JP4474353B2 - Apparatus and method for suppressing flow vibration of gas-liquid two-phase flow in a nuclear reactor, and method for circulating coolant in a natural circulation boiling water reactor using the method - Google Patents

Description

  The present invention relates to a method and apparatus for suppressing flow vibration of a gas-liquid two-phase flow flowing in a chimney above a reactor core.

  A natural circulation boiling water reactor is formed by using a cylindrical chimney in which a coolant circulation channel in a reactor pressure vessel is provided at the top of the core and a core shroud surrounding the core. . A space between the outer peripheral surface of the core shroud or chimney and the inner surface of the reactor pressure vessel is used as a downward flow path called a downcomer, and the inside of the chimney is used as an upward flow path.

  Since natural circulation boiling water reactors are equipped with such a circulation channel in the reactor pressure vessel, the gas-liquid two-phase flow with steam is generated by the coolant heated by the nuclear reaction at the core. The gas and liquid two-phase flow is separated into a liquid and a gas by a separation device, and the vapor accompanying the gas is transferred to a turbine outside the reactor pressure vessel, etc. The liquid is supplied and returned to the descending flow path side.

  In the descending flow path, the coolant has a lower density than the coolant in the chimney and has a higher density, so it descends with a natural circulation force based on the density difference. The descending liquid flow reverses upward at the bottom of the reactor pressure vessel and enters the core again from below and is heated. As described above, the coolant in the reactor pressure vessel is handled so as to repeat natural circulation without using a pump when handling the coolant (see, for example, Patent Document 1 and Patent Document 2).

  Therefore, the natural circulation boiling water reactor has the biggest difference with the forced circulation boiling water reactor that forcibly circulates the coolant with a pump. It can be said that it is simplified.

  In anticipation of efficient circulation of the coolant, the ascending flow path in the chimney is partitioned by a lattice structure above the core into a plurality of upright flow paths (hereinafter also referred to as lattice flow paths). There is also an example in which the inside of the lattice channel is raised through a gas-liquid two-phase flow rising from the core (see, for example, Patent Document 3).

Japanese Patent Laid-Open No. 08-094793 Japanese Patent Laid-Open No. 06-265665 Japanese Patent Publication No. 07-027051

  When a plurality of upright grid channels partitioned in a grid pattern are provided in this chimney, it is generated in the cross section of the core due to the difference in the amount of heat generated inside the core (large at the center and low at the periphery). There is a distribution in the amount of steam, and there is a relatively large amount of steam in the center of the core, and there is little in the periphery.

  Since the amount of steam in the center of the core is large, a large amount of steam is retained in the lattice channel in the chimney above the center, so the density is relatively low compared to the periphery of the core, and the coolant The water head pressure difference with the downcomer, which is the descending flow path, becomes larger, and more cooling water is guided to the center of the core, allowing the coolant to circulate with a good cooling effect of the core.

  In such a natural circulation boiling water reactor with a lattice channel in the chimney, water is also supplied to each chimney lattice channel due to the difference in the flow rate of cooling water and steam in the core located in the reactor core.・ There is a difference in the steam flow rate.

  In consideration of the above, when a flow test of gas-liquid two-phase flow was performed by changing the flow rates of water and air with an experimental device simulating a lattice flow path, pressure fluctuation load might be applied to the inner surface of the lattice flow path. I understood. Such vibrations may have a long-term adverse effect on the joints between the lattice structure plates that partition the lattice flow paths. In addition, damage to the reactor internal equipment is a serious problem in terms of safety and economy. In order to solve this problem, for example, it is conceivable to increase the thickness of the plate, but there arises a problem that the amount of the structure increases.

  Further, as a result of conducting an experiment simulating the chimney lattice channel and the flow in the lattice channel, the gas-liquid two-phase flow mixed with gas and liquid develops as it rises vertically. For example, as shown in FIG. In the state 3 in which the central portion of the flow path in the lattice flow path is occupied by a gas phase, and a liquid phase exists along the inner wall surface of the lattice flow path outside the vapor phase (such a gas phase and a liquid layer). The flow in the separated state is referred to as an annular flow.) And the state 4 in which the liquid phase is filled in the cross section of the flow path are alternately and repeatedly passed to form a flow mode close to a churn flow. At this time, a lattice flow path is formed. It was found that a pressure fluctuation load of several kPa to several tens of kPa is applied to the wall of the plate of the lattice structure.

  Also, in this experiment, in the flow that flows in the state where the water and air flows are separated at the inlet of the flow path, and the liquid phase rises in a state where the wall surface is biased toward one side of the wall, the occurrence of pressure fluctuation is suppressed. It was found that the load can be eliminated or reduced.

  Therefore, an object of the present invention is to make the reactor safe by suppressing the pressure fluctuation load generated when the chimney disposed above the core of the reactor is divided into a plurality of flow paths to be used as the rising flow path of the coolant. Is to do.

The basic requirements of the gas-liquid two-phase flow vibration suppression device of the present invention are chimneys installed above the core in the reactor pressure vessel, and a plurality of channels in the vertical direction in the chimneys. A structure provided with a partitioning structure, and a stirring means that stirs the fluid in the flow path in a structure including protrusions protruding from the structure into the cross section of the flow path and inclined in the vertical direction. is there.

In addition, the basic requirements of the other device invention are as follows: a chimney installed above the core in the reactor pressure vessel, a structure that divides the inside of the chimney into a plurality of vertical channels, and a flow of the channels. directing a liquid film flowing along the road inside wall in one direction of the flow path cross section, and a drift means for liquid phase raises biased to said one direction, said drift means, said flow from said structure It is the structure provided with the protrusion which protruded in the cross section of the path | route and was inclined in the up-down direction .

Further, the basic requirement of the flow vibration suppression method of the gas-liquid two-phase flow of the reactor is to generate a gas-liquid two-phase flow through the coolant through the core in the reactor pressure vessel, and the gas-liquid two-phase flow is A structure in which the inside of the chimney is divided into a plurality of vertical channels in the process in which the gas-liquid two-phase flow rises through a plurality of flow paths that divide the chimney above the core . The gas-liquid two-phase flow in the flow path is agitated by protrusions protruding from the flow path into the cross section of the flow path and inclined in the vertical direction, thereby causing the annular flow to collapse.

In addition, the basic requirement of another method invention is that a gas-liquid two-phase flow is generated through a coolant in a reactor pressure vessel, and the gas-liquid two-phase flow is divided into a chimney above the core. In the process of raising the gas-liquid two-phase flow through the flow path, the liquid film flow flowing along the flow path inner wall of the flow path is transferred from the flow path inner wall to the flow path. The projecting into the cross section and the protrusion inclined in the vertical direction leads to one direction of the cross section of the flow path to make it drift, thereby causing the collapse of the annular flow.

  According to the present invention, the pressure vibration load generated when the chimney disposed above the core of the nuclear reactor is divided into a plurality of flow paths and used as the rising flow path of the coolant is suppressed and the reactor is maintained safely. Reduction of work for maintaining safety can be achieved.

  The first embodiment of the present invention is as follows. That is, in the natural circulation boiling water reactor, as shown in FIG. 2, a reactor core 9 in which a plurality of fuel assemblies 15 are loaded in a reactor pressure vessel 5 and a cylinder that surrounds the outer periphery of the reactor core 9. Core shroud 17, upper lattice plate 10 constituting the upper portion of core 9, cylindrical chimney 11 standing on upper lattice plate 10, and chimney 11 mounted on chimney 11. The steam-water separator 12 with a stand pipe covering the upper end, and the steam dryer 13 installed above the steam-water separator 12 so as to surround the steam-water separator 12 with a lower skirt portion are used as the in-furnace structure. Built-in. The reactor pressure vessel 5 is equipped with a main steam nozzle 14 and a water supply nozzle 6.

  In the cylindrical space in the chimney 11, a lattice structure having a rectangular lattice as viewed from above is provided. Metal plates constituting the sides of the lattice of the lattice structure are joined to adjacent plates by welding or the like, and the lattice structure has a welded structure. By this lattice structure, the area in the chimney 11 is partitioned into a lattice shape, and a plurality of lattice channels 16 standing upright above the core 9 are formed.

  Each lattice channel 16 has a rectangular channel cross section, and has an open end on the upper side at a position lower than the upper end of the chimney. The space from the open end portion of each lattice channel 16 to the upper end of the chimney is not partitioned in a lattice shape, but is a series of regions across.

In the reactor pressure vessel 5, light water is put as a coolant up to a height in the middle of the steam separator 12. The coolant receives heat generated by the nuclear reaction by the nuclear fuel stored in the fuel assembly 15 in the core 9 when the nuclear reactor is operated. The coolant heated by the heat becomes light in specific gravity with a vapor-water two-phase flow of steam and water, so that it naturally rises from the lower end of each lattice channel 16 from the core to each lattice channel 16. Enter and rise.

  Thus, when the coolant ascends and passes through the core 9, it is heated by the heat generated by the nuclear reaction and becomes a gas-liquid two-phase flow of water and steam. Thereafter, the coolant that has become a gas-liquid two-phase flow passes through the upper lattice plate 10 above the core 9 and enters the chimney 11. Then, the coolant rises in the chimney 11 and passes through the upper air / water separator 12. When the coolant in the gas-liquid two-phase flow state passes through the steam-water separator 12, water and steam are separated from the gas-liquid two-phase flow, and the separated water is separated from the core shroud 17 and chimney 11 and the reactor pressure. It is led to the downcomer 7 which is a vertical flow path between the inner wall surface of the container 5. Further, the separated water flows downward using the downcomer 7 as a descending flow path.

On the other hand, the steam separated by the steam separator 12 is guided to the steam dryer 13 to further remove moisture, and after being sufficiently separated by the steam dryer 13, it escapes upward. It passes through the steam nozzle 14 and is sent to a steam turbine using steam as driving energy. In some cases, moisture separation may be performed only by the steam dryer 13 without providing the steam / water separator 12.

  The steam used in the steam turbine is condensed and returned to water, and then flows into the reactor pressure vessel 5 through the water supply nozzle 6 as a coolant, mixes with the coolant in the downcomer 7 and descends. .

  As described above, the flow of the coolant in the reactor pressure vessel 5 is divided into a descending region at the downcomer 7 and an ascending region inside the core 9, and the steam generated in the core 9 is contained in the ascending region of the cooling water. The density is relatively small compared to the descending area. Therefore, there is a head pressure difference between the coolant in the descending region at the downcomer 7 and the ascending region inside the core 9, and the coolant descends the downcomer 7, goes down to the lower plenum 8 region, and reverses and rises. 9 The force that the coolant flows into the lower part is generated.

  In this way, the natural circulation boiling water reactor is naturally circulated by utilizing the density difference of the coolant, so unlike the conventional forced circulation boiling water reactor, There is no system or equipment. In addition, the heating distribution in the cross section of the core occurs such that the degree of heating of the coolant in the core is high in the center of the core and low in the periphery. The distribution of the heating causes a distribution in the rising speed of the coolant, and the flow tends to be disturbed, but the disturbance is prevented by dividing the coolant flow path finely with a lattice flow path, preventing backflow and the like. And circulate the coolant efficiently.

  In the metallic plates 23, 24, 25, 26 of the lattice structure that partitions the adjacent lattice flow paths 16, the stirring device 1 is provided as a stirring means inside the lattice flow paths 16, and the lower end portion of the lattice flow paths 16 or It is deployed at a height part on the way. About the deployment number and arrangement | positioning height of the stirring apparatus 1, it sets arbitrarily as needed.

  As shown in FIG. 3, the stirrer 1 has a configuration in which protrusions 19 having a right-angled triangular longitudinal section are fixed to the four plates 23, 24, 25, and 26 surrounding the lattice channel 16. The oblique side portion of the projection 19 having a right triangle is directed obliquely downward on the inner side of the lattice channel 16, so that the coolant that has risen along the plates 23, 24, 25, and 26 is indicated by an arrow in FIG. As shown by the streamlines shown, the flow is changed toward the central part of the lattice channel 16 and the function of mixing and stirring with the coolant flowing through the central part is exhibited.

  As described above, the plates 23, 24, 25, and 26 constituting the inner wall of the lattice channel 16 guide the liquid phase flow that rises along the inner wall in the direction toward the center of the channel. A protrusion 19 is provided.

  The shape of the protrusion 19 is inclined so as to protrude from the inner wall of the flow path as the distance from the flow path entrance increases. By providing such a projection 19, as shown in FIG. 1, the liquid film flowing in contact with the inner wall of the flow path is forcibly collected toward the central portion of the cross section of the flow path, and the stirring device 1 of FIG. The flow state of the annular flow or the churn flow developed below is broken so as to be above the stirring device 1 to become a mixed two-phase flow 2.

  In FIG. 3, the protrusions 19 are installed on the front surface surrounding the lattice channel 16, that is, on the surface of the channel 4, but this need not be the case. The shape of the protrusion 19 may be a curved surface so that the two-phase flow can be guided more smoothly. In addition, since the stirring will become inadequate if the ratio for which the processus | protrusion 19 occupies in a grid flow path cross section is too small, it is necessary to set appropriately.

  When the gas-liquid two-phase flow stirred by the stirring device 1 rises to a certain level, the scale of the annular flow gradually develops to return to the flow mode of the churn flow, and the pressure fluctuation load increases again. Therefore, it is preferable to install the stirrer 1 in the lattice channel 16 with a certain vertical distance. However, excessive installation of the stirring device 1 causes an increase in pressure loss when the coolant is circulated.

  Thus, the installation place of the stirring device 1 is the outer periphery in the lattice channel 16. Further, dividing the chimney 11 into the lattice flow path 16 creates a state in which the liquid phase of the gas-liquid two-phase flow flows along the inner wall of the lattice flow path, so the liquid phase on the inner wall side of the lattice flow path It is sufficient to install the stirring device 1 only in the region where the flow of the protrusion 19, and the protrusion length of the protrusion 19 is shortened in consideration thereof.

  Preferably, each grid channel is preferably disposed above the core 9 so that one grid channel 16 corresponds to the integral fuel assembly 15. In the case of such a preferred form, when loading / withdrawing the fuel assembly 15 to / from the core 9 from above, the protrusion 19 is likely to interfere with the fuel assembly 15 moving up and down for loading / withdrawing. Therefore, the length which protrudes from the inner wall of a lattice flow path is suppressed to such an extent that there is no interference.

  By suppressing the protrusion length of the protrusion 19 in this manner, the protrusion 19 does not interfere with the fuel change work, thereby suppressing an increase in work steps during the fuel change work and contributing to the improvement of economy. be able to. Moreover, by suppressing the protrusion length of the protrusion 19, it is possible to contribute to suppressing an increase in pressure loss when the gas-liquid two-phase flow passes.

  The second embodiment of the present invention is as follows. That is, in the second embodiment, as shown in FIG. 4, the stirrer 1 of the first embodiment is replaced with a drift device 20. Since other configurations and operations are the same as those of the first embodiment, the description thereof is omitted.

  In the second embodiment, as shown in FIG. 4, the liquid film flow that flows along the inner wall of the lattice channel 16 is guided in one direction of the channel cross section at the entrance or in the middle of the lattice channel 16. A drift device 20 is provided that creates a state 21 in which the liquid phase rises in one direction in the cross section of the flow path. By making the gas-liquid two-phase flow drift with the drift device 20, the plates 23, 24, 25, and 26 of the lattice structure forming the inner wall of the lattice flow path 16 generated when the developed gas-liquid two-phase flow passes. It is possible to suppress the occurrence of a pressure fluctuation load applied to the.

  As in the first embodiment, the drifting device 20 is installed only in the inner periphery of the lattice flow path 16, and the size of the drift device 20 protrudes from the inner wall of the lattice flow path 16 toward the center of the cross section of the lattice flow path 16. This should be kept to the extent that there is no interference when the fuel assembly is loaded or withdrawn.

An example of a specific structure of the drift device 20 is shown in FIG. Here, the liquid flow in the gas-liquid two-phase flow is increased in the lattice flow path 16 toward the plate 23 side, and the gas phase flow is increased along the plate 25 side as the plate 23 is approached. The inclined protrusion 22 is fixed to the plates 24, 25, and 26 in an inclined posture. Such inclined protrusions 22 are formed by inclining a metal plate in the vertical direction to form plates 24, 25,
26 can be configured.

Since the inclined projection 21 inclined in this way is provided so as to protrude into the lattice channel 16, the liquid film in the gas-liquid two-phase flow rising from below along the plates 24, 25 and 26 is obtained. The flow direction is directed to the plate 23 guided by this inclination, and the liquid phase is concentrated in one direction (the plate 23 side) in the cross section of the lattice channel above the drift device 20, and the gas-liquid two-phase is gathered on the plate 25 side. A gas-liquid two-phase flow is created in which the gas phase in the flow is concentrated and gathered. In addition, you may make the shape of the inclination protrusion 21 incline in a curve shape so that the flow in the lattice flow path 16 may be guide | induced more smoothly.

  In the present embodiment, as shown in FIG. 4, the liquid phase of the annular flow of gas-liquid two-phase flow that has risen in the lattice channel 16 in the flow mode of the churn flow is forcibly deflected so that the gas phase and the liquid phase The flow is divided into left and right to break the annular flow, creating a left-right separated state of the gas-liquid two-phase flow above the drift device 20, and the development of the annular flow above the stirring device 1 and the flow pattern of the churn flow Suppresses the occurrence. Thereby, generation | occurrence | production of the pressure fluctuation load applied to the board 23, 24, 25, 26 which comprises the four sides of the grating | lattice of a grating | lattice structure generated when a gas-liquid two-phase flow passes a grating | lattice flow path can be suppressed. .

Thus, according to each embodiment of the present invention, the gas-liquid two-phase flow in the lattice channel 16 is forced even in a nuclear reactor that partitions the inside of the chimney 11 and employs the plurality of lattice channels 16. It is possible to suppress the occurrence of pressure fluctuations that occur in the flow state of the churn flow by providing a function of stirring or drifting to prevent the development of the annular flow.

  Therefore, according to each embodiment of the present invention, it is possible to eliminate or sufficiently reduce the pressure fluctuation load applied to the structure that forms the partition of the lattice flow path 13, and the chimney 11 and the lattice flow path during the reactor operation period. The possibility of 13 damages can be reduced. For this reason, it can withstand long-term use, eliminates the trouble of inspection and maintenance during the periodic inspection of the reactor, and eliminates or reduces the number of replacements of the chimney 11 and the partition structure of the grid channel 13 in the event of an emergency. It is possible to minimize the economic loss due to the plant stoppage at the time of replacement. Furthermore, even if the chimney 11 is provided with a lattice structure, it is possible to prevent an increase in the number of steps at the time of fuel change by making the structure not to interfere with the movement of the fuel assembly at the time of fuel change.

  The present invention is applied to a nuclear power plant nuclear reactor, and is used, for example, to suppress pressure fluctuation caused by a churn flow of a gas-liquid two-phase flow in a chimney in the upper part of the core.

It is a longitudinal cross-sectional view of the lattice flow path showing the flow state of the gas-liquid two-phase flow in the lattice flow path above the reactor core according to the first embodiment of the present invention. 1 is a longitudinal sectional view of a reactor pressure vessel of a natural circulation boiling water reactor in which the present invention is implemented. It is a perspective view by the partial notch display of the stirring apparatus of FIG. It is a longitudinal cross-sectional view of the lattice flow path showing the flow state of the gas-liquid two-phase flow in the lattice flow path above the reactor core according to the second embodiment of the present invention. It is a perspective view by the partial notch display of the drift apparatus of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Stirrer, 2 ... Mixed two-phase flow, 5 ... Reactor pressure vessel, 6 ... Feed water nozzle, 7 ... Downcomer, 9 ... Core, 10 ... Upper lattice plate, 11 ... Chimney, 16 ... Lattice flow path, 17 ... Core shroud, 19 ... projection, 20 ... drifting device, 22 ... inclined projection, 23, 24, 25, 26 ... plate.

Claims (6)

A chimney installed above the core in the reactor pressure vessel;
A structure that divides the inside of the chimney into a plurality of vertical channels;
Stirring means that stirs the fluid in the flow path in a configuration that includes protrusions protruding from the structure into the cross section of the flow path and inclined in the vertical direction ;
An apparatus for suppressing gas-liquid two-phase flow vibrations in a nuclear reactor. A chimney installed above the core in the reactor pressure vessel;
A structure that divides the inside of the chimney into a plurality of vertical channels;
A flow flow unit that guides a liquid film flow that flows along the inner wall of the flow channel in one direction of the flow channel cross-section, and causes the liquid phase to be biased upward in the one direction;
With
The flow drift suppression device for a gas-liquid two-phase flow of a nuclear reactor, wherein the drifting means is provided with a protrusion protruding from the structure into a cross section of the flow path and inclined in the vertical direction. A chimney installed above the core in the reactor pressure vessel;
A core shroud provided around the core and separating the inner and outer flow paths of the core;
A coolant recirculation channel formed in the reactor pressure vessel by the chimney and the core shroud;
A steam dryer that is disposed at a site in the reactor pressure vessel above the chimney and separates the steam generated by the nuclear reaction in the core into moisture;
A main steam nozzle that is installed in the reactor pressure vessel and guides the steam separated by the steam dryer to the outside of the reactor pressure vessel;
A water supply nozzle that is installed in the reactor pressure vessel and guides water supply from outside the reactor pressure vessel into the reactor pressure vessel;
A natural circulation boiling water reactor comprising the gas-liquid two-phase flow vibration suppression device for a nuclear reactor according to claim 1 or 2. A gas-liquid two-phase flow is generated through the coolant through the core in the reactor pressure vessel,
The gas-liquid two-phase flow is raised through a plurality of flow paths that divide the inside of the chimney above the core,
In the process of the gas-liquid two-phase flow rising in the flow path, the flow is caused by a protrusion that protrudes from the structure that divides the inside of the chimney into a plurality of vertical flow paths and is inclined in the vertical direction. A method for suppressing flow vibration of a gas-liquid two-phase flow in a nuclear reactor in which the gas-liquid two-phase flow in a passage is agitated to collapse an annular flow. A gas-liquid two-phase flow is generated through the coolant through the core in the reactor pressure vessel,
The gas-liquid two-phase flow is raised through a plurality of flow paths that divide the inside of the chimney above the core,
In the process in which the gas-liquid two-phase flow ascends through the flow path, a liquid film flow flowing along the flow path inner wall of the flow path is projected from the flow path inner wall into the cross section of the flow path, and in the vertical direction A flow vibration suppression method for a gas-liquid two-phase flow in a nuclear reactor in which an annular flow is collapsed by being guided in one direction by a projection inclined in the direction of the flow path to cause a drift. A coolant shroud that passes through the core in the reactor pressure vessel by dividing a flow path inside and outside the core by a core shroud around the core in the reactor pressure vessel and a chimney installed above the core. Forming a recirculation channel,
The coolant that circulates in the core generates a gas-liquid two-phase flow by heating by a nuclear reaction in the core,
The gas-liquid two-phase flow is raised through the chimney, and the pre-coolant is naturally circulated to the core by the density difference of the coolant in the inner and outer flow paths,
In the course of the natural circulation, the gas-liquid two-phase flow is raised through the chimney,
A natural circulation type boiling water reactor to which the method for suppressing flow vibration of a gas-liquid two-phase flow of a nuclear reactor according to claim 4 or 5 is applied in an ascending process of the gas-liquid two-phase flow in the chimney. Coolant circulation method.

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