US3422766A - Pump assemblies - Google Patents

Description

Jall- 21, 1969 G. w. coNlBEER 3,422,766

PUMP ASSEMBLIES Filed March 29, 1966 Sheet of 5 APPLICANT George william Conibee BY N Misdgages Dou las ATTORNEYS United States Patent Office 3,422,766 Patented Jan. 21, 1969 13,711/ 65 U.S. Cl. 103-103 2 Claims Int. Cl. F04d 7/06, 7/08, 29/40 ABSTRACT F THE DISCLOSURE A liquid-metal pump assembly of minimal plan size, for use especially in a sodium-cooled nuclear reactor, comprises a centrifugal, axial or half-axial pump on a vertical axis with a suction duct coaxially above the impeller, and an outlet duct of the same bore as the suction duct coaxially below the impeller and separated from it by a convergent portion of the pump casing so as to recover velocity head as pressure head. A novel expansion joint for the pump outlet is described: this is associated with a releasable core joint by which the assembly is made withdrawable from the reactor tank together with its drive unit.

This invention relates to pump assemblies for pumping liquid metals, for example for use `as primary coolant circulator assemblies in a liquid-metal cooled nuclear reactor. Such assemblies may include pumps of the centrifugal, half-axial or axial type.

According to the invention, such a pump assembly includes a pump comprising a pump casing and an impeller mounted for rotation by a coaxial vertical shaft in said casing and having inlet means at its top end, wherein said pump casing includes a suction duct coaxial with and arranged vertically above the impeller, a discharge duct coaxial with and arranged vertically below the impeller, so that liquid metal both enters and leaves the pump in a vertical direction, and flow-guiding means arranged between the impeller outlet and the discharge duct so as to cause the direction of ow of liquid metal, when the liquid metal enters the discharge duct, to be generally vertical.

Preferably, said flow-guiding means comprises an annulus provided with a plurality of fixed guide vanes.

According to a preferred feature of the invention, said annulus varies in cross-sectional area from one section thereof to another so as to convert to pressure head at least part of the velocity head imparted to the liquid metal by the impeller.

Preferably, Where the impeller outlet is arranged to give to the liquid metal a direction of exit flow having a radial component, said annulus is frusto-conical.

According to another preferred feature of the invention, the discharge duct has a coaxial frusto-conical exit portion arranged to engage releasably a corresponding frusto-conical inlet portion of a further duct for removal of liquid metal from the pump assembly.

The discharge duct preferably includes expansion means for allowing thermal expansion and contraction thereof.

According to a further preferred feature of the invention, the pump assembly is adapted for pumping liquid metal coolant in a nuclear reactor and includes a hollow body fixed in a containment structure of the reactor, the pump casing being suspended from said hollow body and said shaft extending between the impeller and drive means in said hollow body for driving the pump.

Preferably the pump assembly is arranged for location in the reactor so that the pump and at least the lower part of said hollow body are immersed in liquid metal within a reactor tank forming part of the reactor, and

so that said hollow body in operation contains a gas under pressure, said shaft being arranged to rotate in a bearing at the bottom of said hollow body.

According to yet another preferred feature of the invention, said bearing is arranged to be cooled by said liquid metal, and the pump assembly includes sealing means adjacent to and above said bearing and means for introducing some of said gas under pressure to the sealing means whereby to prevent leakage of liquid metal from said bearing into the hollow body.

In one form of the invention, said sealing means includes a first fixed sleeve coaxial with said shaft above said bearing and a second lixed sleeve coaxial withl and inside said first sleeve, the shaft being free to rotate inside said second sleeve, separate first and second annular spaces being provided respectively around said first sleeve, and between said sleeves in communication with said bearing, and said rst annular space being arranged for tiow of some of said gas therethrough under pressure so as to cause liquid metal in said second annular space to freeze.

According to yet a further preferred feature of the invention, said pump and hollow body are arranged so as to be withdrawable together from said reactor tank.

A pump assembly according to the invention, for pumping liquid metal for use as a primary coolant in a nuclear reactor, and such a reactor incorporating said pump assembly, will now be described by way of example and with reference to the drawings accompanying the provisional specification, of which:

FIG. l is a simplified sectional elevation of the nuclear reactor;

FIG. 2 is an enlarged simplified part-sectional elevation take from FIG. 1 and showing a pump incorporated in the assembly;

FIG. 3 is an enlarged sectional elevation taken from FIG. 2 and showing the pump in greater detail; and

FIGS. 4 and 5 are enlarged sectional elevations taken from FIG. 2 and showing two alternative forms of sealing and bearing unit incorporated in the pump assembly.

With reference firstly to FIG. 1, the reactor comprises a double-walled generally-cylindrical reactor tank 10 supported within a concrete lbiological shield 11 and surmounted by a concrete pile cap 12. The inner wall 10A of tank 10 is of stainless steel. Supported from the pile cap 12 within the tank 10 is a thin-walled vessel 13 in which a reactor core, indicated diagrammatically at 14, is suspended from the pile cap 12 by means not shown.

Within the vessel 13 and below the reactor core 14 is a plenum chamber 15 which communicates with the reactor core and 'which is fed, through a number of coolant ducts 16, with liquid metal coolant, which may for example he sodium, potassium or a sodium-potassium mixture.

The space between the vessel 13 and tank 10 is divided horizontally by a launder plate 17, which is 'penetrated by a number of heat exchangers 18 and a number 0f pump drive units 19. Suspended from each pump drive unit 19, in the lower space 20 below the launder plate 17, is a pump assembly generally indicated at 21.

Preferably there are the same number of pump assemblies 21 and heat exchangers 18, but it will be noted that only one of each is visible in FIG. l.

In operation, the reactor tank 10 contains liquid metal up to a free surface indicated in FIG. l at 22. Above the free surface 22 the tank 10 is filled with an inert gas such as argon.

Each pump assembly includes a pump 23, each .pump' being operated by its respective drive unit 19 so as to pump coolant Imetal from the lower space 20, down through the ducts 16 and so through the plenum chamber 15 to the reactor core 14, where the coolant metal receives heat from nuclear fuel (not shown) therein. The hot coolant metal leaves the reactor core at the top thereof and passes through openings 24 in the vessel 13 to a launder or space 25 above the launder plate 17, whence it passes downwardly through the heat exchangers 18 and so back into the lower space 20.

Heat from the hot coolant metal is transferred in the heat exchangers 18 to a secondary `coolant which enters and leaves the reactor through pipes 26, 27 and which passes to heat exchanger means (not shown) outside the reactor. Such heat exchanger means may for example comprise boilers for generating steam to drive a steam turbine.

Each drive unit 19 comprises a cylindrical drive containment vessel 30 having a lining of insulation 31 (shown in FIG. 2 but, for clarity, not in FIG. 1) and a removable top cap 32 above the pile cap 12. Each vessel 30 is supported from the pile cap 12 and is aligned therein by guides 33 which also provide vibration dam-ping. Within each vessel 30 is a hydraulic motor 34, arranged to drive the pump 23 of the corresponding assembly 21 through a separate gear coupling 35 and drive shaft 37. A reduction gearbox 36 may be interposed between the motor 34 and gear coupling 35.

It will be understood that the launder plate 17 is provided with suitable seals in all appropriate places so that the only path for coolant metal between the launder 25 and lower space 20 is through the heat exchangers 18.

With reference now to FIGS. 2 and 3, each pump assembly 21 comprises three distinct units: a support unit 40, the pump 23 and a discharge unit 41. The support unit 40 comprises a number of axially-extending pump support columns 42, arranged symmetrically around the axis of the assembly and each secured at one end to a bottom plate 43 of the drive containment vessel 30. The pump 23 is fixed (thorugh a flange 44 on the pump casing) to the other end of the columns 42. The support unit 40 also includes a bearing and sealing unit shown diagrammatically at 4S, through which the drive shaft 37 passes into the vessel 30.

FIG. 2 also shows spacing studs 46 lon which the gear coupling 35 and motor 34 (and the reduction gearbox 36, if provided) are supported.

Each pump 23 has a casing 47, split radially and containing an impeller 48 which is keyed to the drive shaft 37 and which is' rotatable in the casing 47. The upper end of the casing 47 has an open bell-mouthed suction piece 49 mounted coaxially thereon. A labyrinth seal (shown diagrammatically at 50 in FIG. 2 and in greater detail in FIG. 3) is provided below the suction piece 49 to restrict coolant metal passing between the impeller 48 and casing 47.

Fixed outlet guide vanes 51 are provided within a frustoconical discharge annulus 52 inside the casing 47, each guide vane 51 being split as between the two parts of the casing. The larger portion 51A of each guide vane 51 is fixed in the lower part of the casing 47, a frusto-conical hub 55 being supported coaxially between the said portions 51A. The annulus 52 tapers inwardly to a discharge connection 56 which is coaxial with the impeller 48 and with the suction piece 49.

The hub 55 carries a 4coaxial journal bearing 57 and a thrust bearing 58, in which the lower end of the drive shaft 37 can rotate. The abutting faces of the bearings 57, 58 are preferably coated with a hard material such as that known as Stellite. The thrust bearing 58 may be of the Michell type `or of the r-oller or the coll-ar type. The weight of the impeller 48 and that of the drive shaft 37 up to the gear coupling 35 (FIG. l), together with axial thrusts are taken by the thrust bearing 58.

The journal bearing 57 and thrust bearing 58 are lubricated by liquid coolant metal, which is taken from the discharge annulus 52 through passages 59, and which leaves the bearings through further passages 60 passing through the guide vanes 57 to the outside of the casing 47.

The discharge unit 41 is the lowest in position of the three units constituting the pump assembly 21, and includes a bellows. 64 fixed at each end to an abutment ring 65. The albutment rings 65 t closely in annuli formed coaxially in the lower end of the pump casing 47 and in the upper end of a connecting piece 66. The lower end of the connecting piece 66 comprises a conical female portion 67, which in normal operation is in close engagement with a conical male end piece 68 on the top end of the corresponding coolant-metal inlet duct 16 leading to the plenum chamber 15 (FIG. l). The female portion 67 and end piece 68 are maintained in engagement with each other by a number of cam-type clamps 69 radially disposed externally and operable by a mechanical linkage (not shown) from outside the pile cap 12.

The discharge unit 41 is supported from the pump 23 through a number of axially-extending tie-bolts 70 secured to flanges 71, 72 on the pump casing 47 and on the connecting piece 66 respectively. Each tie-[bolt 70 has two stops 70A, the lower stops 70A bearing against the flange 72, and the upper stops 70A Ibeing arranged so that when the bellows 64 is extended there is a gap 73 between the upper stops 70A and the flange 71. The bellows 64 can thus expand and contract in response to relative movement between the duct 16 and pump 23 due to thermal expansion or contraction.

The tie-bolts 70, 'bellows 64, rings 65, connecting piece 66 and clamps 69 together constitute the discharge unit 41.

With reference now to FIG. 4, which shows in detail the bearing and sealing unit 45, the drive shaft 37 runs in a journal bearing 75, comprising a bush 76 mounted coaxially in a hub 77, which is secured to the underside of the bottom plate 43 of the drive containment vessel 30 (see FIG. 2) by studs 78. The cooperating faces of the bush 76 and drive shaft 37 are preferably coated with Stellite or the like. The bearing is lubricated lby a forced flow of liquid coolant metal supplied through a pipe 79 leading from the discharge annulus 52 of the pump (FIG. 3); this liquid metal leaves the |bearing 75 by a passage -80 in the hu'b 77.

Above the bearing 75 is a labyrinth seal 81, mounted vertically between the hub 77 and a retaining plate 82 which is set into the underside of the bottom plate 43. Above the retaining plate 82 and surrounding the drive shaft 37 is a lantern ring 83, on which a double gas seal 84 is supported. Any upward leakage of liquid metal past the Abearing 75 is removed through a return passage 85 in the hub 77.

In operation, each drive containment vessel 30 is pressurized with a continuous flow of the same inert gas that is used to lill the launder space 25 (FIG. 1) above the level 22 of liquid metal: the inert gas is circulated through the vessels 30 and cooled in heat exchangers (not shown) external to the reactor, so that the drive motor 34 and its associated equipment can be kept at suitable operating temperatures.

The upper side of the retaining plate 82 is sealed by the same inert gas, supplied under pressure through ducts 86 passing through the lantern ring 83. The pressure of this inert gas is so chosen that it is slightly higher than the pressure of liquid coolant metal at the top end of the bearing 75, so that where the inert gas meets the liquid metal in the labyrinth seal 81 the pressures thereof are equal.

FIG. 5 shows an alternative sealing arrangement which may be used in conjunction with the journal lbearing 75. In this arrangement, any liquid metal leaking past the labyrinth seal 81 passes into an annular space 90 between an insulating sleeve 91 and the inner face of a coaxial cylindrical extension 92 of the retaining plate, which plate is indicated in FIG. 5 at 93. A continuous flow of inert gas is maintained from an inlet 94, through a further annular space 95 around the outside of the extension 92, to an outlet 96. The cooling action of this inert gas causes any liquid metal in the annular space to freeze. A

double gas seal `84 is provided above the inert-gas cooled seal just described, as in FIG. 4.

The pump 23 is arranged suliiciently far below the free surface 22 of liquid metal in the reactor tank to avoid any substantial cavitation.

Although the impeller 48 shown in FIG. 3 is of the half-axial type, a centrifugal or fully-axial impeller may be employed instead.

It will be observed with reference to FIG. 3, that the discharge annulus 52 increases in cross-section from its top point (X in FIG. 3) to the section indicated by chaindotted lines at Y-Y; and that the Ibore of the discharge connection 56 at the bottom of the pump 23 is the same as that of the suction piece 49 immediately upstream of the impeller 48. Velocity head imparted to the coolant metal 'by the impeller `48 is thus recovered as pressure head in the annulus 52.

The equipment Within the drive containment vessel 30 can be attended to for maintenance by purging the inert gas from the vessel 30; then isolating, draining and disconnecting the hydraulic connections (not shown) from the vessel cap 32, removing the cap 32 and finally removing the equipment from the vessel 30.

If maintenance attention becomes necessary for any of the pumps 23, the equipment in the corresponding drive containment vessel 30 is first removed as just described. The clamps 69 are then released, the vessel 30 is released from the pile cap 12 and the Whole pump assembly 21, together with the vessel 30, is lifted upwards by an overhead crane (not shown). lf the members 67 and 68 (FIG. 2) tend to stick together, the bellows 64 extends to its limit as defined by the gap 73, tensioning the tie-bolts 70 so as to provide a force to unstick them.

The crane now continues to lift the assembly until the vessel 30 is above the pile cap 12. When the radio-activity level permits, the reduction gearbox 36 and that half of the gear coupling 35 which is attached to the drive shaft 37 can then be dismantled. The vessel 30 is then raised further; the columns 42 are supported by suitable means (not shown) at the level of the top of the pile cap 12 to prevent the pump assembly falling back into the reactor; and the columns 42 are separated from the vessel 30. The latter can then be removed (for decontamination and storage).

The pump 23 and discharge unit 41 can now be removed from the reactor tank and separated.

It will be noted that the tie-bolts 70 can act as compression members during assembly of the conical joint, to assist alignment of the female member 67 and end piece 68 so as to make it possible to clamp them together using the clamps 69.

Pumps such as that described herein, of the centrifugal, half-axial or axial type having a top suction connection and bottom discharge connection for pumping a liquid metal, may be used in any application in which the plan size of the pump is required to be as small as possible, and not only in nuclear reactors.

I claim:

1. In a pump assembly for pumping liquid metal, comprising a pump having a pump casing, an impeller rotatable by a coxial vertical shaft in said casing, inlet and outlet means at the top and bottom ends respectively of said impeller, a suction duct and discharge means on said casing coaxial with, and respectively vertically above and below said impeller, and a plurality of fixed radial guide vanes in a discharge annulus defined by portions of said casing between said impeller outlet means and discharge means; the improvement wherein said discharge means includes a coxial frusto-conical exit portion engaging releasably a corresponding frusto-conical inlet portion of a further duct for removal of said liquid metal from the pump assembly, a rst duct in communication with said discharge annulus, a second duct coaxial with and below said first duct and carrying said exit portion, thermal expansion means between said first and second ducts, radial extensions on said first and second ducts respectively, and a plurality of axially-extending stepped studs joining said radial extensions whereby to allow limited axial movement between said first and second ducts in response to thermal expansion and contraction of the expansion means.

2. In a pump assembly for pumping liquid metal, comprising a pump having a pump casing, an impeller rotatable 4by a coaxial vertical shaft in said casing, inlet and outlet means at the top and bottom ends respectively of said impeller, a suction duct and discharge means on said said casing coaxial with, and respectively vertically above and below said impeller, and a plurality of fixed radial guide vanes in a discharge annulus defined by portions of said casing between said impeller outlet means and discharge means; the improvement wherein said discharge means comprise a first duct in communication with said discharge annulus, a second duct coaxial with and below said first duct, thermal expansion means between said first and second ducts, a radical extension on each of said first and second ducts, a radial extension on each of said stepped studs joining said radial extensions whereby to allow limited axial movement between said rst and second ducts in response to thermal expansion and contraction of the expansion means.

References Cited UNITED STATES PATENTS 1,042,506 10/1912 De Vallat 103-88 1,369,527 2/1921 Johnston 103-102 1,683,949 9/1928 Bergdoll 103-87 2,693,760 ll/1954 Miller 103-102 2,204,169 6/ 1940 Zerkowitz 103--111 1,387,660 8/1921 Ostenberg 103-102 FOREIGN PATENTS 513,309 10/1920 France. 257,111 8/1926 Great Britain.

HENRY I. RADUAZO, Primary Examiner.

U.S. Cl. X.R.

103-102, lll

Images