Abstract:
A fluid pump utilizing a canned rotor and canned stator is provided. The fluid pump has increased insulative properties over past “spool-type” pumps and has an increased ability to cool the stator, making it suitable for high temperature applications. A nuclear reactor is also provided. The reactor comprises a reactor vessel, that contains a nuclear fuel, control rods, reactor coolant and a reactor coolant pump for providing the reactor coolant to a steam generator. In a preferred embodiment, a steam generator is also provided inside the reactor vessel.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to fluid circulation pumps. More particularly, it relates to fluid pumps suitable for use in connection with a nuclear reactor.  
         DISCUSSION OF RELATED ART  
         [0002]    Spool-type fluid pumps have traditionally been used to move fluids as part of a chemical process, or to propel sub-sea vessels. Spool-type fluid pumps generally comprise two concentric cylinders. The outer cylinder contains the pump stator, while the inner cylinder contains the pump rotor. Impeller(s) are connected to a central hub and extend out to, and connect with, the inner cylinder. When power is supplied to the stator, an electromagnetic field is generated, causing the inner cylinder, including the impeller(s), to rotate.  
           [0003]    The inner and outer cylinders are sealed or “canned” in order to prevent fluid from coming in contact with the internals of the rotor and stator. Generally, there exists a small gap between the inner and outer cylinders, which can be filled with water in order to cool the rotor and stator. The water has been provided through a fluid circulation channel that may be disposed in the central hub and run through one of the impellers to a gap between the cylinders. Alternatively, the fluid circulation channel may begin at one end of the pump as a gap between the inner cylinder and the outer cylinder. The water flows through the channel between the inner cylinder and the outer cylinder and exits through a gap between the inner cylinder and the outer cylinder at the other end of the pump. The traditional designs are inadequate in terms of cooling when the pump is used in connection with high temperature applications.  
           [0004]    Nuclear reactors have traditionally utilized shaft seal pumps or canned motor pumps that are connected between the steam generator and the reactor vessel by large coolant piping for circulating coolant from the reactor vessel through the steam generator. The steam generator and pump are located outside the reactor vessel, with the reactor coolant being circulated by the pumps through the reactor vessel, steam generator, piping system and through the pumps. The pump casing becomes part of the primary pressure boundary surface.  
           [0005]    The shaft seal pump used for nuclear reactor coolant pumping is traditionally a vertical single stage pump having a motor driver connected by a coupling. The motor is either an air cooled or water cooled squirrel cage induction design, but is located outside of the pump casing. A shaft seal assembly seals the reactor coolant inside the pump.  
           [0006]    Because radioactive fluid is being moved through the pump and the coolant piping, any leaks in the shaft seal, pump casing, vessel opening and closure should be avoided. Therefore, it is desirable to provide a nuclear reactor configuration that decreases the likelihood of such leaks.  
         SUMMARY OF THE INVENTION  
         [0007]    In one embodiment the fluid pump comprises a sealed annular stator having a generally cylindrical passage extending therethrough, with the stator having energizing means for electrically connecting a plurality of stator windings to a source of electrical power. The fluid pump further comprises an impeller assembly rotatably mounted in the generally cylindrical passage in the housing. The impeller assembly comprises an impeller and a sealed rotor mounted around the perimeter of the impeller and positioned inside the stator to form an electric motor, the operation of which rotates the impeller to produce a pressurized flow of fluid through the generally cylindrical passage in the housing. The fluid pump further comprises at least one radial bearing mounted between the impeller assembly and the housing, a hub centrally positioned in the generally cylindrical passage in the housing and secured to the housing by at least one impeller blade, the impeller assembly rotatably supported on the hub, and insulation material disposed within the stator, the insulation material consisting essentially of mica, glass and ceramics.  
           [0008]    In another embodiment, the fluid pump comprises a sealed annular stator having a generally cylindrical passage extending therethrough, with the stator having energizing means for electrically connecting a plurality of stator windings to a source of electrical power. The fluid pump further comprises an impeller assembly rotatably mounted in the generally cylindrical passage in the housing. The impeller assembly comprises an impeller and a sealed rotor mounted around the perimeter of the impeller and positioned inside the stator to form an electric motor, the operation of which rotates the impeller to produce a pressurized flow of fluid through the generally cylindrical passage in the housing. The fluid pump further comprises at least one radial bearing mounted between the impeller assembly and the housing, a hub centrally positioned in the generally cylindrical passage in the housing and secured to the housing by at least one impeller blade, and cooling tubes having an inlet downstream of the impeller and an outlet upstream of the impeller, the cooling tubes disposed at least partially within the stator. In another embodiment, the nuclear reactor comprises a reactor vessel, nuclear fuel, a plurality of control rods, reactor coolant, at least one steam generator, and at least one reactor coolant pump, wherein the nuclear fuel, the control rods, the reactor coolant and the reactor coolant pump are all located inside the reactor vessel. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    The various features and benefits of the present invention are apparent in light of the following detailed description and the accompanying drawings, in which:  
         [0010]    [0010]FIG. 1 a  is a largely schematic, cross-sectional view of a nuclear reactor.  
         [0011]    [0011]FIG. 1 b  is an largely schematic, cross-sectional view of the nuclear reactor illustrated in FIG. 1 a , taken along line  1   b - 1   b.    
         [0012]    [0012]FIG. 2 is a cross-sectional view of a spool pump.  
         [0013]    [0013]FIG. 3 is a cross-sectional view of the spool pump illustrated in FIG. 2, taken along line  3 - 3 .  
         [0014]    [0014]FIG. 4 is a partial, cross-sectional view of an the spool pump illustrated in FIG. 2.  
         [0015]    [0015]FIG. 5 is a magnified, cross-sectional view of the dashed portion of FIG. 4.  
         [0016]    [0016]FIG. 6 is a cross-sectional view of an alternate spool pump.  
         [0017]    [0017]FIG. 7 is a cross-sectional view of an alternate spool pump.  
         [0018]    [0018]FIG. 8 is a cross-sectional view of an alternate spool pump.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]    Referring to FIGS. 1 a  and  1   b , nuclear reactor  10  includes a reactor vessel  12  that contains the reactor core  14 . The reactor core  14  contains nuclear fuel  16  that is disposed on a support structure  18 . The nuclear fuel  16  undergoes a fission reaction that generates the heat that is used to generate electric power. The reactor  10  further includes a plurality of control rods  20  that can be inserted into the nuclear fuel  16  in order to control the reaction. The control rods  20  are preferably arranged in a honeycomb configuration, but can be arranged in any configuration known to those skilled in the art.  
         [0020]    The fission reaction generates a significant amount of heat. That heat is transferred to reactor coolant water that is present inside the vessel  12 . A plurality of steam generators  22  may also be included inside the vessel  12 , for example, eight steam generators  22  may be included. Preferably, the steam generators are disposed along the inside walls of the vessel  12 . The steam generators  22  are essentially heat exchangers, such as a shell and tube heat exchanger, designed to extract the heat from the reactor coolant. Feedwater is supplied to the steam generator  22  through a feedwater inlet pipe  24 . The feedwater passes through the steam generator  22  on the outside of pipes  26 , where it absorbs the heat from the reactor coolant flowing through pipes  26  until it becomes steam. The steam leaves the steam generator  22  and the vessel  12  through a steam outlet pipe  28 . The steam is eventually utilized in a plurality of turbines (not shown) to produce electric power. Alternatively, the steam generator  22  may be located outside the vessel, with piping connecting the steam generator  22  to the vessel  12 .  
         [0021]    In accordance with an embodiment of the present invention, the reactor coolant is circulated to the steam generator  22  by a spool pump  30  connected to steam generator  22 . The spool pump  30  and steam generator  22  are located inside the vessel  12 . The spool pump  30  draws coolant from the vessel  12  and pumps it through the steam generator  22 . The coolant flows through pipes  26  as it passes through the steam generator  22 , and heat is transferred from the coolant to the feedwater occurs across the walls of the pipes  26 . Once cooled, the feedwater flows out of the steam generator  22  and back into the coolant in vessel  12 .  
         [0022]    [0022]FIG. 2 illustrates an embodiment of the spool pump  30  used to pump the coolant through the steam generator  22 . The pump  30  includes a generally cylindrical housing  34  having a generally cylindrical passage  36  extending therethrough. The housing  34  also includes end caps  38 ,  40  for connecting the housing  34  in series with the steam generator  22  (as shown in FIG. 1 a ).  
         [0023]    The pump  30  further includes a hermetically sealed annular stator  42  mounted inside the housing  34 . The stator  42  has a terminal gland  44  thereon for connecting the stator  42  to a source of electrical power located outside the vessel  12 . The stator  42  is hermetically sealed by a stator can  46 .  
         [0024]    Impeller assembly  58  is rotatably mounted inside the passage  36  of the housing  34 . The impeller assembly  58  comprises an axial flow impeller  60  and an annular rotor  64  mounted around the perimeter of the impeller  60  on a cylindrical shaft  62 . The rotor  64  and the stator  42  cooperate to form an induction motor. The rotor  64  is preferably a squirrel cage rotor, so that no electrical connections to the rotor are required. It will be appreciated by those skilled in the art, however, that the motor could be a synchronous motor or a permanent magnet motor. If a squirrel cage motor design is used, the rotor  64  will comprise steel laminations and copper alloy rotor bars, as is known in the art. If a synchronous motor is employed, the rotor  64  may be comprised of permanent magnets. The rotor  64  is hermetically sealed by a rotor can  66 . Both the stator can  46  and the rotor can  66  preferably comprise thin-walled alloy cans such as Inconel or Hastelloy cans.  
         [0025]    The impeller  60  has a plurality of blades  68  mounted on and extending radially outwardly from a cylindrical hub  70 . In a preferred embodiment, 5 to 9 blades  68  are provided. It will be appreciated, however, that the optimum number of blades will depend on the desired performance of the pump  30  and may be determined in a manner known to those skilled in the art. The blades  68  are pitched so as to create an axial flow in the pumped fluid in the direction F through the passage  36  in the housing  34  when the impeller  60  is rotated.  
         [0026]    The impeller  60  is preferably a high specific speed impeller. Specific speed (N S ) is a non-dimensional design index used to classify pump impellers as to type and proportion. It is defined as the speed in revolutions per minute at which a geometrically similar impeller would operate if it were of such a size to deliver one gallon per minute against one foot head. N S  is calculated using the formula:  
         N   S     =       NQ     1   2         H     3   4                               
 
         [0027]    where  
         [0028]    N=pump impeller speed in revolutions per minute  
         [0029]    Q=capacity in gallons per minute at the best efficiency point  
         [0030]    H=total head per stage at the best efficiency point.  
         [0031]    In the embodiment illustrated in FIG. 1 a , the impeller  60  is of a configuration to yield a specific speed of about 9,000 or higher at a speed of 1800 rpm.  
         [0032]    As noted above, the nuclear reaction generates a significant amount of heat, which is transferred to the reactor coolant water, which is the fluid pumped by the spool pump  30 . The coolant temperature will often exceed 300° C. At that temperature, the water used as the coolant has a very low viscosity. The higher the specific speed of the impeller, the steeper the pump characteristic curve, with the thrust load being the greatest at zero flow, or what is called “shut off flow.” The higher specific speed requires a larger thrust bearing to accommodate the high thrust at shut off flow. In accordance with an embodiment of the present invention, a double acting thrust bearing  72  is located on one side of impeller  68 . The thrust bearing  72  comprises a thrust bearing runner  74  and two sets of bearing pads  76 ,  78 . The thrust bearing runner  74  is a carbon graphite-based ring that is shrink fitted on to the shaft  62 . The thrust bearing runner  74  may also be manufactured from another hard solid material such as a carbide, a nitride, stainless steel or another appropriate material that is known to those skilled in the art. Two bearing pads  76 ,  78  form the self-aligning tilt pad design and are positioned on opposite sides of the thrust bearing runner  74 . The bearing pads  76 ,  78  are made from 431 stainless steel (or a comparable alloy) that is chrome plated or hard faced, for both corrosion and wear resistance. A plurality of thrust pad retainers  77  are also included in order to keep the thrust bearing pads  76  and  78  in place. The thrust pad retainers are located outside of the bearing pads  76 ,  78 .  
         [0033]    [0033]FIGS. 2 and 3 illustrate radial bearings  80  that are employed to rotatably support the rotor  64 . Radial bearings  80  are mounted between housing  34  and the cylindrical shaft  62 . Preferably, radial bearings  80  are located both upstream and downstream of the impeller  60 . If the pump  30  is installed such that the coolant flow is vertical, then the radial bearings  80  are self-aligning, pivoted pad type bearings. If the pump  30  is installed such that the coolant flow is horizontal, then the radial bearings  80  may be self-aligning, pivoted pad type bearings, or may be simple solid journal bearings. The configuration shown in FIGS. 2 and 3 is for self-aligning, pivoted pad bearings.  
         [0034]    Preferably, the radial bearing journal  82  will be shrink fitted to the cylindrical shaft  62  and will be a  431  stainless steel (or comparable alloy) insert that has been chrome plated or hard faced for corrosion resistance and improved wear properties. When the cylindrical shaft  62  rotates, the radial bearing journal  82  wears against a radial bearing pad  84 . The radial bearing pad  84  which may be ceramic material such as carbon graphite sits on a radial bearing retainer  86 , which in turn, is mounted into a radial bearing flange  88 . The radial bearing flange  88  is mounted to the housing  34 . The radial bearing retainer  86  also sits on the radial bearing seat  90 , which allows the bearing retainer  86  to pivot, and thus, self-align, as is known in the art.  
         [0035]    Referring to FIG. 4, when the stator  42  is energized, it causes the impeller assembly  58  to rotate. Pump parts that rotate include the rotor  64 , the rotor can  66 , the thrust bearing runner  74  (that is shrink fitted on the rotor  64 ) the radial bearing journal  82  (which is also shrink fitted on the rotor  64 ), impeller  60  and shaft  62 . All other pump parts ideally remain stationary to the impeller assembly  58 .  
         [0036]    The cylindrical shaft  62  has a forward end  63  that forms a forward gap  65  relative to the end cap  38  on the inlet side of the impeller assembly  58 . The cylindrical shaft  62  also has an aft end  67  that forms an aft gap  69  relative to the end cap  40 . During operation, water flowing through the cylindrical shaft  62  enters the aft gap  69 . The water flows between the thrust bearing runner  74  and the bearing pad  76 , and thereby lubricates the thrust bearing runner  74  as it moves relative to the bearing pad  76 .  
         [0037]    Likewise, the water proceeds to flow between, and thereby, lubricate, the bearing pad  78  and the bearing runner  74 .  
         [0038]    The water proceeds to flow between the radial bearing journal  82  and the radial bearing pad  84  of the radial bearing  80  located on the downstream side of impeller assembly  58 . In this way, the water also lubricates and cools the radial bearing  80 . The water proceeds through the gap between the rotor can  66  and the stator can  46 , thereby cooling the rotor  64  and the stator  42 .  
         [0039]    The water flows between the radial bearing journal  82  and the radial bearing pad  84  of the radial bearing  80  located on the upstream side of impeller assembly  58 , thereby lubricating and cooling the radial bearing  80 . Finally, the water proceeds through the forward gap  65  and back into the cylindrical passage  36 .  
         [0040]    Due to the high reactor coolant temperature mentioned above, as well as the heat generated by the stator windings  41 , the stator  42  must have adequate insulation or cooling, otherwise the stator windings  41  may be damaged. Therefore, in accordance with an embodiment of the present invention, the pump  30  further includes insulation  43 . The insulation material  43  is disposed around the stator windings  41 . The insulation material preferably is rated at 500° C., and comprises a combination of mica, glass and ceramics. The insulation material preferably comprises a plurality of solid pieces of insulation that are shaped so as to fit inside the stator  42  and around the stator windings  41 . In prior systems, strips of insulation were laid upon, or taped to, the stator windings. Resin was used to fill the remainder of the stator and hold the insulation in place on the stator windings. However, due to the high temperatures to which the pump  30  will be subjected, resin cannot be used, as it will likely degrade under high temperatures. Thus, in accordance with the present invention, the insulation material will be formed as a plurality of solid pieces that are shaped to fit snugly around the stator windings, similar to pieces of a three-dimensional jigsaw puzzle. In this way, the insulation material will not need resin in order to keep it in contact with the stator windings.  
         [0041]    As shown in further detail in FIG. 5, the terminal gland  44  connects the pump  30  to a source of electrical power outside the vessel  12 , such as an electric generator (not shown). Terminal gland  44  is part of the pump pressure barrier. As such, the terminal gland  44  must be constructed to withstand design pressures up to approximately 2500 psi. As illustrated in FIG. 5, the terminal gland  44  comprises a body  48  that provides the capability of welding the terminal gland  44  to the housing  34 . Preferably, the body  48  is made of stainless steel. The body  48  encases a cylindrical ceramic insulator  50 , and is connected to the ceramic insulator  50  by a cylindrical first glass preform  52 . Preferably, a ceramic insulator  50  may be used. The ceramic insulator  50 , in turn, encases a terminal gland stud  54  through which electrical wires pass though to provide the electrical power to the stator  42 . The ceramic insulator  50  is also connected to the terminal gland stud  54  by a second glass preform  56 . Preferably, the terminal gland stud  54  is made of a conducting material such as molybdenum or copper. An external ceramic insulating sleeve  55  surrounds the upper portion of the terminal gland stud  54 , while an internal ceramic insulating sleeve  57  surrounds the lower portion of the terminal gland stud  54 . Due to the various thermal expansion rates of the several materials, the assembly is held together in compression. The compression must be great enough to provide the required sealing integrity. The compression achieved is dictated by the selection of the glass material used for the first and second glass preforms  52 ,  56 . A grade of glass must be chosen such that the terminal gland  44  may operate in a temperature range of between approximately 350° C. and approximately 400° C. Electrical strike and creep distances for air operation is maintained by the ceramic insulator  50  and first and second glass preforms  52 ,  56  configuration.  
         [0042]    Should further motor cooling be desirable, the pump  30  may be provided with cooling tubes  92 , as illustrated in FIG. 6. The cooling tubes  92  act as a heat exchanger to transfer heat from the stator  42  to the reactor coolant. The cooling tubes  92  are disposed within the end cap  40  of the downstream end of the pump  30 , run through the housing  34 , through the “back iron” area of the stator  42 , and through the end cap  38  at the upstream end of the pump  30 . The reactor coolant enters the cooling tubes  92  at the downstream end of the pump  30 , where the reactor coolant is at a higher pressure than at the upstream end of the pump  30 . The pressure difference is enough to drive the reactor coolant through the cooling tubes  92 . Preferably, the cooling tubes  92  are made from stainless steel, Inconel or other non-magnetic alloy. The reactor coolant flows through the cooling tubes  92  and absorbs heat from the stator  42 , which will typically be operating at a higher temperature than the reactor coolant. If a higher cooling capacity is required, cooling tubes may be installed in the stator slots. Externally-supplied cooling water, from outside reactor vessel  12 , may also be provided, if necessary.  
         [0043]    An alternate embodiment of the present invention is illustrated in FIG. 7. It is noted that the embodiments illustrated in FIGS. 7 and 8 are comparable to the embodiments illustrated in FIGS. 2 and 3, respectively, with similar parts referenced by similar reference numbers, increased by a factor of  100 . In this embodiment, the impeller assembly  158  is designed to produce a mixed flow, as is known to those of skill in the art. Generally, the cylindrical hub  170 , is moved downstream relative to the blades  168 . Further, the blades are pitched so as to create a mixed flow in the pumped fluid in the direction F through the passage  136  in the housing  134  when the impeller assembly  158  is rotated. Also, the cylindrical shaft  162  is narrowed in most areas except for the area corresponding to the position of the cylindrical hub  170 , as illustrated in FIG. 7. In this configuration, the impeller assembly  158  yields a specific speed of about 5,000 to about 9,000 at a speed of 1800 rpm.  
         [0044]    Should further motor cooling be desirable for the pump  130  illustrated in FIG. 7, the pump  130  may be provided with cooling tubes  190 , as illustrated in FIG. 8. The cooling tubes  190  act as a heat exchanger to transfer heat from the stator  142  to the reactor coolant. The cooling tubes  190  are disposed within the end cap  140  of the downstream end of the pump  130 , run through the housing  134 , through the “back iron” area of the stator  130 , and through the end cap  138  at the upstream end of the pump  130 . The reactor coolant enters the cooling tubes  190  at the downstream end of the pump  130 , where the reactor coolant is at a higher pressure than at the upstream end of the pump  130 . The pressure difference is enough to drive the reactor coolant through the cooling tubes  190 . Preferably, the cooling tubes  190  are made from stainless steel, Inconel or other non-magnetic alloy. The reactor coolant flows through the cooling tubes  190  and absorbs heat from the stator  142 , which will typically be operating at a higher temperature than the reactor coolant. If a higher cooling capacity is required, cooling tubes may be installed in the stator slots. Externally-supplied cooling water may also be provided, if necessary.  
         [0045]    While specific embodiments and methods for practicing this invention have been described in detail, those skilled in the art will recognize various manifestations and details that could be developed in light of the overall teachings herein. Accordingly, the particular mechanisms disclosed are meant to be illustrative only and not to limit the scope of the invention which is to be given the full breadth of the following claims and any and all embodiments thereof.