The invention generally relates to pumps for causing a heat-transfer fluid to flow in a fluid circuit.
More specifically, according to a first aspect, the invention relates to a pump for causing a heat-transfer fluid to flow in a fluid circuit, of the type including: - a main flange;
- a volute inwardly delimiting a flow chamber of the heat-transfer fluid, the volute being rigidly fastened to the main flange;
- a pump wheel housed in the flow chamber;
- a diffuser housed in the flow chamber, arranged so as to channel the heat-transfer fluid set in motion by the pump wheel;
- a drive shaft rotating the pump wheel around a rotation axis, axially traversing the main flange and the diffuser, the pump wheel being rigidly fastened to the drive shaft;
- a device for cooling the drive shaft, including a thermal barrier flange axially inserted between the main flange and the volute, and a cooling circuit connected to the thermal barrier flange and surrounding the drive shaft.
It is possible to fasten the diffuser to the thermal barrier flange using dowels. In this case, the axial alignment of the cooling device and the diffuser with one another can be provided by a cylindrical portion arranged at the upper end of the diffuser. The free upper surface of the cylindrical part is stair-stepped, and has a radially inner part protruding slightly relative to the radially outer part. A sealing gasket is inserted between the radially inner part and the thermal barrier flange.
With such an arrangement, the sealing gasket is positioned in a zone greatly deformed by the forces resulting from thermal gradients in the parts. As a result, it is difficult to obtain a high degree of sealing between these two parts. Furthermore, during maintenance operations of the equipment, the axial alignment of the diffuser and the cooling device relative to one another often requires repair machining. The maintenance of the pump is therefore complex. Lastly, the dowels may undergo corrosion under stresses.
In this context, the invention aims to propose a pump that does not have the above flaws.
To that end, the invention relates to a pump of the aforementioned type, characterized in that the diffuser comprises a diffuser flange clamped axially between the thermal barrier flange and the volute, one of the diffuser and the thermal barrier flange comprising an outer groove surrounding the rotation axis, the other of the diffuser and the thermal barrier flange including an outer tenon engaged in the outer groove and providing the axial alignment of the cooling device and the diffuser with one another.

Thus, the maintenance in position of the diffuser relative to the volute is provided by clamping the diffuser flange axially between the thermal barrier flange and the volute. Such an arrangement is simple, and makes it possible to eliminate the dowels fastening the diffuser to the thermal barrier flange.
Due to the presence of the flange, and because the axial alignment of the cooling device and the diffuser is done by the outer tenon and the outer groove, the part of the diffuser facing the thermal barrier flange is less susceptible to deformation. Yet the axial alignment of the cooling device and the diffuser is essential to the alignment of the guide bearings of the shaft of the pump, and therefore the proper vibrational behavior of the pump. The invention can improve the axial alignment of the pump, in that it makes it possible to avoid the deformations and repair operations during disassembly of the pump.
Thus, the volute, the diffuser and the cooling device are kept in position relative to one another stably over the long term, which contributes to guaranteeing sealing between the parts.
The pump may further have one or more of the features below, considered individually or according to any technical possible combination(s):
- the diffuser flange is in contact with the thermal barrier flange by a contact plane,
the outer groove being radially inwardly delimited by an inner tenon arranged on said one
of the diffuser and the thermal barrier flange, the inner tenon extending axially past the
contact plane and being engaged in an inner groove arranged inside said other of the
diffuser and the thermal barrier flange;
- the pump comprises a diffuser sealing gasket inserted between the diffuser flange and the volute;
- the pump comprises a thermal barrier sealing gasket inserted between the thermal barrier flange and the diffuser flange;
- the cooling circuit includes at least one cooling duct having a segment welded on the thermal barrier flange, the inner tenon or the outer tenon protruding axially toward the diffuser, relative to a contact plane between the diffuser flange and the thermal barrier flange, over a height smaller than 200 mm;
- the diffuser includes a cylindrical part surrounding the rotation axis, inserted radially between the volute and the cooling circuit, and radially having a thickness greater than 100 mm;
- the cooling device includes a cover positioned around the cooling circuit, having a shroud arranged in the immediate vicinity of the cylindrical part of the diffuser without inserting a thermally insulating layer in between; and

- the diffuser includes an annular part secured to the cylindrical part, insulating the
cooling circuit from the flow chamber, the cover having a bottom inserted axially between
the cooling circuit and the annular part, arranged in the immediate vicinity of the part
without inserting a thermally insulating layer in between.
According to a second aspect, the invention relates to a nuclear reactor comprising:
- a vessel, in which a core is placed including nuclear fuel assemblies;
- a primary circuit fluidly connecting the vessel to a heat exchanger or a steam turbine, the primary circuit comprising a pump having the above features for circulating a primary fluid in the primary circuit.
The heat exchanger is for example a steam generator.
Other features and advantages of the invention will emerge from the following detailed description, provided for information and non-limitingly, in reference to the appended figures, in which:
- figure 1 is a sectional illustration in an axial plane of a pump according to the invention;
- figure 2 is an enlarged sectional illustration of a detail d of the pump of figure 1, showing the connection between the diffuser and the cooling device.
The pump 1 shown in figure 1 is provided for causing a heat-transfer fluid to flow in a fluid circuit.
Typically, this pump is a nuclear reactor primary pump, provided for causing a primary fluid of this reactor to flow in the primary circuit. The nuclear reactor, aside from the primary circuit, includes a pressurized vessel, containing the core of the reactor. The core is made up of nuclear fuel assemblies.
In a reactor of the PWR type, the primary circuit connects the vessel of the reactor to a steam generator. The primary fluid is heated in contact with nuclear fuel assemblies, and gives part of its heat energy to a secondary fluid in the steam generator. The primary pump sees to the flow of the primary fluid along the primary circuit, from the vessel of the reactor to the steam generator, then the return of the primary fluid from the steam generator to the vessel.
In a nuclear reactor of the BWR type, the primary circuit connects the vessel of the reactor to a steam turbine. The primary fluid is vaporized in the vessel of the reactor, coming into contact with nuclear fuel assemblies. The primary pump sees to the flow of the heat-transfer fluid from the vessel to the steam turbine, and brings the heat-transfer fluid back from the steam turbine to the vessel of the reactor.

Alternatively, the pump is provided to be implemented in another circuit of a nuclear reactor, for example a secondary circuit or a tertiary circuit or any other circuit. According to still another alternative, the pump is provided for causing a heat-transfer fluid to flow in an industrial installation other than a nuclear reactor.
The heat-transfer fluid is of any type. For example, the heat-transfer fluid essentially comprises water.
The pump 1 includes:
- a main flange 3;
- a volute 5 inwardly delimiting a flow chamber 7 for the heat-transfer fluid;
- a pump wheel 9 housed in the flow chamber 7;
- a diffuser 11 housed in the flow chamber 7, arranged so as to channel the heat-transfer fluid set in motion by the pump wheel 9;
- a drive shaft 13 rotating the pump wheel 9 around a rotation axis X, the pump wheel 9 being rigidly fastened to the drive shaft 13;
- a device 15 for cooling the drive shaft 13.
The rotation axis X is typically vertical. In the following description, the terms "top", "bottom", "below", "above", "upper" and "lower" are to be understood relative to the vertical direction.
As visible in figure 1, the main flange 3 is a thick part, made from a metal such as steel. It is substantially perpendicular to the rotation axis X.
The volute 5 is a boiler-made part made from metal.
The volute 5 is rigidly fastened to the main flange 3.
To that end, the volute 5 includes a volute flange 17, substantially perpendicular to the axis X and including a central orifice 18 traversed by the drive shaft 13. The volute flange 17 is fastened to the main flange 3 by main dowels 19, visible in figure 1.
The pump 1 is typically of the centrifugal type. Thus, the volute 7 has a suction inlet 21 for the heat-transfer fluid located in the extension of the drive shaft 13, and emerging inside the flow chamber 7.
The inlet 21 is situated below the pump wheel 9.
The volute 5 also has a discharge outlet 23 for the heat-transfer fluid, substantially radial relative to the rotation axis X. More specifically, the central axis of the outlet 23 is substantially perpendicular to the axis X.
The pump 1 further includes a motor, not shown, arranged above the main flange 3. The motor is placed inside a case 25, rigidly fastened by the main dowels 19 to the main flange 3. The case 25 is located above the main flange, and rests on an upper face of the main flange 3.

The pump 1 further includes multiple gaskets providing rotary sealing along the drive shaft 13. These gaskets are placed in gasket housings collectively designated by reference 27.
Furthermore, the pump 1 includes bearings for guiding the rotation of the shaft 13. The lower bearing 29 is shown in the figures.
The cooling device 15 includes a thermal barrier flange 31 and a cooling circuit 33 connected to the thermal barrier flange 31 and surrounding the drive shaft 13.
The thermal barrier flange 31 extends in a plane substantially perpendicular to the rotation axis X. It is placed immediately below the main flange 3, and is in direct contact with a lower face of the main flange 3.
The thermal barrier flange 31 is axially inserted between the main flange 3 and the volute 5. More specifically, it is inserted between the main flange 3 and the volute flange 17.
The drive shaft 13 axially traverses the main flange 3, the thermal barrier flange 31 and the diffuser 11.
The cooling circuit 33 includes one or several coils 35, in particular visible in figure 2. It further includes a device (not shown) arranged to cause a coolant to flow in the coils 35. Each coil 35 includes one or several tubes, arranged so as to form circular turns around the drive shaft 13. The turns are arranged in several webs perpendicular to the rotation axis X, each web including several turns.
As visible in figure 2, the lower bearing 29 includes a cage 37 rigidly fastened to the thermal barrier flange 31 and a plurality of rolling members 39 inserted between the cage 37 and the drive shaft 13. For example, the rolling members 39 are rollers.
The coils 35 are arranged axially at the lower bearing 29, and surround the rolling members 39.
The diffuser 11 is a metal part with a complex shape.
It includes an upper part intended to block the diffuser 11 in position relative to the volute 5, and a lower part 41 provided to channel the heat-transfer fluid.
As shown in figure 1, the lower part 41 of the diffuser is hollow and delimits a central housing 43 in which the pump wheel 9 is arranged. The housing 43 is downwardly open, and thus has an inlet opening 45 arranged across from the suction inlet 21 of the volute.
A duct 47 channels the heat-transfer fluid from the inlet 21 to the suction opening 45.
The lower part 41 of the diffuser also has, around the pump wheel 9, a plurality of discharge channels 49, circumferentially distributed around the rotation axis X. The

channels 49 are arranged and oriented so as to channel the heat-transfer fluid set in motion by the pump wheel 9 toward the discharge outlet 23 of the volute.
The diffuser 11 further includes a diffuser flange 51 clamped axially between the thermal barrier flange 31 and the volute 5.
The diffuser flange 51 is part of the upper part of the diffuser.
It extends substantially perpendicular to the rotation axis X. It is clamped in that the diffuser flange 51 is directly in contact with a lower face of the thermal barrier flange 31 on one side, and directly in contact with the volute 5 on another side.
More specifically, a lower face 53 of the diffuser flange 51 is pressed against an upper face 55 of the diffuser flange 17.
Thus, the diffuser flange 51 is stressed axially against the diffuser flange 17 by the main dowels 19, which stress the main flange 3 against the thermal barrier flange 31 and the thermal barrier flange 31 against the diffuser flange 51.
The diffuser 5 further includes a cylindrical part 57, inserted radially between the cooling device 33 and the volute 5. The cylindrical part 57 and the cooling device 33 are arranged in the central orifice 18 of the volute flange 17. The diffuser flange 51 protrudes radially outward from an upper end of the cylindrical part 57.
The diffuser 11 further includes an annular part 59, secured to the cylindrical part 57, delimiting a passage orifice 61 for the drive shaft 13. The annular part 59 protrudes radially inward from the cylindrical part 57. It is secured to a lower end of the cylindrical part 57. It thus delimits, with the cylindrical part 57, a toroid volume 63, surrounding the drive shaft 13, in which the cooling circuit 33 is housed.
To provide the axial alignment of the cooling device 15 and the diffuser 11 with one another, the diffuser 11 includes a circumferential outer grooves 65, centered on the rotation axis X.
Furthermore, the thermal barrier flange 31 includes an outer tenon 67 engaged in the outer groove 65.
The outer grooves 65 is upwardly open, i.e., toward the thermal barrier flange 31. It is hollowed in the cylindrical part 57 of the diffuser. Alternatively, it is hollowed in the diffuser flange 51.
It extends circumferentially all the way around the axis X. Alternatively, it does not extend circumferentially all the way around the rotation axis X. For example, in this case, it includes several circumferential segments distributed around the axis X.
As shown in figure 2, the outer groove 65 considered in section in a plane containing the rotation axis X has a U-shaped section. Alternatively, the outer groove 65 has a V-shaped section or any other appropriate section.

The outer groove 65 is radially outwardly delimited by a radially outer wall and inwardly by a radially inner wall. Cold, the centering of the diffuser 11 is done by the outer tenon 67 bearing against the radially outer wall. Warm, the centering of the diffuser 11 is done by the outer tenon 67 bearing against the radially inner wall.
The outer groove 65 is delimited radially inwardly, i.e., toward the rotation axis X, by an inner tenon 69, engaged in an inner groove 71 arranged in the thermal barrier flange 31. The inner groove 71 is hollowed in a large face 73 of the thermal barrier flange facing downward, i.e., toward the diffuser 11. The inner tenon 69 protrudes axially from the cylindrical part 57 of the diffuser 5. It defines the radially inner wall of the outer groove 65.
Like before, typically, the groove 71 extends circumferentially all the way around the axis X. Alternatively, it only extends over part of the periphery of the rotation axis X, and for example includes several circumferential segments distributed around the axis X.
The diffuser flange 51 is in contact with the thermal barrier flange 31 at a contact plane P embodied in figure 2. More specifically, the large face 73 of the thermal barrier flange 31 is in contact with a large face 75 of the diffuser flange 51, facing upward, at the contact plane P.
The outer tenon 67 radially, relative to the axis X, has a width substantially equal to that of the outer groove 65. Conversely, the outer tenon 67 has an axial height smaller than the depth of the outer groove 65, considered axially. The height of the outer tenon 67 is taken from the contact time [sic] P. Likewise, the depth of the outer groove 65 is taken between the contact plane P and the bottom 77 of the outer groove. A ring 79 occupies the majority of the space left free between the tenons 67 and the bottom 77 of the outer groove. This ring is rigidly fastened to the diffuser 11 by screws 81. One thus limits the quantity of heat-transfer fluid that may accumulate in the groove 65.
As visible in figure 2, the coils 35 have end segments 83 fastened by welds 85 to the thermal barrier flange 31. The end segments 83 are oriented axially, and are therefore substantially perpendicular to the contact plane P. The welds 85 are in the immediate vicinity of the large face 73. For example, the welds 85 secure the end segments 83 to bosses 87 arranged on a large face 73.
The end tenon 67 protrudes axially relative to the contact plane P over a height smaller than 200 mm, preferably smaller than 100 mm.
Thus, the outer tenon 67, due to its small height, does not hinder the displacement of the welding tools making it possible to produce the welds 85.
The inner tenon 69 has, radially relative to the rotation axis X, a width substantially equal to or slightly smaller than that of the inner groove 71. Axially, it has a height

substantially equal to the depth of the inner groove 71. The height of the inner tenon 69 and the depth of the inner groove 71 are taken axially from the contact plane P.
It should be noted that the cooling device 15 typically includes a cover 89 arranged around the cooling circuit 33. The cover 89 is housed inside the toroid space 63. In the illustrated example, the cover 89 includes a shroud 91 arranged in the immediate vicinity of the cylindrical part 57 of the diffuser, with no inserted thermally insulating layer. The shroud 91 has a generally cylindrical shape, centered on the axis X. It is fastened by an upper edge 93 to the thermal barrier flange 31.
The shroud 91 extends in the immediate vicinity of the cylindrical surface 95 radially inwardly delimiting the cylindrical part 57. It passes between the end segments 83 of the coils and the cylindrical surface 95.
The cover 89 further includes a bottom 97, inserted axially between the cooling circuit 33 and the annular part 59 of the diffuser. The bottom 97 is arranged in the immediate vicinity of the annular part 59, without inserting a thermally insulating layer.
The bottom 97 has an annular shape, and extends radially inward, i.e., toward the rotation axis X, from a lower edge of the shroud 91. The bottom 97 extends practically up to the cage 37.
As visible in figure 2, the cylindrical part 57 radially has a thickness greater than
100 mm, preferably greater than 150 mm.
As a result, it is not necessary to provide a heat screen between the cover and the diffuser.
Furthermore, the pump 1 comprises a diffuser sealing gasket 99 between the diffuser flange 51 and the volute 5. Typically, this diffuser sealing gasket 99 is a graphite gasket, with a spiral shape. It extends over the entire periphery of the rotation axis X. It is inserted between the lower large face 53 of the diffuser flange and the upper large face 55 of the volume flange 17.
Advantageously, the pump 1 includes an additional diffuser sealing gasket 101 inserted between the diffuser flange 51 and the volute 5. The gasket 101 is housed in a groove arranged either in the lower large face 53 or in the upper large face 55. It is placed radially toward the outside of the gasket 99. Thus, in the event of a leak through the diffuser gasket 99, the heat-transfer fluid is captured in the groove receiving the gasket
101 and discharged through channels provided to that end in the pump.
The pump 1 also comprises a thermal barrier sealing gasket 103 inserted between the thermal barrier flange 31 and the diffuser flange 51. This gasket 103 is typically a spiral graphite gasket. It is inserted between the upper large face 73 of the diffuser flange and the lower large face 75 of the thermal barrier flange.

Like before, the pump 1 advantageously has an additional thermal barrier flange 105, housed in a groove arranged either in the large face 73 or in the large face 75. The gasket 105 is arranged radially outside the thermal barrier sealing gasket 103. Thus, in the event of a leak through the gasket 103, the heat-transfer fluid is collected in the groove receiving the gasket 105 and discharged through channels provided to that end in the pump.
One can therefore see that the axial alignment of the cooling device 15 and the diffuser 11 is obtained particularly simply, due to the existence of the outer groove 65 and the outer tenon 67. The inner groove 71 and the inner tenon 69 also facilitate this alignment.
The sealing between the parts is particularly easy to obtain, due to the presence of the thermal barrier flange and the diffuser flange. These flanges offer large planar surfaces making it possible to arrange sealing gaskets simply and to obtain a good level of sealing. The planar surfaces also make it possible to use effective gaskets for a high differential pressure, withstanding friction with the opposite planar surface.
According to one non-preferred alternative, the pump includes a heat screen between the cylindrical part 57 and the shroud 91 of the cover and/or includes a heat screen between the bottom 97 of the cover and the annular part 59 of the diffuser.
According to another alternative embodiment, the outer tenon 67 is arranged on the diffuser, and the outer groove 65 is hollowed in the thermal barrier flange 31. In this case, the inner tenon 69 is supported by the thermal barrier flange 31 and the inner groove 71 is hollowed in the diffuser. It protrudes axially relative to the contact plane P over a height smaller than 400 mm, preferably 200 mm.

WE CLAIM

1.- A pump (1) for causing a heat-transport fluid to flow in a fluid circuit, the pump (1) including:
- a main flange (3);
- a volute (5) inwardly delimiting a flow chamber (7) of the heat-transfer fluid, the volute (5) being rigidly fastened to the main flange (3);
- a pump wheel (9) housed in the flow chamber (7);
- a diffuser (11) housed in the flow chamber (7), arranged so as to channel the heat-transfer fluid set in motion by the pump wheel (9);
- a drive shaft (13) rotating the pump wheel (9) around a rotation axis (X), axially traversing the main flange (3) and the diffuser (11), the pump wheel (9) being rigidly fastened to the drive shaft (13);
- a device (15) for cooling the drive shaft (13), including a thermal barrier flange (31) axially inserted between the main flange (3) and the volute (5), and a cooling circuit (33) connected to the thermal barrier flange (31) and surrounding the drive shaft (13);
characterized in that the diffuser (11) comprises a diffuser flange (51) clamped axially between the thermal barrier flange (31) and the volute (5), one of the diffuser (11) and the thermal barrier flange (31) comprising an outer groove (65) surrounding the rotation axis (X), the other of the diffuser (11) and the thermal barrier flange (31) including an outer tenon (67) engaged in the outer groove (65) and providing the axial alignment of the cooling device (15) and the diffuser (11) with one another.
2.- The pump according to claim 1, characterized in that the diffuser flange (51) is in contact with the thermal barrier flange (31) by a contact plane (P), the outer groove (65) being radially inwardly delimited by an inner tenon (69) arranged on said one of the diffuser (11) and the thermal barrier flange (31), the inner tenon (69) extending axially past the contact plane (P) and being engaged in an inner groove (71) arranged inside said other of the diffuser (11) and the thermal barrier flange (31).
3.- The pump according to claim 2, characterized in that the cooling circuit (33) includes at least one cooling duct (35) having a segment (83) welded on the thermal barrier flange (31), and in that the inner tenon (69) protrudes axially toward the diffuser (11), relative to a contact plane (P) between the diffuser flange (51) and the thermal barrier flange (31), over a height smaller than 200 mm.
4.- The pump according to claim 1 or 2, characterized in that the cooling circuit (33) includes at least one cooling duct (35) having a segment (83) welded on the thermal

barrier flange (31), the outer tenon (67) protruding axially toward the diffuser (11), relative to a contact plane (P) between the diffuser flange (51) and the thermal barrier flange (31), over a height smaller than 200 mm.
5.- The pump according to any one of the preceding claims, characterized in that the pump (1) comprises a diffuser sealing gasket (99) inserted between the diffuser flange (51) and the volute (5).
6.- The pump according to any one of the preceding claims, characterized in that the pump (1) comprises a thermal barrier sealing gasket (103) inserted between the thermal barrier flange (31) and the diffuser flange (51).
7.- The pump according to any one of the preceding claims, characterized in that the diffuser (11) includes a cylindrical part (57) surrounding the rotation axis (X), inserted radially between the volute (5) and the cooling circuit (33), and radially having a thickness greater than 100 mm.
8.- The pump according to claim 7, characterized in that the cooling device (15) includes a cover (89) positioned around the cooling circuit (33), having a shroud (91) arranged in the immediate vicinity of the cylindrical part (57) of the diffuser (11) without inserting a thermally insulating layer in between.
9.- The pump according to claim 8, characterized in that the diffuser (11) includes an annular part (59) secured to the cylindrical part (57), insulating the cooling circuit (33) from the flow chamber (7), the cover (89) having a bottom (97) inserted axially between the cooling circuit (33) and the annular part (59), arranged in the immediate vicinity of the annular part (59) without inserting a thermally insulating layer in between.
10.- The pump according to any one of the preceding claims, characterized in that the outer groove (65) has a U-shaped section, considered in section in a plane containing the rotation axis (X).
11.- The pump according to any one of the preceding claims, characterized in that the centering of the diffuser (11) cold is done by the outer tenon (67) bearing against an outer wall of the groove (65), and is done warm by the outer tenon (67) bearing against a radially inner wall of the outer groove (65).
12.- The pump according to any one of the preceding claims, characterized in that the outer groove (65) is circumferential, centered on the rotation axis (X).

13.- A nuclear reactor, comprising:
-a vessel, in which a core is placed including nuclear fuel assemblies;
-a primary circuit fluidly connecting the vessel to a heat exchanger or a steam turbine, the primary circuit comprising a pump according to any one of the preceding claims for circulating a primary fluid in the primary circuit.