JP2010243266A - Boiling water reactor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steam separator that reduces carry-over and carry-under. <P>SOLUTION: The steam separator 6 has a stand pipe 7, a diffuser 8, a swirler 9 and three-stage steam separation units 10a to 10c. An external cylinder 12a forming a drainage channel 15a between an internal cylinder 11a and the external cylinder is set up on a pick-off ring 13a. Similarly, the internal cylinder 11b and the pick-off ring 13b are mounted on the upper end of a pick-off ring 13 and that of the internal cylinder, respectively, and part of the water which is not separated by the pick-off ring 13a passes through a drainage channel 15b and is discharged from an exhaust port 18b into steam. The discharged and falling water is captured by a reinforcing plate 21 and a scattering prevention plate 26 set up below the exhaust port 18b and gently flows into the surface of cooling water along the scattering prevention plate 26. Part of droplets and steam generated by the collision of the water falling directly on the surface of partial cooling water are captured by the scattering prevention plate 26. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a boiling water reactor.

  A boiling water reactor (hereinafter referred to as BWR) has a reactor pressure vessel (hereinafter referred to as RPV), and the RPV includes a reactor core loaded with a plurality of fuel assemblies. The cooling water supplied to the core is heated and boiled by the heat generated in the fuel assembly in the core. A part of the cooling water becomes steam by this boiling. The generated steam is discharged from the RPV and supplied to the turbine to rotate the turbine. A generator connected to the turbine rotates to generate electric power.

  In this boiling water reactor, a steam separator is disposed in the RPV and above the core. The steam separator is supplied with a gas-liquid two-phase flow containing steam and water generated in the core and separates the gas-liquid two-phase flow into steam and water to generate dry steam.

  Patent Document 1 discloses the structure of a steam separator. In this steam separator, a capture ring is installed at the upper part of the outlet that is discharged into the steam. Entrapment is reduced by capturing the scattered droplets with the capture ring.

Japanese Patent Laid-Open No. 8-179077

  However, since the droplets scattered into the vapor are distributed over a wide range, the capture ring needs to cover a wide range outside the steam separator. Moreover, the steam separator of patent document 1 needs to further improve carry-under. Moreover, since the pressure at the upper surface of the water surface increases due to the installation of the capture ring, there is a possibility that the mixing of bubbles into the cooling water increases.

  An object of the present invention is to provide a boiling water reactor capable of reducing both carry-under and entrainment with a simple structure.

  The present invention installs a reinforcing plate for connecting adjacent steam separators below the outlet of the second drainage passage from the upstream among the drainage passages formed between the inner cylinder and the outer cylinder. It is characterized by that.

  According to the present invention, carry under and entrainment in the steam separator can be reduced while maintaining structural strength with a simple structure.

It is a longitudinal cross-sectional view of the steam separator which is one Example of this invention. It is a top view of the steam-water separator shown in FIG. It is a block diagram of the steam-water separator shown in FIG. It is a perspective view of a reinforcing member. It is a longitudinal cross-sectional view of the steam separator which is one Example of this invention. It is a longitudinal cross-sectional view of the steam separator which is one Example of this invention. It is a top view of a steam separator. It is an Example of the reinforcement member of the steam-water separator shown in FIG. It is an Example of this structure plan which provided the scattering prevention board. FIG. 10 is a top view of the steam separator shown in FIG. 9. It is an Example of the reinforcement member of the steam-water separator shown in FIG. It is a perspective view of a reinforcing member. It is an enlarged view near the discharge port of the steam separator.

  Inventors examined the shape of the reinforcing member and drain outlet which have a simple structure and can reduce carry-under and entrainment. Specific examples are shown below.

  A steam separator applied to a boiling water nuclear power plant (BWR plant) will be described with reference to FIGS. 1, 2, 3, and 5. As shown in FIG. 5, the steam separator has a stand pipe 7, a diffuser 8, a swirler 9, an inner cylinder 11, an outer cylinder 12, and a pick-off ring 13. The inner cylinder 11, the outer cylinder 12 and the pick-off ring 13 constitute a steam / water separator 10, and the steam / water separator 6 has a three-stage steam / water separator 10. In FIG. 5, the steam / water separators 10 at each stage are distinguished by a, b, and c. That is, the steam / water separator 10a is a first-stage steam / water separator, the steam / water separator 10b is a second-stage steam / water separator, and the steam / water separator 10c is a third-stage steam / water separator. . In FIG. 5, the component with “a” is the component of the steam-water separator 10 a, the component with “b” is the component of the steam-water separator 10 b, and the component with “c” is the steam-water It is a component of the separation part 10c.

  The stand pipe 7 is attached to the shroud head 5. The diffuser 8 whose internal cross-sectional area increases upward (downstream) has a lower end (upstream end) joined to the upper end (downstream end) of the stand pipe 7 by welding. A swirler 9 having a plurality of blades is installed in the diffuser 8. The steam / water separator 10a is installed at the upper end of the diffuser 8, the steam / water separator 10b is installed at the upper end of the steam / water separator 10a, and the steam / water separator 10c is installed at the upper end of the steam / water separator 10b. The steam / water separator 10a includes an inner cylinder 11a, an outer cylinder 12a, and a pick-off ring 13a. The inner cylinder 11a is attached to the upper end of the diffuser 8, and the pick-off ring 13a is attached to the upper end of the inner cylinder 11a. The pick-off ring 13a has a configuration in which a cylindrical portion is attached to a disc portion, and the cylindrical portion extends downward (upstream) from the disc portion. An opening 17a is formed in the cylindrical portion. In order to reduce the pressure loss of the steam / water separator 6, the outer surface of the lower end portion of the cylindrical portion of the pick-off ring 13a is tapered. Pick-off rings 13b and 13c, which will be described later, also have the same configuration as the pick-off ring 13a. An outer cylinder 12a surrounding the inner cylinder 11a is attached to the pick-off ring 13a and extends downward from the pick-off ring 13a. An annular drainage passage 15a is formed between the inner cylinder 11a and the outer cylinder 12a. A gap 14a that connects the inside of the inner cylinder 11a and the drainage passage 15a is formed at the upper end of the inner cylinder 11a.

  The steam / water separator 10b includes an inner cylinder 11b, an outer cylinder 12b, and a pick-off ring 13b. The lower end of the inner cylinder 11b is attached to the pick-off ring 13a, and the pick-off ring 13b is attached to the upper end of the inner cylinder 11b. The outer cylinder 12b surrounding the inner cylinder 11b is attached to the pick-off ring 13b and extends downward from the pick-off ring 13b. An annular drainage passage 15b is formed between the inner cylinder 11b and the outer cylinder 12b. A gap 14b that connects the inside of the inner cylinder 11b and the drainage passage 15b is formed at the upper end of the inner cylinder 11b. A discharge port 18b communicating with the drainage passage 15b is formed at the lower end of the outer cylinder 12b.

  The steam / water separator 10c includes an inner cylinder 11c, an outer cylinder 12c, and a pick-off ring 13c. The lower end of the inner cylinder 11c is attached to the pick-off ring 13b, and the pick-off ring 13c is attached to the upper end of the inner cylinder 11c. An outer cylinder 12c surrounding the inner cylinder 11c is attached to the pick-off ring 13c and extends downward from the pick-off ring 13c. An annular drainage passage 15c is formed between the inner cylinder 11c and the outer cylinder 12c. A gap 14c that connects the inside of the inner cylinder 11c and the drainage passage 15c is formed at the upper end of the inner cylinder 11c. A discharge port 18c communicating with the drainage passage 15c is formed at the lower end of the outer cylinder 12c.

  The function of the steam separation in the steam separator 6 will be specifically described. A gas-liquid two-phase flow including steam and cooling water that has risen from the core 3 flows into the stand pipe 7 of the steam separator 6 and rises in the stand pipe 7. The steam flows through the central portion of the cross section of the stand pipe 7, and most of the cooling water adheres to the inner surface of the stand pipe 7 and exists as a liquid film, and rises along the inner surface of the stand pipe 7 in a liquid film state.

  The gas-liquid two-phase flow flows into the diffuser 8. This gas-liquid two-phase flow is given a turning force by the swirler 9, water having a high density is blown to the outside by the centrifugal separation action, and the steam having a low density gathers at the center of the inner cylinder 11a and rises. The water blown to the outside adheres to the inner surface of the inner cylinder 11a and forms a liquid film. This liquid film rises along the inner surface of the inner cylinder 11a, hits the pick-off ring 13a, is separated from the vapor, and is discharged to the drainage passage 15a through the gap 14a. The separated water descends the drainage passage 15a, passes through the bent portion 25, and returns to the cooling water 35 existing outside the steam / water separator 6 from the discharge port 18a.

  The gas-liquid two-phase flow whose water content is reduced after the water is removed by the steam-water separation unit 10a passes through the opening 17a of the pick-off ring 13a and turns in the inner cylinder 11b of the steam-water separation unit 10b Flow into. The water contained in the gas-liquid two-phase flow that has passed through the opening 17a is blown to the outside and forms a liquid film on the inner surface of the inner cylinder 11b. The liquid film ascends along the inner surface of the inner cylinder 11b and hits the pick-off ring 13b to be separated from the vapor. The separated liquid film, that is, moisture is discharged to the drainage passage 15b through the gap 14b. This moisture descends the drainage passage 15b and is discharged into the steam from the discharge port 18b.

  The water separated by the steam separator is discharged from the steam separator to the outside of the steam separator. The drained water flows into the cooling water filled in the lower fixed region of the external space of the steam / water separator. As shown in FIG. 13, the cooling water surface is adjusted to be positioned above the discharge port 1 and below the discharge port 2 of the steam / water separation unit. Therefore, the water discharged from the discharge port 2 falls toward the water surface 24 due to gravity. At this time, the fallen drainage collides with the water surface 24, and the impact causes the steam 29 to be mixed into the cooling water or the droplets 28 to be scattered into the steam. A part of the steam 29 mixed in the cooling water is caught in the flow of the cooling water flowing into the downcomer in the RPV. The amount of steam entrained is called carry-under. Since the carry-under causes cavitation of an internal pump (or recirculation pump) that supplies cooling water to the core, the current core is designed so that the carry-under value is within an allowable range. In addition, some of the droplets 28 scattered into the steam are transported to the rising steam flow 22 and reach the dryer installed on the upper part of the steam separator, causing the steam / water separator performance of the steam / water separator to deteriorate. It becomes. This phenomenon is called entrainment. The amount of water that reaches the dryer is called carry-over. The above carry-under and carry-over are each kept below the allowable value in the current core, but further reduction of carry-under and carry-over is desired for the development of the next generation plant with further improved economic efficiency.

  Therefore, in this embodiment, the reinforcing member is installed at a position lower than the drain port 2 and the structure of the drain port 2 is changed so that the drain port 2 is positioned directly above the reinforcing member.

  With the structure of the present embodiment, the structural strength can be maintained as compared with the conventional steam separator, and both carry-under and entrainment can be reduced as the added value from the following two effects. The first effect is that a part of the water discharged from the drain outlet is captured by the reinforcing member before falling onto the water surface, and then passes through the splash prevention plate provided on the outer casing or the reinforcing member of the water separator. Therefore, it is possible to reduce the generation of steam and droplets generated by the impact of water falling on the water surface. The second effect is that the generated vapor and droplets can be recaptured by the scattering prevention plate.

  In this embodiment, unlike Japanese Patent Laid-Open No. 8-179077 which captures a droplet after being lifted by vapor, the impact of the water discharged from the discharge port, which is the source of the droplet, dropping onto the water surface. This reduces the generation of droplets. Moreover, the droplet immediately after generation | occurrence | production can be captured by the stage before being conveyed to a vapor | steam by a scattering prevention board. In addition, it is possible to reduce droplet scattering with a small installation area, and it is possible to reduce steam mixing into the cooling water that causes carry-under. Moreover, since the installation area is small, the pressure rise near the water surface can be reduced.

  Specifically, the structure of the reinforcing plate will be described. In the steam separator of the present embodiment, the cooling water surface exists between the discharge port 18a and the discharge port 18b. Therefore, in the steam separator according to the first embodiment, the reinforcing plate 21 is installed as shown in FIG. 1, and the three outlets are installed on the upper portion of the reinforcing plate 21 as shown in FIG. The reinforcing plate 21 is installed below the discharge port 18b. The reinforcing plate 21 has a semi-cylindrical shape as shown in FIG. 4 and has an inner wall facing upward, and is inclined so as to descend in the direction of the discharge port 18b among the two steam-water separators connected as shown in FIG. It is installed.

  In this embodiment, since the reinforcing plate 21 is provided, most of the water discharged from the discharge port 18b is captured in the flow path formed on the inner wall surface of the reinforcing plate 21 and travels through the flow path. It reaches the steam / water separator outer cylinder, and further flows along the steam / water separator outer cylinder to the cooling water surface. Since it gently flows into the water surface, it is possible to reduce the mixing of steam into the cooling water and the scattering of droplets into the steam.

  The steam whose water content is reduced by removing water in the steam-water separating unit 10b flows into the inner cylinder 11c of the steam-water separating unit 10c through the opening 17b of the pick-off ring 13b while turning. The water contained in the steam that has passed through the opening 17b is blown out and forms a liquid film on the inner surface of the inner cylinder 11c. This liquid film rises along the inner surface of the inner cylinder 11c, hits the pick-off ring 13c, and is separated from the vapor. The water, which is the separated liquid film, is discharged to the drainage passage 15c through the gap 14c. This moisture descends the drainage passage 15c and is discharged from the discharge port 18c. Since the amount of water discharged from the discharge port 18c is very small and the impact upon dropping to the cooling water surface is small, the reinforcing plate 21 is not installed below the discharge port 18c in this embodiment.

  The structure of the reinforcing plate 21 of Example 2 is shown in FIG. A structure in which inclined plates descending toward both ends of the steam separator connected from the center of the reinforcing plate 21 is provided. In the present embodiment, as shown in FIG. 7, six outlets 18b are provided for each steam separator. Since the total outlet area of the discharge port 18b is increased by providing the six discharge ports 18b, the discharge rate of water per one point is reduced. Therefore, as shown in FIG. 6, since the discharged water flows into the water surface more gently, the effect of reducing the mixing of steam into the cooling water and the scattering of droplets into the steam is improved as compared with the first embodiment. .

  The structure of the reinforcing plate 21 of Example 3 is shown in FIG. In this embodiment, the scattering prevention plate 26 is provided in parallel with the reinforcing plate 21 and the central axis of the steam / water separator. As shown in FIG. 10, six outlets 18b were provided.

  As shown in FIG. 9, a part of the water discharged from the discharge port 18b is captured by the reinforcing plate 21, reaches the steam / water separator outer cylinder or the scattering prevention plate 26 at both ends through the reinforcing plate 21, and It gently flows into the water surface through the outer shell of the steam separator or the scattering prevention plate 26. A part of the discharged water collides with the scattering prevention plate 26, descends along the scattering prevention plate 26, and flows into the water surface. Part of the discharged water falls directly on the surface of the water, and the collision generates steam and droplets in the steam. However, a part of the generated steam and droplets is captured by the scattering prevention plate and returned to the water surface again, thereby reducing the occurrence of entrainment and carry-under.

  Since the structure of the anti-scattering plate 26 according to the third embodiment recaptures the vapor and droplets generated as described above, the longer the structure is in both the upper and lower directions than the water surface, the greater the effect.

  Moreover, the structure of a reinforcement board can also consider FIG. 12 which combined the semi-cylindrical reinforcement board of Example 1, and the scattering prevention board of Example 3. FIG.

  The boiling water reactor of the present embodiment will be described with reference to FIG. The boiling water reactor of this embodiment is provided with the steam / water separator according to any of the first, second, and third embodiments. The reinforcing plate 21 installed in the embodiment has sufficient structural strength. As an additional effect, carry-under and entrainment in the steam separator can be reduced as described above.

7 Standpipe 8 Diffuser 9 Swirler 10, 10a, 10b, 10c Air-water separator 11, 11a, 11b, 11c Inner cylinder 12, 12a, 12b, 12c Outer cylinder 13, 13a, 13b, 13c Pickoff rings 15a, 15b, 15c Drainage passages 18a, 18b, 18c Discharge port 21 Reinforcement plate 26 Splash prevention plate

Claims (3)

A stand pipe for guiding a gas-liquid two-phase flow; a diffuser connected to the downstream end of the stand pipe and expanding toward the downstream; a first stage inner cylinder communicating with the upper end face of the diffuser to form a flow path; A first stage outer cylinder that surrounds the first stage inner cylinder and forms a drainage passage with the first stage inner cylinder, and a pick-off that is attached to the upstream end of the first stage outer cylinder and has an opening. A boiling water mold comprising a plurality of steam / water separators having a ring and forming a gap between the inner cylinder and the pick-off ring, wherein the steam / water separators are sequentially arranged downstream In the reactor,
Among the drainage passages formed between the inner cylinder and the outer cylinder, a reinforcing plate for connecting adjacent steam separators is installed below the outlet of the second drainage passage from the upstream. Boiling water reactor. The boiling water reactor according to claim 1,
A boiling water reactor characterized in that the reinforcing plate is attached with an inclination. The boiling water reactor according to claim 1,
A boiling water reactor characterized in that a splash prevention plate is provided in parallel with the central axis of the steam separator.

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