WO2025214616A1

WO2025214616A1 - Device, system and method for lubricating a fuel rod

Info

Publication number: WO2025214616A1
Application number: PCT/EP2024/060066
Authority: WO
Inventors: Andreas Falge
Original assignee: Framatome GmbH
Current assignee: Framatome GmbH
Priority date: 2024-04-12
Filing date: 2024-04-12
Publication date: 2025-10-16
Anticipated expiration: 2026-10-12

Abstract

A device (1) for lubricating a fuel rod (3) by producing a film of water droplets on a moving surface comprising a housing (4), defining a cavity (7), the housing (4) delimiting a passage (9) for the fuel rod (3) in the cavity (7) and at least one injector (5), configured for forming a water mist in the cavity (7) and for covering a fuel rod (3) passing through the passage with water droplets. The housing (4) comprises a frame (11) and a hollow insert (14), the hollow insert (14) separating the passage (9) from an injection region (16) of the cavity (7) and delimiting with the frame (11) a lubrication gap (18) fluidically connecting the passage (9) and the injection region (16).

Description

Device, system and method for lubricating a fuel rod

The invention relates to the field of nuclear fuel assemblies and in particular to systems for improving the insertion of fuel rods on structures retaining such fuel rods in nuclear fuel assemblies.

Generally, in the field of nuclear fuel assemblies, it is known to assemble at least one fuel rod on a structure, called skeleton, in order to form a nuclear fuel assembly.

During this process, the nuclear fuel rod is inserted through corresponding through- holes in grid-shaped structures of the skeleton. Due to the tight dimensional constraints, such an assembly may sometime be difficult and/or result in damaging the outer surface of the fuel rod, for example by scratching the outer surface of the fuel rod.

In order to solve such a problem, it has been proposed to use a lubricating device to lubricate the fuel rod before its insertion in the skeleton, thus resulting in an easier assembly and in less damage to the fuel rods.

Known lubrication devices generally comprise a lubricant dispenser, configured to pour a lubricant, such as glycerine, on the fuel rod to be lubrified.

Such known devices are not entirely satisfying. Indeed, since the glycerine remains on the fuel rods after their insertion in the skeleton, it is necessary to remove the glycerine from the fuel rods after their insertion in the skeleton, which is particularly labour intensive.

One purpose of this invention is thus to provide a lubrication device that offers a good lubrication while being labor efficient.

To this end, the present invention relates to a lubrication device comprising:

- a housing defining a cavity, the housing delimiting a passage for the fuel rod in the cavity; and

- at least one injector, configured for forming a water mist in the cavity and configured for covering a fuel rod passing through the passage with water droplets, wherein the cavity further comprises a injection region, the housing comprising a frame and a hollow insert, the hollow insert separating the passage from the injection region of the cavity and delimiting with the frame a lubrication gap fluidically connecting the passage and the injection region.

With the device according to the invention, the fuel rod passing through the cavity is covered with water droplets, which act as a lubricant and facilitate the introduction of the fuel rods in the skeleton. The water then evaporates after the introduction of the fuel rods in the skeleton, such that no removing of the lubricant is required, leading to a particularly efficient lubrication. In addition, in the device according to the invention, the lubrication gap, which is delimited between the hollow insert 14 and the frame, allows deposition of water droplets on only a limited portion of the fuel rod. This ensures the formation of droplets of optimal size on the surface of the fuel rod, which, in turn, results in an improved lubrication.

According to further embodiments, the device may comprise one or more of the following features, which may be combined in any technical feasible combination:

- the device comprises three injectors, configured for forming a water mist in the cavity and configured for covering a fuel rod passing through the passage with water droplets;

- the orthoradial distance between two adjacent injectors is identical for all injectors;

- the hollow insert comprises a tubular portion and an annular portion, the lubrication gap being defined between the annular portion and the frame;

- the hollow insert is movable relative to the frame;

- the hollow insert is movable relative to the frame along a longitudinal axis of the passage;

- the frame comprises two opposed walls and, the first wall configured to support the hollow insert and the second wall configured to delimit, with the hollow insert, the lubrication gap; and

According to another aspect of the present invention, a system for mounting fuel rods on a skeleton of a nuclear fuel assembly is provided, comprising a device for lubricating a fuel rod as described above.

According to a further aspect of the present invention, a method for lubricating a fuel rod is provided comprising the steps of:

- forming a water mist in the lubrication gap using the injectors,

- displacing the fuel rod through the passage, the fuel rod passing through the water mist in the lubrication gap so as to be covered with droplets as it is passes in front of the lubrication gap.

The invention will be better understood upon reading the following description, provided only by way of example and with reference to the accompanying drawings, where:

Fig. 1 is a schematic front view of a device for lubricating fuel rods;

Fig. 2 is a schematic cross-sectional view, taken along the plane ll-ll of Figure 1 , of the device shown in Fig. 1 ; and

Fig. 3 is an enlarged view of a part of Fig. 2.

As shown in Figs. 1 and 2, the device 1 for lubricating a fuel rod 3 according to the invention comprises a housing 4 and at least one injector 5. The housing 4 defines a cavity 7 and comprises a passage 9 for the fuel rod 3, delimited in the cavity 7.

In the example shown in Figs. 1 to 3, the passage 9 extends along a longitudinal axis L defining a longitudinal direction. The passage 9 is configured for receiving the fuel rod 3 with the longitudinal axis of the fuel rod 3 extending along the longitudinal direction of the passage 9. More particularly, the longitudinal axis of the fuel rod 3 extends along the longitudinal axis L of the passage 9 when the fuel rod 3 is received in the passage 9.

The fuel rod 3 is intended to be displaced through the passage 9 in translation along the longitudinal direction, and more particularly along the longitudinal axis L.

The or each injector 5 is configured for forming a water mist in the cavity 7 and for covering the fuel rod 3 passing through the passage 9 with water droplets.

In the example shown in the Figures, the device 1 comprises a plurality of injectors 5.

According to one example, the injectors 5 are arranged in the housing 4 with an equal angular distance between two neighbouring injectors 5. In other words, the orthoradial distance between two adjacent injectors 5 in this embodiment is identical for all injectors 5. Such a configuration allows for a homogeneous distribution of the mist in the cavity 7. However, alternative configurations with different orthoradial distances between two adjacent injectors 5 may be used depending on the requirements.

The device 1 for example comprises three injectors 5 with an angular distance of 120° between each of the neighboring injectors 5.

The or each injector 5 comprises an outlet 6 configured for ejecting the water mist along a direction of injection D.

As shown in Figure 1 , each injector 5 is pointing toward the longitudinal axis of the passage 9. For example, the direction of injection D of each injector 5 intersects with the longitudinal axis of the passage 9. In the example shown in Figure 1 , in which the device 1 comprises more than one injector 5, the directions of injection D of the plurality of injectors 5 intersect at the longitudinal axis L.

In the example shown in the Figures, in which the device 1 comprises a plurality of injectors 5, the distance between the longitudinal axis L and the outlet 6 of the injector 5 is preferably identical for each injector 5. More particularly, the outlets 6 of the injectors 5 are located on a circle centered on the longitudinal axis L, when viewed in a plane perpendicular to the longitudinal axis L.

The injectors 5 are mounted on a support 8. They may be oriented and moved on this support 8.

As shown in Figure 1 , the or each injector 5 further comprises a connector 28 for connection to a water supply. The water supply is configured to supply the or each injector 5 with water. In the example shown in Figure 1 , the injectors 5 are connected to a common water supply through the connectors 28.

The injectors 5 preferably have an outlet 6 with a diameter smaller than or equal to 80 pm. Such a diameter allows the formation of water mist at the outlet of the injector 5.

As shown in the Figures, the cavity 7 comprises an injection region 16, in which the or each injector 5 is arranged. The injection region 16 is the region of the cavity 7 in which the mist is being injected into the cavity 7 by the or each injector 5.

In the example shown in the Figures, the housing 4 comprises a frame 11 and a hollow insert 14.

The hollow insert 14 separates the passage 9 from the injection region 16 of the cavity 7 and delimits with the frame 1 1 a lubrication gap 18 fluidically connecting the passage 9 and the injection region 16. The lubrication gap 18 forms a passage for the mist between the injection region 16 and the passage 9.

In the example shown in the Figures, the lubrication gap 18 has a substantially annular shape, in particular centered on the longitudinal axis L of the passage 9. In this example, the lubrication gap 18 extends around a section of the passage 9. More particularly, in the example shown in the Figures, the injection region 16 is located on a side of the lubrication gap 18 opposite the passage 9, taken along a direction perpendicular to the longitudinal axis L of the passage 9.

The device 1 is configured such that the mist injected into the injection region 16 by the injectors 5 flows from the injection region 16 through the lubrication gap 18 onto the fuel rod 3 travelling through the passage 9.

More particularly, the hollow insert 14 and the frame 1 1 are configured such that the passage 9 is only fluidically connected to the injection region 16 through the lubrication gap 18. In other words, the fuel rod 3 is only in contact with the mist originating from the injectors 5 at the lubrication gap 18. Therefore, water droplets only form on the fuel rod 3 as the fuel rod 3 passes the lubrication gap 18.

During use, the fuel rod 3 moves through the passage 9 along the direction of the longitudinal axis L so as to be covered with water droplets from the or each injector 8 when passing in front of the lubrication gap 18, and in particular only in the area of the lubrication gap 18.

More particularly, the frame 11 comprises a first wall 12 and a second wall 15. The first and second walls 12, 15 are located opposite each other along the direction of the longitudinal axis L. In the example shown in the Figures, the first wall 12 and the second wall 15 are connected with each other at their ends so as to delimit the cavity 7. The first wall 12 is configured to support the hollow insert 14. The hollow insert 14 may in particular be inserted through an insertion opening 30 provided in the first wall 12. As shown in Figure 2, the first wall 12 forms a support sleeve 38, delimiting the insertion opening 30 at one of its ends, in which the hollow insert 14 is at least partially received. The support sleeve 38 is for example substantially cylindrical, and is more particularly coaxial with the longitudinal axis L.

More particularly, in the example shown in Figs. 2 and 3, the first wall 12 of the housing 4 comprises a planar wall section 37, surrounding the support sleeve 38. The support sleeve 38 protrudes from the planar wall section 37 on both sides of the planar wall section 37 along the direction of the longitudinal axis L. The support sleeve 38 thus has a larger extension along the longitudinal axis L of the passage 9 compared to the planar wall section 37.

The second wall 15 is configured to delimit, with the hollow insert 14, the lubrication gap 18.

In the example shown in the Figures, the second wall 15 forms a substantially planar wall, extending perpendicular to the longitudinal axis L.

The longitudinal axis L preferably extends normal to the first and second walls 12, 15 of the housing 4.

The second wall 15 further comprises a through-opening 20 intended for the passage of the fuel rod 3. The through-opening 20 more particularly forms one end of the passage 9. The through-opening 20 is more particularly an exit opening, through which the fuel rod 3 is intended to exit the device 1 .

On the side of the passage 9, opposite the exit opening, taken along the direction of the longitudinal axis L, the housing 4 comprises an entrance opening, though which the fuel rod 3 is intended to enter into the device 1 . According to one embodiment, the entrance opening corresponds to the insertion opening 30 provided in the first wall 12.

In the example shown in the Figures, the fuel rod 3 is intended to enter the device 1 through the entrance opening, to move through the device 1 , and more particularly through the passage 9, towards the second wall 15, and then exit the device 1 through the exit opening provided in the second wall 15. During this displacement, the fuel rod 3 is intended to pass through the mist present in the lubrication gap 18 so as to be covered with water droplets from the injectors 5.

The hollow insert 14 is preferably movable relative to the frame 11 for adjusting the size of the lubricating gap 18. In particular, a displacement of the hollow insert 14 towards the second wall 15 results in a decrease of the size of the lubricating gap 18, whereas a displacement of the hollow insert 14 away from the second wall 15 results in an increase of the size of the lubricating gap 18. The size of lubricating gap 18 is for example adjusted as a function of the displacement speed of the fuel rod 3 through the device 1 .

In the example shown in the Figures, the hollow insert 14 is movable in translation along the longitudinal axis L relative to the frame 1 1 , for adjusting the thickness t of the lubricating gap. In this context, the thickness t of the lubricating gap 18 corresponds to the dimension of the lubricating gap 18 taken along the longitudinal axis L of the passage 9.

According to one example, the hollow insert 14 is movable manually relative to the frame 11. According to an alternative embodiment, the device 1 comprises a mechanism for moving the hollow insert 14 relative to the frame 11 .

As shown more particularly in Fig. 3, the hollow insert 14 for example comprises a tubular portion 22 and an annular portion 24. In this example, the lubrication gap 18 is defined between the annular portion 24 and the frame 11 , more particularly the second housing wall 15 of the frame 11 in this embodiment.

The tubular portion 22 interiorly delimits at least a section of the passage 9. In this example, the tubular portion 22 extends coaxially to the longitudinal axis L of the passage 9. The tubular portion 22 is preferably substantially cylindrical.

The annular portion 24 extends the tubular portion 22 along the longitudinal direction of the passage 9 and forms an annular flange protruding outwards, i.e. away from the longitudinal axis L, relative to the tubular portion 22.

The annular portion 24 in particular extends facing a section of the first wall 12 of the frame 1 1 . The annular portion 24 prevents the diffusion of mist through the insertion opening 30 provided in the first wall 12.

The tubular portion 24 is more particularly inserted into a passage delimited interiorly by the support sleeve 38 of the first wall 11 , while the annular portion 24 protrudes outside of this passage, away from this passage in a direction perpendicular to the longitudinal axis L of the passage 9.

The injection region 16 is more particularly delimited between the second wall 15 of the housing 4, the lubricating gap 18, the hollow insert 14 neighboring the first wall 12 of the housing 4 and the injector(s) 5 mounted between the first wall 12 and second wall 15 of the housing 4. The water droplets may thus diffuse from the injector 5 through the injection region 16, passing through the lubricating gap 18, before reaching the passage region 9 where they may settle on the fuel rod 3 in the form of water droplets.

The hollow insert 14 may comprise a second tubular part on the opposite side of the tubular portion of the first wall 12 of the housing, i.e. from the side entering the passage 9, in order to protect the first wall 12 of the housing 4. The second wall 15 of the housing 4 may also have a tubular portion delimiting the through-hole 20 for the passage 9 of the fuel rod 3.

According to one embodiment, the housing 4 is transparent in at least a portion thereof. For example, a section of the first wall 12 and/or of the section wall 15 is transparent. This transparent implementation allows observing the interior of the housing 4 during use of the device 1 .

The injection region 16 between the plurality of injectors 5 may be connected across the frame 1 1 and housing 4.

The housing 4 further comprises an evacuation opening (not shown), intended for the evacuation of surplus water from the injectors 5.

The present invention also relates to a system for inserting fuel rods 3 into a skeleton of a nuclear fuel assembly, comprising a device 1 for lubricating a fuel rod 3 as described above.

During the installation of the fuel rod 3 into the skeleton of the nuclear fuel assembly, the device 1 is integrated into the skeleton directly above and facing the first or topmost insertion grid for inserting the fuel rod 3. In this configuration, the longitudinal axis L of the device 1 extends substantially vertically.

The present invention also relates to a method for lubricating a fuel rod 3 using a device 1 for lubricating a fuel rod as described above. The method comprises the steps of:

- forming a water mist in the lubrication gap 18 using the or each injector 5, and

- displacing the fuel rod 3 through the passage 9, the fuel rod 3 passing through the water mist in the lubrication gap 18 so as to be covered with droplets as it is passes in front of the lubrication gap 18.

The device 1 and method for lubricating a fuel rod 3 according to the present invention is advantageous. Indeed, with this device 1 , the fuel rod 3 passing through the cavity 7 is covered with water droplets, which act as a lubricant and facilitate the introduction of the fuel rods in the skeleton. The water evaporates after the introduction of the fuel rods 3 in the skeleton, such that no removing of the lubricant is required, leading to a particularly efficient lubrication.

In addition, in the device according to the invention, the lubrication gap 18, which is delimited between the hollow insert 14 and the frame 11 , allows deposition of water droplets on only a limited portion of the fuel rod 3. This ensures the formation of droplets of optimal size on the surface of the fuel rod 3, which in turn results in an improved lubrication.

The present invention thus achieves the goal to provide a lubrication device that offers a good lubrication while being labor efficient.

Claims

1 . Device (1 ) for lubricating a fuel rod (3), comprising:

- a housing (4) defining a cavity (7), the housing (4) delimiting a passage (9) for the fuel rod (3) in the cavity (7); and

- at least one injector (5), configured for forming a water mist in the cavity (7) and configured for covering a fuel rod (3) passing through the passage (9) with water droplets ; characterized in that the cavity (7) further comprises a injection region (16), the housing (4) comprising a frame (1 1 ) and a hollow insert (14), the hollow insert (14) separating the passage (9) from the injection region (16) of the cavity (7) and delimiting with the frame (11 ) a lubrication gap (18) fluidically connecting the passage (9) and the injection region (16).

2. Device (1 ) for lubricating a fuel rod (3) according to claim 1 , wherein the device comprises three injectors (5), configured for forming a water mist in the cavity (7) and configured for covering a fuel rod (3) passing through the passage (9) with water droplets.

3. Device (1 ) for lubricating a fuel rod (3) according to claim 1 or claim 2, wherein the orthoradial distance between two adjacent injectors (5) is identical for all injectors (5).

4. Device (1 ) for lubricating a fuel rod according to any one of claims 1 to 3, wherein the hollow insert (14) comprises a tubular portion (24) and an annular portion (22), the lubrication gap (18) being defined between the annular portion (22) and the frame (11 ).

5. Device for lubricating a fuel rod (3) according to any one of claims 1 to 4, wherein the hollow insert (14) is movable relative to the frame (11 ).

6. Device for lubricating a fuel rod (3) according to claim 5, wherein the hollow insert (14) is movable relative to the frame (11 ) along a longitudinal axis (L) of the passage (9).

7. Device for lubricating a fuel rod (3) according to any one of claims 1 to 6, wherein the frame (1 1 ) comprises two opposed walls (12) and (15), the first wall (12) configured to support the hollow insert (6) and the second wall (15) configured to delimit, with the hollow insert (14), the lubrication gap (18).

8. System for mounting fuel rods (3) on a skeleton, comprising a device for lubricating a fuel rod (3) according to any one of claims 1 to 7.

9. Method for lubricating a fuel rod (3) using a device according to any one of claims 1 to 7, comprising the steps of:

- forming a water mist in the lubrication gap (18) using the injectors (5), - displacing the fuel rod (3) through the passage (9), the fuel rod (3) passing through the water mist in the lubrication gap (18) so as to be covered with droplets as it is passes in front of the lubrication gap (18).