JP2010196567A - Jet pump of boiling water reactor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a jet pump improving efficiency of the jet pump and inhibiting vibration of a throat, and to provide a reactor using the same. <P>SOLUTION: A spreading angle of a tapered surface of an inlet mixer inner wall of the throat is set at an optimum inclination angle with a small pressure loss, a lower end of the inlet mixer for insertion in a slip joint part is formed in a vertical cylindrical part having no inclination, an extension is provided on an lower portion of the cylindrical part, and an inner surface of the extension is provided with a tapered surface gradually expanding toward an upper end inner wall of a diffuser, so that a pressure loss of the throat is reduced and the efficiency is improved. The outer diameter of the extension is set slightly smaller than the inner diameter of the slip joint part at the diffuser upper end. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a jet pump, and more particularly to a jet pump suitable for a boiling water reactor.

  A conventional boiling water reactor (BWR) has a plurality of jet pumps installed in a reactor pressure vessel. The jet pump has a nozzle, a bell mouth, a throat, and a diffuser, and the nozzle, the bell mouth, and the throat provided integrally are detachably joined to the diffuser. The throat is composed of a throat straight pipe and an inlet mixer provided below the throat straight pipe. Cooling water whose pressure has been increased by driving a recirculation pump provided in a recirculation system pipe connected to the reactor pressure vessel passes through the recirculation system pipe and is ejected from the nozzle into the jet pump as drive water. The nozzle increases the speed of the driving water, sucks the driven water that is the cooling water around the nozzle by the jetted driving water, and causes the driven water to flow into the throat from the bell mouth. The cooling water discharged from the diffuser through the throat is supplied to the core through the lower plenum (see Patent Document 1).

  Patent Document 1 describes a structure in which an elastic body such as a leaf spring is provided at a joint portion between an inlet mixer and a diffuser at the bottom of the throat to reduce leakage water from the joint portion and suppress vibration. Patent Document 2 describes a structure in which a labyrinth seal mechanism is provided at a joint portion between an inlet mixer and a diffuser to reduce leakage water from the joint portion and suppress vibration. Patent Document 3 describes a structure in which a seal ring is provided at the upper part of the joint between the inlet mixer and the diffuser to reduce leakage water from the joint and suppress vibration.

  Patent Document 4 describes a structure in which a slip joint is provided at a portion where the internal pressure of the throat is negative so that the leak from the jet pump is eliminated and suction is performed in the opposite direction.

  Patent Document 5 describes that a plurality of thin vertical grooves extending in the axial direction are formed on the inner surface of a throat of a jet pump to reduce pressure loss.

  Here, Patent Documents 1 to 3 all have a special structure to reduce leakage water from the joint and suppress vibration. Patent Document 4 is intended to increase the suction water and increase the efficiency, and Patent Document 5 is intended to increase the efficiency by reducing pressure loss with a complicated structure.

JP 2008-170272 A Japanese Patent Publication No.59-48360 Japanese Patent Laid-Open No. 2002-221589 Japanese Patent Laid-Open No. 58-15798 JP-A-8-135600

  A schematic structure of a boiling water reactor (BWR) equipped with a conventional jet pump will be described below with reference to FIG. The BWR has a core shroud 2 installed in a reactor pressure vessel 1. A core 3 loaded with a plurality of fuel assemblies (not shown) is disposed in the core shroud 2. A steam separator 4 and a steam dryer 5 are disposed above the core 3 in the reactor pressure vessel 1.

  A jet pump 6 is disposed in a downcomer 7 formed between the reactor pressure vessel 1 and the core shroud 2. The jet pump 6 includes a nozzle 11, a bell mouth 17, a throat 18, and a diffuser 19. The reactor pressure vessel 1 is provided with a recirculation system having a recirculation system pipe 8 and a recirculation pump 9. One end of the recirculation pipe 8 is connected to the reactor pressure vessel 1 and connected to the downcomer 7, and the other end is connected to the nozzle 11 of the jet pump 6 via a riser pipe 10 disposed in the downcomer 7. . A main steam pipe 12 and a water supply pipe 13 are connected to the reactor pressure vessel 1.

  Cooling water 14, which is a driven fluid existing in the upper part of the reactor pressure vessel 1, is mixed with the feed water 15 supplied from the feed water pipe 13 to the reactor pressure vessel 1 and descends in the downcomer 7. The cooling water 14 flows into the recirculation system pipe 8 by driving of the recirculation pump 9 and is boosted by the recirculation pump 9. This boosted cooling water is referred to as driving water 16 for convenience.

  The driving water 16 is ejected from a porous nozzle 11 provided in the jet pump 6 through the recirculation system pipe 8 and the riser pipe 10. The cooling water 14 existing around the nozzle 11 is sucked by the driving water 16 and sucked into the throat 18 from the bell mouth 17. The cooling water 14 descends in the throat 18 together with the driving water 16 and is discharged from the diffuser 19. The cooling water including the cooling water 14 and the driving water 16 discharged from the diffuser 19 is referred to as cooling water 20.

  The cooling water 20 is supplied to the core 3 through the lower plenum 21 and is heated when passing through the core 3 to become a two-phase flow containing water and steam. The steam / water separator 4 separates the steam and water, and the separated steam is further dehumidified by the steam dryer 5 and discharged to the main steam pipe 12. This steam is guided to a steam turbine (not shown) to rotate the steam turbine. The steam discharged from the steam turbine is condensed into water by a condenser (not shown), and supplied as water 15 into the reactor pressure vessel 1 through the water supply pipe 13 again. The cooling water separated by the steam separator 4 and the steam dryer 5 falls and becomes cooling water 14 again.

  The jet pump 6 effectively transmits the power of the recirculation pump 9 from the driving water 16 to the cooling water 14, and makes the flow rate of the cooling water 20 discharged from the jet pump 6 larger than the flow rate of the driving water 16. The kinetic energy of the driving water 16 provided by the recirculation pump 9 effectively acts on the cooling water 14, the flow rate of the cooling water 14 sucked into the bell mouth 17 is increased, and the flow rate of the cooling water 20 is further increased. . Therefore, the flow rate of the driving water 16 at the outlet of the nozzle 11 is increased so that the kinetic energy of the driving water 16 is increased, and cooling is performed by making the flow path area smaller than that of the bell mouth 17 at the inlet portion of the throat 18. The speed of water 14 is increased to reduce the static pressure. As a result, the cooling water 14 can be sucked into the throat 18 and a necessary core flow rate can be secured with a small amount of power.

  FIG. 9 is a cutaway perspective view showing details of the state of jet pump installation in the nuclear reactor. The jet pump 6 is composed of a set of two units, and includes a porous nozzle 11, a bell mouth 17, a throat 18 having a throat straight pipe 24 and an inlet mixer 25, and a diffuser 19. The driving water 16 is divided into two hands by the branch pipe 22 at the upper part of the riser pipe 10, and each is supplied to the nozzle 11 of each jet pump 6. The nozzle 11 is arranged to face the upper opening of the bell mouth 17.

  Between the nozzle 11 and the bell mouth 17, a cooling water suction passage is formed for guiding the cooling water 14 existing around the nozzle 11 into the bell mouth 17. The cooling water 14 sucked by the driving water 16 ejected from the nozzle 11 passes through the cooling water suction passage and flows into the throat straight pipe 24. Qa is the flow rate of the driving water 16, and Qb is the flow rate of the cooling water 14. A fixing plate 23 is provided in the cooling water suction channel, and the nozzle 11 is fixed to the bell mouth 17. The driving water 16 ejected from the nozzle 11 flows from the bell mouth 17 through the throat straight pipe 24 having the narrowest channel cross-sectional area located below to the inlet mixer 25 whose inner wall is spread downward with a tapered surface. To do. At the lower end of the inlet mixer 25, the throat 18 and the diffuser 19 are connected by a slip joint 26. The diffuser 19 has a tapered surface in which the channel cross-sectional area is narrow at the upper end portion having the slip joint 26 and the channel cross-sectional area gradually increases toward the lower side.

  Since the jet pump 6 has a length of about 6 m from the branch pipe 22 to the lower end of the diffuser 19 and has a large thermal deformation, the slip joint 26 is provided as a thermal expansion absorption mechanism, and the nozzle 11 side can be easily disassembled and maintained. I have to.

  10 and 11 are cross-sectional views showing the configuration of a jet pump using the nozzle 11 in the conventional example. In FIG. 10, squirting water 27 (a part of the driving water 16) from the porous nozzle 11 squirts into the bell mouth 17, sucks the cooling water 14, and forms a throat straight pipe 24, an inlet mixer 25, which constitutes a throat 18. Cooling water 20 to be supplied to the reactor core via the slip joint 26 and the diffuser 19 is generated. Details of the structure of the slip joint 26 are shown in FIG. Stellite layers 28 are provided on the opposing surfaces of the inlet mixer 25 and the diffuser 19 of the slip joint 26 to reduce wear of the slip joint 26. L3 is a gap of the slip joint 26.

  In the conventional example, the expansion angle θ1 of the inner wall taper surface of the inlet mixer 25 is as small as about 1.5 °. Therefore, the inner diameter of the slip joint 26 portion is suddenly widened at a short distance L1 with an expansion angle θ2 of about 6 °. Was structured. In this structure, since the inner diameter D1 is reduced at the end of the inlet mixer 25 and the distance L2 from the diffuser upper inner wall 19a is increased, the pressure loss of the cooling water 20 due to the expanded flow is increased. The pressure loss is also increased by widening the reduced pressure region 30 generated by the lower streamline 29 of the inlet mixer 25.

  Furthermore, since the pressure fluctuation in the decompression region 30 is large and the pulsation of leaked water is also large, the vibration of the throat 18 may increase and the upper part of the throat 18 may be damaged. The vibration of the throat 18 is also greatly influenced by the length of the slip joint 26. If the length of the slip joint 26 is short, the pressure loss at the slip joint 26 is reduced, and the amount of leaked water Qr is increased to adversely affect the vibration. Physical strength increases.

  The performance of a jet pump is generally expressed by the M ratio, N ratio, and efficiency as shown below. The M ratio is the ratio of the flow rate Qb of the driven water (cooling water 14) to the flow rate Qa of the drive water 16, and is expressed by the equation (1).

M ratio = Qb / Qa (1)
The N ratio is the total head ratio of the driven water with respect to the driving water, and is expressed by equation (2).

N ratio = (Hc−Hb) / (Ha−Hc) (2)
Here, as shown in FIG. 9, Ha is the total head at the nozzle driving water inlet, Hb is the total head at the driven water inlet of the jet pump, and Hc is the total head at the jet pump outlet.

  Efficiency is the ratio of the energy of the driven water to the driving water, and is expressed by the equation (3) as the product of the M ratio and the N ratio.

Efficiency = M ratio x N ratio (3)
As a jet pump, it is desirable that the M ratio, the N ratio and the efficiency be higher. If the flow rate of cooling water discharged from the jet pump can be increased by using a highly efficient small-capacity recirculation pump, the recirculation system can be made compact and the installation space of the recirculation system can be reduced. .

  For example, in the case of improving the output in an existing nuclear reactor such as BWR, the range of improvement in the reactor output can be expanded by increasing the core flow rate of the cooling water. Further, by increasing the control range of the core flow rate, the change rate of the void ratio in the core can be increased, and the fuel economy can be improved. In order to increase the core flow rate, it is better to improve the recirculation pump, feed water pump and jet pump. However, in the modification of the existing reactor for the purpose of improving the output, the large scale equipment such as the recirculation pump and the feed water pump is modified or replaced. Compared to the above, it is effective to improve the jet pump which requires a small modification. A new problem in the improvement of the jet pump will be described below.

  First, in order to improve output with a BWR having an existing jet pump, it is necessary to increase the efficiency of the jet pump. When recirculation pumps with the same output are used and the N ratio is the same, an increase in the efficiency of the jet pump can be achieved by improving the M ratio. However, increasing the M ratio increases the pressure loss at the minimum bore throat and decreases the N ratio. Bring. Therefore, in order to increase the efficiency of the jet pump with a high M ratio and N ratio, it is necessary to reduce the pressure loss of the throat.

  Secondly, the jet pump installed in the existing BWR that improves output uses a slip joint, and the cooling water in the jet pump leaks outside through the gap of the slip joint, resulting in a loss of the jet pump. . Furthermore, hydrodynamic vibration is generated based on the leaked water, which causes the diffuser and throat connection to wear. Furthermore, if the performance of the jet pump is improved, the internal pressure of the throat and diffuser will rise, and the leakage water will also increase. Therefore, in order to ensure the soundness of the jet pump, it is necessary to reduce the leakage water to reduce the loss and to suppress the wear at the connecting portion between the diffuser and the throat due to the fluid vibration.

  The above-described problems have been newly found by examining conventional jet pumps in order to achieve improvement in reactor power and reduction in vibration.

  When the inner diameter of a conventional jet pump is simply increased, the outer diameter of the diffuser needs to be increased over the entire length, and a large-scale modification work is required. Therefore, the inner diameter at the joint at the lower end of the throat is increased. Can not do it.

  An object of the present invention is to provide a jet pump and a nuclear reactor using the jet pump that can suppress the pressure loss of the jet pump and wear due to hydrodynamic vibration, and can further increase the efficiency without requiring major modification. .

  In particular, the present invention has newly found that the performance can be improved by improving the shape of a throat that can be replaced by a jet pump.

  The present invention includes a nozzle for ejecting a driving fluid, a bell mouth into which the driving fluid and the driven fluid sucked by the driving fluid flow, a throat straight pipe and an inlet mixer for mixing the driving fluid and the driven fluid. In a jet pump having a throat and a diffuser connected to the throat and a slip joint at the lower end of the inlet mixer, a cylindrical portion having a vertical surface is provided at the lower end of the inlet mixer forming the slip joint. It is characterized by.

  Moreover, the spread inclination angle of the inner wall taper surface of the inlet mixer is set to 1.6 to 2.0 °.

  In addition, an extension is provided below the cylindrical portion at the lower end of the inlet mixer, a tapered surface that gently spreads downward is provided on the inner wall of the extension, and the outer wall of the extension is a vertical that is slightly smaller than the outer diameter of the slip joint at the lower end of the throat. A cylindrical surface is provided.

  Further, in the boiling water reactor, the plurality of jet pumps installed in the reactor vessel and supplying coolant to the core formed in the reactor vessel are the above-described jet pumps. .

  According to the present invention, in order to improve the efficiency of the jet pump, the throat spreading angle is set to an optimum inclination angle with little pressure loss, and a cylindrical portion extending vertically to the lower end of the throat to be inserted into the slip joint is provided, and the upper end of the diffuser is further provided. An extension portion having a tapered surface where the inner wall gradually expands toward the inner wall can be provided in the cylindrical portion to reduce pressure loss. In addition, the outer diameter of the extension added to the cylindrical part is a cylinder slightly smaller than the inner diameter of the slip joint part at the upper end of the diffuser, increasing the pressure loss of the leaked water using a minute gap as a flow path, reducing the amount of leaked water, Wear of the throat can be reduced by reducing the vibration of the throat due to the pressure fluctuation of the leaked water.

It is sectional drawing of the jet pump in a present Example. It is the D section enlarged view in FIG. It is a characteristic view of the inlet mixer of a present Example. It is a graph which shows the relationship between the amount of leaked water of a jet pump, and pressure loss. It is a graph which shows the relationship between M ratio and efficiency. It is a frequency characteristic figure of the fluctuation | variation pressure in the pressure reduction area of an inlet mixer lower end. It is a throat vibration characteristic figure. It is a schematic diagram of the boiling water reactor of a prior art example. It is a fractured perspective view of the jet pump shown in FIG. It is sectional drawing of the jet pump by a prior art example. It is the A section enlarged view in FIG.

  Details of the embodiment of the jet pump according to the present invention will be described below.

  An embodiment of the present invention will be described with reference to FIG. FIG. 1 is a sectional view showing the configuration of a jet pump using a porous nozzle 11 as in FIG.

  Here, the squirting water 27 (driving water 16) from the nozzle 11 is similarly squirted into the bell mouth 17, sucking a part of the cooling water 14, and a throat 18A comprising a throat straight pipe 24 and an inlet mixer 25A, The core coolant 20 is formed via the slip joint 26 and the diffuser 19.

  The structure of the jet pump of the present embodiment is that of a throat 18A that can be replaced with the throat 18 used in the conventional jet pump. From the viewpoint of compatibility, the distance L0 from the bell mouth 17 to the upper end of the diffuser 19 is the conventional one. Is fixed to the same value. Therefore, optimization is aimed at in other parts.

FIG. 2 shows a structure in the vicinity of the slip joint 26 which is a point of the present invention. In FIG. 2, the lower shape of the conventional inlet mixer 25 is indicated by a dotted line 31.
As the spread angle θ1a of the inner wall taper surface of the inlet mixer 25A in this embodiment, an optimum inclination angle that minimizes the pressure loss and maximizes the efficiency is adopted. As shown in FIG. 3, it was confirmed by experiment that the spread angle that gives the maximum efficiency is about 1.8 °. Furthermore, since the spread angle θ1a is not so different in the maximum efficiency between 1.6 and 2.0 °, this range was adopted as the optimum inclination angle. This is an inclination angle larger than the spread angle of about 1.5 ° of the conventionally used inlet mixer 25.

  If this optimum inclination angle is adopted and the inlet mixer is configured as in the conventional example, the outer diameter of the lower end of the inlet mixer 25A becomes larger than the inner diameter D0 of the upper portion of the diffuser 19, and compatibility cannot be maintained. Therefore, a cylindrical portion C having vertical inner and outer walls without being inclined is provided at the lower end portion of the inlet mixer 25A. The spread angle of the inlet mixer 25A is set larger than the conventional one, and the cylindrical portion C is formed at the lower end joined to the diffuser 19, so that the lower end inner diameter D1a of the inlet mixer 25A is the minimum lower end of the inlet mixer 25A indicated by the dotted line 31 of the conventional example. Since the inner diameter D1 can be made larger and the distance L2 from the diffuser upper inner wall 19a can be made smaller, the pressure loss due to the generation of the enlarged flow can be reduced.

  Further, in the conventional example, the stellite layer 28 is the final lower end of the inlet mixer 25, whereas in this embodiment, a skirt portion 32 having an inner wall made of a tapered surface is provided as an extension portion below the cylindrical portion C. The length L1 of the skirt portion 32 is set above the position of the pressure conduit 33 to avoid interference with the existing pressure conduit 33, the inner wall thereof is gently inclined as a tapered surface, and the tip is rounded with a radius of about 2 mm to be inserted into the diffuser 19 To make it easier. The outer wall of the skirt portion 32 is provided with a vertical cylindrical surface 32a, and its outer diameter D3 is slightly smaller than the outer diameter D2 of the stellite layer 28 portion provided in the inlet mixer 25A by about 0.2 to 0.3 mm. Avoid damage due to contact with 19a.

  The enlarged flow loss and the friction loss are reduced by the gently tapered surface of the inner wall of the skirt part 32, and the enlarged loss of the discharge part is reduced by shortening the distance L3 from the diffuser upper inner wall 19a at the tip. Further, the pressure reduction region 30 generated at the tip is narrowed to reduce the pressure fluctuation of the leaked water. Furthermore, by newly providing a minute gap 34 between the diffuser upper inner wall 19a and the cylindrical surface 32a of the skirt portion 32, the pressure loss of the leaked water is increased, the leaked water flow rate Qr is reduced, and the amount of water corresponding to the leakage reduction is increased. It contributes to the efficiency increase by using effectively.

  FIG. 4 shows the present embodiment in which the gap 34 between the diffuser upper inner wall 19a and the cylindrical surface 32a of the skirt portion 32 is 0.3 mm, and the length of the skirt portion 32 is 7 times that of the conventional slip joint. The relationship between leakage flow rate and pressure loss is shown. From this, when the leakage water pressure loss is the same (one-dot chain line), the leakage water flow rate Qr is about 1/3 of the leakage flow rate z of the conventional example. As is clear from this, in this embodiment, 2/3 of the amount of leaked water in the conventional example can be effectively used, which contributes to an increase in efficiency.

  FIG. 5 shows the relationship between the M ratio and the efficiency of the jet pump according to this embodiment. From this, by adopting the present embodiment, the maximum efficiency can be increased to the efficiency Y1 of the conventional example up to Y2. Further, the M ratio can increase the point of use X1 according to the conventional example to X2, which can contribute to an increase in the jet pump flow rate when the output is improved.

  Next, vibration reduction of the throat 18A of the jet pump in the present embodiment will be described. The vibration of the throat is caused by the pressure fluctuation in the reduced pressure region at the lower end of the inlet mixer, and the vibration of the throat is generated by the fluid vibration of the leaked water. Therefore, vibration is greatest when the pressure fluctuation is large and the amount of leaked water is large.

  In order to solve these problems, in the present embodiment, as described above, the reduced pressure region 30 at the lower end of the inlet mixer 25A is reduced, and the fluctuation range is reduced, thereby reducing the flow vibration of the leaked water. In addition, the lower end of the inlet mixer 25A is inserted into the diffuser long, and at the insertion portion, the gap 34 between the diffuser upper inner wall 19a and the cylindrical surface 32a of the skirt portion 32 is made a minute gap, thereby increasing the pressure loss of leaked water. Therefore, the vibration of the throat 18 was reduced by reducing the flow rate and further providing a damper (vibration damping) effect.

  FIG. 6 shows the frequency characteristics of the fluctuating pressure in the decompression region 30 at the lower end of the inlet mixer 25A. From this, in the decompression area 30, there are pressure fluctuation components of the jet flow from the nozzle and pressure fluctuations induced at the outlet portion of the inlet mixer 25A. According to this embodiment, the decompression area 30 is reduced and the leakage water amount Qr is reduced. , Pressure fluctuation is reduced. When the pressure fluctuation related to the leaked water is reduced in this way, the vibration acceleration of the throat 18 is also reduced as shown in FIG.

6 ... Jet pump, 11 ... Nozzle, 16 ... Drive water, 17 ... Bellmouth, 18A ... Throat, 19 ... Diffuser, 24 ... Throat straight pipe, 25A ... Inlet mixer, 26 ... Slip joint, 32 ... Skirt part, 32a ... Cylindrical surface, C ... cylindrical part

Claims (4)

A nozzle that ejects the driving fluid, a bell mouth into which the driving fluid and the driven fluid sucked by the driving fluid flow, a throat straight pipe that mixes the driving fluid and the driven fluid, and a tapered surface that extends downward on the inner wall. In a jet pump of a boiling water reactor comprising a throat constituted by an inlet mixer, and a diffuser connected to the throat and a slip joint at the lower end of the inlet mixer,
A boiling water reactor jet pump characterized in that a cylindrical portion having a vertical surface on both the inner and outer walls is provided at the lower end of the inlet mixer forming the slip joint.   2. The boiling water reactor jet pump according to claim 1, wherein an inclination angle of a taper surface of the inner wall of the inlet mixer is set to 1.6 ° to 2.0 °. 3. Jet pump.   3. The boiling water reactor jet pump according to claim 1 or 2, wherein an extension is provided below the cylindrical portion of the lower end of the inlet mixer, and an inner wall of the extension is provided with a tapered surface that gradually spreads downward. The outer wall of the extension is provided with a vertical cylindrical surface slightly smaller than the outer diameter of the slip joint at the lower end of the inlet mixer.   A plurality of jet pumps installed in a nuclear reactor vessel and supplying coolant to a core formed in the nuclear reactor vessel are the jet pumps according to any one of claims 1 to 3. Boiling water reactor is a feature.

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