Patent Number: 051184664
Section: description

DETAILED DESCRIPTION OF THE INVENTION In the following description, like reference characters designate like or corresponding parts throughout the several views. Also in the following description, it is to be understood that such terms as "forward", "rearward", "left", "right", "upwardly", "downwardly", and the like, are words of convenience and are not to be construed as limiting terms. In General Referring now to the drawings, and particularly to FIG. 1, there is shown a prior art nuclear reactor core vessel 10 and coolant system 12 connected thereto. The reactor coolant system 12 includes two coolant loops, generally indicated by the numerals 14A and 14B. Each of the coolant loops 14A, 14B includes a single steam generator 16, a pair of high inertia canned motor pumps 18, a single hot leg pipe 20, and a pair of cold leg pipes 22. The pair of prior art pumps 18 in each coolant loop 14A, 14B are hermetically sealed and mounted in inverted positions to the one steam generator 16 in the respective coolant loop. Each pump 18 has a casing 24 which is attached, such as by welding, directly to the bottom of a channel head 26 of the steam generator 16 so as to effectively combine the two components into a single structure. The hot leg pipes 20 extend between and interconnect the reactor vessel 10 and the respective steam generators 16 for routing high temperature reactor coolant from the vessel 10 to the steam generators 16. The cold leg pipes 22 extend between and interconnect the pumps 18 and the reactor vessel 10 for routing lower temperature reactor coolant from the steam generators 16 via the pumps 18 back to the reactor vessel 10. Further, a pressurizer tank 28 is connected by a surge line 30 to one of the hot leg pipes 20. Prior Art Coolant Pump With External Heat Removal Arrangement Referring to FIG. 2, there is illustrated in greater detail one of the prior art reactor coolant pumps 18. In addition to its casing 24, the pump 18 has a central rotor 32 extending axially through the casing 24 and rotatably mounted to the casing adjacent a lower end 32A by a pivot pad bearing 34 and adjacent an upper end 32B by a thrust bearing 36. A canned motor 38 is located about the pump rotor 32 between the opposite lower and upper bearings 34, 36. The motor 38 includes a rotor section 40 mounted to the pump rotor 32 for rotation therewith and a stator section 42 mounted stationarily to the casing 24 about the rotor section 40. For removing heat to cool the lower and upper bearings 34, 36 and the motor 38, the pump 18 also includes a heat removal arrangement 44 which is separate from the reactor coolant water circulated through the coolant loop 14A, 14B. Further, the pump 18 has an impeller 46 mounted at the upper end 32B of the rotor 32 which rotates therewith. One end 24A, such as the upper end, of the pump casing 24 has a central inlet nozzle 48, a peripheral outlet nozzle 50 and an annular passage 51 which interconnects the inlet and outlet nozzles 48, 50. The pump impeller 46 is disposed across the annular passage 51 and in flow communication with reactor coolant water flowing in a main stream therethrough. Operation of the motor 38 causes rotation of the rotor 32 and the impeller 46 therewith. Rotation of the impeller 46 draws water axially through the central inlet nozzle 48 from the steam generator 16 and discharges the water tangentially through the outlet nozzle 50 to the respective one of the cold leg pipes 22, after flowing through the annular passage 51. In such manner, operation of the pumps 18 creates lower pressure at their inlet nozzles 48 which sucks or draws water from the reactor vessel 10 via the respective hot leg pipes 20 to and through the steam generators 16 and positive pressure at their outlet nozzles 50 which pumps water through the cold leg pipes 22 back to and through the reactor vessel 10. The heat removal arrangement 44 includes an annular hollow jacket 52 surrounding the motor 38, a set of coils 54 contained in the jacket 52 and surrounding the motor 38, and other respective sets of coils (not shown) located adjacent the lower and upper bearings 34, 36. The multiple sets of coils are connected in flow communication so as to define a closed path for circulation of an internal coolant fluid therein for cooling the bearings 34, 36 and motor 38. The annular hollow jacket 52 of the heat removal arrangement 44 has an inlet 52A and an outlet 52B connected in flow communication with an external source (not shown) of a secondary coolant fluid which can then flow through the jacket 52 over the set of coils 54 contained therein. The secondary coolant fluid is typically at a temperature much lower than the temperature of the internal coolant fluid circulating about the closed path such that the heat carried by the internal coolant fluid gained from cooling the bearings 34, 36 and motor 38 is readily transferred to the secondary coolant fluid through the set of coils 54 in the jacket 52. Improved Coolant Pump With Self-Cooling Arrangement Turning to FIGS. 3 and 4, there is illustrated an improved version of the pump 18 having a self-cooling arrangement 56 in accordance with the principles of the present invention. The self-cooling arrangement 56 employs some of the reactor coolant water to cool the pump rotor bearings 34, 36 and pump motor 38. Only a fraction, for example one percent, of the reactor coolant water is diverted from the main stream of coolant water flowing through the annular passage 51 by the self-cooling arrangement 56 before return to the main stream. The self-cooling arrangement 56 can be used in reactor applications where the temperature of the reactor coolant water entering the pump 18 is below approximately 200.degree. F. Reactor coolant water at that temperature can readily remove motor heat generated by electrical losses and bearing heat generated by friction, eliminating the need for use of the external secondary coolant fluid and separate internal closed path coolant fluid as in the case of the prior art heat removal arrangement 44. Referring to FIG. 3, the self-cooling arrangement 56 provided in the pump 18 defines a fluid flow loop 58, with the arrows in FIG. 3 identifying the direction of coolant water flow about the loop 58. The fluid flow loop 58 provides flow of reactor coolant water from the annular passage 51 into a heat transfer relationship with the bearings 34, 36 and the motor 38 before returning the flow back to the annular passage 51. As mentioned above, the self-cooling arrangement 56 is operable for diverting only a fraction, such as approximately one percent, of the reactor coolant water from and back to the main stream through the annular passage 51 to cool the bearings and motor. The fluid flow loop 58 of the self-cooling arrangement 56 is composed of outer and inner annular loop portions 60, 62. The outer loop portion 60 extends generally coaxial with, but is located farther radially outwardly from, the central rotor 32 than is the inner loop portion 62. The annular configurations of the outer and inner loop portions 60, 62 promote uniform flow of the coolant water about the loop 58 and past the bearings 34, 36. The coolant water flows from the lower end toward the upper end of the pump 18 along the outer annular loop portion 60 and in the opposite direction along the inner annular loop portion 62. The fluid flow loop 58 also includes a plurality of entry and exit ports 64, 66 which open respectively into and from the outer and inner loop portions 60, 62. The entry and exit ports 64, 66 are defined in flow communication with the annular passage 51. Particularly, the entry ports 64 are defined in the casing 24, whereas the exit ports 66 are defined through the rotor 32. Also, the entry ports 64 are located downstream of the exit ports 66. Thus, the entry ports 64 are defined at the high pressure discharge side of the pump 18 or at points of greater pressure in the main stream of the coolant water through the annular passage 51, whereas the exit ports 66 are defined at the low pressure suction side of the pump 18 or at points of lesser pressure in the main stream of water flow through the passage 51. The outer portion 60 of the fluid flow loop 58 is formed by an outer annulus 68 which surrounds the exterior of the motor 38 and a plurality of channels 70 which extend between the outer annulus 68 and the entry ports 64. More particularly, the casing 24 has the cylindrical hollow jacket 52 which surrounds and is spaced outwardly from the exterior of the stator section 42 of the motor 38 to define the outer annulus 68. The inner portion 62 of the fluid flow loop 58 is formed by an inner annulus 72 which surrounds the exterior of the central rotor 32 and motor rotor section 40 and is defined by the clearance between rotary rotor and stationary stator sections 40, 42 of the motor 38. The inner loop portion 62 also includes lower and upper pathways 74, 76 defined along and past the lower and upper bearings 34, 36. The lower pathways 74 interconnect in flow communication the lower end of the inner annulus 72 with the exit ports 66, whereas the upper pathways 76 interconnected in flow communication the upper end of the inner annulus 72 with the upper end of the outer annulus 68. The outer and inner loop portions 60, 62 thus generally extend coaxially with the central rotor 32. Further, the self-cooling arrangement 56 includes foreign particle deflectors provided with respect to the fluid flow loop so as to minimize passage of particles into the fluid flow loop 58 and to collect those particles which do pass into the loop 58 at a desired location along the loop 58. More particularly, one form of the foreign particle deflectors is a plurality of deflector elements 78 mounted to casing 24 adjacent entry ports 64 and projecting into the annular passage 51 upstream of the entry ports 64 for impeding particles entrained in the main stream of fluid flow from leaving the main stream and passing through the entry ports 64 into the outer portion 60 of the fluid flow loop 58. Most particles moving at greater momentum will tend to pass the entry ports 64 or be deflected downstream past the ports 64. Another form of the foreign particle deflectors is a centrifugal separator element 80 mounted to the rotor 32 upstream of the lower bearing 34 for rotation with the rotor. The separator element 80 extends across the inner loop portion 62 for striking particles still entrained in the flow of fluid in loop 58 and flinging the particles outwardly thereof. An annular deadend cavity 82 is defined in a radial portion of the casing 24 radially spaced outwardly from and surrounding the rotational path of the separator element 80 which is capable of receiving and trapping particles flung therein by the separator element 80 upon rotation of the rotor 32. Such collected particles are thus prevented from entering the lower bearing 34 where they could cause damage. It is thought that the present invention and many of its attendant advantages will be understood from the foregoing description and it will be apparent that various changes may be made in the form, construction and arrangement thereof without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the form hereinbefore described being merely a preferred or exemplary embodiment thereof.