JP2011069751A - Chimney of natural circulation type boiling water reactor, fuel exchange method of natural circulation type boiling water reactor using the same, inspection method of natural circulation type boiling water reactor using the same, and natural circulation type boiling water reactor using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve structural stiffness of a cross-sectional periphery of a chimney and to facilitate mounting and dismounting, while maintaining a structure that enables removal of only a lattice part at the time of fuel exchange or inspection. <P>SOLUTION: The chimney structure of a natural circulation type boiling water reactor including a core loaded with a plurality of fuel assemblies forming a circular cross section and a chimney 11 located above the core has the following characteristics. The chimney includes: a chimney trunk 11d; and a plurality of lattice channels 11a and lattice channels partitioned by channel bulkheads 11b1 removable from the chimney structure and channel bulkheads 11b2 joined to the chimney trunk 11d, which are vertically disposed in the chimney trunk 11d; wherein all of the channel bulkheads 11b1 make angles and have a closed structure. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a chimney provided in a natural circulation boiling water reactor.

  In a forced circulation boiling water reactor (hereinafter referred to as BWR) that has been commercially operated so far, a fuel assembly having a square cross section is placed in a X axis direction and a Y direction (both in a cylindrical core shroud). The core is composed of forests arranged horizontally. A control rod having a substantially cross-shaped cross section is disposed so as to be insertable between four fuel assemblies surrounding the periphery of the control rod. A unit of the four fuel assemblies surrounding the control rod is called a control rod cell. .

  In recent years, a natural circulation type BWR has been proposed. In the natural circulation type BWR, a chimney that does not exist in the forced circulation type BWR is provided on the core in order to secure a driving force for natural circulation (see, for example, Patent Document 1). The chimney described in Patent Document 1 has a configuration in which a flow path partition wall is configured by a partition plate to have a plurality of lattice flow paths. In that case, the coolant flow rate distributed to the individual fuel assemblies is distributed to each fuel assembly when it flows into the core from the lower plenum, cooling the fuel assembly to become a gas-liquid two-phase flow of coolant, Fuel assembly pressure loss and lattice after the individual fuel assemblies are merged in the chimney lattice channels and after passing through the chimney, until the entire gas-liquid two-phase flow in each lattice channel is merged in the upper plenum. It is determined by the driving force due to the difference in specific gravity of the coolant mainly determined by the pressure loss of the flow path and the void ratio in the lattice flow path.

In addition, the following literature is mentioned about chimney. For the attachment and detachment of the chimney cylinder and the chimney grid, an upper support plate having a channel opening at the upper end of the channel partition wall and a lower support plate having a channel opening at the lower end of the channel partition wall are provided. There is also an example in which a wedge is driven in between and the chimney flow path forming portion is supported in the horizontal direction. (For example, see Patent Document 2)
Further, with regard to the strengthening of the chimney structure, there is an example in which the middle of one side of the chimney cross-sectional rectangle is supported by one side of the adjacent cross-sectional rectangle (for example, see Patent Document 3).

  Further, there is an example in which the chimney lattice is partially detachable as a rectangular tube (see, for example, Patent Document 4).

Japanese Patent Publication No. 7-27051 JP 2007-232546 A JP 2007-232434 A JP 2007-232421 A

  In order to ensure the safety of nuclear reactors, it is necessary to periodically inspect the reactor. In addition, work in the furnace is also required when changing fuel. Chimney must be removed and installed during inspections and fuel changes in these furnaces. Therefore, it is necessary to remove the chimney and to have good mountability. For easy removal and installation, it is desirable that only the chimney grid portion can be taken out.

  Therefore, the problem to be solved by the present invention is to reduce the weight of the chimney structure taken out during work.

  The present invention adopts the following means in order to solve the above problems. A chimney of a natural circulation boiling water reactor comprising a core in which a cross section of a plurality of fuel assemblies is loaded in a circular shape, and a chimney installed on the core, wherein the chimney has a chimney body A plurality of grid channels defined by channel partitions suspended in the chimney cylinder, and a part of the channel partitions defining the plurality of grid channels are joined to the inner surface of the chimney cylinder. The chimney of a natural circulation boiling water reactor, wherein the remainder of the flow path partition walls that divide the plurality of lattice flow paths is detachable from the chimney structure.

  In the present invention, a part of the flow path partition wall is left on the inner surface of the chimney cylinder when the fuel is changed or inspected, so that the weight of the lattice part to be removed at the time of changing the fuel or inspecting can be reduced.

1 is a longitudinal sectional view of a natural circulation boiling water reactor according to an embodiment of the present invention. It is a cross-sectional view showing a chimney structure in a conventional natural circulation type BWR. (A) is a top view of the chimney of the natural circulation type boiling water reactor which concerns on one Embodiment of this invention, (b) is a longitudinal cross-sectional view of (a). FIG. 4 is a cross-sectional view of a chimney of a natural circulation boiling water reactor according to an embodiment of the present invention, and is an XX cross-sectional view of FIG. 3. It is a side view of the chimney of the natural circulation type boiling water reactor which concerns on one Embodiment of this invention, (a) is a cross-sectional view of the flow-path partition part which can be attached or detached from a chimney structure, (b) is (a). It is a cross-sectional view of the chimney after removing). (A) is a top view of the chimney of the natural circulation type boiling water reactor which concerns on one Embodiment of this invention, (b) is a longitudinal cross-sectional view of (a). It is a cross-sectional view of the chimney of the natural circulation boiling water reactor according to an embodiment of the present invention, and is a cross-sectional view taken along the line XX of FIG. It is a side view of the chimney of the natural circulation type boiling water reactor which concerns on one Embodiment of this invention, (a) is a cross-sectional view of the flow-path partition part which can be attached or detached from a chimney structure, (b) is (a). It is a cross-sectional view of the chimney after removing).

  The present invention has the above-described features, but other features include the following points.

  Another object of the present invention is to perform a fuel change and inspection work without removing the entire chimney. Therefore, the grid partition bonded to the inner surface of the chimney cylinder is a plurality of grid channels divided by the channel partition walls suspended in the chimney cylinder, as viewed in a horizontal cross section. Among them, a means for making a chimney of a natural circulation boiling water reactor, which is characterized by being formed by a lattice channel that does not surround the lattice channel on all four sides, was adopted. Thereby, there is an effect that the operation can be performed by removing only the flow path partition wall which affects the implementation of the fuel exchange and the inspection work.

  Other objects of the present invention are as follows. When the gas-liquid two-phase flow of the coolant flows through the chimney lattice flow path, differential pressure between the lattices due to the flow and vibration (fluid vibration) due to fluid force occur. Since the differential pressure and the hydrodynamic vibration give stress to the flow path partition walls forming the lattice flow path, the flow path partition walls are required to have high structural integrity to counter this stress. As shown in FIG. 2, the chimney structure in the conventional natural circulation type BWR has lattice channels arranged in a square lattice pattern in the cross section. Furthermore, high rigidity is required so that the end portion is not deformed by its own weight when removed. Therefore, the grid partition bonded to the inner surface of the chimney cylinder is a plurality of grid channels as viewed in a horizontal cross-section among the plurality of grid channels partitioned by the channel partitions suspended inside the chimney cylinder. Among them, a means characterized in that it is a chimney of a natural circulation boiling water reactor, characterized in that it is formed by a lattice channel that does not surround the lattice channel on all four sides. As a result, the lattice ends are all angled, so the structural rigidity of the chimney periphery can be improved, and when removing and installing the flow path partition during fuel replacement or inspection, etc. Compared with the conventional structure (see FIG. 2), the deflection at the periphery of the flow path partition wall can be considered as a ratio between the fixed beam at one end and the fixed type at one end and the free beam at one end. % Can be suppressed to%.

  Other objects of the present invention are as follows. It is to facilitate the installation and removal of chimneys that are removed during refueling and inspection. Accordingly, a chimney of a natural circulation boiling water reactor characterized in that a channel partition wall detachable from the chimney structure and a channel partition wall joined to the inner surface of the chimney body partially support the horizontal direction. Adopted the means. As a result, a part of the flow path partition walls remaining on the inner surface of the chimney cylinder supports the grid portion in the horizontal direction during the mounting, thereby providing an effect of facilitating the positioning of the grid.

  Each of the features described above can be combined with each other without departing from the spirit of the present invention.

  Hereinafter, embodiments will be described with reference to the drawings.

(Outline of the reactor)
In general, there are two methods of driving coolant (light water) in boiling water reactors, one is forced circulation using a recirculation pump, and the other is natural circulation without using a recirculation pump. It is. This embodiment is the latter method based on natural circulation.

  As shown in FIG. 1, the natural circulation method is a method of cooling voids generated in a reactor core 7 housed in a reactor pressure vessel (hereinafter referred to as a pressure vessel) 6, that is, vapor (gas phase) and a liquid phase having a saturation temperature. A driving force necessary for natural circulation is obtained by a difference in specific gravity between the coolant having a low density mixed with the material and the liquid phase coolant mixed with the water supplied from the water supply pipe 16b.

  As shown in FIG. 1, a natural circulation boiling water reactor (hereinafter referred to as “reactor”) 1 according to the present embodiment has a core shroud 8 provided in a cylindrical pressure vessel 6 in a concentric cylindrical shape. Yes. The core shroud 8 forms an annular space in the gap between the outer side surface and the inner side surface of the pressure vessel 6, and this is called a downcomer 9. Further, the core 7 in which a large number of fuel assemblies 21 are arranged is housed inside the core shroud 8.

  Above the downcomer 9, the coolant supplied from the feed water inlet nozzle 17 into the pressure vessel 6 after being heated by the feed water heater 5 from the condenser 3 via the feed water pump 4 is evenly placed in the pressure vessel 6. A water supply sparger (not shown) is provided in an annular shape.

  The core shroud 8 is supported by a shroud leg 8a. The coolant descending the downcomer 9 is introduced into the core lower plenum (hereinafter referred to as the lower plenum) 10 below the core 7 from the flow path between the shroud legs 8a.

  A core support plate 22 is provided in the lower part of the core 7 and an upper lattice plate 23 is provided in the upper part, and the lateral arrangement of the fuel assemblies 21 and the control rods 24 is determined.

  The core support plate 22 is provided with circular through holes (not shown) at predetermined intervals. A control rod guide tube 25 is inserted into the through holes, and the lower portion of the control rod guide tube 25 penetrates the bottom of the pressure vessel 6. Thus, it is combined with an upper part of a control rod drive mechanism housing (hereinafter referred to as CRD housing) 26a that houses a control rod drive mechanism (hereinafter referred to as CRD) 26 that moves the control rod 24 in the vertical direction.

  The fuel assembly 21 is placed on a fuel support bracket (not shown) attached to the upper end of the control rod guide tube 25, and the load is applied to the bottom of the pressure vessel 6 via the control rod guide tube 25 and the CRD housing 26a. Reportedly.

  The fuel support fitting (not shown) has a coolant inlet on a side surface, and an orifice (not shown) is provided there to regulate the coolant flow rate. An opening is provided in the side surface of the control rod guide tube 25 corresponding to the coolant inlet of the fuel support bracket, and the coolant guided to the lower plenum 10 is guided into the fuel assembly 21 through the fuel support bracket.

  Each fuel assembly 21 is surrounded by a rectangular tube channel box (not shown) to form individual flow paths in the axial direction, and the channel box is configured to reach the upper surface of the upper lattice plate 23.

  The control rod 24 has an effective portion containing a neutron absorbing material (not shown), and the effective portion is inserted between the surrounding four fuel assemblies 21 using the outer surface of the channel box as a guide.

  Provided on the core 7 is a chimney 11 for guiding the gas-liquid two-phase flow of the coolant coming out of the core upward and increasing the natural circulation driving force. The chimney 11 has, for example, a cylindrical chimney cylinder 11d concentric with the pressure vessel 6, and has a lattice channel 11a in which the inside is partitioned into a lattice shape by a partition plate. Hereinafter, the partition plate constituting the lattice channel 11a is referred to as a channel partition wall 11b.

  In addition, the upper plenum 11c is provided in the upper part of the chimney 11 so that the coolant flowing upward through the individual lattice channels 11a merges in the upper part of the chimney 11.

  The upper lattice plate 23 and the lower end of the chimney 11 have a combined structure in which the coolant that descends the downcomer 9 and the coolant that exits the core 7 are not mixed.

  The upper end of the chimney 11 is closed by a chimney head 12a. The chimney head 12a is provided with a predetermined number of coolant passage holes, and the holes are connected to a steam / water separator 12 that separates saturated steam and saturated water from the gas / liquid two-phase flow through a stand pipe 12b. ing. A steam dryer 13 is provided above the steam / water separator 12 to remove moisture contained in the saturated steam exiting the steam / water separator 12. The steam that has passed through the steam dryer 13 is sent to the turbine 2 via the steam dome 14, the steam outlet nozzle 15, and the main steam pipe 16a.

  Note that the chimney head 12a, the stand pipe 12b, and the steam / water separator 12 are integrally assembled, and are configured to be detachable from the upper end of the chimney 11 at the time of fuel replacement.

  Thus, in the nuclear reactor 1 schematically described, the coolant supplied from the feed water inlet nozzle 17 is mixed with the saturated water separated by the steam separator 12, and the coolant indicated by the arrow A in FIG. Moves down the downcomer 9, flows into the core shroud 8 from a flow path formed by a gap (not shown) of the shroud leg 8 a, and is heated by the core 7. By the heating from the core 7, the coolant A becomes a gas-liquid two-phase flow in a saturated state indicated by an arrow B. This gas-liquid two-phase flow passes through the lattice channel 11a, the upper plenum 11c, and the stand pipe 12b to separate the water and gas. The vessel 12 separates the gas phase saturated steam indicated by the arrow C and the liquid phase saturated water indicated by the arrow D. The saturated steam C passes through the steam dryer 13, is led from the steam outlet nozzle 15 to the turbine 2 through the main steam pipe 16 a, and is used for power generation.

  On the other hand, the saturated water D is mixed with the coolant in the pressure vessel 6, further mixed with the coolant supplied from the feed water inlet nozzle 17, and descends the downcomer 9 again to circulate in the pressure vessel 6.

(Chimni Structure Example 1)
FIGS. 3, 4 and 5A and 5B show a chimney structure example 1 according to the present embodiment.

  As shown in FIG. 3, the chimney 11 includes a chimney cylinder 11 d that separates an upward flow and a downward flow of the coolant, a flow path forming device 11 A that forms a plurality of flow paths through which the upward flow flows, and a flow path forming device 11 A. 11g for supporting The chimney cylinder 11d has a cylindrical shape, and a flow path forming device 11A is installed in the cylinder.

  As shown in FIG. 4, the flow path forming apparatus 11A includes a flow path partition wall 11b1 (hereinafter referred to as a flow path partition wall 11b1) that can be attached to and detached from the chimney structure, and a plurality of flow path partition walls 11b2 (hereinafter referred to as “welding” to the chimney cylinder). And an upper support plate 11e and a lower support plate 11f, which are joined to the flow channel partition 11b1 by welding or the like, as shown in FIG. 11e has a hook 31 joined to 11e.

  As shown in FIG. 4, the chimney 11 has a cylindrical chimney cylinder 11d concentric with the pressure vessel 6 (see FIG. 1), and the inside of the chimney 11 is a lattice-shaped grid with a flow path partition wall 11b1 such as a partition plate. The grid channel 11a is divided into two. Further, the flow path partition wall 11b1 constituting the lattice flow path 11a has a closed structure with all the corners forming a corner. Therefore, the lattice flow path 11a is compared with the chimney trunk central part. In the vicinity of the chimney cylinder, the lattice shape is a small rectangle (see FIG. 5A). The channel partition wall 11b1 is manufactured by joining portions and corners of the channel partition wall by welding or the like so that the channel partition wall 11b1 can be integrally attached and detached. The material is made of a metal such as stainless steel.

  As shown in FIG. 4, the chimney structure according to the present embodiment is formed by a channel partition wall 11b2 joined to the inner surface of the chimney cylinder and a channel partition wall 11b1 detachable from the chimney structure in the cross section of the lattice channel 11a. 11b1 and 11b2 have a lattice channel 100. The end portions of the flow path partition 11b2 form an angle perpendicular to each other, or are joined to the inner surface of the chimney cylinder 11d, and all have a closed structure (see FIG. 5B). Moreover, as shown in FIG. 4, it has the structure which supports the position of the horizontal surface of the flow-path partition 11b1 by the flow-path partition 11b2.

  The flow path partition 11b1 of the flow path forming device 11A is supported by a pedestal 11g attached to the chimney cylinder 11d, and the flow path partition 11b2 is joined to the chimney cylinder. When the chimney 11 is installed, first, the chimney cylinder 11 d is attached to the upper lattice plate 23. Thereafter, the flow path partition 11b1 of the flow path forming device 11A is hung on the hook 31 by a crane or the like and passes along the flow path partition 11b2 joined to the inner surface of the chimney cylinder 11d. At this time, since the flow path partition 11b1 supported by each flow path partition 11b2 is determined by the way of dividing the flow path partition 11b in the horizontal cross section of the chimney cylinder 11d, the arrangement position of the flow path partition 11b1 is determined and suspended. Can do.

  The flow of the flow path forming device 11A, which affects the fuel exchange and inspection work in the furnace, can be performed without removing the chimney cylinder 11d by performing the reverse procedure to the above during the fuel replacement and inspection in the furnace. Only the road partition wall 11b1 can be removed.

  As shown in FIG. 2, in the conventional chimney structure, the partition wall forming the flow path is supported at equal intervals by the flow path partition perpendicular to it, and is supported anywhere at the end of the flow path partition wall. The structure that is not done, that is, the free end. As shown in FIGS. 4 and 5, by leaving a part of the channel partition wall on the chimney cylinder side, the corner of the channel partition is suppressed while suppressing an increase in the weight of the channel partition unit that must be removed during fuel replacement or inspection. The structure is all closed, and the free end in the cross section can be eliminated.

  Normally, when considering a side that receives an evenly distributed load, the maximum stress generated at the fixed end of a side that is fixed only on one side is about six times greater than that of a side that is fixed at both ends. As shown in FIGS. 3 and 4, by eliminating the free end in the cross section of the flow path partition wall, the differential pressure load between the lattices, the fluid stress and the maximum stress generated by its own weight are reduced, and the structure around the chimney Stiffness can be improved.

  The flow path forming device 11A is installed in the chimney cylinder 11d and has a very close positional relationship. Since the rigidity of the periphery of the flow path forming device 11A is increased according to the present invention, the maximum deflection is reduced to about 2% when the flow path partition wall 11b1 is suspended at the time of inspection in the furnace or at the time of fuel replacement. In addition to being suppressed, the flow partition wall 11b2 plays the role of a guide support, whereby the handleability can be improved.

(Chimni structure example 2)
FIGS. 6, 7, 8 (a) and 8 (b) show a chimney structure example 2 according to the present embodiment.

  Compared with the chimney structure example 1 shown in FIGS. 3, 4, and 5, the structure example 2 is different from the chimney structure in the channel partition wall 11 b 1 that can be detached from the chimney structure. All of the arranged flow path partition walls are arc-shaped flow path partition walls having a concentric diameter and a concentric horizontal cross section, whereby the flow path partition wall 11b1 is closed. Further, the plurality of flow path partition walls 11b2 joined to the chimney cylinder 11d are plate-shaped so that the horizontal cross section has a string shape with respect to the circular shape of the inner surface of the chimney cylinder 11d due to the engagement with the flow path partition wall 11b1. The flow path partition walls are vertically joined. The horizontal support of the flow path partition 11b1 is achieved by supporting the corners of the grid of the flow path partition 11b1 by the respective surfaces of the flow path partition 11b2.

  By setting it as the chimney structure example 2, compared with the chimney structure 1, the joint location such as welding in the chimney cylinder 11d and the flow path partition wall 11b2 can be reduced. On the other hand, the flow path partition 11b2 has an increased number of processing steps because the flow path partition that is the outermost from the chimney cylinder center has a curvature.

  The upper support plate 11e of the flow path forming apparatus A has an annular shape in the horizontal section, and the upper surface of the flow path partition wall that is the outermost side from the chimney cylinder center of the flow path partition wall 11b1 is joined to the upper support plate 11e. The inner diameter is the same as the inner diameter of the channel partition wall that is the outermost from the chimney cylinder center, and the outer diameter is slightly larger than the outer shape of the channel partition wall that is the outermost from the chimney cylinder center. Yes. Thereby, the stability of the flow path partition 11b1 when attaching and removing the flow path partition 11b1 using the hook 31 is improved.

  The horizontal positioning of the flow path partition 11b1 can be performed by associating the corners of the grid of the flow path partition 11b1 with the surface of the flow path partition 11b2.

  The specific configuration of the embodiment of the present invention is not limited to the above-described embodiment, the chimney structure example 1 and the chimney structure example 2, and the relationship between the flow path partition wall 11b1 and the flow path partition wall 11b2. The way of dividing the flow path partition walls in the chimney cylinder may be different depending on the fuel assembly filled in the core. Further, a method combining the features of the chimney structure example 1 and the chimney structure example 2 may be employed.

  Applicable to overseas ESBWR.

DESCRIPTION OF SYMBOLS 1 Natural circulation boiling water reactor 2 Turbine 3 Condenser 4 Feed water pump 5 Feed water heater 6 Reactor pressure vessel 7 Core 8 Core shroud 8a Shroud leg 9 Downcomer 10 Core lower plenum 11 Chimney 11A Flow path formation device 11a Grid Channel 11b Channel partition 11b1 Removable channel partition 11b2 Channel partition 11c joined to chimney cylinder 11d Upper plenum 11d Chimney cylinder 11e Upper support plate 11f Lower support plate 11g Base 12 Air / water separator 12a Chimney head 12b Stand pipe 13 Steam dryer 14 Steam dome 15 Steam outlet nozzle 16a Main steam pipe 16b Feed water pipe 17 Feed water inlet nozzle 21 Fuel assembly 22 Core support plate 23 Upper lattice plate 24 Control rod 25 Control rod guide tube 26 Control rod drive mechanism 26a Control rod Drive mechanism housing 31 hook 100 11b1 And a lattice channel formed by 11b2

Claims (7)

A chimney of a natural circulation boiling water reactor comprising a core loaded with a plurality of fuel assemblies in a circular cross section, and a chimney installed on the core,
The chimney includes a chimney cylinder and a plurality of lattice channels partitioned by a channel partition wall suspended from the chimney cylinder,
A part of the flow path partition walls defining the plurality of lattice flow paths are joined to the inner surface of the chimney body, and the remaining flow path partition walls defining the plurality of lattice flow paths are detachable from the chimney structure. Chimuni is a natural circulation boiling water reactor. In the chimney of a natural circulation boiling water reactor according to claim 1,
The grid partition bonded to the inner surface of the chimney cylinder is a plurality of grid channels partitioned by the channel partition walls suspended in the chimney cylinder, and viewed from a horizontal cross-section, A chimney of a natural circulation boiling water reactor characterized in that it is formed by a lattice channel that does not surround the lattice channel on all sides. In the chimney of a natural circulation boiling water reactor according to claim 1,
In the flow path partition wall removable from the chimney,
A chimney for a natural circulation boiling water reactor, characterized in that all of the ends of the horizontal cross section of the flow channel partition wall are corners and the lattice flow channel is closed. In the chimney of a natural circulation boiling water reactor according to claim 1,
A chimney of a natural circulation boiling water reactor characterized in that a flow passage partition detachable from the chimney structure and a flow passage partition joined to the inner surface of the chimney body partially support the horizontal direction. . Using the chimney of the natural circulation boiling water reactor according to claim 1,
Remove only the removable partition wall from the chimney,
Then, a fuel replacement method for a natural circulation boiling water reactor, characterized by performing fuel replacement. Using the chimney of the natural circulation boiling water reactor according to claim 1,
Remove only the removable partition wall from the chimney,
After that, the inspection method of the natural circulation boiling water reactor characterized by performing the inspection. Using the chimney of the natural circulation boiling water reactor according to claim 1,
A natural circulation boiling water reactor characterized by forming a plurality of lattice flow paths for coolant from the core.

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