pipes 57. The steam-water two-phase flow generated in the core 40 at this steam-water separator 58 is used as water. Separated into steam.

The steam separated by the steam separator 58 is guided to the upper steam dryer 59, where moisture is removed and becomes dry steam. This dry steam is the steam outlet nozzle 6
0 to the steam turbine (not shown) via the reactor main steam system 61 (see FIG. 1).

The steam that has worked in the steam turbine is cooled by a condenser (not shown) to become condensate, and this condensate passes through the reactor condensate / water supply system 62 (see FIG. 1) and the water supply nozzle 63.
Is guided to the water supply sparger 6 from the water supply nozzle 63.
Water is supplied into the reactor pressure vessel 32 via No. 4. This water supply can mix the high temperature water separated by the steam separator 58.

On the other hand, a cylindrical core shroud 66 is provided in the central portion of the reactor core 40 housed in the reactor pressure vessel 32 so as to vertically penetrate therethrough. The core shroud 66 has an upper end extending from the upper grid plate 42 into the upper plenum 54, and a flange formed at the upper end is flanged to the central opening 67 of the shroud head 55. By opening a central opening 67 in the central portion of the shroud head 55, which opens into the core shroud 66, the core outlet flow from the core 40 and the downward flow in the core shroud 66 are completely separated.

Further, the lower end of the core shroud 66 is integrally or integrally supported by a shroud supporting leg 68 extending from the core supporting plate 41 through the lower core plenum 46 and provided at the bottom (end plate) of the tooth reactor pressure vessel 32. To be done.

The upper and lower ends of the core shroud 66 are made of, for example, short tubes made of stainless steel, and the effective core length between them is a cylinder made of zirconium alloy. In the core shroud 66, a swirl flow preventing flow straightening plate 70 is provided above the core 40. The current plate 70 may have various shapes such as a radial lattice, a square lattice, and a concentric disc.

Therefore, the core 40 is the reactor pressure vessel 32.
And a core shroud 66. A large number of four fuel assemblies 6 shown in FIG. 9 are arranged in this annular core 40, one group for each group, and a peripheral fuel assembly 71 is arranged on the outermost periphery of the core 40. In the peripheral fuel assembly 71, the flow rate of the fuel assembly coolant (cooling water) is restricted by the orifice.

Outside the peripheral fuel assembly 71, a non-boiling water region (reflection region) 72 of 30 cm or more is provided between the reactor pressure vessel and the reactor pressure vessel in order to reflect neutron flux and decelerate fast neutrons. The non-boiling water region 72 may be made up of stainless rods or plates in order to promote the decay of fast neutrons. In addition, the annular core 40 adjacent to the core shroud 66
The coolant flow rate of the innermost center fuel assembly 73 may be reduced by the orifice. The orifices of the fuel assemblies 71 and 73 may have different throttles.

A pump impeller 76 of an internal pump 75 is provided below the core shroud 66. The pump impeller 76 is housed in an impeller casing 78 attached to a pump deck 77. The impeller casing 78 plays the role of a diffuser.
A shroud support leg 79 below the pump deck 77 is provided with a water flow window communicating with the lower plenum. The shroud support legs 79 transmit the load acting on the core shroud 66 and the load of the pump deck 79 to the bottom of the reactor pressure vessel 32.

The internal pump 75 is larger than the internal pump 27 (see FIG. 7) installed in the conventional downcomer section, and one is installed below the core shroud 66. The pump shaft 80 supporting the pump impeller 76 of the internal pump 75 is connected to a pump motor 82 through the inside of the pump casing 81, and is rotationally driven by the pump motor 82. In the pump casing 81, an upper small diameter portion (shaft casing) 81a is fixed by welding or the like in a vertical state to a nozzle portion 84 provided in the central bottom portion of the reactor pressure vessel 32, and a lower large diameter portion serves as a motor casing 81b. The pump motor 8 is formed in the motor casing 81b.
2 is accommodated. The internal pump 75 is a wet type pump, but may be a dry type as described later and is not limited to a wet type internal pump.

Next, the operation of the boiling water reactor will be described.

The feed water supplied from the condenser (not shown) into the reactor pressure vessel 32 through the reactor condensate / feed water system 62 is injected from the feed water sparger 64 through the feed water nozzle 63. This feed water is mixed with the high temperature water separated by the steam separator 58 and the steam dryer 59, and is guided from the central opening 67 of the shroud head 55 into the pump suction side passage 85 of the core shroud 66.

The reactor water guided to the core shroud 66 is
After being rectified by the swirling flow prevention rectifying plate 70, it becomes a downward flow and passes through the pump suction side flow path 85, and then the internal pump 7
5, pumped up by the pump impeller 76, and sent to the lower core plenum 46 through the window.

The distribution of the flow of the reactor water (cooling water) entering the lower core plenum 46 is adjusted while passing through the lower core plenum 46, and the fuel support exposed in the upper opening of the control rod guide pipe 50 is supported. The fuel of the peripheral portion of the core 40 (the outermost peripheral portion and the innermost peripheral portion of the annular core) is provided by the orifice of the metal fitting (not shown in FIG. 1).
And after adjusting the flow rate to the intermediate fuel to the required ratio,
It is guided to the fuel assembly 6.

As shown in FIG. 9, the channel box 1 passes through the through hole of the lower tie plate 15 of the fuel assembly 6.
It is guided to the cooling water flow path 17 surrounded by 0. The water in the cooling water passage 17 boils due to the heat generation of the fuel rods, and the fuel assembly 6
In the cooling water flow path 17, the gas-liquid two-phase flow rises and enters the upper plenum 54. Part of the cooling water flows into the bypass flow passage 18 and mixes with the two-phase flow of the cooling water flow passage 17 in the channel box 10 in the upper plenum 54.

The upper plenum 54 is provided in order to uniformly mix the gas-liquid two-phase mixed flow coming out separately for each fuel assembly 6 before entering the stand pipe 57 of the steam separator 58. The gas-liquid two-phase mixed flow sent to the steam separator 58 is separated into steam and water by the centrifugal separation effect. The steam further enters the steam drier 59 to finally remove moisture in the steam, and then exits the reactor pressure vessel 32 from the plurality of steam outlet nozzles 60 of the reactor pressure vessel 32 to the steam turbine. Go to

On the other hand, the steam separator 58 and the steam dryer 5
The water separated in 9 merges with the feed water coming into the reactor pressure vessel 32 from the feed water sparger 64 on the outside of the stand pipe 57, descends in the core shroud 66 at the central portion, and reaches the internal pump 75. enter.

By the way, since the Coriolis force acts on the flow descending the core shroud 66 in the central portion, a swirling flow may occur and the flow velocity may decrease. However, a swirling flow preventing flow straightening plate 70 is provided at the inlet of the core shroud 66,
The generation of swirling flow is prevented, and the flow velocity is prevented from decreasing. In this embodiment, the current plate 70 is provided at the inlet of the core shroud 66 above the core, but the stand pipe 57 on the shroud head 55 may be radially connected by a current plate (not shown).

In the conventional nuclear reactor, as shown in FIG. 7, since the internal pump 27 is arranged in the narrow downcomer portion 26 sandwiched between the core shroud 2 and the reactor pressure vessel 1, the diameter of the impeller is relatively large. It is about 50 cm small. As a result of discretely arranging pumps of this small diameter in an annular shape,
A large space is formed between the internal pumps 27, which is a problem in effectively utilizing the internal space of the reactor pressure vessel 1, and there is a lot of wasted space.

However, in the boiling water reactor shown in FIG. 2 and FIG. 3, the empty space outside the conventional shroud 2 is reduced, and the reactor pressure can be increased without increasing the diameter of the reactor pressure vessel 32. The number of loaded fuel assemblies 6 in the container 32 is significantly increased. For example, in the core of a conventional type internal pump arrangement as shown in FIG. 8, the inner diameter of the reactor pressure vessel 1 is about 7.3 m and the fuel assembly pitch is about 19 m.
In the case of cm, only 624 fuel assemblies 6 could be arranged in the core 3, but according to this embodiment, a core shroud 66 having an inner diameter of about 2 m is provided in the center of the core and a large internal pump 75 is adopted. Thus, as shown in FIG. 3, 932 fuel assemblies 6 can be arranged in the reactor pressure vessel 32 having the same diameter.

As a result, it is possible to increase the capacity of the reactor without enlarging the inner diameter of the reactor pressure vessel 32 so much in response to the request for increasing the capacity of the reactor. Increasing the inner diameter of the reactor pressure vessel 32 necessarily increases the wall thickness of the reactor pressure vessel, and increasing the diameter of the reactor pressure vessel makes it impossible to manufacture the cylindrical portion of the reactor pressure vessel by integral forging. become,
The result is the use of a longitudinal (axial) welded reactor pressure vessel barrel. This will increase the number of countermeasures for inspecting the deterioration of the reactor pressure vessel due to the irradiation of fast neutrons, especially the deterioration of the weld. According to this embodiment, the manufacturing cost of the reactor pressure vessel is reduced, and it is useful for reducing the number of man-hours for the inspection of the welded portion of the reactor pressure vessel which should be performed during the regular inspection.

Conventionally, since the downcomer portion 26 is provided on the outer peripheral portion of the core, the core shroud 2 for partitioning the downcomer portion 26 and the core portion 3 is a considerably large in-core structural material. In particular, the core shroud 2 has a large diameter (about 6 to 7 m) in terms of strength with respect to internal and external differential pressure, a requirement for supporting the load of the upper lattice plate 5, and a reactor core 3 which supports the core 3 laterally. Although it is made of a stainless steel cylindrical tube having a considerable thickness (about 5 cm) in order to transmit the load, the cylindrical shroud 66 having an outer diameter of about 2 m is replaced in this embodiment. Therefore, the pressure applied to the core shroud 66 is a pressure from the outside to the inside, and a compressive stress acts, and the wall thickness can be significantly reduced in combination with the reduction of the shroud diameter.

Further, according to this embodiment, the core support plate 4
Since the load of No. 1 is supported by the central shroud support leg 79 and the core support plate support bracket 45 on the outer peripheral portion, the stress of the core support plate 41 is significantly smaller than the conventional one, and the lower reinforcing structure of the core support plate is smaller than the conventional one. It can be made small and simple.

Conventionally, since the internal pump 27 is arranged in a narrow space, the diameter of the pump impeller is made small so that the pump efficiency is low, the inertia is small, and the core flow rate is rapidly increased within a short time when the pump is stopped. There is a problem that the temperature drops too much and the heat removal of the fuel deteriorates. As a countermeasure, it is necessary to insert a small number of control rods to lower the core output when a few of the internal pumps have failed and to quickly insert control rods (scram) when the internal pumps have stopped a certain number or more. there were. Further, the small gap of the pump impeller of the internal pump 27 causes a decrease in the natural circulation capacity of the core as compared with a boiling water reactor of the type that employs a jet pump.

On the other hand, in this embodiment, the large internal pump 75 is arranged in the center of the core. In this internal pump 75, it is possible to reduce the pump rotational speed as compared with the conventional one, increase the twist angle of the pump impeller 76, and change the twist angle in the blade length direction to obtain the optimum impeller shape. As a result, pump efficiency is improved.
Further, the internal pump 75 is large in size, has a large inertia, and the reduction time constant of the core flow rate at the time of pump failure stop becomes long, whereby the reduction of the heat removal capacity is improved. As a result, the MG set required in the conventional nuclear reactor becomes unnecessary. In addition, the impeller gap can be increased, and the natural circulation capacity is improved.

Further, according to this embodiment, since there is no shroud inside the reactor pressure vessel 32 so as to surround the core 40, the piping for injecting cooling water into the core in the event of an accident becomes simple. For example, conventionally, in FIG. 7, high-pressure core water injection is required to be piped through the core shroud 2, so that the pipe entering from the high-pressure core water injection nozzle absorbs the difference in elongation between the core shroud 2 and the reactor pressure vessel 1 It has a piping structure that alleviates However, in the case of this embodiment, as shown in FIG. 2, such stress relaxation piping is unnecessary. In addition, low-pressure water injection can be easily made into a structure that can be sprayed directly onto the core. Furthermore, the reactor pressure vessel 32
When the water supply sparger 64 is provided on the inner wall, it becomes difficult for the spray water to reach the central portion of the core, but the annular core 40 reduces the distance to be sprayed, thus alleviating this problem.

In this embodiment, the upper end of the core shroud 66 is joined to the central opening of the shroud head 55 to separate the outlet flow of the gas-liquid mixed flow from the core and the suction flow into the internal pump 75. The high temperature water does not flow to the internal pump 75. Also, the reactor pressure vessel 3
(2) Since the mixed flow of the feed water from the feed water sparger 64 provided near the inner wall and the separated water from the gas-liquid mixed flow are guided to the core shroud 66 from the central opening of the shroud head 55, a swirling flow may be generated by the Coriolis force. But there is
This fear can be eliminated by installing the swirling flow preventing flow straightening plate 70.

By the way, in this embodiment, since the core effective portion of the core shroud 66 is made of a zirconium alloy which absorbs a small amount of neutrons, the core reactivity is more advantageous than that of stainless steel. Further, since the fuel assembly output in the center of the conventional core becomes too large by using the annular core 40, a fuel assembly having a low reactivity was arranged to cope with this, but this is not necessary. In addition, since there is a non-boiling water region in the center of the core, neutrons are well decelerated in the central shroud part in the part with a large void ratio in the upper part of the core, and the energy spectrum of the neutron flux becomes soft,
It is effective in flattening the axial output distribution and reducing the negative absolute value of the void coefficient. The loss effect of reactivity due to the existence of the over-deceleration region due to the large amount of non-boiling water in the central part is relatively small in the large core.

Next, a second embodiment of the boiling water reactor is shown in FIG.
And it demonstrates with reference to FIG.

In explaining the boiling water reactor,
The same members as those of the boiling water reactor shown in FIGS. 1 to 3 are designated by the same reference numerals and the description thereof will be omitted.

4 and 5, the drive motor 91, which is the pump motor of the internal pump 90, is isolated from the lower dry well 36b. The drive motor 91 is placed in an electric motor room 92 that can be entered during operation.
A table is provided, and each electric motor 91 includes a speed reducer 93 and a transmission gear 94.
Is connected to one pump shaft (not shown) housed in the shaft housing 95 via the shaft housing 95, and the rotational force of the drive motor 91 is transmitted to this pump shaft. The pump shaft is water-sealed by a shaft seal at the bottom of the furnace housed in the shaft sealing housing 96.

The speed reducer 93 of each drive motor 91 has a clutch mechanism, and when one of the motors 91 fails, the motor 91 on the failed side is automatically disconnected from the pump shaft.

As a result, the electric motor 91 can be an air motor (dry motor), and a highly reliable and efficient electric motor 91 can be selected. Further, even when one electric motor 91 is stopped due to a failure, the remaining one can continue the operation, so that the reliability of the continuation of the core cooling is further enhanced. In addition, maintenance management of the electric motor 91 during operation of the nuclear reactor becomes easy. In this example, the speed reducer 93 is added to the electric motor 91, but the speed reducer 93 may be deleted by reducing the design rotation speed of the electric motor 91. In this case, a clutch mechanism may be added to the transmission gear 94.

FIG. 6 shows a third embodiment of the boiling water reactor.

The boiling water reactor shown in this embodiment is
While one large internal pump 100 is arranged on the central side of the core as shown in FIGS. 1 and 2, even if the pump or motor of the central internal pump 100 should fail. In order not to lose the forced circulation ability of the reactor coolant (reactor water), a plurality of, for example, four, internal pumps similar to those shown in FIG. 7 are installed as the peripheral internal pumps 101.

In the peripheral internal pumps 101, pump impellers are incorporated in shroud pipes 102 discretely arranged on the outer peripheral portion of the core 40, and each peripheral internal pump 101 causes a part of the core flow rate (for example, 40% or less). Are covered.

The upper end of the shroud pipe 102 is connected to the peripheral opening of the shroud head by flange joining, and the cooling water is taken in from the peripheral opening of the shroud head.

The downward flow flowing in the shroud pipe 102 is separated from the core outlet flow by flange-joining the shroud pipe 102 to the shroud head.

The lower end of the shroud pipe 102 is supported by the lower mirror of the reactor pressure vessel 32 to support the load,
The cooling water pressurized by the pump impeller of the peripheral internal pump 101 is guided to the lower core plenum through the opening in the lower part of the shroud pipe 102.

By providing the peripheral internal pump 101 on the outer peripheral portion of the core 40 of the reactor pressure vessel 32, the number of loaded fuel assemblies 6 is reduced as compared with the boiling water reactor shown in FIGS. However, combining the large central internal pump 100 and the small internal pump 101,
By using a plurality of internal pumps, the core cooling capacity can be secured even in the unlikely event of failure of the central internal pump 100, and reliability is improved.

[0079]

As described above, in the boiling water reactor according to the present invention, the core shroud which vertically penetrates the central portion of the core housed in the reactor pressure vessel is provided, and the lower part of the core shroud is provided. Since the pump impeller of the internal pump is installed in the internal pump, it is possible to prevent the formation of dead space outside the core shroud, effectively utilize the internal space of the reactor pressure vessel, and increase the diameter of the reactor pressure vessel. Also, it is possible to increase the capacity by increasing the number of fuel assemblies mounted in the reactor pressure vessel and increase the reactor output.

Further, since an opening into the core shroud is opened at the center of the shroud head covering the upper part of the core to separate the core outlet flow from the core and the downflow in the core shroud, gas flow into the downflow Two-phase flow can be prevented from mixing in. Therefore, it is possible to effectively prevent the temperature of the downflow from becoming high, prevent cavitation from occurring in the internal pump in advance and effectively, maintain pump performance, and improve pump reliability. It is also possible to prevent deterioration of steam generation efficiency of the nuclear reactor.

Further, since the internal pump is installed in the core shroud which is arranged in the center of the core in the lower center of the reactor pressure vessel, the internal pump can be increased in size and the pump efficiency can be improved. While the amount of inertia can be increased, the pressure acting on the core shroud is the pressure from the outside to the inside, and compressive stress acts.Therefore, the core shroud should be thinned in combination with the reduction of the shroud diameter. It is possible to significantly reduce the weight.

Further, when the peripheral internal pumps are set on the outer periphery of the core, the core flow rate can be secured and core cooling can be performed even in the unlikely event of a failure of the central internal pump, thus improving reliability. Can be planned.

[Brief description of drawings]

FIG. 1 is a sectional view showing a reactor building equipped with a boiling water reactor according to the present invention.

FIG. 2 is a vertical sectional view showing an embodiment of a boiling water reactor according to the present invention.

3 shows a core structure of the boiling water reactor shown in FIG. 2, and is a plan view taken along line III-III of FIG.

FIG. 4 shows a second embodiment of the boiling water reactor according to the present invention, and is a cross-sectional view of a reactor building equipped with the boiling water reactor.

FIG. 5 is a vertical sectional view showing a second embodiment of a boiling water reactor according to the present invention.

FIG. 6 is a vertical sectional view showing a third embodiment of the boiling water reactor according to the present invention.

FIG. 7 is a vertical cross-sectional view showing a conventional boiling water reactor.

FIG. 8 is a diagram showing the core structure of a conventional boiling water reactor of FIG.
The top view which follows the VIII-VIII line.

FIG. 9 is a vertical cross-sectional view showing a fuel assembly loaded in the core of a boiling water reactor.

[Explanation of symbols]

 6 Fuel Assembly 30 Reactor Building 31 Reactor Containment Vessel 32 Reactor Pressure Vessel 33 Reactor Pressure Vessel Support Pedestal 36 Drywell 37 Suppression Chamber 40 Core 41 Core Support Plate 42 Upper Lattice Plate 46 Core Lower Plenum 49 Control Rod Drive Mechanism 54 Upper Plenum 55 Shroud Head 58 Steam Separator 59 Steam Dryer 61 Reactor Main Steam System 62 Reactor Condensation / Water Supply System 66 Core Shroud 67 Openings 68 Shroud Support Legs 70 Swirling Flow Prevention Rectifiers 75, 90 Inter Null pump 76 Pump impeller 78 Impeller casing 79 Pump support leg 91 Drive motor 92 Reducer 93 Transmission gear 100 Central internal pump 101 Peripheral internal pump 102 Shroud pipe

Claims (2)

[Claims] 1. A reactor pressure vessel having a core provided therein,
In a boiling water reactor having an internal pump provided with a pump impeller arranged in this reactor pressure vessel, a core shroud is installed extending vertically downward through the central portion of the core, and the core shroud is installed. While installing the pump impeller of the internal pump at the bottom of the shroud,
A boiling water reactor characterized in that an opening into the core shroud is opened in the central part of the shroud head covering the upper part of the core, and a core outlet flow from the core and a downward flow in the core shroud are separated. . 2. A plurality of shroud pipes are discretely arranged on an outer peripheral portion of a core adjacent to an inner peripheral wall of a reactor pressure vessel, and a pump impeller of a peripheral internal pump is incorporated in a lower portion of each shroud pipe to form the peripheral internals. The boiling water reactor according to claim 1, wherein the pump is smaller than the central internal pump arranged on the central side of the core.