Abstract:
A jet pump comprising:
       a nozzle apparatus having a header portion including, inside, a first pipe member forming a suction fluid passage for introducing suction fluid and the header portion surrounding the first pipe member, for introducing driving fluid, and a nozzle portion connected to the header portion, surrounding the first pipe member and forming an annular ejection outlet for ejecting the driving fluid;   a jet pump body for mixing the driving fluid and the suction fluid sucked by the ejection of the driving fluid, and discharging the mixed fluid; and   a second pipe member having one end connected to the nozzle apparatus, for introducing the driving fluid to the header portion,   wherein the first pipe member is disposed through the one end inside a driving fluid passage formed in the second pipe member, and forms an opening portion of the suction fluid passage opened to the outside of the second pipe member; and   the driving fluid passage is formed so that the driving fluid flowing toward the one end hits the first pipe member diagonally to the axial direction of the first pipe member.

Description:
CLAIM OF PRIORITY 
       [0001]    The present application claims priority from Japanese Patent application serial no. 2008-001077, filed on Jan. 8, 2008, the content of which is hereby incorporated by reference into this application. 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to jet pump and reactor and more particularly, to a jet pump and a nuclear reactor suitable for application in a boiling water reactor. 
         [0003]    A conventional boiling water reactor (BWR) has a jet pump installed in its reactor pressure vessel. The jet pump has a nozzle, a bell mouth, a throat, and a diffuser. A recirculation pipe is connected to the reactor pressure vessel. Cooling water pressurized by operation of a recirculation pump provided on the recirculation pipe, passes through the recirculation pipe and is ejected from the nozzle into the jet pump as a driving flow. The nozzle increases the speed of the driving flow. The ejected driving flow causes the cooling water present around the nozzle to flow into the throat as a suction flow. The cooling water discharged from the diffuser is supplied to a core through a lower plenum (for example, see U.S. Pat. No. 3,625,820). 
         [0004]    A jet pump disclosed in Japanese Patent Laid-open No. 2002-89499 has a suction pipe for sucking a conveying object (rainwater, wastewater flowed into a grit pound, solid matter, etc.) and an annular member surrounding the suction pipe. In addition, this jet pump forms a high-pressure water feed chamber between the suction pipe and the annular member, provided around the suction pipe. A plurality of water injection openings opened to the high-pressure water feed chamber are disposed around the suction pipe. High-pressure water supplied into the high-pressure water feed chamber is jetted from those injection openings to suck the conveying object into the suction pipe. 
         [0005]    The jet pump disclosed in FIG. 3 of Japanese Patent Laid-open No. 2001-90700 has a venturi pipe and a nozzle for ejecting a driving flow to the upper course of the venturi pipe. This nozzle has an inner cylinder and an outer cylinder surrounding the inner cylinder. A driving flow passage formed between the inner cylinder and the outer cylinder is an annular passage for the driving flow, the cross section of which passage gradually diminishes toward the discharging side of the driving flow. The driving flow supplied to the driving flow passage is ejected from one end of the passage (a discharge outlet) into the venturi pipe. Washing water present around the nozzle is sucked into the venturi pipe due to the driving flow ejected from the nozzle. To be more precise, this washing water flows into the venturi pipe through each of a first coolant suction passage formed between the nozzle and the venturi pipe and a second coolant suction passage formed inside the inner cylinder. The driving flow in a cylindrical form is ejected from the nozzle. The cross sections of the driving flow in a cylindrical form look like continuous rings. 
       SUMMARY OF THE INVENTION 
       [0006]    Performance of a jet pump can be indicated by the M ratio, N ratio and efficiency as shown below. M ratio is the ratio of a flow rate Qs of the suction flow (cooling water) flowed into a throat portion, to a flow rate Qn of the driving flow (recirculating water) at a nozzle portion, represented as in an equation (1). 
         [0000]        M  ratio= Qs/Qn   (1) 
         [0007]    N ratio is the total pressure ratio of the suction flow to the driving flow, represented as in an equation (2). 
         [0000]        N  ratio=( Pd−Ps )/( Pn−Pd )  (2) 
         [0008]    Here, Pd is the total pressure of a diffuser portion, Ps is the total pressure of the throat portion, and Pn is the total pressure of the nozzle portion. Efficiency η is the ratio of energy of the suction flow to the driving flow, represented as a product of the M ratio and the N ratio. 
         [0000]      η= M  ratio× N  ratio  (3) 
         [0009]    It is preferable for a jet pump to have a larger M ratio, N ratio and efficiency η. If the flow rate of the cooling water discharged from the jet pump could be efficiently increased using a recirculation pump of small capacity, the recirculation system can be downsized and installation space for the recirculation system can be reduced. 
         [0010]    For example, when a power uprate in an existing nuclear reactor (BWR, for example) is to be implemented, the reactor power can be increased by increasing the core flow to enhance the cooling capability of the core. In addition, since expanding the control range of the core flow rate increases the range of void fraction change in the core, the economical efficiency of fuel can be improved. In order to increase the core flow rate, the recirculation pump, the feed water pump, and the jet pump may be modified. The inventors have found out that modification of the jet pump was more effective than reconstruction or replacement of large equipment such as the recirculation pump and the feed water pump, for the reconstruction of the existing reactor for the power uprate. Since performance of the jet pump heavily depends on the shape of the mixing part for mixing the driving flow and the suction flow, the performance may be improved by modifying the nozzle for ejecting the driving flow. 
         [0011]    The jet pump disclosed in Japanese Patent Laid-open No. 2002-89499, which has the suction pipe for sucking a conveying object, and the annular member surrounding the suction pipe to supply a driving flow inside, cannot be used as a jet pump of the nuclear reactor to supply coolant to the core. If the jet pump disclosed in the patent document is installed in a downcomer, which is an open area inside the reactor pressure vessel, pressure loss at the suction portion will be too large to increase the M ratio. If the diameter of the suction pipe is made larger to reduce the pressure loss at the suction portion and also to increase the M ratio, the high-pressure water feed chamber that is the annular portion, will be large, causing the jet pump to be uninstallable in the small downcomer area above a set of two jet pumps in a current BWR. 
         [0012]    The jet pump disclosed in FIG. 3 of Japanese Patent Laid-open No. 2001-90700 flows a suction flow present around the nozzle into the venturi pipe through each of the first coolant suction passage and the second coolant suction passage by ejecting a driving flow from the nozzle. By using the nozzle disclosed in Japanese Patent Laid-open No. 2001-90700 in the jet pump disclosed in U.S. Pat. No. 3,625,820, the efficiency of the jet pump can be increased. 
         [0013]    However, in the jet pump disclosed in FIG. 3 of Japanese Patent Laid-open No. 2001-90700, the driving flow is supplied to the driving flow passage formed between the inner cylinder and the outer cylinder, from the side at a right angle through a driving flow feeding pipe. Because of this, the driving flow flowing into the driving flow passage hits the inner cylinder from the side and turns downward at a right angle, causing great pressure loss and applies large forces to the connection part between the nozzle and the driving flow feeding pipe connected to the nozzle. The connection part between the nozzle and the driving flow feeding pipe needs to be strengthened. In addition, a jet pump disposed in the reactor pressure vessel of a BWR has an inverted U-shaped elbow pipe, a nozzle, and a throat portion joined as a single detachable unit. A raiser pipe connected to the elbow pipe is fixed to a core shroud surrounding the core and disposed in the reactor pressure vessel. In order to install the nozzle having the inner cylinder and the outer cylinder, the raiser pipe and a nozzle fixture need to be modified. 
         [0014]    To increase the degree of the power uprate of the reactor, further improvement in the efficiency of the jet pump is expected. 
         [0015]    An object of the present invention is to provide a jet pump and a nuclear reactor which can further increase efficiency of the jet pump. 
         [0016]    A feature of the present invention for achieving the above object is that a nozzle apparatus having a header portion including, inside, a first pipe member forming a suction fluid passage for introducing suction fluid and the header portion surrounding the first pipe member, for introducing driving fluid, and a nozzle portion connected to the header portion, surrounding the first pipe member and forming an annular ejection outlet for ejecting the driving fluid; and a second pipe member having one end connected to the nozzle apparatus, for introducing the driving fluid to the header portion are comprised, 
         [0017]    wherein the first pipe member is disposed through the one end inside a driving fluid passage formed in the second pipe member, and forms an opening portion of the suction fluid passage opened to the outside of the second pipe member; and 
         [0018]    the driving fluid passage is formed so that the driving fluid flowing toward the one end hits the first pipe member diagonally to the axial direction of the first pipe member. 
         [0019]    Since the driving fluid passage formed inside the second pipe member is formed so that the driving fluid flowing toward the one end hits the first pipe member diagonally to the axial direction of the first pipe member, pressure loss inside the driving fluid passage is decreased. Since the speed of the driving fluid ejected from the annular ejection outlet of the nozzle portion becomes faster, the flow rate of the suction fluid sucked inside the jet pump body is increased. From above, efficiency of the jet pump is improved. 
         [0020]    The above object can also be achieved by a feature that a nozzle apparatus having aheader portion including, inside, a first pipe member forming a suction fluid passage for introducing suction fluid and the header portion surrounding the first pipe member, for introducing driving fluid, and a nozzle portion connected to the header portion, surrounding the first pipe member and forming an annular ejection outlet for ejecting the driving fluid; and an inverted U-shaped second pipe member having one end connected to the nozzle apparatus, for introducing the driving fluid to the header portion are comprised, 
         [0021]    wherein the first pipe member extending to the axial direction of the nozzle apparatus is disposed through the one end inside a driving fluid passage formed in the second pipe member, and forms an opening portion of the suction fluid passage opened to the outside of the second pipe member; and 
         [0022]    a fixing position of the first pipe member to the second pipe member is disposed lower than the top point of the outer surface of the second pipe member. 
         [0023]    According to the present invention, efficiency of the jet pump can be further increased. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  is a longitudinal sectional view showing vicinity of a nozzle apparatus of the jet pump according to first embodiment applied to a BWR, which is a preferred embodiment of the present invention. 
           [0025]      FIG. 2  is a perspective view showing the nozzle apparatus shown in  FIG. 1 . 
           [0026]      FIG. 3  is a longitudinal sectional view showing a boiling water reactor to which the jet pump of the first embodiment is applied. 
           [0027]      FIG. 4  is a side view showing the jet pump of the first embodiment. 
           [0028]      FIG. 5  is an explanatory diagram showing properties of the jet pump according to first embodiment and a jet pump of a comparative example. 
           [0029]      FIG. 6  is a longitudinal sectional view showing vicinity of a nozzle apparatus of the jet pump according to second embodiment applied to a BWR, which is another embodiment of the present invention. 
           [0030]      FIG. 7  is a perspective view showing vicinity of a nozzle apparatus of a jet pump according to third embodiment applied to a BWR, which is another embodiment of the present invention. 
           [0031]      FIG. 8  is a longitudinal sectional view sowing vicinity of the nozzle apparatus shown in  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0032]    Various embodiments of the present invention are described below using figures. 
       First Embodiment 
       [0033]    A jet pump according to first embodiment is described the first embodiment which is a preferred embodiment of the present invention below. Before the structure of the jet pump in the present embodiment is explained, a general structure of a boiling water reactor (BWR) is described below using  FIGS. 3 and 4 . 
         [0034]    A boiling water reactor (BWR)  1  has a reactor pressure vessel (hereinafter, referred to as a RPV)  2  and a core  3  disposed in the RPV  2 . A plurality of fuel assemblies (not shown) are loaded in the core  3 . A core shroud  4  disposed in the RPV  2  surrounds the core  3 . A separator  5  and a dryer  6  are disposed above the core  3  in the RPV  2 . A plurality of jet pumps  7  are disposed in a downcomer  31  which is an annular passage formed between the RPV  2  and the core shroud  4 . The RPV  2  is provided with a recirculation system. This recirculation system has a recirculation pipe  32  and a recirculation pump  33 . The recirculation pipe  32  is provided with the recirculation pump  33 . One end of the recirculation pipe  32  is connected to the RPV  2 , connecting with the downcomer  31 . The other end of recirculation pipe  32  reaches in the RPV  2  and connects to a raiser pipe  34  (see  FIG. 4 ) disposed in the downcomer  31 . A feed water pipe  36  and a main steam pipe  35  are connected to the RPV  2 . 
         [0035]    The jet pump  7  has a nozzle apparatus  8 , an inverted U-shaped elbow pipe (a second pipe member)  19 , a bell mouth  24 , a throat  25  and a diffuser  26 . The diffuser  26  is disposed to a dividing member installed to the core shroud  4 . The throat  25  is joined to an upper end portion of the diffuser  26  by a joint  27 . The bell mouth  24  is installed on the upper end of the throat  25 . The nozzle apparatus  8  is disposed above the bell mouth  24 , and is fixed to the bell mouth  24  with a plurality of support plates  37 . An outside cooling water suction passage  38  is formed between the nozzle apparatus  8  and the bell mouth  24 . One end of the elbow pipe  19  is fixed to the upper end of the nozzle apparatus  8 . Two jet pumps  7  are disposed on both sides of the single raiser pipe  34 . Each nozzle apparatus  8  of the jet pumps  7  is connected to the single raiser pipe  34  through the individual elbow pipe  19 . 
         [0036]    Cooling water (suction fluid, coolant) present in the upper part in the RPV  2  is mixed with feed water supplied to the RPV  2  from the feed water pipe  36  and goes down in the downcomer  31 . This cooling water flows into the recirculation pipe  32  by operation of the recirculation pump  33 , and pressurized by the recirculation pump  33 . This pressurized cooling water is called a driving flow (driving fluid) for convenience. This driving flow flows into the elbow pipe  19  of the jet pump  7  through the recirculation pipe  32  and the raiser pipe  34 , and after the flow direction is changed  1800  by the elbow pipe  19 , ejects from the nozzle apparatus  8 . Cooling water present around the nozzle apparatus  8  is sucked into the bell mouth  24  through the outside cooling water suction passage  38  by the ejection of the driving flow, and further sucked into the throat  25 . This cooling water, with the driving flow, goes down in the throat  25  and the diffuser  26 , and is discharged from the diffuser  26 . The discharged cooling water (including the driving flow) is supplied to the core  3  via a lower plenum  39 . The cooling water is heated when passing the core  3 , and becomes a two-phase flow including water and steam. The separator  5  separates the steam and the water discharged from the core  3 . Moisture in the separated steam is further eliminated by the dryer  6 , and the steam is discharged to the main steam pipe  35 . This steam is introduced to a steam turbine (not shown) and turns the steam turbine. The steam discharged from the steam turbine becomes water through condensation in a condenser (not shown). This water is supplied into the RPV  2  through the feed water pipe  36  as feed water. The water separated by the separator  5  and the dryer  6  goes down the downcomer  31 . 
         [0037]    The jet pump  7  effectively sucks the cooling water around the nozzle apparatus  8  by using the driving force of the driving flow discharged from the recirculation pump  33 , and increases the flow rate of the cooling water discharged from the jet pump  7  more than the flow rate of the driving flow. The effective use of the kinetic energy of the driving flow generated by the recirculation pump  33  increases the rate of the cooling water discharged from the jet pump  7 . The flow speed of the driving flow at the outlet of the nozzle apparatus  8  is increased to increase the kinetic energy of the driving flow, and at the same time, the passage area of the throat  25  is made smaller than that of the bell mouth  24  to increase the speed of the cooling water, so that static pressure can be reduced. From these, the cooling water can be sucked in the throat  25 , and a required core flow rate can be obtained with little power. 
         [0038]    In the jet pump  7 , in order to increase the M ratio and the N ratio and to further improve the efficiency η, it is important to minimize pressure loss and to optimize suction power induced by the driving flow. Thus, in the jet pump  7  in the present embodiment, an inner cooling water suction passage  17  which runs through the nozzle apparatus  8  in the axial direction, is formed inside the nozzle apparatus  8 , forming an opening portion  18  connecting with the downcomer  31 , at the upper end. In addition, in the jet pump  7 , the inner cooling water suction passage  17  extends upward inside the elbow pipe  19 , and the opening portion  18  is formed on the outer surface of the elbow pipe  19  at a lower position than a top point TP of the elbow pipe  19 . 
         [0039]    A detailed structure of vicinity of the nozzle apparatus  8  in the jet pump  7  according to the present embodiment is explained using  FIGS. 1 and 2 . The jet pump  7 , as described above, has the nozzle apparatus  8 , the elbow pipe (the second pipe member)  19 , the bell mouth  24 , the throat  25  and the diffuser  26 . The bell mouth  24 , the throat  25  and the diffuser  26  are referred to as a jet pump body. The throat  25  has the smallest passage cross section in the jet pump body. The passage cross section of the bell mouth  24  expands upward from the connection portion with the throat  25 . The passage cross section of the diffuser  26  gradually expands downward from the connection portion with the throat  25 . 
         [0040]    The nozzle apparatus  8 , as shown in  FIG. 1 , has a nozzle portion  9  and a nozzle header portion  13 . The nozzle header portion  13  has an outer cylinder member  14  and an inner cylinder member  15  disposed inside the outer cylinder member  14 . An annular header portion  16  is formed between the outer cylinder member  14  and the inner cylinder member  15 , which are concentrically disposed. The nozzle portion  9  is disposed below the nozzle header portion  13  and fixed to the lower end portion of the nozzle header portion  13 . 
         [0041]    The nozzle portion  9  has an outer cylinder member  10 , an inner cylinder member  11 , an outer funnel portion  40 , and an inner funnel portion  41 . The outer cylinder member  10  surrounds the inner cylinder member  11 , and the outer cylinder member  10  and the inner cylinder member  11  are concentrically disposed. The outer funnel portion  40  surrounds the inner funnel portion  41 , and the outer funnel portion  40  and the inner funnel portion  41  are concentrically disposed. Each cross section of the outer funnel portion  40  and the inner funnel portion  41  diminishes downward. The outer funnel portion  40  is fixed to the upper end of the outer cylinder member  10 , and the inner funnel portion  41  is fixed to the upper end of the inner cylinder member  11 . The outer funnel portion  40  is disposed to the lower end of the outer cylinder member  14 . The inner funnel portion  41  is disposed to the lower end of the inner cylinder member  15 . An annular ejection outlet  12  is formed between the outer cylinder member  10  and the inner cylinder member  11 . 
         [0042]    An outlet end  21  of the elbow pipe  19  is fixed to the nozzle header portion  13 , that is, the upper end of the outer cylinder member  14 . An inlet end  20  of the elbow pipe  19  is disposed to the upper end of the raiser pipe  34 . The elbow pipe  19  is provided with a fixing pedestal  29  having a through-hole  42 . The elbow pipe  19  is detachably coupled with the raiser pipe  34  by a fixture  30 . The center of the outlet end  21  of the elbow pipe  19  matches the axis of the nozzle header portion  13 , or the outer cylinder member  14 . The nozzle portion  9 , the nozzle header portion  13 , and the elbow pipe  19  are joined into a single unit by welding. 
         [0043]    The inner cylinder member  15  is inserted in the elbow pipe  19  from the outlet end  21  and extends upward. An opening portion  18  located at an upper end portion of the inner cylinder member  15  is formed on the outer surface of the elbow pipe  19  and connecting with the downcomer  31 . The upper end of the inner cylinder member  15  is welded to the elbow pipe  19 . A joint portion (fixed portion)  23  being at the highest point in the joint portion (fixed portion) of the inner cylinder member  15  to the elbow pipe  19  is disposed lower than the top point TP which is the highest point on the outer surface of the elbow pipe  19 . A flow-adjusting plate (flow-adjusting member)  22  having the same curvature as the elbow pipe  19  is installed inside the elbow pipe  19 , and disposed from the inlet end  20  of the elbow pipe  19  toward the inner cylinder member  15  along the axis of the elbow pipe  19 . The flow-adjusting plate  22  is disposed to the upper course of the inner cylinder member  15 . An upper passage  44  and a lower passage  45  are formed in the elbow pipe  19  by the installation of the flow-adjusting plate  22 , which passages are separated into the top and bottom. Since the joint portion  23  is located lower than the top point TP, the upper passage  44  and the lower passage  45  in the elbow pipe  19  toward the outlet end  21  are formed diagonal to the axis of the inner cylinder member  15 . In other words, the upper passage  44  and the lower passage  45  are formed so that the driving flow in the passages flows toward the outlet end  21 , hitting the inner cylinder member  15  diagonally to the axial direction of the inner cylinder member  15 . 
         [0044]    The inner cooling water suction passage  17  connecting with the downcomer  31  through the opening portion  18  is formed inside of the inner cylinder member  15 , the inner funnel portion  41  and the inner cylinder member  11  all joined together. The joined inner cylinder member  15 , the inner funnel portion  41  and the inner cylinder member  11  are first pipe members. The passage cross section of the inner cooling water suction passage  17  gradually diminishes downward in the inner funnel portion  41 , and the lower end of the inner cooling water suction passage  17  opens toward the bell mouth  24 . An annular passage  43  formed between the outer funnel portion  40  and the inner funnel portion  41  connects between the annular header portion  16  and the annular ejection outlet  12 , and the passage cross section of the annular passage  43  gradually diminishes downward. 
         [0045]    A driving flow pressurized by the recirculation pump  33 , that reaches the raiser pipe  34  is introduced into the annular header portion  16  through the elbow pipe  19 . Since the flow-adjusting plate  22  is disposed in the elbow pipe  19 , pressure loss in the elbow pipe  19  is reduced. In the elbow pipe  19 , a part of the driving flow inside each of the upper passage  44  and the lower passage  45  flows toward the outlet end  21  hitting the outer surface of the inner cylinder member  15  diagonally to the axial direction of the first pipe member (especially the inner cylinder member  15 ). The driving flow introduced into the annular header portion  16  passes through the annular passage  43  and is ejected at a high speed toward the bell mouth  24  from the annular ejection outlet  12 . The cross section of the driving flow ejected from the annular ejection outlet  12  is annular. Supplying the driving flow into the throat  25  at high speed reduces static pressure in the throat  25 , and cooling water present around the nozzle apparatus  8  in the downcomer  31  is sucked into the bell mouth  24 . 
         [0046]    There are two patterns for sucking the cooling water, which is the suction flow, present around the nozzle apparatus  8  into the bell mouth  24  due to the reduction of the static pressure in the throat  25 . The first pattern is that the cooling water present above the elbow pipe  19  introduces into the inner cooling water suction passage  17  from the opening portion  18 , and reaches the bell mouth  24  through the inner cooling water suction passage  17 . In this pattern, the cooling water sucked into the inner cooling water suction passage  17  flows inside of the ejected annular flow. The second pattern is that the cooling water in the downcomer  31  reaches the bell mouth  24  through the outside cooling water suction passage  38  outside of the ejected annular flow. 
         [0047]    The driving flow ejected from the annular ejection outlet  12  and the cooling water (suction flow) sucked into the bell mouth  24  due to the effect of the driving flow are mixed in the throat  25  while exchanging their momentum, and introduced to the diffuser  26  placed below the throat  25 . In the diffuser  26 , the passage cross section gradually expands so that the flow of the cooling water (including the driving flow) would not be separated, and its kinetic energy is converted to pressure. In the diffuser  26 , the pressure of the cooling water will be higher than the pressure at the position where the cooling water is sucked into the bell mouth  24 . The cooling water with the increased pressure is discharged from the diffuser  26  and introduced to the core  3 . 
         [0048]    In the present embodiment, since the joint portion  23  is positioned lower than the top point TP, the upper passage  44  and the lower passage  45  in the elbow pipe  19  are formed toward the outlet end  21 , diagonally to the inner cylinder member  15  forming the inner cooling water suction passage  17  in the axial direction of the inner cylinder member  15 . From this, pressure loss is reduced in the elbow pipe  19  where the inner cylinder member  15  exists, and the flow speed of the cooling water ejected from the annular ejection outlet  12  is increased. The reduction range of the static pressure in the throat  25  becomes larger, and the flow rate of the cooling water sucked into the bell mouth  24  through the inner cooling water suction passage  17  and the outside cooling water suction passage  38  is increased. This increase in the flow rate of the cooling water improves efficiency for the jet pump  7 . 
         [0049]    This efficiency improvement of the jet pump  7  is specifically explained using  FIG. 5 .  FIG. 5  shows a relationship between the M ratio and the efficiency of the jet pump for the jet pump in the present embodiment and the jet pump of a comparative example. In  FIG. 5 , the solid line shows the properties of the jet pump  7  in the present embodiment, and the broken line shows the properties of the jet pump of the comparative example. The jet pump of the comparative example uses the nozzle apparatus shown in FIG. 3 of Japanese Patent Laid-open No. 2001-90700 as a nozzle for the jet pump disclosed in U.S. Pat. No. 3,625,820 for a BWR. While the pressurized driving flow hits the inner cylinder of the nozzle apparatus at a right angle in the comparative example, in the jet pump  7 , the driving flow flowing through the cooling water passage in the elbow pipe  19  hits the inner cylinder member  15  diagonally as described above. Because of such difference in the driving flows, the pressure loss in the jet pump  7  is less than that of the comparative example, which makes the efficiency of the jet pump  7  more than that of the comparative example. 
         [0050]    In the present embodiment, since the flow-adjusting plate  22  is disposed in the elbow pipe  19 , the pressure loss in the elbow pipe  19  is further reduced. Because of this reduction in the pressure loss, the efficiency of the jet pump  7  is further increased. Since the flow-adjusting plate  22  is disposed to the upper course of the inner cylinder member  15 , separation and uneven speed distribution of the flow in the elbow pipe  19  are improved, and the pressure loss in the elbow pipe  19  is reduced. 
         [0051]    Since the cooling water passages (the upper passage  44  and the lower passage  45 ) formed in the elbow pipe  19  are diagonal to the inner cylinder member  15  as described above, the driving flow flowing in the cooling water passages hits the outer surface of the inner cylinder member  15  diagonally to the axial direction of the inner cylinder member  15 . This causes the stress generated at the contact portion between the inner cylinder member  15  and the elbow pipe  19  to be small. Thus, when the nozzle apparatus  8  is applied to a current BWR, it is not necessary to reinforce the joint portion by making the member particularly thick, or to modify the raiser pipe  34  and the fixture  30 . 
         [0052]    In the present embodiment, since the inner cooling water suction passage  17  is formed in the nozzle apparatus  8 , the effect of the pressure reduction in the area inside the ejected annular flow can be effectively used. From this, the flow of the cooling water reaching the bell mouth  24  through the inner cooling water suction passage  17  can be generated. Thus, the flow rate of the cooling water flowing into the bell mouth  24  is increased since the cooling water can flow into the bell mouth  24  through each of the inner cooling water suction passage  17  and the outside cooling water suction passage  38 . 
         [0053]    Since the inner cooling water suction passage  17  is disposed in the axial direction of the RPV  2  and the opening portion  18  opens upward, the flow power of the cooling water moving down in the downcomer  31 , supplied to the inner cooling water suction passage  17 , can be effectively used to increase the suction power of the jet pump  20 . From this, the rate of the cooling water sucked into the throat  25  can be increased. In addition, since the outer funnel portion  40 , the outer diameter of which diminishes downward, is used in the nozzle portion  9 , the nozzle apparatus  8  has a structure which allows the cooling water moving down in the downcomer  31  to be easily sucked into the bell mouth  24  through the outside cooling water suction passage  38 . From this also, the flow rate of the cooling water flowing into the bell mouth  24  can be increased, thus the efficiency of the jet pump  7  can be increased. 
         [0054]    In a BWR, the flow rate of the cooling water to be supplied to the core  3  (core flow rate) is adjusted by controlling the rotation speed of the recirculation pump  33 . By improving the M ratio and the efficiency of the jet pump, the core flow rate can be increased with less recirculation pump power. Thus, the power consumption required for operation of the recirculation pump  12  can be reduced. In addition, when a power uprate of a nuclear reactor implemented in the U.S. is to be implemented, the core flow rate can be further increased without increasing the capacity of the recirculation pump  33  by using the jet pump  7  in the present embodiment to the current nuclear reactor, which jet pump  7  increases the M ratio and the efficiency of the jet pump. For this reason, the power uprate can be easily handled by merely replacing the nozzle of each jet pump in the current nuclear reactor to the nozzle apparatus  8 . 
         [0055]    Furthermore in the present embodiment, since the inverted U-shaped elbow pipe  19  is connected to the nozzle apparatus  8 , each elbow pipe  19  connected to each nozzle apparatus  8  of two jet pumps  7  can be connected to the single raiser pipe  34  disposed in the downcomer  31 , adjacent to the two jet pumps  7 . Because of this, the space between the jet pumps  7  can be made equal to that of the current BWR. 
       Second Embodiment 
       [0056]    A jet pump according to second embodiment, which is another embodiment of the present invention is explained using  FIG. 6 . A jet pump  7 A in the present embodiment has a nozzle apparatus  8 A replacing the nozzle apparatus  8  of the jet pump  7  in the first embodiment. The other structure of the jet pump  7 A is the same as the jet pump  7 . The jet pump  7 A is disposed in the downcomer  31  in the RPV  2  of a BWR also. The nozzle apparatus  8 A has an inner cylinder member  15 A replacing the inner cylinder member  15  of the nozzle apparatus  8 , having a curved surface  46  on the inner surface of the upper end portion. The other structure of the nozzle apparatus  8 A is the same as the nozzle apparatus  8 . Because such inner cylinder member  15 A is provided, the passage cross section of an opening portion  18 A gradually diminishes downward due to the formation of the curved surface  46 . The opening portion  18 A is formed at the upper end portion of the inner cooling water suction passage  17  formed in the connected inner cylinder member  15 A, the inner funnel portion  41 , and the inner cylinder member  11 . 
         [0057]    The inlet end  20  of the elbow pipe  19  is connected to the raiser pipe  34  using the fixture  30  in the same manner as the first embodiment. The flow-adjusting plate  22  is disposed in the elbow pipe  19 . The outlet end  21  of the elbow pipe  19  is fixed to the upper end of the outer cylinder member  14  of the nozzle header portion  13  by welding. In the jet pump  7 A in the present embodiment also, the joint portion  23  which is at the highest position in the joint portion between the inner cylinder member  15 A and the elbow pipe  19 , is located lower than the top point TP on the outer surface of the elbow pipe  19 . Thus, the cooling water passages (the upper passage  44  and the lower passage  45 ) formed in the elbow pipe  19  are formed in such a way that the driving flow flowing toward the outlet end  21  hits the inner cylinder member  15 A diagonally to the axial direction of the inner cylinder member  15 A in the elbow pipe  19 . In such jet pump  7 A in the present embodiment also, the pressure loss in the elbow pipe  19  is reduced and efficiency of the jet pump is increased in the same manner as the jet pump  7 . Since the jet pump  7 A has the flow-adjusting plate  22 , the efficiency of the jet pump is further increased. 
         [0058]    In the present embodiment in which the curved surface  46  is formed at the opening portion  18 A of the inner cooling water suction passage  17 , the following effects can occur. The cooling water sucked into the bell mouth  24  from the inner cooling water suction passage  17  is sucked in the inner cooling water suction passage  17  from a wider range than the opening size of the opening portion  18 A. When the edge angle of the upper end of the inner cylinder member  15 A is sharp, pressure loss will occur due to the abrupt change in the flow direction of the sucked cooling water; and in addition, the pressure loss may be further increased by possible flow separation. By forming the curved surface  46  on the inner surface of the upper end portion of the inner cylinder member  15 A, the change in the flow direction of the sucked cooling water will be smooth as well as preventing flow separation, and thus, the pressure loss can be reduced. 
         [0059]    The larger the passage cross section of the opening portion  18 A sucking the cooling water, the easier for the cooling water to be sucked into the inner cooling water suction passage  17 . On the other hand, the smaller the outer diameter of the inner cylinder member  15 A is, the larger the passage cross section of the annular header portion  16  formed in the nozzle header portion  13  will be. Since the flowing speed of the driving flow flowing in the annular header portion  16  can be reduced, the pressure loss in the nozzle header portion  13  can be decreased. Since the curved surface  46  is formed at the opening portion  18 A of the inner cooling water suction passage  17 , the passage cross section of the opening portion  18 A can become larger and the outer diameter of the inner cylinder member  15 A can become smaller. As discussed above, the reduction of passage drag at the opening portion  18 A of the inner cooling water suction passage  17  and the reduction of the pressure loss inside the nozzle apparatus  8 A can further improve the efficiency of the jet pump. 
       Third Embodiment 
       [0060]    A jet pump according to third embodiment which is another embodiment of the present invention is explained using  FIGS. 7 and 8 . A jet pump  7 B of the present embodiment has a nozzle apparatus  8 B replacing the nozzle apparatus  8  of the jet pump  7  in the first embodiment. The other structure of the jet pump  7 B is the same as the jet pump  7 . The jet pump  7 B is disposed in the downcomer  31  in the RPV  2  of a BWR also. An inner cylinder member  15 B provided to the nozzle apparatus  8 B is longer than the inner cylinder member  15  provided to the nozzle apparatus  8  in the first embodiment. A protruding portion  47  is formed at the upper end portion of the inner cylinder member  15 B. Since the inner cylinder member  15 B is long, when the outlet end  21  of the elbow pipe  19  is welded to the upper end of the outer cylinder member  14 , the protruding portion  47  protrudes upward from the outer surface of the elbow pipe  19 . The joint portion  23  located at the highest position in the joint portion between the inner cylinder member  15 B and the elbow pipe  19  is positioned lower than the top point TP on the outer surface of the elbow pipe  19 . A curved surface  46 A is formed on the inner surface of the upper end portion of the protruding portion  47 . An opening portion  18 B formed at the upper end portion of the inner cooling water suction passage  17  formed inside the connected inner cylinder member  15 B, the inner funnel portion  41  and the inner cylinder member  11  is formed in the protruding portion  47 . The cross section of the opening portion  18 B gradually diminishes downward due to the formation of the curved surface  46 A. 
         [0061]    The jet pump  7 B in the present embodiment can also obtain the effects generated by the jet pump  7  in the first embodiment. In the present embodiment, since the inner cooling water suction passage  17  protrudes upward from the outer surface of the elbow pipe  19 , the inner diameter of the opening portion  18 B of the inner cooling water suction passage  17  can be made larger without being limited by the elbow pipe  19 . Although the inner diameter of the opening portion  18 B is large, the passage cross section of the protruding portion  47  can be moderately made smaller. Because of this, the outer diameter of the lower part of the inner cylinder member  15 B below the protruding portion  47  can be made smaller. In the present embodiment, an inner diameter d 2  at the upper end of the opening portion  18 A is larger than an inner diameter d 1  of the protruding portion  47  at the lower end of the protruding portion  47  (fixing position of the inner cylinder member  15 B to the elbow pipe  19 ). Thus, drag in the inner cooling water suction passage  17  is reduced. From above, pressure loss in the annular header portion  16  can be reduced while increasing the suction rate of the cooling water into the inner cooling water suction passage  17 . The present embodiment can improve efficiency of the jet pump. 
         [0062]    In the present embodiment, the effects generated in the first embodiment can be obtained. 
         [0063]    In the first embodiment and second embodiment, each upper end of the opening portions  18  and  18 A are tilted, so the shape of each upper end of these openings is oval. However, in the third embodiment, the shape of the opening portion  18 B is circular. Because of this, the inner cooling water suction passage  17  can evenly suck the cooling water in the circumferential direction of the passage. In the present embodiment such as this, the pressure loss at the time of the cooling water being sucked into the inner cooling water suction passage  17  can be further reduced, and the efficiency of the jet pump can be further improved.