PUMP INCLUDING A SHIELD FOR PROTECTING A PUMP WHEEL AGAINST A COOLANT LEAK ALONG THE HUB OF THE WHEEL

Abstract

A pump is provided. The pump includes a flow chamber for the heat-transport fluid, a pump wheel which is placed entirely in the flow chamber and which comprises a hub, a shaft for rotating the pump wheel, having an axial end section rigidly connected to the pump wheel and fitted in the hub of the pump wheel, a motor for rotating the shaft around its axis, and means for causing a coolant for cooling the driveshaft to flow, at a temperature lower than that of the heat-transport fluid, along the driveshaft. The pump also includes a shield for protecting the pump wheel against a coolant leak along an outer peripheral surface of the hub of the pump wheel, the protective shield being attached to the pump wheel.

Description

The present invention relates to a pump for causing a heat-transport fluid to flow in a fluid circuit, of the type comprising:

• • a flow chamber for the heat-transport fluid,
  • a pump wheel which is placed entirely in the flow chamber and which comprises a hub,
  • a shaft for rotating the pump wheel, having an axial end section rigidly connected to the pump wheel and fitted in the hub of the pump wheel,
  • a motor for rotating the shaft around its axis, and
  • means for causing a coolant for cooling the driveshaft to flow, at a temperature lower than that of the heat-transport fluid, along the driveshaft.

BACKGROUND

In nuclear reactors cooled by pressurized water, the pressurized cooling water of the nuclear reactor is made to flow in the cooling circuit of the core of the nuclear reactor, or primary circuit, by a pump, called primary pump, and including a single pump wheel submerged in the pressurized water filling the primary circuit.

The pump wheel is driven by an electric motor, positioned outside and at a certain distance from the primary circuit, via a driveshaft at one of the ends of which the pump wheel is bound. This driveshaft crosses through a set of cooling means and sealing means between its first end segment, secured to the pump wheel, and a second end segment, secured to the rotor of the electric motor.

Inside the body of the pump, which is connected to a line of the primary circuit, the pump wheel and the first end segment of the driveshaft are submerged in the pressurized water at a temperature of approximately 300° C. The shaft is, between its first and second segments, surrounded by an enclosure containing a thermal barrier made up of a network of tubes inwardly cooled by the flow of an exchange fluid, a bearing guiding the rotation of the shaft, and means making it possible to ensure a tight passage of the shaft between the body of the pump receiving the pressurized water and the outer part of the pump including the drive motor.

The role of the heat barrier is to prevent the heat from the primary water from rising toward the upper parts of the pump. Furthermore, during normal operation, cold water at a temperature below 60° C. is injected at the thermal barrier to form a dam between the primary circuit and the sealing device of the shaft. To that end, the pressure of that injection circuit is slightly higher than the pressure of the primary circuit. The injection flow rate is divided in two:

• • part of the flow rate flows downward, i.e., through the play between the shaft and the thermal barrier, and
  • another part of the flow rate flows upward, i.e., through the pump bearing and the sealing device.

Thus, the water from the primary circuit, which is contaminated by radioactive elements taken from the core of the nuclear reactor, cannot leak through the sealing device.

Under these conditions, when the pump is operating, the pump wheel is at a temperature close to that of the water of the primary circuit, while the shaft, the upper part of which is cooled by the thermal barrier and the injection water, is at a temperature below that of the pump wheel. This causes a loss of binding between the shaft and the pump wheel, which in turn causes contact wear in the connection between the shaft and the pump wheel, and subsequently, a deterioration of the shaft and the pump wheel at their contact surfaces. Regular maintenance of the primary pump is therefore necessary to ensure optimal holding of the pump wheel on the shaft.

To resolve this problem, a system has been proposed for causing the water from the primary circuit to flow in the first end segment of the shaft. Such a system in fact makes it possible to keep said first end segment at a temperature close to that of the pump wheel, and prevents the losses of binding due to the presence of a temperature gradient between the shaft and the pump wheel. Such a system is described in EP-A-0,257,140.

SUMMARY OF THE INVENTION

However, such a system is not fully satisfactory. In fact, despite the presence of this system for causing water of the primary circuit to flow in the first end segment of the shaft, traces of deterioration of the shaft and the pump wheel by contact wear are still observed.

One aim of the invention is therefore to reduce the maintenance costs of the primary pump, in particular by minimizing the contact wear between the pump wheel and the driveshaft.

To that end, the invention provides a pump of the aforementioned type, further comprising a shield for protecting the pump wheel against a coolant leak along an outer peripheral surface of the hub of said pump wheel, said protective shield being attached to the pump wheel.

According to preferred embodiments of the invention, the pump also has one or more of the following features, considered alone or according to any technically possible combination(s):

• • the protective shield is formed by an annular crown comprising a substantially cylindrical peripheral wall, coaxial to the hub and surrounding the hub;
  • the peripheral wall has an inner diameter with a difference in diameter relative to an outer diameter of the hub, said difference in diameter being less than 1.5 mm;
  • the difference in diameter is greater than 0.1 mm;
  • the annular crown comprises an inner rim extending substantially radially toward the axis of the peripheral wall, from the peripheral wall;
  • the inner rim is flush with the shaft;
  • the annular crown further comprises an outer rim protruding from the peripheral wall opposite the axis of the peripheral wall, said outer rim running along a surface of the pump wheel;
  • the protective shield is fastened to the pump wheel by means of the outer rim;
  • a seal is inserted between the outer rim and the pump wheel;
  • the inner rim protrudes from a first axial end of the peripheral wall, and the outer rim protrudes from a second axial end of the peripheral wall, opposite the first axial end;
  • it comprises means for causing the heat-transport fluid to flow in the axial end segment of the shaft fitted into the hub;
  • it comprises a key connecting the pump wheel to the shaft, the pump wheel having a first axial slot for receiving the key and the shaft having a second axial slot for receiving the key, the key and the pump wheel comprising complementary members for axial blocking of the key relative to the pump wheel;
  • the first axial slot emerges in an axial end of the pump wheel through a window, and the protective shield obstructs said window;
  • the pump wheel is bound on the shaft;
  • the protective shield is attached to the pump wheel;
  • the driveshaft is oriented substantially vertically, the axial end segment fitted into the hub being a lower end segment of the shaft; and
  • the pump is a primary pump, the fluid circuit being a primary circuit of a nuclear reactor, in particular a pressurized water nuclear reactor.

BRIEF SUMMARY OF THE DRAWINGS

Other features and advantages of the invention will appear upon reading the following description, provided solely as an example and done in reference to the appended drawings, in which:

FIG. 1 is an elevation and partial sectional view of a pump according to an embodiment of the invention,

FIG. 2 is a view of a detail marked II in FIG. 1, and

FIG. 3 is a view of a detail marked III in FIG. 2.

DETAILED DESCRIPTION

The pump 1, shown in FIG. 1, is a primary pump of a pressurized water nuclear reactor. This pump 1 is suitable for causing a heat-transport fluid to flow, in this case pressurized water at a temperature close to 300° C., in a fluid circuit, in the case at hand the primary circuit of the nuclear reactor.

To that end, the primary pump 1 includes a pump body 2 delimiting a chamber 4, or volute, for causing a heat-transport fluid to flow, fluidly connected by means of a first tubing 6 to a first line of the primary circuit and by a second tubing 8 to a second line of the primary circuit, between which the pump 1 establishes a certain pumping pressure to cause the heat-transport fluid to flow.

The pump 1 further includes a pump wheel 10 for establishing the pumping pressure between the first and second tubings 6, 8. This pump wheel 10 is bound on a lower axial end segment 12 of a driveshaft 14 oriented substantially vertically and the upper axial end segment 16 of which is connected, by means of the coupler 18, to the rotor of an electric motor 20 for driving the rotation of the pump wheel 10.

A bearing 22 provides the connection of the shaft 14 to the pump body 2, and guides the shaft 14 in rotation around its axis.

In reference to FIG. 2, at the periphery of the driveshaft 14, means 32 for cooling the shaft 14 are positioned in an enclosure 30 surrounding the shaft 14.

The pump body 2 separates the flow chamber 4 from the enclosure 30. In other words, a wall 34 of the pump body 2 extends between the flow chamber 4 and the enclosure 30. Said wall 34 has a through orifice 36, emerging in the flow chamber 4 and in the enclosure 30, for the passage of the driveshaft 14.

The cooling means 32 in particular comprise a thermal barrier 38 formed by a network of tubes traveled by an exchange fluid and housed in the enclosure 30. This thermal barrier 38 serves to prevent heat from the heat-transport fluid from rising toward the upper parts of the pump 1.

The cooling means 32 also comprise, in a known manner, means (not shown) for injecting a pressurized coolant, at a temperature below 60° C., into the enclosure 30, and for causing said coolant to flow in the enclosure 30, along the driveshaft 14. This coolant flows partially downward through the orifice 36, and partially upward through the bearing 22.

The pump wheel 10 is arranged completely in the flow chamber 4. In other words, it does not extend in the enclosure 30. It is thus completely submerged, like the end segment 12, in the heat-transport fluid flowing inside the flow chamber 4.

Still in reference to FIG. 2, the pump wheel 10 comprises a hub 40, an annular ring 42 extending around the hub 40, and a plurality of blades 44 supported by the ring 42.

The hub 40 is tubular. It is coaxial with respect to the shaft 14 and is fitted on the lower axial end segment 12. It has an inner peripheral face 46, in contact with the shaft 14, and an outer peripheral face 48, opposite the inner peripheral face 46.

The inner peripheral face 46 has a substantially frustoconical shape, narrowing toward the bottom, to facilitate the mounting of the wheel 10 on the shaft 14.

The annular ring 42 surrounds the hub 40. It protrudes outward and upward from a lower end of the hub 40. It is thus substantially in the shape of a hollow cone portion narrowing downward and widening upward.

The annular ring 42 has an upper face 50 forming, at the junction with the outer peripheral face 48 of the hub 40, an annular plate 52, defining a substantially radial plane. Said plate 52 is withdrawn downward relative to the upper ends 54, 56 of the hub 40 and the ring 42.

The annular ring 42 further has a lower face 58, opposite the upper face 50.

Each blade 44 protrudes downward from the lower face 58 of the ring 42.

The pump wheel 10 is a single piece.

The driveshaft 14 comprises, in addition to the lower axial end segment 12, a central segment 60, surrounded by the enclosure 30, and an intermediate segment 62, inserted between the central 60 and lower axial end 12 segments.

The central segment 60 is substantially cylindrical of revolution, and has a first diameter. It defines a radial shoulder 64, oriented downward, at the junction with the intermediate segment 62.

The intermediate segment 62 is substantially cylindrical of revolution, and has a second diameter, smaller than the first diameter. It extends through the through orifice 36.

A thermal protection ring 66 is fitted on the intermediate segment 62, bearing against the shoulder 64. Said ring 66 is in particular bound on the segment 62. It is designed to protect the shaft 14 against the temperature gradient existing inside the enclosure 30 and inside the flow chamber 4.

The lower axial end segment 12 is completely fitted in the hub 40. It has a slightly frustoconical shape narrowing downward. This shape is in particular complementary to that of the inner peripheral face 46 of the hub 40.

The maximum diameter of the lower axial end segment 12 is preferably substantially equal, as shown, to the second diameter.

The pump 1 also comprises, still in reference to FIG. 2, a nut 70 for axially securing the pump wheel 10 to the shaft 14, and a key 72 for rotatably securing the pump wheel 10 to the shaft 14.

The lower axial end segment 12 defines a recess 74 for receiving the nut 70, emerging in the lower axial end 76 of the shaft 14. Said recess 74 is substantially cylindrical of revolution, coaxial with respect to the shaft 14, and has an inner tapping.

The nut 70 is screwed to the shaft 14. It comprises a nut body 80 and a nut head 82.

The nut body 80 is substantially cylindrical of revolution. It has a diameter substantially equal to the diameter of the recess 74, and has an outer thread cooperating with the tapping of the recess 74.

The nut head 82 has a diameter larger than the diameter of the lower end 76 of the shaft 14. It defines a radial shoulder 84 oriented upward, bearing against the pump wheel 10. Thus, the pump wheel 10 cannot move downward relative to the shaft 14.

The nut 70 advantageously has an axial passage 86 for a check-screw 88. The check-screw 88 is screwed to the lower axial end segment 12 with a pitch opposite the screw pitch of the nut 70 of the lower axial end segment 12, and the head 90 of the check-screw 88 bears against the head 82 of the nut 70. In particular, the head 90 of the check-screw 88 is welded on the wheel nut 70 so as to prevent loosening of the wheel nut 70.

The hub 40 of the pump wheel 10 has a first axial slot 92 for receiving the key 70, and the lower axial end segment 12 has a second axial slot 94 for receiving the key 70. Said slots 92, 94 are positioned across from one another, and the key 70 is engaged in each of the two slots 92, 94. Thus, in case of binding loss, the key 70 may transmit the rotational torque from the shaft 14 to the pump wheel 10.

The first slot 92 emerges through a window 96 in the upper end 54 of the hub 40.

The pump wheel 10 and the key 70 comprise complementary means for axially securing the key 70 to the wheel 10. Thus, the pump wheel 10 can be mounted on the driveshaft 14 with the key 70 already engaged in the first slot 92. In the illustrated example, these complementary means are made up of a lug 100 secured to the key 72, and an orifice 102 for receiving the lug 100, arranged in the hub 40. The lug 100 in particular protrudes radially outward from the key 70.

Still in reference to FIG. 2, the pump 1 also comprises means for causing a heat-transport fluid to flow inside the lower axial end segment 12. In the example illustrated here, these flow means are formed by a centrifugal auxiliary wheel integrated into the wheel nut 70.

To that end, the wheel nut 70 has a plurality of inclined channels 104 arranged in the nut head 82 and fluidly connecting the passage 86 to the flow chamber 4, a plurality of axial channels 106 arranged in the nut body 80 around the passage 86, and a plurality of radial channels 108 arranged in the nut head 82 fluidly connecting each axial channel 106 to the flow chamber 4. Furthermore, the nut body 80 has an upper axial end segment with a smaller diameter for the placement of a ring 110 welded to the nut 70 in the extension of the radial channels 106, an interstice 112 (FIG. 3) being left free between the axial channels 106 and the nut 110. Lastly, an axial space 114 is arranged between the bottom of the recess 74 and the wheel nut 70, and a peripheral space 116 is arranged between the peripheral wall of the recess 74 and the ring 110, to place the passage 86 in fluid communication with each axial channel 106 by bypassing the ring 110.

According to the invention, the pump 1 further comprises, in reference to FIG. 3, a shield 120 for protecting the pump wheel 10 from a flow of the coolant along the outer peripheral face 48 of the hub 40 of the wheel 10.

This protective shield 120 is attached to the pump wheel 10. It is formed from an annular metal crown, typically made from stainless steel or a nickel alloy (INCONEL), comprising a substantially cylindrical peripheral wall, an inner rim 124 extending substantially radially toward the axis of the peripheral wall 122, from the peripheral wall, and an outer rim 126 protruding from the peripheral wall 122 opposite the axis of the peripheral wall 122.

The peripheral wall 122 is coaxial to the hub 40, and surrounds the hub 40. It has an inner diameter having a difference in diameter with respect to the outer diameter of the hub 40, said difference in diameter being greater than 0.1 mm, and preferably less than 1.5 mm, so as to form a narrow fluid cavity, commonly called “water space”, between the protective shield 120 and the hub 40.

The inner rim 124 protrudes toward the inside of the peripheral wall 122 from an upper end 130 of the peripheral wall 122. It substantially runs along the upper end 54 of the hub 40, an interval (not shown) with a height comprised between 0.1 mm and 1.5 mm being left free between the inner rim 124 and said upper end 54.

The inner rim 124 obstructs the window 96 through which the first slot 92 emerges in the upper end 54 of the hub 40. To that end, the inner rim 124 extends from the peripheral wall 122 until it is flush with the shaft 14. In particular, the inner rim 124 is flush with the shaft 14 over its entire contour.

The inner rim 124 is axially inserted between the upper end 54 of the hub 40 and the thermal protection ring 66. Preferably, it is axially spaced several millimeters from the thermal protective ring 66.

The outer rim 126 protrudes toward the outside of the peripheral wall 122 from a lower end 132 of the peripheral wall 122. It runs along the plate 52.

A plurality of screws 134 extend through the outer rim 126 and are screwed in the pump wheel 10, to fasten the outer rim 126 to the pump wheel 10. Alternatively, the outer rim 126 is welded to the pump wheel 10. The protective shield 120 is thus fastened to the pump wheel 10 by means of the outer rim 126, the protective shield 120 not being fastened to the pump wheel at any other point and being fastened exclusively to the pump wheel 10.

As shown in FIG. 3, an annular seal 136 is inserted between the outer rim 126 and the plate 52. This seal 136 is typically a metal seal of the C-ring type.

Owing to the invention described above, the binding losses between the pump wheel 10 and the driveshaft 14 are avoided.

In fact, due to the presence of the protective shield 120, the part of the coolant flow rate flowing downward cannot flow directly against the hub 40 of the wheel 10. This results in slower cooling of the hub 40 under the effect of the coolant when the pump 1 is stopped when the reactor is stopped hot. This makes it possible to prevent the hub 40 from cooling faster than the shaft 14, and in so doing, deforming by gripping around the shaft 14 having remained expanded, causing a loss of binding. This slowing of the cooling of the hub 40 is even more significant given that, due to the difference in diameter between the peripheral wall 122 and the hub 40, water is trapped between the shield 120 and the hub 40, that water not being able to flow downward due to the presence of the seal 136, the water consequently forming a stagnant water space reinforcing the thermal insulation provided by the shield 120.

Furthermore, the shield 120 obstructing the window 96, the coolant cannot flow in the first slot 92. This avoids more pronounced local cooling of the hub 40 and the shaft 14 that may cause the appearance of cracks in the pump wheel 10 and the shaft 14.

Thermomechanical simulations have been conducted to compare the residual binding forces between the invention described above and the pump described in EP-A-0,257,140. To that end, each of the two pumps was subjected to a series of ten cycles each comprising the following series of steps:

• • heating the heat-transport fluid from 20 to 300° C. at a rate of 40° C. per hour;
  • stopping heating of the pump, the heat-transport fluid being at 300° C., the injection of coolant being maintained, the temperature of the fluid in the flow chamber, at the back of the pump wheel, dropping very quickly to stabilize at 150° C. after 120 seconds;
  • restarting the pump hot, the wheel quickly being heated by the heat-transport fluid to the temperature of 300° C.;
  • cooling the reactor, the temperature of the heat-transport fluid going from 300 to 20° C. at a rate of 55° C. per hour.

After these ten cycles, the stabilization of the deformations is observed. The pump 1 then has a residual binding pressure gain of 360% for the hot rotation and 180% for the cold rotation compared to the pump described in EP-A-0,257,140.

These results therefore clearly and unambiguously show the interest of the invention relative to the state of the art.

It will be noted that although the described pump is a primary pump of a pressurized water nuclear reactor, the invention is not limited to this type of pump alone. The invention generally relates to any type of pump for causing a heat-transport fluid to flow in a fluid circuit, and is in particular applicable to the primary pumps of other nuclear reactors, such as boiling water reactors.

Claims

1-15. (canceled)

16. A pump for causing a heat-transport fluid to flow in a fluid circuit, the pump comprising: a flow chamber for the heat-transport fluid;a pump wheel placed entirely in the flow chamber, the pump wheel including a hub;a shaft configured to rotate the pump wheel, the shaft having an axial end section rigidly connected to the pump wheel and fitted in the hub of the pump wheel;a motor configured to rotate the shaft around an axis of the shaft;a cooler configured to cause a coolant for cooling the driveshaft to flow, at a temperature lower than that of the heat-transport fluid, along the driveshaft; anda protective shield configured to protect the pump wheel against a coolant leak along an outer peripheral surface of the hub of the pump wheel, the protective shield being attached to the pump wheel.

17. The pump as recited in claim 16 wherein the protective shield is formed by an annular crown comprising a substantially cylindrical peripheral wall, coaxial to the hub and surrounding the hub.

18. The pump as recited in claim 17 wherein the peripheral wall has an inner diameter with a difference in diameter relative to an outer diameter of the hub, the difference in diameter being less than 1.5 mm.

19. The pump as recited in claim 18 wherein the difference in diameter is greater than 0.1 mm.

20. The pump as recited in claim 17 wherein the annular crown comprises an inner rim extending substantially radially toward an axis of the peripheral wall from the peripheral wall.

21. The pump as recited in claim 20 wherein the inner rim is flush with the shaft.

22. The pump as recited in claim 17 wherein the annular crown comprises an outer rim protruding from the peripheral wall opposite the axis of the peripheral wall, the outer rim running along a surface of the pump wheel.

23. The pump as recited in claim 22 wherein the protective shield is fastened to the pump wheel by the outer rim.

24. The pump as recited in claim 22 further comprising a seal inserted between the outer rim and the pump wheel.

25. The pump as recited in claim 22 wherein the annular crown comprises an inner rim extending substantially radially toward an axis of the peripheral wall from the peripheral wall, the inner rim protruding from a first axial end of the peripheral wall, the outer rim protruding from a second axial end of the peripheral wall opposite the first axial end.

26. The pump as recited in claim 16 further comprising an injector for causing the heat-transport fluid to flow in the axial end segment of the shaft fitted into the hub.

27. The pump as recited in claim 16 further comprising a key connecting the pump wheel to the shaft, the pump wheel having a first axial slot for receiving the key and the shaft having a second axial slot for receiving the key, the key and the pump wheel comprising complementary members for axial blocking of the key relative to the pump wheel.

28. The pump as recited in claim 16 wherein the first axial slot emerges in an axial end of the pump wheel through a window, the protective shield obstructing the window.

29. The pump as recited in claim 16 wherein the pump wheel is shrunk on the shaft.

30. The pump as recited in claim 16 wherein the driveshaft is oriented substantially vertically, the axial end segment fitted into the hub being a lower end segment of the shaft.