WO2017149081A1

WO2017149081A1 - Sealing mechanism for the volute of a pump in the main circuit of a nuclear power plant

Info

Publication number: WO2017149081A1
Application number: PCT/EP2017/054924
Authority: WO
Inventors: Laurent SZURCZEC; Hugues PRZYLECKI; Yann FOUIN
Original assignee: Electricite De France
Priority date: 2016-03-02
Filing date: 2017-03-02
Publication date: 2017-09-08
Also published as: FR3048463A1; FR3048463B1

Abstract

Mechanism (5) for sealing a volute (41) of a pump in a main circuit of a nuclear power plant, characterized in that said mechanism (5) comprises: - a disk (51) having attachment means (51c) that allow the mechanism (5) to be attached to the volute (41); - a central member (52) that projects from a first face (51a) of the disk (51); - an expandable joint (6) located about a contour (52a) of the central member (52) such that said expandable joint (6) forms a tight seal between the contour (52a) and the volute (41) when the mechanism (5) is mounted on the volute (41).

Description

Shutter for volute of a pump of a primary circuit of a nuclear power station

Field of the invention

The present invention relates to a device for closing a volute of a pump of a primary circuit of a nuclear power plant.

The present invention also relates to a method for maintaining a primary circuit of a nuclear power plant in which such a device for closing the volute of the pump of the primary circuit is used.

More particularly, the invention relates to a device forming a lid which is adapted to be fixed on a joint plane of the volute of the pump of the primary circuit when the motor portion of said pump is separated from the volute during a cooling operation. maintenance.

State of the art

Figures 1a and 1b schematically illustrate the operation of a primary circuit 1 of a nuclear power plant.

A nuclear power plant comprises a reactor comprising a vessel 2 in which a large amount of heat is produced by a nuclear reaction (for example the fission of uranium atoms).

The heat generated in the tank 2 of the reactor is transmitted to a closed circuit in which water circulates, this circuit being called "primary circuit". The water circulates in the primary circuit 1 at a temperature which is of the order of 320 ° C. The water is maintained under pressure in the primary circuit 1 by a pressurizer 11 which prevents the water from passing from the liquid to the gaseous state.

The primary circuit 1 communicates with a second closed circuit in which circulates water called "secondary circuit". The heat of the water circulating in the primary circuit 1 is transmitted to the water of the secondary circuit in steam generators 3. In the steam generators 3, the water of the secondary circuit is heated by the water of the primary circuit 1 so that that it turns into steam. This steam thus generated is then used to rotate a turbine which itself drives an alternator to produce an electric current.

In order to circulate the water in the primary circuit 1, and as illustrated in FIG. 1b, said primary circuit 1 comprises the tank 2, commonly called boiler, the pressurizer 1 1, and several identical primary loops (the number of loops primary can for example vary between three or four loops). These primary loops are each connected to the tank 2, and comprise a steam generator 3 and a primary pump 4. The pressurizer January 1 is connected to a primary loop.

The primary pump 4 is composed of a volute 41 and a motor part 42, also called pump part, which is fixed to said volute 41. As shown in FIG. 2, the volute 41 is a one-piece metal element which forms a cavity 41 in which the water of the primary circuit 1 circulates. The volute 41 comprises a first orifice 41b forming an inlet through which water from the steam generator 3 enters the volute 41, and a second orifice 41c forming an outlet through which the water present in said volute 41 is expelled to the reactor 2. The volute 41 also comprises a third orifice 41 d located in the center of a joint plane 41 e on which is fixed the motor portion 42 of the primary pump assembly 4 so that said motor portion 42 can suck the water through the inlet of the volute 41 and expel the output of said volute 41.

Maintenance operations are performed regularly on the primary circuit 1, during which the components of the primary circuit 1 are repaired, tested, modified, replaced, and / or requalified.

Maintenance operations are of course also performed on the primary pump 4. During these maintenance operations of the primary pump 4, in order to carry out the maintenance of the elements of the motor part 42, said motor part 42 is disassembled by being separated from the volute 41, said volute 41 remaining fixed. When the motor portion 42 is separated from the volute 41, the third orifice 41 d of the volute 41 is open, preventing any flow of water in the primary circuit 1.

However, during maintenance operations of the primary circuit 1, it is necessary to circulate water in the primary circuit 1 in order to conduct tests verifying the proper operation of certain elements of the plant, such as for example the pumps of emergency used to pump water from the primary circuit 1 during an incident. At present these tests can not be carried out as long as the maintenance of the motor part 42 of the primary pump 4 is not completed and the motor part 42 has not been refixed on the volute 41. However, the downtime for maintenance of the motor portion 42 of the primary pump 4 can last up to several weeks. This time of immobilization for maintenance of the motor part 42 of the primary pump 4 delays the return to operation of the nuclear power plant.

General presentation of the invention

An object of the invention is to provide a device for sealing a volute of a pump of a primary circuit of a nuclear power plant when a motor portion of said pump is separated from the volute, in order to allow circulation of water in the primary circuit while the motor portion of said primary pump is separated from the volute.

For this purpose, there is provided a device for closing a volute of a pump of a primary circuit of a nuclear power plant characterized in that it comprises: a disk comprising fastening means adapted to allow the device to be fixed to the volute,

a central body projecting from a first face of the disc,

an inflatable seal located on an outline of the central body.

The inflatable seal thus forms a tight barrier between the contour and the volute when the device is mounted on the volute.

Such a device makes it possible to seal the volute during maintenance of the motor part of the primary pump, thus making it possible to carry out the tests for which it is necessary to circulate water in the primary circuit.

The device according to the invention is advantageously completed by the following features, taken alone or in any of their technically possible combinations:

- A channel is dug in the central body, said channel opening on the one hand on an area of the contour of the central body located between the inflatable seal and the disk, and on the other hand in a cavity formed in the central body. Such a characteristic makes it possible to detect whether the inflatable seal has a sealing defect by detecting that the cavity formed in the central body is filled with water.

- The device comprises a safety seal formed of an O-ring located in a groove dug in the first face of the disk and which surrounds the central body. Such a characteristic makes it possible to compensate for a lack of tightness of the inflatable seal.

- The central body comprises an end which is opposite to the first face of the disc and which is in the form of a tip. Such a feature facilitates the dripping of the device. - The central body comprises an end which is opposite to the first face of the disc and which is covered with a layer of rubber. Such a characteristic makes it possible not to damage a joint plane of the volute during the installation of the device on the volute. According to another aspect, the invention also relates to an assembly comprising a volute of a pump of a primary circuit of a nuclear power station and a device according to any one of the preceding characteristics, the volute comprising a joint plane forming a flat surface on which said volute is adapted to receive a fixing motor part of the pump, the volute comprising an internal cavity opening through a hole in the center of the joint plane, the device being attached to the seal plane of the volute so that the central body is disposed inside the orifice. According to an additional feature, the device and the volute are fixed by a plurality of studs, two studs having a first length, the other studs having a second length, the first length being greater than the second length. Such a characteristic allows that the two studs having the first length serve as a guide for fixing the device on the volute.

According to an additional characteristic, the volute comprises a circular groove dug in its plane of joint around the orifice, the groove dug in the first face of the disk and the O-ring having a diameter smaller than the circular groove dug in the joint plane. of the volute.

According to an additional aspect, the invention furthermore relates to a method of maintaining a primary circuit of a nuclear power station comprising the steps of: - purge the primary circuit by emptying the water contained in said primary circuit;

- Dismantling a pump of the primary circuit by separating a motor portion of said pump from a volute of said pump, so as to leave open a cavity of the volute opening through a hole in the center of a joint plane of the volute on which fixes the motor part;

- Fix the device according to any one of the preceding characteristics on the seal plane of the volute by arranging the central body inside the orifice of the volute;

- Fill the primary circuit with water.

Such a method makes it possible to carry out tests requiring the circulation of water in the primary circuit before having finished the maintenance of the motor part of the pump.

According to a particular characteristic, the device is fixed to the volute by studs screwed into bores made in the disk, said bores being numbered, the studs being screwed in an order indicated by the numbers of the bores. Such a characteristic makes it possible to indicate to an operator the order in which the studs must be screwed.

Presentation of figures

Other features, objects and advantages of the invention will appear on reading the following description of various embodiments shown in the following drawings:

Figure 1a schematically shows part of a primary circuit of a nuclear power plant;

Figure 1b shows a schematic view of a primary circuit with the various loops that are shown;

FIG. 2 represents a sectional view of a volute of a pump of a primary circuit;

3 shows a sectional view of a device according to a possible embodiment of the invention which is fixed on a volute of a pump of a primary circuit;

FIG. 4 represents a perspective view of a device according to the invention which is alone;

FIG. 5 represents a device according to a possible embodiment of the invention which is fixed on a volute of a pump of a primary circuit;

FIG. 6 schematically represents the steps of a maintenance method of the primary circuit of a nuclear power plant according to one possible implementation of the invention.

Description of the invention

As represented in FIGS. 3, 4 and 5, a device 5 according to the invention comprises a disc 51 comprising a first face 51 a and a second face 51 b, said first face 51 a and said second face 51 b forming both a circular surface.

The device 5 also comprises a central body 52 which projects from the first face 51a of the disc 51 at its center. The body central has a shape which is adapted so that said central body 52 can be introduced inside the third orifice 41 d of the volute 41. The third orifice 41 d of the volute 41 generally has a circular shape centered on an axis Ω, the central body 52 may therefore have a cylindrical shape of revolution centered on the axis Ω with an annular contour 52a and two circular ends 52b . One end 52b is located against the first face 51a of the disk 51, and the other end 52b is opposite the first face 51a of said disk 51. The disc 51 is centered on the axis Ω when the device 5 is disposed on the volute 41. The central body 52 is also centered on the axis Ω when the device 5 is disposed on the volute 41, so that the contour 52a is a ring centered around the axis Ω and the ends 52b are perpendicular discs to the axis Ω.

The diameter of the central body 52 (or in other words the diameter of the contour 52a) is smaller than the diameter of the third orifice 41d so that said central body 52 can be introduced inside said third cavity 41d. In addition, the diameter of the disc 51 is greater than the diameter of the third orifice 41d, so that said disc 51 can not be introduced inside said third orifice 41d.

During the maintenance of the primary circuit 4 of the nuclear power plant, after having separated the motor portion 42 of the primary pump 4 of the volute 41, the device 5 is fixed to said volute 41. To do this, the central body 52 is placed inside the third hole 41 d of the volute 41, and the first face 51 of the disc 51 is placed against the joint plane 41 e. The joint plane forms a surface perpendicular to the Ω axis.

In order to seal the third orifice 41 d of the volute 41, an inflatable seal 6 is fixed on the outside of the contour 52a of the central body 52, so that water can flow in the volute 41 without leaving by said third orifice 41 d, said inflatable seal 6 forming a sealed barrier between the contour 52a of the central body 52 and the volute 41. The inflatable seal 6 forms a tight barrier between the contour 52a of the central body 52 and the volute 41 being located radially outwardly relative to the contour 52a of the central body 52 along the axis Ω, and radially inwards by relative to the volute 41 along the axis Ω.

According to a possible variant, the inflatable seal 6 can also form a sealed barrier between the contour 52a of the central body 52 and the volute 41 being fixed on said volute 41.

In general, the pressure of the water inside the primary circuit 1 during tests carried out during the maintenance of said primary circuit 1 is 1.2 bars.

The inflatable seal comprises a deformable rubber (annular butadiene polymer and nitrile-acrylic copolymer commonly known as NBR) sheath 6a which is formed of a flexible and waterproof material so that said sheath 6a can be inflated by filling it with a liquid . The sheath 6a of the inflatable seal 6 is connected by a circuit 61 to a reservoir 60 comprising a liquid under pressure, such as water, so that said sheath 6a can be inflated with said liquid.

The circuit 61 comprises a pressure sensor 62 for measuring the pressure at which the sheath 6a is inflated. The fact of measuring the pressure at which the sheath 6a is inflated makes it possible to ensure that said sheath 6a is not underinflated, which could lead to a leakage of said inflatable seal 6, or that said sheath 6a is not over inflated, which could deteriorate said inflatable seal 6.

Furthermore, the circuit 61 comprises a valve 63 for controlling the circulation of the liquid in the circuit 61. The valve thus makes it possible to fill the sheath 6a with the liquid as long as the desired pressure is not reached, then to close the circuit 61 when said sheath 6a has reached said desired pressure. The fact that the tightness of the assembly between the device 5 and the volute 41 is provided by the inflatable seal 6 disposed on the contour 52a of the central body 52 has several advantages.

First, the fact that the tightness of the assembly of the device 5 with the volute 41 is performed on the contour 52a of the central body 52 protects the joint plane 41 e of the volute 41. Indeed, the joint plane 41 e is a fragile surface because it is necessary for the proper operation of the primary pump 4 it has a very good surface. However, if the seal of the assembly between the device 5 and the volute 41 was ensured at the joint plane 41 e, it would be necessary to press the disc 51 on the joint plane 41 e of the volute 41 with a high pressure to ensure sealing, which could deteriorate the surface of said joint plane 41 e.

In addition, the fact that the seal is provided on the contour 52a of the central body can make effective the solutions based on static seals, such as O-rings for example, since it is necessary that the two walls surrounding a gasket are pressed against each other so that the seal provided by said gasket is maximum. The use of an inflatable seal makes it possible to overcome the fact that the contour 51 of the central body 51 is not pressed against the rim of the third orifice 41d.

Finally, the fact of using an inflatable seal 6 makes it easier to place the device 5 on the volute 41. Indeed, using an inflatable seal 6, the diameter of the central body 52 may be much smaller than the diameter of the third port 41 d, facilitating the insertion of said central body 52 in said third orifice 41 d. Indeed, the inflatable seal 6 allows a difference of 60mm between the diameter of the central body 52 and the diameter of the third orifice 41d, while an O-ring would require a diameter difference of less than 10mm. The simplicity of setting up the device 5 on the volute 41 is a very important criterion, because the more the put is simple, less there is risk of damaging the joint plane 41 e volute 4.

The disc 51 comprises fixing means which are adapted to allow the attachment of the device 5 to the volute 41. Preferably, these fixing means are bores 51c made in the disk 51. The holes 51c are distributed on the disc 51 so that each of said holes 51c is situated opposite a hole 41f made in the joint plane 41e of the volute 41. The holes 41f made in the joint plane 41e of the volute 41 are the holes which are used for fixing by studs of the motor part 42 to the volute 41. Thus, the fact that the disc 51 includes holes 51c also makes it possible to use studs 7 to fix the device 5 to the volute 41, so that said device 5 can be used on any volute 41 of existing primary pump 4.

The holes 51c are preferably numbered so that an operator can tighten or loosen the studs 7 in the order of the numbers marked on the holes 51c (ascending order or descending order for example). The screwing or unscrewing of the studs 7 must indeed be carried out in a precise order so as not to damage the volute 41 or the device 5. The holes 51c are numbered by entering the numbers on the second face 51b of the disc 51 , so that when the device 5 is disposed on the volute 41, the numbers are visible to the operator.

According to an advantageous variant, at least one channel 8 directed radially with respect to the axis Ω is hollowed out in the central body 52. The channel 8 comprises a first end which opens out on the contour 52a of the central body 52, and a second end which opens into a cavity 9 which is formed in said central body 52. The first end of the channel 8 opens between the inflatable seal 6 and the first face 51 of the disk 51, or in other words between the inflatable seal 6 and the end 52b of the main body 52 which is located against the first face 51a of said disk 51. Thus, if the inflatable seal 6 has a sealing defect, part of the water coming from the cavity 41 of the volute 41 which has passed the inflatable seal 6 enters the channel 8 via the first end of said channel 8, and filled the cavity 9 formed in the central body 52. Thus, the fact that the cavity 9 fills with water signals a leakage of the inflatable seal 6.

In the embodiment illustrated in FIGS. 3 to 5, the cavity 9 is formed by recessing the central body 52 between the first face 51a of the disc 51 and the end 52b of the central body 52 which is opposed to said first face 51a. of the disc 51. In addition, the cavity 9 opens at the second face 51b, so that the device 5 has a hat shape.

The number of channels 8 can be varied according to the different possible variants of the device 5, it is however preferably between 1 and 4. It is indeed preferable that the number of channels 8 is not too important so as not to To complicate the device 5. At the outlet of channels 8 it is possible to place valves capable of closing the outlet of said channels 8 in order to prevent too much water from leaving said channels 8 once a leakage has been detected. It is also possible to place pressure gauges at the outlet of the channels 8 in order to detect a leakage by detecting an overpressure. Furthermore, it is preferable for the device to comprise several channels 8 distributed regularly over the body contour 52a. central 52, in order to better detect the leakage defects of the inflatable seal 6.

According to a possible variant, the device 5 comprises a safety seal 10 making it possible to overcome a leakage of the inflatable seal 6 the time that said leakage of the inflatable seal 6 is corrected or that the primary circuit 1 is purged . The safety seal 10 may be formed of an O-ring which is disposed in a groove 51d formed in the first surface 51a of the disk 51. The groove 51d and the O-ring are located around the central body 52 and the third port 41d of the volute 41.

The fact that the safety seal 10 is located on the joint plane 41 e is acceptable because most of the sealing of the assembly of the device 5 and the volute 41 is provided by the inflatable seal 6, and it n It is therefore not necessary for the first face 51 of the disk 51 to be plated with a very large force on the joint plane 41 e of the volute 41. Moreover, since the water circulating in the primary circuit 1 is radioactive, it is preferable to dispose of the safety seal 10 rather than to risk a leak due to a leakage of the inflatable seal 6.

According to one possible variant, the volute comprises a groove 41f etched in the joint plane 41e which surrounds the third orifice 41d, this groove 41f serving to receive a seal which serves to seal the assembly of the motor part. 42 and the volute 41 of the primary pump 4. The safety seal 10 is located between the inflatable seal 6 and the groove 41 f located on the joint plane 41 e.

The fact that the safety seal 10 is located between the inflatable seal 6 and the groove 41 f makes it possible to prevent water from entering said groove 41 f in the event of leakage of the inflatable seal 6. , the groove 41f is the most fragile portion of the joint plane 41 e, so it is preferable not to seal the assembly of the device 5 and the volute 41 at said groove 41 f.

In the embodiment illustrated in FIGS. 3 to 5, the groove 51 d etched into the first surface 51 a of the disk 51 and the o-ring located in said groove 51 d both have a diameter smaller than the groove 41 f etched in the joint plan 41 e. Thus, the groove 51d located on the first surface 51a of the disc 51 and the O-ring are located between the groove 41f etched in the joint plane 41 e and the inflatable seal 6.

According to an advantageous variant, the end 52b of the central body which is opposite to the first face 51a of the disc 51 has a pointed shape, so as to promote the draining of the central body 52.

According to the embodiment illustrated in Figure 5, the device 5 is made of metal, preferably a corrosion-resistant metal, such as stainless steel or aluminum. The device 5 may also be made of a plastic material.

Furthermore, according to a possible variant of the invention, the end 52b of the central body 52 which is opposite the first surface 51a of the disc 51 is covered with a layer of a material with a hardness lower than the hardness of the material constituting the volute 41, so that said end 52b does not scratch the joint plane 41 e of the volute 41 when the device 5 is placed on said volute 41. Thus, the end 52b of the central body 52 which is opposite the first surface 51a of the disc 51 may be covered with a rubber layer.

According to a variant of the invention to facilitate the establishment of the device 2 on the volute 41, at least one stud 7 has a first length, while the other studs have a second length. The first length is greater than the second length, so that said at least one pin 7 forms a guide for setting the device 2 on the volute 41. Preferably, and as illustrated in Figure 5, two studs 7 have the first length and the other studs have the second length. Thus, by placing the two studs 7 which have the first length in their respective bore 51c, all other studs 7 which have the second length are aligned with their respective bore 51c. The device 5 may comprise means for attaching to a cable in order to be able to carry said device 5 with a crane. Indeed, the mass of the device 5 may be greater than 1000kg when it is metal, it may be necessary to use a crane or a traveling crane to move said device 5. Thus, according to the embodiment illustrated in the figures 1 to 5, the device 5 comprises rings 1 1 located on the second face 51 b of the disk 51, in which cables can be passed in order to allow the manipulation of the device 5 by a crane or a traveling crane. According to one possible variant illustrated in FIG. 5, the device 5 comprises three rings 1 1 separated by 120 ° on the disk 51.

FIG. 6 also illustrates a method for maintaining the primary circuit 1 of the nuclear power station according to one possible implementation of the invention.

Thus, at the beginning of the maintenance operation, a step 100 is performed during which the primary circuit 1 is purged so as to empty said primary circuit 4 of the water that it contains. The fact of purging the primary circuit 1 makes it possible to dismount the primary pump 4 without the water contained in the primary circuit 1 exiting said primary circuit 1.

Then, a step 200 is performed during which the primary pump 4 of the primary circuit 1 is disassembled by separating the motor portion 42 of the volute 41. The fact of disassembling the primary pump 4 makes it possible to carry out the maintenance of the motor part 42 of said primary pump 4.

Subsequently, a step 300 is performed in which the device s is fixed on the joint plane 41 e of the volute 41. The device 5 is fixed on the volute 41 by arranging the central body 52 inside the third orifice 41 d of the volute 41 which opens at the joint plane 41 e of said volute 41, so as to seal said third orifice 41 d of the volute 41. Finally, a step 400 is performed by filling the primary circuit 1 with water. Such a step 400 makes it possible to be able to carry out tests on equipment of the nuclear power station requiring that water circulates in the primary circuit 1, such as, for example, emergency pumps which serve to pump the water from the primary circuit 1 into case of incident.

Claims

1. Device (5) for closing a volute (41) of a pump (4) of a primary circuit (1) of a nuclear power plant, characterized in that it comprises:

a disk (51) comprising fixing means (51c) adapted to allow the device (5) to be fixed to the volute (41),

a central body (52) projecting from a first face of the disc (51),

an inflatable seal (6) situated on a contour (52a) of the central body (52), so that said inflatable seal (6) forms a tight barrier between the contour (52a) and the volute (41) when the device ( 5) is mounted on the volute (41).

2. Device (5) according to claim 1, wherein a channel (8) is hollowed in the central body (52), said channel (8) opening on the one hand on an area of the contour of the central body (52) located between the inflatable seal (6) and the disc (51), and secondly in a cavity (9) formed in the central body (52).

3. Device (5) according to any one of claims 1 or 2, wherein the device (5) comprises a safety seal (10) formed of an O-ring located in a groove (51 d) dug in the first face (51a) of the disk (51) and which surrounds the central body (52).

4. Device (5) according to any one of claims 1 to 3, wherein the central body (52) comprises an end (52b) which is opposite to the first face (51 a) of the disc (51) and which is in the shape of a point.

5. Device (5) according to any one of claims 1 to 4, wherein the central body (52) comprises an end (52b) which is opposed to the first face (51 a) of the disc (51) and which is covered with a layer of rubber.

6. An assembly comprising a volute (41) of a pump (4) of a primary circuit (1) of a nuclear power station and a device (5) according to any one of claims 1 to 5, the volute (41 ) comprising a joint plane forming (41 e) a flat surface on which said volute (41) is adapted to receive a motor portion (42) of the pump (4) with fixation, the volute (41) comprising an internal cavity ( 41 a) opening through an orifice (41 d) located in the center of the joint plane (41 e), the device (5) being fixed to the joint plane of the volute (41) so that the central body (52) is disposed within the hole (41 d).

7. An assembly according to claim 6, wherein the device (5) and the volute (41) are fixed by a plurality of studs (7), two studs (7) having a first length, the other studs (7) having a second length, the first length being greater than the second length.

8. An assembly according to any one of claims 6 or 7 in its dependence on claim 3, wherein the volute (41) comprises a groove (41 f) circular hollowed in its joint plane (41 e) around the orifice (41 d), the groove (51 d) hollowed in the first face (51 a) of the disc (51) and the O-ring having a smaller diameter than the circular groove (41f) hollowed in the joint plane (41). e) the volute (41).

A method of maintaining a primary circuit (1) of a nuclear power plant comprising the steps of:

- (100) purging the primary circuit (1) by emptying the water contained in said primary circuit (1); - (200) disassembling a pump (4) of the primary circuit (1) by separating a motor portion (42) of said pump (4) from a volute (41) of said pump (4), so as to leave open a cavity (41 a) of the volute opening through an orifice (41 d) in the center of a joint plane of the volute (41) on which the motor portion (42) is fixed;

- (300) fix the device (5) according to any one of claims 1 to 5 on the joint plane (41 e) of the volute (41) by arranging the central body (52) inside the orifice of the volute (41);

- (400) fill the primary circuit (1) with water.

10. Method according to the preceding claim according to claim 9 wherein the device (5) is fixed to the volute (41) by studs (7) screwed into bores (51 c) made in the disk (51), said bores (51 c) being numbered, the studs (7) being screwed in an order indicated by the numbering of the holes (7).