A device for holding two elements together, particularly in a compact nuclear reactor.

Abstract

A device for retaining two elements attached one to the other, particularly in a compact nuclear reactor. The retaining device (10) comprises a fixing screw (16), including a screw head (16a) and a screw body (16b), and a threaded portion (18) for receiving the screw body (16b), the threaded portion (18) being integral with the first element (12), and a tubular retaining sleeve (24), including a central passage (26) for the screw (16). The retaining sleeve (24) has at least one portion (32) projecting radially outwards, intended to be inserted into a recess (34) formed in the second element (14). The retaining sleeve (24) has, at a proximal end, a portion (36) deformable between a screw (16) passage configuration and a screw head (16a) retention configuration. Figure for the abbreviation: Figure 2

Description

Title of the invention: Device for holding two elements attached to one another, particularly in a compact nuclear reactor

[0001] The present invention relates to a device for holding two elements attached to one another, particularly in a compact nuclear reactor.

[0002] Such a holding device is for example intended for holding a flow separation shell on a steam generator tube plate in a compact nuclear reactor, allowing the shell and the tube plate to be handled together during their assembly or disassembly in the compact nuclear reactor.

[0003] In such a compact nuclear reactor, particularly a type K reactor, water from a primary circuit is heated in the reactor vessel containing the nuclear fuel rods and circulates through pipes passing into a steam generator that receives water from the secondary circuit. This allows for heat exchange between the water circulating in the primary circuit and the water in the secondary circuit. After this exchange, the water from the primary circuit, cooled in the pipes, returns to the reactor vessel where it is reheated. The portion of the primary circuit containing the hot water is known as the hot leg, and the portion containing the cold water is called the cold leg. At the point where the reactor vessel passes into the steam generator, it is known to hermetically seal the hot leg from the cold leg using a flow separation sleeve.

[0004] The flow separator ferrule is fixed to the tube plate of the steam generator by means of fixings known per se. A retaining device is provided to hold the flow separator ferrule on the tube plate to prevent manipulation of the assembly during assembly or disassembly. Such a retaining device comprises screws.

[0005] The present invention aims to provide a retaining device that prevents screw heads from falling out in the event of breakage, thereby preventing the presence of a migrating object in the primary circuit. Since the retaining device is dedicated to securing the flow separation ferrule to the steam generator tube plate, it must be removable for maintenance, taking into account the accessibility and radiation protection constraints this entails.

[0006] To this end, the invention relates to a device for retaining a first element with a second element, comprising at least one fixing screw, including a screw head and a screw body, and, for each fixing screw:

[0007] - a threaded receiving portion of the screw body, the threaded portion being integral with the first element,

[0008] - a retaining sleeve, generally tubular in shape, comprising a passage central for the screw, the central passage being delimited by an inner wall, the inner wall comprising an annular portion radially projecting inwards intended to be clamped longitudinally between the screw head and the threaded portion,

[0009] characterized in that:

[0010] - the retaining sleeve has at least one radially projecting part towards the exterior, intended to be inserted into a housing provided in the second element,

[0011] - the retaining sleeve comprises, at a proximal end, a deformable part between a screw passage configuration, and a screw head retention configuration.

[0012] In the event of breakage of the screw head, it would remain held by the retaining sleeve, in particular by its deformable part, the retaining sleeve remaining held to the second element by the part radially projecting outwards.

[0013] According to other advantageous aspects of the invention, the fastening device comprises one or more of the following features, taken individually or in all technically possible combinations:

[0014] - The threaded part is formed by a pin integral with the first element.

[0015] - The pin is welded to the first element, preferably in a receiving cavity of this pawn.

[0016] - The second element has a through opening opposite the part tapped, the through opening being delimited by an internal wall of general revolution shape around a longitudinal axis, the internal wall having an annular shoulder, arranged, in the longitudinal direction, between the pin and the screw head, and the socket also having one opposite said annular shoulder.

[0017] - The protruding part is formed by a folding tab.

[0018] - The housing for receiving the radially protruding part is delimited on the one hand by the second element and on the other hand by the first element.

[0019] - The deformable part is formed by a thin part of the sleeve.

[0020] The invention also relates to a nuclear reactor comprising a plate and a flow separation shell, characterized in that it comprises a holding device as defined above, in which the first element is formed by the plate and the second element is formed by the flow separation shell.

[0021] The invention finally relates to a method for mounting a retaining device as defined above, characterized in that it comprises the following steps:

[0022] - arrangement of the socket in an opening of the second element,

[0023] - arrangement of the radial part in the housing,

[0024] - arrangement of the second element on the first element by placing each opening opposite the corresponding threaded section,

[0025] - insertion of the screw by screwing it into the threaded hole, and

[0026] - deformation of the deformable part towards its head-holding configuration screw.

[0027] The invention will become clearer upon reading the following description, given solely by way of non-limiting example, and made with reference to the drawings in which:

[0028] [Fig-1] [Fig. 1] is an axial cross-sectional view of a compact nuclear reactor comprising a holding device according to an example of an embodiment of the invention;

[0029] [Fig.2] [Fig.2] is an axial cross-sectional view of said retaining device.

[0030] Figure 2 shows a device 10 for holding a first element 12 with a second element 14, according to an example of an embodiment of the invention.

[0031] For example, the invention is implemented in a compact nuclear reactor.

[0032] Such a compact nuclear reactor is, for example, part of a nuclear propulsion system, intended, for example, to equip a submarine. It is understood, however, that the retaining device 10 can be used in other applications requiring the retention of a screw head in the event of its breakage.

[0033] In a conventional manner, the nuclear reactor 100 mainly comprises a vessel 102, containing nuclear fuel rods 104 and water from a primary circuit set in motion by a pump 106 and compressed by a compressor 108, and a steam generator 110 containing water from a secondary circuit injected into the steam generator 110 by a cold water inlet 112 and exiting the steam generator 110 as steam by an outlet 114 to supply, for example, a turbine of a propulsion system.

[0034] The water in the secondary circuit is heated by the water in the primary circuit by heat exchange between the water in the secondary circuit contained in the steam generator 110 and the hot water in the primary circuit circulating in pipe bundles 116 extending into the steam generator 110, the water in the primary circuit passing from the tank 102 to the pipe bundles 116, after having been heated by the nuclear fuel rods 104, through a separation plate separating the tank 102 from the steam generator 110.

[0035] The arrows C in [Fig. 1] represent the path of the hot water in the primary circuit. The water in the primary circuit, cooled after heat exchange, returns to the tank 102 due to the shape of the pipes in the pipe bundles 116, as shown by the arrows F in [Fig. 1], which represent the path of the cold water in the primary circuit. In the tank 102, the cold water, referred to as the cold leg, is separated from hot water, referred to as the hot leg, is supplied by a wall 120 surrounding the fuel rods 104. At the level of the separation plate, the nuclear reactor 100 includes a flow separation shell above the wall 120 and ensuring a seal between the hot leg and the cold leg to prevent water from the hot leg from entering the cold leg.

[0036] In the context of the present invention, the separating plate forms said first element 12, and the flow separation ferrule forms said second element 14.

[0037] The retaining device 10 comprises at least one fixing screw 16, and preferably a plurality of fixing screws 16, only one of which is shown in [Fig. 2]. The retaining device 10 is identical with respect to the other fixing screws.

[0038] Each fixing screw 16 extends in a longitudinal direction.

[0039] Each fixing screw 16 conventionally comprises a screw head 16a and a screw body 16b extending in the longitudinal direction. The screw head 16a is shaped to cooperate with a suitable screwing tool, and the screw body 16b is threaded.

[0040] Preferably, the screw head 16a has a chamfer 15.

[0041] The first element 12 comprises a threaded portion 18, integral with this first element 12, and complementary to the screw body 16b, such that the screw body 16b can be screwed into the threaded portion 18. The threaded portion 18 is preferably formed by a pin welded to the first element 12 and pierced with a threaded hole. The threaded hole is defined around a longitudinal axis X parallel to the longitudinal direction. The pin preferably has a general shape of revolution about the longitudinal axis X.

[0042] The second element 14 has a through opening 17 opposite the threaded part 18, extending parallel to the longitudinal direction X. The through opening 17 is delimited by an internal wall 17a of general shape of revolution around the longitudinal axis X. The internal wall 17a has an annular shoulder 17b, disposed, in the longitudinal direction, between the pin 18 and the screw head 16a.

[0043] Advantageously, the first element 12 has a cavity 19 for receiving the pin 18, into which the pin 18 is fitted before welding.

[0044] Said pin 18 extends longitudinally between a distal end 20 welded to the first element 12, and a proximal end 22 into which the tapped orifice opens.

[0045] The fastening device 10 also includes a retaining sleeve 24 of generally tubular shape, comprising a central passage 26 for the screw.

[0046] The central passage 26 is delimited by an inner wall 28. The inner wall 28 comprises an annular portion 30 projecting radially inwards. The portion annular 30 is disposed between the pin 18 and the screw head 16a, so as to be clamped between them when tightening the screw 16 into the pin 18.

[0047] The retaining sleeve 24 has at least one portion 32 projecting radially outwards, intended to be inserted into a recess 34 formed in the second element 14. In the described embodiment, said recess 34 is formed by a recess in the second element 14 on one side, and by a wall of the first element 12 on the other. The projecting portion 32 is preferably formed at a distal end of the retaining sleeve 24.

[0048] The protruding part 32 is preferably formed by a folding tab.

[0049] The retaining sleeve 24 has an outer wall 35 with a diameter very slightly smaller than that of the inner wall 17a in a distal portion between the shoulder 17b and the first element 12, so as to allow the retaining sleeve 24 to be inserted into the opening 17, while permitting the smallest possible, or even virtually zero, transverse movement. This virtually zero transverse movement allows, in particular, for the centering of the sleeve 24 relative to the opening 17.

[0050] The outer wall 35 also includes a shoulder 35a, intended to be arranged opposite the shoulder 17b.

[0051] The retaining sleeve 24 has, at a proximal end, a deformable portion 36 between a screw passage configuration 16 and a screw head retention configuration 16a. The deformable portion 36 is, for example, formed by a thin section of the sleeve 24. The portion 36 is deformable by means of a tool provided for this purpose, for example, a clamping tool for tightening the deformable portion 36 onto the screw head 16a. More specifically, the portion 36 is deformed against the chamfer 15 of the screw head 16a.

[0052] Alternatively, the deformable part could be formed by a plurality of deformable tabs.

[0053] The assembly method for the retaining device 10 will now be described.

[0054] Initially, the pin 18 is placed in the cavity 19 of the first element 12, before being welded to it.

[0055] Furthermore, the sleeve 24 is disposed in the opening 17, from a proximal end of the opening 17 to a distal end. The insertion of the sleeve 24 is limited by the shoulders 17b and 35a, which are opposite each other.

[0056] In a subsequent step, each radial part 32 is put in place, for example by radially bending the tab(s) forming the radial part(s) 32. The radial part thus extends into the housing 34.

[0057] It should be noted that at this stage, the sleeve 34 is held in the opening 17, towards the proximal end by the radial part 32 and towards the distal end by the shoulder 35a.

[0058] The second element 14 can therefore be handled without risk of the socket 34 falling off.

[0059] The second element 14 is then attached to the first element 12, by putting Each opening 17 is positioned opposite its corresponding pawn 18. The second element 14 is put in place, ensuring that the pawn 18 fits into the socket 24. Thus, the socket 24 surrounds the pawn 18.

[0060] The screw 16 is then inserted through the opening 17 to be screwed into the threaded hole of the pin 18. The screw is tightened until the annular portion 30 is clamped between the pin 18 and the screw head 16a. The screw is tightened using a conventional screwing tool, through the opening 17.

[0061] Once screwed in, screw 16, along with the other screws, holds the first 12 and second 14 elements together. More specifically, when the first element 12 moves away from the second element 14, shoulder 17b comes into contact with shoulder 35a, this shoulder 35a being connected to screw 16 via sleeve 24. The first 12 and second 14 elements cannot therefore move further apart than the gap between shoulders 17b and 35a.

[0062] It should be noted that the transverse forces are transmitted from the second element 14 to the first element 12 via the sleeve 24 and the pin 18. The retaining device 10 thus allows the assembly of the first 12 and second 14 elements to be held transversely. It should be noted that the forces do not pass through the screw, although the latter is subjected to little stress, which limits the risk of breakage of the screw head.

[0063] Finally, the method includes clamping the deformable part 36 onto the screw head 16a.

[0064] In the event of breakage of the screw head 16a, it remains held by the deformable part 36 of the sleeve 24. This sleeve 24 then remains held in the opening 17 by the radially projecting part 32.

[0065] It should be noted that the dismantling of the retaining device 10 is easy, by simply loosening the deformable part 36.

Claims

Demands

1. Device (10) for retaining a first element (12) with a second element (14), comprising at least one fixing screw (16), including a screw head (16a) and a screw body (16b), and, for each fixing screw (16): - a threaded portion (18) for receiving the screw body (16b), the threaded portion (18) being integral with the first element (12), - a retaining sleeve (24), generally tubular in shape, including a central passage (26) for the screw (16), the central passage (26) being delimited by an inner wall (28), the inner wall (28) including an annular portion (30) projecting radially inwards for being clamped longitudinally between the screw head (16a) and the threaded portion (18), in which: - the retaining sleeve (24) includes at least one portion (32) projecting radially outwards, intended to be inserted into a housing (34) provided in the second element (14), - the retaining sleeve (24) comprises,at a proximal end, a deformable portion (36) between a screw (16) passage configuration and a screw head (16a) retention configuration, characterized in that the protruding portion (32) is formed by a foldable tab.

2. Retaining device (10) according to claim 1, wherein the threaded part (18) is formed by a pin integral with the first element (12).

3. Retaining device (10) according to claim 2, wherein the pin is welded to the first element (12), preferably in a cavity (19) for receiving this pin.

4. A retaining device (10) according to any one of the preceding claims, wherein the second element (14) has a through opening (17) opposite the threaded portion (18), the through opening (17) being delimited by an internal wall (17a) generally of the shape of revolution about a longitudinal axis (X), the internal wall (17a) having an annular shoulder (17b) disposed, in the longitudinal direction, between the threaded portion (18) and the screw head (16a), and the sleeve (24) comprising a shoulder (35a) opposite said annular shoulder (17b).

5. Retaining device (10) according to any one of the preceding claims, wherein the housing (34) for receiving the radially projecting part (32) is delimited on one side by the second element (14) and on the other side by the first element (12).

6. Retaining device (10) according to any one of the preceding claims, wherein the deformable part (36) is formed by a thin part of the sleeve (24).

7. Nuclear reactor (100) comprising a plate (12) and a flow separation shell (14), characterized in that it comprises a retaining device (10) according to any one of the preceding claims, in which the first element is formed by the plate (12) and the second element is formed by the flow separation shell (14).

8. Method of mounting a retaining device (10) according to any one of claims 1 to 6, comprising the following steps: - arranging the sleeve (24) in an opening (17) of the second element (14), - arranging the radial part (32) in the housing (34), by folding the tab forming this radial part, - arranging the second element (14) on the first element (12) by placing each opening (17) opposite the corresponding threaded part (18), - inserting the screw (16) by screwing it into the threaded hole (18), and - deforming the deformable part (36) towards its configuration for retaining the screw head (16a).