JP2020515763A - Reactor pump - Google Patents

Abstract

The pump comprises a guide structure 15 having a tubular portion 19 arranged around the pump shaft 9, a thermal barrier 37 with a heat exchanger 45 arranged in a recess 47 defined by a thermal barrier cover 41, and a guide structure. A heat shield 57 radially interposed between the heat barrier 37 of 15 and the tubular portion 19 is provided. The heat shield 57 includes an upper heat shield 73 radially interposed between the heat barrier body 39 and the tubular portion 19, and a lower heat shield 75 radially interposed between the heat barrier cover 41 and the tubular portion 19. Equipped with. The upper heat shield 73 is pressed against the heat barrier body 39, and the lower heat shield 75 is pressed against the tubular portion 19.

Description

  The present invention relates generally to nuclear reactor pumps, particularly primary pumps, for operating primary fluids of a nuclear reactor.

More specifically, according to a first aspect, the present invention relates to a reactor fluid pump. This pump is
A stationary structure,
-A pump shaft rotatable about a rotation axis with respect to a stationary structure,
-A pump wheel rigidly fixed to the pump shaft,
-A fluid guide structure fixed to a stationary structure and moved by a pump wheel, the guide structure comprising a tubular part installed around a pump axis, the guide structure for a fluid in which the pump wheel is installed. A guide structure defining an interior of the circulation chamber;
A thermal barrier radially interposed between the tubular portion and the pump shaft, the thermal barrier being axially interposed along the pump axis between the thermal barrier body and the thermal barrier body and the pump wheel. A thermal barrier cover, the thermal barrier comprising a heat exchanger installed in a housing defined by the thermal barrier cover;
A heat shield radially interposed between the heat barrier and the tubular portion of the guide structure.

  Such pumps typically include a diffuser forming a tubular section. It is possible to fix the heat shield to the tubular part. In that case, there is a gap between the heat shield and the heat barrier body.

  Such pumps generally include a dynamic fluid resistant device with injection of a sealing fluid along the pump axis. This sealing fluid flows in the fluid resistant device as well as along the pump axis into the housing that receives the heat exchanger, then into the chamber above the wheel of the pump, and finally to the primary Pour into fluid.

  If the dynamic fluid withstand device fails, the hot primary fluid rises axially from the circulation chamber into the housing that receives the heat exchanger. The primary fluid flows to the dynamic fluid resistant device. In parallel with this mainstream, recirculation of the hot primary fluid occurs in the gap between the heat shield and the heat barrier body.

  Heat from the primary fluid spreads through the thermal barrier body to a fluid resistant gasket located around the pump axis.

  The heat output of the primary fluid rising through the exchanger is partially extracted by the exchanger. The main fluid recirculation between the shield and the thermal barrier, which is not cooled by the heat exchanger, provides the heat output directly to the top of the heat barrier body and by diffusion to the cavity upstream of the fluid resistant body. .. As a result, the temperature of the dynamic fluid tolerant device will be higher than during pump operation with injection.

  Nevertheless, the temperature of the seal must be kept below 90°C at all times for the pump to operate effectively.

  Heat flow diffused through the thermal barrier body is difficult to obtain this result.

  In this context, the invention aims to propose a pump in which it is easier to keep the fluid resistant gasket of the pump shaft below its maximum certified temperature.

  To that end, the present invention provides a heat shield in which a heat shield is radially inserted between the heat barrier body and the tubular portion and a heat shield is radially inserted between the heat barrier cover and the tubular portion. An upper heat shield and a pump of the above type. The upper heat shield is pressed against the heat barrier body and the lower heat shield is pressed against the tubular portion.

  Since the upper heat shield is pressed against the thermal barrier, there is only a very thin gap between the body and the upper heat shield. There may be no actual fluid circulation between the thermal barrier body and the upper heat shield. The heat flow diffused through the thermal barrier body towards the pump shaft seal is reduced.

The pump may further comprise one or more of the following features, considered individually or according to all technically possible combinations.
The upper heat shield is rigidly fixed to the heat barrier body.
The upper heat shield has a lower axial end towards the lower heat shield, which is rigidly fixed to the tubular part by means of fluid-resistant peripheral welding.
The upper heat shield is separated from the tubular part by an upper gap, the cavity between the upper and lower heat shields fluidly connecting the upper gap to the housing.
The thermal barrier comprises at least one head loss or fluid resistant device located in the upper gap or cavity.
The lower heat shield is firmly fixed to the tubular part.
The lower heat shield comprises an extension that engages the upper gap and is rigidly fixed to the tubular part.
The lower heat shield is separated from the thermal barrier cover by a lower gap in fluid communication with the housing.
The lower heat shield and/or the upper heat shield comprises a box and a plurality of flat plates arranged parallel to each other in the box, the flat plates being separated from each other by a liquid blade having a thickness of less than 1.5 mm.
-The thickness of each plate is less than 0.8 mm.
-Comprising at least one shaft seal arranged around the pump shaft and a chamber arranged radially between the heat barrier body and the pump shaft, the chamber comprising the pump shaft between the shaft seal and the housing. Axially disposed along the pump, the pump further comprises a barrier fluid injecting device comprising an injection circuit for injecting the barrier fluid into the chamber, the barrier fluid flowing along the pump axis while following the path from the chamber to the housing. , Then from the housing to the fluid circulation chamber.
The guide structure comprises a spiral defining an internal circulation chamber, and a diffuser arranged in the spiral forming a tubular part.
The upper heat shield and the lower heat shield are two mutually independent structures.
The thermal barrier body and the thermal barrier cover are two separate structures.
The tubular portion is defined radially inward by a substantially cylindrical surface coaxial with the axis of rotation and the thermal barrier body is radially outwardly defined by a substantially cylindrical surface coaxial with the axis of rotation; The upper heat shield is located between the surface of the tubular section and the surface of the thermal barrier body.

  According to a second aspect, the invention relates to a nuclear reactor comprising a container in which a nuclear fuel assembly is installed and a primary circuit. The container has a primary fluid inlet and a primary fluid outlet. The primary circuit comprises a pump having the above features arranged to fluidly connect the primary fluid outlet to the primary fluid inlet and to ensure circulation of the primary fluid from the primary fluid outlet of the container to the primary fluid inlet.

Other features and advantages of the present invention will become apparent from the detailed description thereof provided below for informational purposes, with reference to the accompanying drawings.
1 is a partial view of a primary reactor pump according to the present invention. FIG. 2 is an enlarged view of the heat barrier and heat shield of the pump of FIG. 1. FIG. 3 is an enlarged view of a detailed portion III of FIG. 2. FIG. 4 is an enlarged view of a detailed portion IV of FIG. 2.

  The pump shown in FIG. 1 is for operating the fluid of a nuclear reactor. Typically, this pump is the primary pump for operating the primary fluid of the reactor.

  In a pressurized water reactor (PWR), the reactor comprises a vessel containing a nuclear fuel assembly and a steam generator. The steam generator has a primary side and a secondary side, the primary fluid and the secondary fluid circulate, respectively, and the primary fluid imparts a part of its thermal energy to the secondary fluid in the steam generator. The nuclear reactor comprises a primary circuit that connects the primary fluid outlet of the vessel to the primary inlet of the steam generator and connects the primary outlet of the steam generator to the primary fluid inlet of the vessel. The pump is inserted in the primary circuit to ensure circulation of the primary fluid in the primary circuit.

  In a variant, the pump is a secondary pump inserted in the secondary circuit of the nuclear reactor. The secondary pump ensures circulation of secondary fluid between the secondary side of the steam generator and the steam turbine.

    In a boiling water nuclear reactor (BWR), the primary circuit connects the reactor vessel directly to the steam turbine. In this case, the pump is inserted in the primary circuit between the turbine and the primary fluid inlet of the vessel.

  In a variant, the pump is used in other circuits of the nuclear reactor to operate any type of fluid.

  As shown in FIG. 1, the pump comprises a stationary structure 3 arranged to be rigidly connected to the civil engineering structure of the reactor by various devices not shown in FIG. The stationary structure 3 is only partially shown in FIG. The stationary structure 3 comprises in particular a primary flange 5 and a motor support 7. Such parts are connected to each other by any suitable means.

  The pump 1 further comprises a pump shaft 9 rotatable about a rotation axis X with respect to the stationary structure 3. The axis of rotation X is typically substantially vertical.

  The pump 1 typically includes a motor (not shown) housed above the motor support 7. The motor drives the rotation of the pump shaft 9.

  The pump 1 further comprises a pump wheel 11 rigidly fixed to the pump shaft 9.

  In the illustrated example, the pump wheel 11 is firmly fixed to the lower end portion 13 of the pump shaft 9.

  Furthermore, the pump 1 comprises a guide structure 15 for the fluid driven by the pump wheel 11. The guide structure 15 internally defines a fluid circulation chamber 17 in which the pump wheel 11 is located.

  In FIG. 1 it can be seen that the guide structure 15 comprises a tubular section 19 arranged around the pump axis. The tubular portion 19 is coaxial with the axis X.

  More specifically, the guide structure 15 comprises a spiral section 21 which defines a circulation chamber 17 inside. The spiral portion 21 is firmly fixed to the stationary structure 3, more specifically, the main flange 5.

  In the example shown, the pump 1 is of the spiral centrifugal type and the spiral 21 has at its extension along the axis X a fluid inlet 23 located below the pump wheel 11. The fluid outlet (not shown) is arranged in the spiral portion 21 along the radial direction with respect to the axis X.

  Furthermore, the guide structure 15 includes a diffuser 25 arranged inside the spiral portion 21. Advantageously, the diffuser 25 forms a tubular section 19. The diffuser 25 may also be rigidly fixed to the stationary structure 3 by any suitable means.

  The diffuser 25 typically comprises a fluid guide portion 27 extending the tubular portion 19 downward. The guide part 27 is arranged in an extension part of the pump wheel 11 and has an internal passage 29 for guiding the fluid discharged by the pump wheel toward the chamber 17.

  The spiral part 21 has an upper part 31 forming a flange 31 which is rigidly fixed to the main flange 5.

  The tubular portion 19 comprises an upper segment 33 forming a flange arranged inside the flange 31. The tubular part 19 additionally comprises an intermediate segment 35 connecting the upper segment 33 to the lower guide part 27.

  The tubular portion 19 is a pipe for passing the pump shaft 19, and defines a pipe for accommodating various devices described later therein.

  The pump 1 further comprises a thermal barrier 37 radially inserted between the tubular portion 19 and the pump shaft 9.

  The thermal barrier 37 includes a thermal barrier body 39 and a thermal barrier cover 41.

  The thermal barrier body 39 is tubular and surrounds the pump shaft 9. The thermal barrier body 39 is disposed along the axis X substantially at the flanging upper segment 33.

  The cover 41 is axially inserted along the pump shaft 9 between the heat barrier body 39 and the pump wheel 11.

  The cover 41 and the thermal barrier body 39 are two separate structures.

  The cover 41 is fixed to the thermal barrier body 39 at its lower surface. The cover 41 is disposed substantially on the upper segment 33 and the intermediate segment 35.

  More specifically, in FIG. 1 it can be seen that the tubular section 19 defines an annular volume, which houses the thermal barrier 37, with the pump shaft 9. This annular volume is closed axially towards the pump wheel 11 by a ring-shaped wall 43 forming part of the diffuser 25. This annular volume is defined radially outward by the segments 33 and 35. This annular volume is defined radially inward by the pump shaft 9.

  The thermal barrier 37 further comprises a heat exchanger 45 disposed within a housing 47 defined by the thermal barrier cover 41. The housing 47 has a cylindrical shape and completely surrounds the pump shaft 9. The housing 47 is closed axially towards the pump wheel 11 by an annular wall 49 of the thermal barrier cover. The housing 47 is closed radially outward by the cylindrical wall 51 of the thermal barrier cover. The housing 47 is axially closed on the opposite side of the pump wheel by a thermal barrier cover 39. The housing 47 is closed radially inward by a labyrinth ring 53 fixed to the heat barrier body.

  The thermal barrier 37 further comprises a coolant supply 55. The heat barrier 37 is connected to the heat exchanger 45 and circulates the coolant therein.

  Further, a heat shield 57 is radially inserted between the heat barrier 37 and the tubular portion 19. The heat shield 57 will be described in detail below.

  The pump 1 typically comprises one or several shaft seals installed around the pump shaft 9. In the example shown, the pump comprises three axial seals 59, 61, 63 axially mounted behind one another. Such a seal is axially separated from the pump wheel 11 by the bearing 65 as well as the thermal barrier 37. The exchanger incorporated in the thermal barrier 37 allows the shaft seal to be thermally protected in the event of a loss of barrier fluid supply.

  The bearing 65 provides a rotation guide for the pump shaft 9. The bearing 65 is housed in a chamber 66 defined radially between the thermal barrier body 39 and the pump shaft 9. The bearing 65 is fixed to the lower portion of the heat barrier body 39 in the radial direction.

  The chamber 66 is axially arranged along the pump shaft 9 between the shaft seal 59 and the thermal barrier housing 47. The chamber 66 is arranged radially between the thermal barrier body 39 and the pump shaft 9.

  Typically, pump 1 further comprises a device 67 for injecting a barrier fluid. The barrier fluid helps prevent fluid from rising through the pump assembly to the shaft seal devices 59, 61, 63.

  The device 67 comprises a circuit 69 provided for injecting a cold barrier fluid into the chamber 66. The cold barrier fluid circulates through the shaft seals 59, 61, 63 as well as towards the chamber 17 of the spiral 21.

  The flow of barrier fluid follows a path 71 along the pump axis 9 from the chamber 66 to the housing 47 and then from the housing 47 to the circulation chamber 17.

  As shown in more detail in FIG. 2, the heat shield 57 includes an upper heat shield 73 radially interposed between the heat barrier body 39 and the tubular portion 19, and a heat barrier cover 41 and the tubular portion 19. And a lower heat shield 75 interposed in the radial direction.

  The upper and lower heat shields are two independent structures. That is, they are not firmly fixed to each other.

  The upper heat shield 73 has a cylindrical shape and is coaxial with the axis X. The upper heat shield 73 is arranged around the heat barrier body 19.

  The upper heat shield 73 is pressed against the heat barrier body 39. Here, "pressed" refers to the fact that the upper heat shield 73 is in contact with the thermal barrier body or is separated from the thermal barrier body by a very thin gap. This thickness is typically less than 2 mm, preferably less than 1 mm.

  Conversely, the upper heat shield 73 is separated from the tubular section 19 by an upper gap 76, which can be seen more clearly in the detailed FIGS. 3 and 4. This gap 76 has a thickness of more than 3 mm and preferably more than 5 mm.

  In FIG. 1 it can be clearly seen that the upper heat shield 73 is radially interposed between the heat barrier body 39 and the flanged upper segment 33 of the tubular part.

  More specifically, the thermal barrier body 39 comprises a tubular portion 78 that defines the chamber 66 radially outward. The thermal barrier body 39 further comprises a flange 79 projecting radially outward from the upper end of the portion {79}. The flange 79 is axially sandwiched between the main flange 5 and the upper segment 33.

  The thermal barrier body {79} further comprises a retracting portion 80 extending radially inwardly at the lower end of the tubular portion {79} and extending axially towards the pump wheel. Retracted portion 80 separates chamber 66 from housing 47.

  The upper heat shield 73 is firmly fixed to the heat barrier body 39.

  More specifically, the upper heat shield 73 has a lower axial end 81 facing the lower heat shield 75 fixed to the heat barrier body 19.

  The lower axial end 81 is secured to the thermal barrier body 39 by a fluid resistant circumferential weld 82. This weld 82 extends around the entire circumference of the thermal barrier body {79}. For this reason, the gap between the heat barrier body 39 and the upper part {screen} 73 is closed by the welded portion 82 and the lower part so as to prevent fluid from passing therethrough, and the liquid between the upper heat shield 73 and the heat barrier body 39 is prevented. Prevent any circulation.

  Tubular portion 19 is defined radially inward by a substantially cylindrical surface 83 coaxial with axis X. The thermal barrier body 39, and more specifically the cylindrical portion 79 of the body, is defined radially outward by a substantially cylindrical surface 84 coaxial with the axis X. The upper heat shield 73 is disposed between the surface 83 and the surface 84.

  The upper heat shield 73 is defined radially inward by the inner surface 85. This surface 85 is typically substantially cylindrical and coaxial with the axis X.

  The inner surface 85 is pressed against the surface 84 of the thermal barrier body 39.

  Typically, the axially lower zone of surface 85 is in direct contact with the facing zone of surface 84 or is separated from the facing zone by a gap less than 1 mm thick, for example 0.5 mm thick. The rest of the surface 85 is separated from the surface 84 by a slightly larger thickness, for example a gap of 0.5-1.5 mm.

  As described above, the lower heat shield 75 is pressed against the tubular portion 19. The lower heat shield 75 is firmly fixed to the radially inner surface 83 by welding. The lower heat shield 75 is pressed against the middle segment 35 of the tubular section 19. The lower heat shield 75 has a cylindrical shape and is coaxial with the axis X.

  The lower heat shield 75 is separated from the thermal barrier cover 41 by a lower gap 86 and is in fluid communication with the housing 47. As shown, the lower heat shield 75 is inserted between the wall 51 of the thermal barrier cover and the tubular portion 19. The wall 51 is defined radially outward by a substantially cylindrical surface 87. The lower gap 86 is defined radially inward by the surface 87 and radially outward by the lower heat shield 75.

  In particular, as shown in FIGS. 2 and 3, there is a cavity 88 between the upper and lower heat shields. The volume of this cavity 88 depends on the connection between the thermal barrier cover 39 and the thermal barrier body, the design of the lower and upper heat shields, their fixing, as well as their respective deformations during various operating conditions of the pump. The volume of this cavity 88 will be minimized to limit the thermal bridge between the chamber 17 and the thermal barrier 37.

  In other words, the upper heat shield 73 and the lower heat shield 75 are slightly axially separated from each other. However, this spacing must be maintained above a minimum value, for example 1.5 mm.

  The lower gap 86 is also in fluid communication with the cavity 88. A gap 89 is located between the thermal barrier body 39 and the thermal barrier cover 41 (FIG. 3) to fluidly connect the cavity 88 and the housing 47.

  As seen in FIGS. 3 and 4, the lower heat shield 75 includes an extension 91 that engages the upper gap 76 and is rigidly secured to the tubular portion 19. The extension portion 91 has a cylindrical shape. The extension 91 extends the outer wall of the lower heat shield 75 in the radial direction. The extension 91 extends over the entire axial height of the upper heat shield 73. The upper edge 93 of the extension 91 is welded to the tubular section 19 by means of the welding bead 95 visible in FIG.

  This extension allows the lower heat shield to be conveniently fixed to the tubular section 19. The extension 91 is actually raised to the level of the flanging upper segment 33 and can be easily welded.

  As can be seen in particular in FIGS. 2 and 3, the thermal barrier 37 advantageously comprises at least one head loss or anti-fluid device 97 located in the upper gap 76 or the cavity 88. This device is provided to limit or prevent the circulation of fluid in the upper gap 76, especially the primary fluid that rises from the housing 47 in the absence of the dynamic fluid resistant device 67. In the example shown, the device 97 is inserted between the upper heat shield 73 and the extension 91.

  In a variant, the device 97 is inserted in the cavity 88 between the upper heat shield 75 and the lower heat shield 73. The device 97 is of all types such as metal blades, braids, labyrinth seals, fluid resistant gaskets, segments and the like.

  In the example shown in FIGS. 2 and 3, the device 97 is fixed to the lower end of the upper heat shield. In a variant, the device 97 is mounted differently, for example compressed between two screens.

  As seen in FIGS. 3 and 4, the upper heat shield 73 and the lower heat shield 75 typically have the same structure. Both heat shields each advantageously comprise a cylindrical box 99 and a plurality of flat plates 101 arranged parallel to each other in the box 99. The box 99 and the flat plate 101 are typically made of metal. The flat plates 101 each have a cylindrical shape, and are installed concentrically in parallel with each other. The flat plate 101 has a thickness of, for example, less than 0.8 mm, typically 0.4 mm.

  The plates are preferably separated from each other by a liquid blade 103 having a thickness of less than 1.5 mm. The thickness of the liquid blade is, for example, 1 mm. Each screen comprises a number of flat plates, preferably at least 30 flat plates 101, and even more preferably at least 40 flat plates 101.

  By choosing to provide thin liquid blades and thus multiple flat plates, convection of liquid between the flat plates can be limited.

  The spacers 105 allow the separation between the flat plates 101 to be maintained. In the example shown in FIG. 3, the spacer 105 is fixed to the upper cover 107 of the box.

  The use of an orifice, such as orifice 109, allows the top shield to be emptied during pump hydraulic maintenance operations.

  During normal operation, supply 55 injects coolant into heat exchanger 45. Furthermore, the device 67 injects a barrier fluid into the chamber 66, which flows into the housing 47 along with the anti-fluid gaskets 59, 61, 63 as well as the circulation path 71, and then from the housing 47 into the circulation chamber 17. Flow into. Therefore, this barrier fluid fills the chamber 47, the cavity 88, and the upper gap 76 and the lower gap 86. Besides, the upper heat shield 73 and the lower heat shield 75 are filled with a fluid, for example, a barrier fluid. This barrier fluid is typically water.

  Due to the injection of the barrier fluid, the primary fluid does not rise along the pump shaft 9 and the seals 59, 61, 63 and is thus held at their respective nominal temperatures.

  Furthermore, the heat transfer from the circulation chamber 17 to the seals 59, 61, 63 through the diffuser 25 is limited by the presence of the cold barrier fluid 67 injector, the heat exchanger 47, the upper heat shield 73 and the lower heat shield 75. It

  If the dynamic fluid tolerant device fails due to the injection of the barrier fluid, no further circulation of the barrier fluid will occur along the pump shaft 9. The pressurized primary fluid filling the circulation chamber 17 then rises along the axis to the housing 47 and is partially cooled by the heat exchanger 45. Recirculation occurs between the housing 47 and the gap 86 defined between the thermal barrier cover 41 and the lower heat shield 73.

  The head loss or anti-fluid device 97 limits the recirculation of the upper gap 76. Conversely, the primary fluid cannot circulate between the thermal barrier body 39 and the upper heat shield 73. The heat output contribution caused by the possible recirculation at the top is eliminated. This limits heat transfer by conduction through the thermal barrier body 39. As a result, the temperature rise of the seal 59 and the seals 61 and 63 is limited.

  On the contrary, the fact that the lower gap 86 is always in fluid communication with the housing 47 makes it possible to obtain a uniform temperature inside the thermal barrier cover 41. This becomes advantageous over time for the mechanical strength of this cover.

Claims (15)

A pump for fluid of a nuclear reactor, wherein the pump (1) is
A stationary structure (3),
A pump shaft (9) rotatable about the axis of rotation (X) with respect to the stationary structure (3),
A pump wheel (11) rigidly fixed to said pump shaft (9),
A fluid guide structure (15) fixed to said stationary structure (3) and moved by said pump wheel (11), said guide structure (15) around said pump shaft (9); A guide structure (15) having an installed tubular portion (19), wherein the guide structure (15) internally defines a fluid circulation chamber in which the pump wheel (11) is installed;
A thermal barrier (37) radially interposed between the tubular part (19) and the pump shaft (9), the thermal barrier (37) comprising a thermal barrier body (39) and the thermal barrier (37). A thermal barrier cover (41) axially interposed along the pump shaft (9) between the barrier body (39) and the pump wheel (11), wherein the thermal barrier (37) comprises the thermal barrier A thermal barrier (37) comprising a heat exchanger (45) mounted in a housing (47) defined by a barrier cover (41);
A heat shield (57) in a pump, comprising: a heat shield (57) radially interposed between the heat barrier (37) and the tubular portion (19) of the guide structure (15); Includes an upper heat shield (73) radially inserted between the thermal barrier body (39) and the tubular portion (19), the thermal barrier cover (19) and the tubular portion (19). A lower heat shield (75) radially inserted therebetween, the upper heat shield (73) being pressed against the heat barrier body (39), and the lower heat shield (75) being the tubular portion (19). ) Is pressed against the pump.   The pump according to claim 1, characterized in that the upper heat shield (73) is rigidly fixed to the heat barrier body (39).   The upper heat shield (73) has a lower axial end (81) towards the lower heat shield (75) rigidly secured to the tubular portion (19) by a fluid resistant peripheral weld (82). The pump according to claim 1 or 2, characterized in that.   The upper heat shield (73) is separated from the tubular portion (19) by an upper gap (76), and a cavity (88) between the upper heat shield (73) and the lower heat shield (75) is Pump according to any one of claims 1 to 3, characterized in that the upper gap (76) is fluidly connected to the housing (47).   The thermal barrier (37) according to claim 4, characterized in that it comprises at least one head loss or fluid resistant device (97) installed in the upper gap (76) or the cavity (88). Pump.   Pump according to any one of claims 1 to 5, characterized in that the lower heat shield (75) is rigidly fixed to the tubular part (19).   The lower heat shield (75) is characterized in that it comprises an extension (91) that engages the upper gap (76) and is rigidly fixed to the tubular portion (19). 7. The pump according to claim 6 combined with 5.   The lower heat shield (75) is separated from the thermal barrier cover (41) by a lower gap (86) in fluid communication with the housing (47). The pump according to item.   The lower heat shield (75) and/or the upper heat shield (73) comprises a box (99) and a plurality of flat plates (101) arranged in parallel with each other in the box (99), Pump according to any one of claims 1 to 8, characterized in that the flat plates (101) are separated from each other by a liquid blade (103) having a thickness of less than 1.5 mm.   Pump according to claim 9, characterized in that the thickness of each plate (101) is less than 0.8 mm.   At least one shaft seal (59, 61, 63) arranged around the pump shaft (9) and a chamber radially arranged between the thermal barrier body (39) and the pump shaft (9) (66), the chamber (66) being axially arranged along the pump shaft (9) between the shaft seal (59, 61, 63) and the housing (47). , The pump further comprises a barrier fluid injection device (67) comprising an injection circuit (69) for injecting a barrier fluid into the chamber (66), the barrier fluid flowing from the chamber (66) to the housing (47). 11. A flow according to claim 1, characterized in that it follows a path (71) to the) along the pump shaft (9) and then from the housing (47) to a fluid circulation chamber (17). The pump according to item 1.   The guide structure (15) has a spiral portion (21) defining the circulation chamber (17) inside, and a diffuser disposed in the spiral portion (21) to form the tubular portion (19). (25) It is provided, The pump of any one of Claims 1-11 characterized by the above-mentioned.   Pump according to any one of the preceding claims, characterized in that the upper heat shield (73) and the lower heat shield (75) are two mutually independent structures.   Pump according to any one of claims 1 to 13, characterized in that the thermal barrier body (39) and the thermal barrier cover (41) are two separate structures.   The tubular portion (19) is defined radially inward by a substantially cylindrical surface (83) coaxial with the axis of rotation (X) and the thermal barrier body (39) is defined by the axis of rotation (X). Radially outwardly defined by a substantially cylindrical surface (84) coaxial with, said upper heat shield (73) is said surface (83) of said tubular section (19) and said thermal barrier body (39). 15. Pump according to claim 14, characterized in that it is installed between said surface (84) and.

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