Method for repairing a steam generator tube in a nuclear reactor, and corresponding steam generator

Abstract

Method for repairing a steam generator tube of a nuclear reactor, and corresponding steam generator. The tube (5, 115) is integral with an outer casing (3) of the steam generator (1) and includes an outer end (7) connected to an outer conduit (9, 118) for the circulation of a secondary heat transfer fluid, the tube (5, 115) having an inner passage (15) delimited by an inner surface (17), the steam generator (1) including an inner conduit (13, 117) housed inside the outer casing (3) and a thermal sleeve (19, 119) having a proximal end (21) connected to the inner conduit (13, 117) and a distal end (23) engaged in the inner passage (15) of the tube (5, 115), such that the inner passage (15) is in fluidic communication with the inner conduit (13, 117) through the thermal sleeve (19, 119),the distal end (23) extending against or in the immediate vicinity of an annular area (35) of the inner surface (17) of the tubing (5, 115). The method includes a step of introducing a protective sleeve (45) into the inner passage (15), the protective sleeve (45) being pressed against the inner surface (17) and covering the annular area (35). Figure for the abstract: 4,

Description

Title of the invention: Method for repairing a tube of a steam generator of a nuclear reactor, and corresponding steam generator

[0001] The invention relates generally to the maintenance of steam generators of nuclear reactors.

[0002] More specifically, the invention relates to a method of maintenance of a tube of a nuclear reactor steam generator, the tube being attached to an external casing of the steam generator, the tube comprising an external end connected to an external conduit for the circulation of a secondary heat transfer fluid.

[0003] The tubing has an internal passage delimited by an internal surface.

[0004] The steam generator is of the type comprising an internal conduit housed within the outer casing and a thermal sleeve having a proximal end connected to the internal conduit and a distal end engaged in the internal passage of the tubing. Thus, the internal passage of the tubing is in fluidic communication with the internal conduit through the thermal sleeve.

[0005] The distal end of the thermal sleeve extends in the immediate vicinity of an annular area of ​​the inner surface of the tubing.

[0006] The external duct is typically part of the ARE (Feed Water Flow Regulation) circuit, supplying the steam generator with secondary heat transfer fluid from the condenser. The internal duct is, in this case, the ARE torus, distributing the secondary heat transfer fluid to the upper part of the steam generator, at its periphery.

[0007] The secondary heat transfer fluid arriving via the external circulation duct has a temperature significantly lower than that of the inner surface of the tubing. The thermal sleeve is designed to protect this inner surface thermally and prevent it from coming into contact with a low-temperature fluid. This could generate mechanical stresses in the tubing and lead to premature wear.

[0008] It was observed that the annular area of ​​the inner surface of the tubing against which the distal end of the thermal sleeve was positioned could show wear. This area thus presents a concave surface.

[0009] The distal end of the cuff may also show wear.

[0010] Wear on the inner surface and distal end of the sleeve may be the result of vibrational instability of the thermal sleeve and / or the environment potentially corrosive. Due to wear, a flow occurs between the thermal sleeve and the internal surface of the tubing, so that this internal surface is less well protected against thermal shock.

[0011] It is possible to restore the seal between the inner surface of the tubing and the thermal sleeve by implementing a process consisting of separating the tubing from the external circulation conduit, removing the original thermal sleeve, and installing a new sleeve from the outside of the steam generator, welded to the inner surface of the tubing or to the external conduit.

[0012] Such a process is however very restrictive, because it requires cutting the external circulation duct of the secondary heat transfer fluid to access the inside of the tubing.

[0013] In this context, the invention aims to propose a repair method that does not have the above defects.

[0014] To this end, the invention relates to a method for repairing a tube of a steam generator of a nuclear reactor, the tube being integral with an external casing of the steam generator and comprising an external end connected to an external conduit for circulating a secondary heat transfer fluid, the tube having an internal passage delimited by an internal surface, the steam generator comprising an internal conduit housed inside the external casing and a thermal sleeve having a proximal end connected to the internal conduit and a distal end engaged in the internal passage of the tube, such that the internal passage is in fluidic communication with the internal conduit through the thermal sleeve, the distal end extending against or in the immediate vicinity of an annular area (of the internal surface of the tube,The method includes a step of introducing a protective cuff into the internal passage, the protective cuff being pressed against the internal surface and covering the annular area.

[0015] The protective sleeve provides protection against wear on the inner surface of the tubing. It restores the seal between the thermal sleeve and the inner surface of the tubing.

[0016] It can be easily introduced from inside the steam generator, so the repair method does not require the removal of the external circulation duct.

[0017] The method of the invention may further have one or more of the following characteristics, considered individually or in all technically possible combinations:

[0018] - the protective sleeve is inserted from inside the steam generator, without separating the outer end of the tubing from the external conduit;

[0019] - the method includes, before the introduction step, a disassembly step of the thermal sleeve, and after the introduction step: - a step of reassembling the thermal sleeve, the protective sleeve creating a seal between the distal end of the thermal sleeve and the internal surface; Or - a step of reassembling a replacement thermal sleeve, the protective sleeve creating a seal between a distal end of the replacement thermal sleeve and the internal surface;

[0020] - a stop is planned on the thermal sleeve or on the thermal sleeve of replacement, blocking the protective sleeve in translation towards the inside of the steam generator;

[0021] - the stop includes a sealing ring surrounding the protective sleeve and in support on the protective cuff;

[0022] - the protective cuff is elastically compressible and has at rest a rest section greater than an internal section of the internal passage;

[0023] - the protective sleeve is a split tube;

[0024] - the protective sleeve has a central axis, the protective sleeve featuring a slit extending along the entire axial length of the protective cuff, delimited between a lower edge and an upper edge covering the lower edge;

[0025] - the protective sleeve has an external face bearing against the surface internal of the tubing and an internal face opposite to the external face, the lower edge having a lower hollowed area hollowed out in the external face and the upper edge having an upper hollowed area hollowed out in the internal face resting against the lower hollowed area;

[0026] - the lower recessed area is circumferentially delimited opposite the edge upper by a side wall, a gap being delimited between the side wall and the upper edge, the protective sleeve having a cover closing an axial end of the gap;

[0027] - the protective sleeve is a helical spring, made of a wire having preferably a rectangular section;

[0028] - the protective cuff has a central axis and comprises: - an externally split tube supported against the internal surface of the tubing, the externally split tube having an external split extending along its entire axial length, and

[0029] - an internally split tube pressed against an inner side of the externally split tube, the tube internally split having an internal split extending along an entire axial length of the internally split tube;

[0030] the external slot and the internal slot being circumferentially offset from each other around the central axis;

[0031] - the protective sleeve includes a ring sealing the gap between the tube externally split and the internally split tube and sealing one end of the external slit;

[0032] - the protective cuff includes an anti-rotation lock, blocking rotation the internal split tube and the external split tube relative to each other.

[0033] According to a second aspect, the invention relates to a steam generator for a nuclear reactor, the steam generator comprising an outer casing and a tube attached to the outer casing, the tube comprising an outer end connected to an external conduit for circulating a secondary heat transfer fluid, the tube having an internal passage delimited by an internal surface, the steam generator comprising an internal conduit housed inside the outer casing and a thermal sleeve having a proximal end connected to the internal conduit and a distal end engaged in the internal passage of the tube, such that the internal passage is in fluidic communication with the internal conduit through the thermal sleeve, the distal end extending against or in the immediate vicinity of an annular area of ​​the internal surface of the tube,The steam generator includes a protective sleeve positioned in the internal passage, the protective sleeve being pressed against the internal surface and covering the annular area, the protective sleeve creating a seal between the distal end of the thermal sleeve and the internal surface.

[0034] Other features and advantages of the invention will become apparent from the detailed description given below, by way of example and not limitation, with reference to the accompanying figures, among which: - [Fig-1] The [Fig. 1] is an axial cross-sectional view of the upper part of a steam generator; - [Fig.2] The [Fig.2] is a cross-sectional view of the steam generator of the [Fig.1], taken along the incidence of arrows II, only a part of the internal conduit being shown; - [Fig.3] The [Fig.3] is an enlarged cross-sectional view of the tubing and thermal sleeve of the steam generator of figures 1 and 2, taken at the incidence of arrows III; - [Fig.4] The [Fig.4] is a section of an upper part of the tubing and thermal sleeve of the [Fig.3], after the protective sleeve has been put in place; - [Fig.5] The [Fig.5] is a top view of the protective cuff of the [Fig.4]; - [Fig.6] The [Fig.6] is a cross-sectional view of the protective sleeve of the [Fig.5], taken according to the incidence of arrows VI; - [Fig.7] [Fig.7] is a similar view to [Fig.4], showing a thermal sleeve used as a replacement for the original thermal sleeve, and showing a variant of the stop provided on [Fig.4] to block the protective sleeve in translation; - [Fig.8] The [Fig.8] is a view similar to that of the [Fig.4], showing a protective cuff according to a second embodiment of the invention; - [Fig.9] The [Fig.9] is a perspective view of a protective cuff according to a third embodiment of the invention; - [Fig. 10] [Fig. 10] is a top view of the protective cuff of [Fig. 9]; and - [Fig. 11] The [Fig. 11] is a cross-sectional view of a detail of the protective cuff of figures 9 and 10, taken along the incidence of arrows XI of the [Fig.10].

[0035] The steam generator 1 shown in figures 1 to 3 is intended to equip a nuclear reactor.

[0036] This nuclear reactor is typically of the PWR type, i.e. pressurized water.

[0037] A conventional pressurized water nuclear reactor comprises a vessel containing the core of the nuclear reactor, and several steam generators of the type shown in figures 1 to 3, typically three or four steam generators.

[0038] The primary heat transfer fluid is heated in the nuclear reactor vessel by passing through contact with the core fuel assemblies, and is then directed to each of the steam generators. In each steam generator, it transfers some of its heat energy to the secondary heat transfer fluid.

[0039] The secondary heat transfer fluid is supplied to the steam generator via a feedwater supply line, designated by the abbreviation ARE. The secondary heat transfer fluid enters the steam generator in liquid form and is vaporized by the heat energy received from the primary heat transfer fluid. It exits the steam generator as vapor. The vapor is then directed to a turbine to generate electricity. After passing through the turbine, it is directed to a condenser and then returns to the steam generator in liquid form.

[0040] The steam generator comprises an outer casing 3 and a tube 5 ([Fig.2]) attached to the outer casing 3.

[0041] The tubing 5 has an external end 7 connected to an external conduit 9 for circulating the secondary heat transfer fluid.

[0042] Here, the term tubing refers to an accessory through which the external conduit 9 is connected to the external envelope 3. The tubing can also be referred to as "connecting" in French or "nozzle" in English.

[0043] The external conduit 9 is integrated into the ARE circuit. The ARE circuit, under normal conditions, allows the supply of feedwater to the steam generator 1.

[0044] The outer casing 3 is generally cylindrical in shape, with a substantially vertical axis A. It encloses the internal structures of the steam generator, in particular the heat exchange tube bundle between the primary heat transfer fluid and the secondary heat transfer fluid (here feedwater), this bundle not being shown in [Fig. 1]. This tube bundle is placed inside a substantially cylindrical bundle casing 11.

[0045] The steam generator 1 further includes an internal conduit 13 housed inside the external casing 3.

[0046] In the example shown, the internal conduit 13 is toroidal in shape. It is generally referred to as the ARE torus.

[0047] As can be seen in [Fig.3], the tubing 5 has an internal passage 15 delimited by an internal surface 17.

[0048] The steam generator 1 also includes a thermal sleeve 19 having a proximal end 21 connected to the internal conduit 13 and a distal end 23 engaged in the internal passage 15 of the tubing 5. The internal passage 15 is thus in fluidic communication with the internal conduit 13 through the thermal sleeve 19.

[0049] The secondary heat transfer fluid thus circulates from the external conduit 9 through the sleeve 19 into the internal conduit 13.

[0050] The beam envelope 11 delimits with the outer envelope 3 an annular passage 25 for the secondary heat transfer fluid, the internal conduit 13 is placed above the annular passage 25 ([Fig.l]).

[0051] J-tubes 27, visible in figures 2 and 3, allow the secondary heat transfer fluid to be distributed from the internal conduit 13 over the entire periphery of the annular passage 25. The secondary heat transfer fluid flows downwards in the annular passage 25, and upwards inside the bundle envelope 11, in contact with the tube bundle.

[0052] The secondary heat transfer fluid escapes from the bundle jacket 11 upwards, and passes inside a set of separators 29 and dryers 31, occupying the entire upper part of the outer jacket 3. The dry steam leaves the steam generator 1 through an outlet 33 provided at the top of the outer jacket 3, then circulates in the turbine, in the condenser before being returned to the steam generator 1 through the external conduit 9.

[0053] As indicated above, the distal end 23 of the thermal sleeve 19 extends against or in the immediate vicinity of an annular area 35 of the internal surface 17 of the tubing 5 ([Fig.3]).

[0054] The proximal end 21 of the thermal sleeve 19 is connected to a part 37 of the internal conduit 13 known as the T-connector.

[0055] This T-fitting 37 has a branch 39 substantially radial with respect to axis A, to which the proximal end 21 of the thermal sleeve is connected. It also has two circumferential branches 41 and 43. The circumferential branches 41 and 43 extend circumferentially around axis A on either side of the radial branch 39.

[0056] As indicated above, in the event of vibrational instability of the thermal sleeve 19, wear may occur at the level of the annular area 35 and the distal end 23 of the thermal sleeve 19. This wear results in the formation of a hollow 44 in the annular area 35, and in possible degradation of the distal end 23 of the thermal sleeve ([Fig.4]).

[0057] The repair method aims to restore the seal between the thermal sleeve and the internal surface of the tubing.

[0058] The repair method includes a step of introducing a protective sleeve 45 into the internal passage 15 of the tubing 5, the protective sleeve 45 being pressed against the internal surface 17 and covering the annular area 35.

[0059] The method also includes, before the introduction step, a step of dismantling the thermal sleeve 19.

[0060] The method further comprises, after the introduction step:

[0061] - a step in reassembling the thermal sleeve 19, the protective sleeve 45 creating a seal between the distal end 23 of the thermal sleeve 19 and the internal surface 17; or

[0062] - a step in reassembling a replacement thermal sleeve 47, the protective sleeve 45 creating a seal between a distal end 48 of the replacement thermal sleeve 47 and the internal surface 17.

[0063] As illustrated in [Fig. 3], the thermal sleeve 19 is typically attached to the internal duct 13 by a removable fastener 49, for example a clamp. The removal step comprises the following substeps: - Cutting of the T-fitting 37; - Separation of the thermal sleeve 19 and the T-fitting 37; - Relocation of the T-fitting 37 and its storage inside the steam generator 1; - Evacuation of the thermal sleeve 19 out of the tubing 5.

[0064] In the cutting sub-step, the circumferential branches 41, 43 are separated from the neighbouring sections of the internal conduit 13, by cutting in two planes L materialised on the [Fig.2].

[0065] The thermal sleeve 19 is separated from the T-fitting 37 using the removable fastener 49. The T-fitting 37 is moved and stored in any suitable location, inside the outer casing 3.

[0066] The thermal sleeve 19 is extracted out of the tubing 5 on the inner side of the steam generator 1, taking advantage of the volume freed up by the evacuation of the T-fitting 37.

[0067] The thermal sleeve 19 is removed from the steam generator 1 through a manhole if it is not reused. If it is reused, it is stored inside the steam generator 1, in any suitable location.

[0068] The protective sleeve 45 is introduced inside the steam generator 1, without separating the external end of the tubing 5 from the external conduit 9.

[0069] It is introduced into the outer casing 3 of the steam generator through a manhole, and put in place by taking advantage of the volume freed up by the evacuation of the T-fitting 37.

[0070] The protective cuff 45 is elastically compressible.

[0071] It has a tubular shape and at rest has a resting section greater than the internal section of the internal passage 15.

[0072] The section here is the right section of the protective cuff, taken perpendicular to the central axis of the protective cuff.

[0073] The protective sleeve 45 is elastically compressible in the sense that it is possible to compress the protective sleeve 45 and elastically move it from its resting cross-section to a reduced cross-section, smaller than its resting cross-section. When the compression is released, the protective sleeve 45 spontaneously returns to its resting cross-section.

[0074] According to a first embodiment shown in figures 4 to 6, the protective sleeve 45 is a split tube.

[0075] The protective sleeve 45 has a central axis C. It has a slot 50 extending over an entire axial length of the protective sleeve.

[0076] As can be seen in [Fig.6], the slot is delimited between a lower edge 51 and an upper edge 53 covering the lower edge 51.

[0077] The lower edge 51 extends axially along the entire length of the cuff of protection 45. Similarly, the upper edge 53 extends axially along the entire length of the protective cuff 45. The edges 51 and 53 are free relative to each other and can therefore move relative to each other.

[0078] The protective sleeve 45 has an external face 55 bearing against the internal surface 17 of the tubing 5, and an internal face 57 opposite the external face 55.

[0079] The lower edge 51 circumferentially forms one end of the tube. Similarly, the upper edge 53 circumferentially forms another end of the tube. These two ends partially overlap.

[0080] The lower edge 51 has a lower recessed area 59 cut into the outer face 55 of the cuff. This recessed area 59 is circumferentially delimited on one side by a lateral wall 61 and is open on the other side, at the end of the cuff. In other words, it extends circumferentially to the end of the cuff 45.

[0081] The upper edge 53 has an upper recessed area 63 cut into the inner face 57 of the cuff. The upper recessed area 63 rests on the lower recessed area 59. The upper recessed area 63 is circumferentially closed on one side by a lateral wall 65, and is open on the opposite side, at the end of the cuff. It extends to the circumferential end of the cuff.

[0082] As can be seen in [Fig. 5], the lower edge 51 is axially slightly longer than the upper edge 53. The lower recessed area 59 is closed at one axial end by an end wall 67. The lower recessed area 59 is axially open at its opposite end. The edge of the protective sleeve 45, at the level of the upper edge 53, is pressed against the end wall 67.

[0083] The upper recessed area 63, on the contrary, is open axially at its two opposite ends.

[0084] In the example shown, the lower recessed area 59 and the upper recessed area 63 have substantially the same circumferential width.

[0085] Because they only partially overlap in the circumferential direction, there is a gap 69 between the side wall 61 and the upper edge 53.

[0086] There is also a gap 70 between the side wall 65 and the lower edge 51.

[0087] The protective sleeve 45 includes a cover closing one axial end of the gap 69.

[0088] This cover is formed by the terminal wall 67 in the example shown. It prevents the circulation of secondary heat transfer fluid in the gap 69, in contact with the internal surface 17 of the pipe 5.

[0089] The gaps 69, 70 make the protective sleeve compressible, allowing its diameter to be reduced by sliding the edges 51 and 53 against each other. Figure 6 shows the protective sleeve 45 in its rest state, in the absence of stress. The upper edge 53 is circumferentially separated from the lateral wall 61. The lower edge 51 is circumferentially away from the side wall 65. When a stress is exerted to reduce the cross-section of the protective sleeve, the lower and upper edges 51, 53 slide circumferentially against each other, the upper edge 53 moving closer to the wall 61 and the lower edge 51 moving closer to the wall 65.

[0090] The lower hollow area 59 and the upper hollow area 63 are each hollowed out over approximately 50% of the thickness of the split tube.

[0091] Thus, the lower edge 51 and the upper edge 53 stacked one on top of the other together have substantially the same thickness as the rest of the split tube.

[0092] The protective sleeve 45 is made of stainless steel or a material resistant to flow or the surrounding environment. It is made of a material having sufficient elasticity so that the sleeve can be compressed to a reduced cross-section and elastically return to its resting cross-section.

[0093] To install the protective sleeve 45 in the internal passage 15, this sleeve is compressed to its reduced cross-section, inserted into the internal passage 15, and then the compression is released so that the protective sleeve 45 returns to its resting cross-section. In doing so, the protective sleeve 45 comes to rest against the internal surface 17 of the tubing 5.

[0094] As can be seen in [Fig.4], the protective sleeve 45 extends axially from the annular area 35 to the end of the internal passage 15 opening into the inside of the steam generator.

[0095] The protective cuff 45 completely covers the annular area 35, and in particular covers the hollow 44.

[0096] Advantageously, it extends beyond the transition surface SI connecting the internal surface 17 of the tubing to the internal surface S2 of the external shell 3 of the steam generator.

[0097] This surface Sla has a general torus shape and is particularly thermally fragile. It is protected by the protective sleeve 45.

[0098] When the original thermal sleeve 19 is reused, during the reassembly step, the thermal sleeve 19 is engaged inside the protective sleeve 45. Its distal end 23 bears against the inner face 57 of the protective sleeve, at the level of the end 71 of this sleeve which covers the hollow 44. The end 71 is thus wedged between the distal end 23 and the annular area 35. This creates a seal between the thermal sleeve 19 and the inner surface 17 of the tubing 5.

[0099] Then, the T-fitting 37 is reattached to the internal conduit 13.

[0100] The tubular sections 41, 43 are re-welded onto the adjacent portions of the internal conduit 13. The proximal end 21 of the thermal sleeve 19 is fixed to the radial section 39 by means of the removable fastener 49.

[0101] When the original thermal sleeve 19 is replaced by a replacement protective sleeve 47, the design of the latter is advantageously slightly different from the design of the original thermal sleeve 19 (see [Fig.7]).

[0102] It typically has the same geometry as the thermal sleeve 19, except at its proximal end 72.

[0103] This proximal end 72 is designed to be welded onto the radial section 39 of the T-fitting 37. This increases the rigidity of the connection and limits the vibrational instabilities of the thermal sleeve.

[0104] The reassembly step is carried out as before. The replacement thermal sleeve 47 is engaged inside the protective sleeve 45, its distal end 48 bearing against the end 71 of the protective sleeve 45 and wedging the protective sleeve against the inner surface 17 of the tubing.

[0105] Then, the T-fitting 37 is reassembled on the internal conduit 13, as described previously. Finally, the proximal end 72 of the replacement thermal sleeve 47 is welded onto the radial conduit 39.

[0106] Advantageously, a stop 73 is provided on the thermal sleeve 19 or on the replacement thermal sleeve 47, blocking the protective sleeve 45 in translation towards the inside of the steam generator.

[0107] The stop 73 is positioned axially along the thermal sleeve 19, 47 such that, when the end 75 of the protective sleeve is against the stop 73, the opposite end 71 covers the annular area 35 and the hollow 44.

[0108] Stop 73 is constituted by a relief projecting radially outwards from the thermal sleeve 19, 47.

[0109] According to an alternative embodiment illustrated in [Fig.4], the stop 73 is constituted by an annular rib, carried by the thermal sleeve 19, 47.

[0110] Stop 73 extends circumferentially around the entire periphery of cuff 19, 47.

[0111] According to another particularly advantageous embodiment, illustrated in [Fig. 7], the stop 73 comprises an annular portion 77 integral with the thermal sleeve 47, extended by a cylindrical portion 79. The cylindrical portion 79 defines with the outer surface of the protective sleeve 45 a circular groove 81 open axially on one side and closed by the annular portion 77 on the other. The end 75 of the protective sleeve 45 is engaged in the circular groove 81.

[0112] Advantageously, the stop 73 includes a sealing ring 83 surrounding the protective sleeve 45 and bearing on the protective sleeve 45.

[0113] The sealing ring 83 is fixed on the stop 73, and more precisely on the cylindrical part 79. It bears on the external side 55 of the protective sleeve, at the end 75.

[0114] Thus, the secondary heat transfer fluid infiltrating between the protective sleeve and the thermal sleeve can flow into the annular groove 81. On the other hand, it cannot infiltrate between the ring 83 and the protective sleeve 45, and therefore cannot flow out of the annular groove 81 towards the internal surface 17 of the tube or towards the surface SI.

[0115] A second embodiment of the invention will now be described, with reference to [Fig. 8]. Only the points by which this second embodiment differs from the first will be detailed below. Identical elements or elements performing the same function will be designated by the same reference numerals.

[0116] In this second embodiment, the protective sleeve 45 is a helical spring.

[0117] This helical spring is formed by a wire with a rectangular cross-section.

[0118] The helical spring has contiguous coils.

[0119] When the protective sleeve is in place against the inner surface of the tubing, the coils of the helical spring are pressed against each other. They are also pressed by their radially external surfaces against the inner surface of the tubing.

[0120] The cross-section of the protective sleeve can be reduced by exerting a circumferential force on the helical spring.

[0121] A third embodiment will now be described, with reference to Figures 9 to 11. Only the points by which this third embodiment differs from the first will be detailed below. Identical elements or elements performing the same function will be designated by the same reference numerals.

[0122] In the third embodiment, the protective sleeve 45 has a central axis C. It comprises:

[0123] - an externally split tube 85 bearing against the internal surface 17 of the tubing, the tube externally slotted 85 having an external slot 87 extending along the entire axial length of the externally slotted tube 85; and

[0124] - an internally split tube 89 pressed against an inner side of the externally split tube 85, the internally split tube 89 having an internal split 91 extending over an entire axial length of the internally split tube 89.

[0125] As can be seen in [Fig.9], the outer slot 87 and the inner slot 91 are circumferentially offset from each other around the central axis C.

[0126] The externally split tube 85 has two straight edges 93, parallel to each other, delimiting between them the external slot 87. The external slot 87 is therefore also straight.

[0127] The edges 93 do not overlap and are circumferentially separated from each other.

[0128] On its external surface, the external split tube 85 has one or more hollow areas 95.

[0129] In the example shown, the recessed areas 95 form two parallel bands, extending circumferentially all around the external split tube. When the protective sleeve is in place in the tubing 5, the areas 97 of the external surface that are not recessed are in contact with the internal surface 17 of the tubing. Conversely, the recessed areas 95 are filled by a thermally protective layer of water, interposed between the protective sleeve 45 and the internal surface 17 of the tubing 5.

[0130] The internal slot 91 is delimited between two edges 99, 101 of the internally slotted tube. Edge 99 is straight along most of its length, but forms a tab 103 projecting circumferentially from one axial end of the internal slot 91. Edge 101 is also straight along most of its length, and forms a notch 105 opposite the tab 103. The tab 103 is engaged in the notch 105, such that it axially closes the internal slot 91.

[0131] On its radially external face, the internally split tube 89 has two circular ridges 107. The ridges 107 are formed at the two axial ends of the internally split tube 89. The externally split tube 85 is arranged between the two ridges 107, and is axially blocked in translation by the two ridges 107.

[0132] The two ridges 107 close the external slot 87 at its two axial ends.

[0133] Each bead 107 constitutes a ring sealing the gap existing between the external split tube 85 and the internal split tube 89, and sealing one end of the external slot 87.

[0134] As seen in [Fig. 10], the protective sleeve 45 includes an anti-rotation block 109, blocking the internal split tube 85 and the external split tube 89 from rotating relative to each other around the central axis C.

[0135] The anti-rotation block 109 comprises at least one mass 111, projecting on the external surface of the internal split tube 89. In the example shown, the anti-rotation block comprises two masses 111.

[0136] The masses 111 have rectangular shapes or any other suitable shape, and extend from the ridges 107, axially towards each other. They are placed axially opposite each other.

[0137] The solid or each solid 111 is received in a notch 113 formed in the external split tube 85. The notch 113 has the same shape as the solid 111.

[0138] In the example shown, notch 113 has a rectangular shape.

[0139] The or each solid 111 cooperates with the corresponding notch 113 to lock the two split tubes in rotation relative to each other.

[0140] The method has been described as being applied to the tubing 5 through which the ARE circuit is connected to the ARE toroid allowing the secondary heat transfer fluid to be distributed in the passage 25.

[0141] It is also applicable to the pipe 115 visible in [Fig.2]. The pipe 115 allows the ASG circuit 118 to be connected to the internal conduit 117. The ASG circuit provides the steam generator with emergency feedwater in the event of a loss of the main supply.

[0142] The internal conduit 117 is an annular conduit placed under the conduit 13. It is connected to the tubing 115 by a sleeve 119, visible on [Fig.2], arranged like the thermal sleeve 19.

[0143] The invention also relates to the steam generator obtained after implementation of the above repair method.

[0144] The steam generator 1 is of the type described above.

[0145] It includes a protective sleeve 45 placed in the internal passage 15, the protective sleeve 45 being pressed against the internal surface 17 of the tubing and covering the annular area 35.

[0146] The protective sleeve is placed in tubing 5 or in tubing 115.

[0147] The protective sleeve 45 advantageously conforms to one of the three embodiments described above.

[0148] The thermal sleeve is the original thermal sleeve 19 / 119, or the replacement thermal sleeve 47.

[0149] The protective sleeve 45 creates a seal between the distal end 23 of the thermal sleeve 19 / 119 and the internal surface 17, or between the distal end 48 of the replacement thermal sleeve 47 and the internal surface 17.

[0150] The repair method has multiple advantages.

[0151] Because the protective sleeve is inserted from inside the steam generator, it is not necessary to separate the external end of the tubing from the external conduit. This method is minimally invasive and allows work to be carried out exclusively from inside the steam generator.

[0152] The repair method is flexible, since it allows either the same thermal sleeve to be reused, or a replacement thermal sleeve of improved design to be used.

[0153] Because a stop is provided on the thermal sleeve or the replacement thermal sleeve, the protective sleeve is wedged in an axial position relative to the tubing. This ensures that the annular area of ​​the inner surface of the tubing, which is susceptible to damage or gouging, remains covered by the protective sleeve.

[0154] When the stop includes a sealing ring surrounding the protective sleeve and resting on the protective sleeve, the secondary heat transfer fluid that could enter between the protective sleeve and the thermal sleeve is blocked at the stop, and cannot flow into the inside of the tubing.

[0155] Because the protective cuff is elastically compressible, its installation is particularly easy.

[0156] When the protective sleeve is a split tube, its design is particularly simple and economical.

[0157] The fact that the protective sleeve has a delimited slot between a lower edge and an upper edge covering the lower edge makes it possible to limit the leakage area between the two edges of the protective sleeve, without preventing the protective sleeve from contracting when it is put in place.

[0158] When the protective sleeve has an outer face bearing against the inner surface of the tubing and an inner face opposite the outer face, with the lower edge having a recessed area lower than the outer face and the upper edge having a recessed area higher than the lower face resting against the recessed area of ​​the lower edge, it is possible to give the protective sleeve a substantially constant thickness around its entire periphery. This ensures a minimum level of leakage between the thermal sleeve and the inner surface of the tubing.

[0159] When the lower recessed area is circumferentially delimited opposite the upper edge by a side wall, a gap being delimited between the side wall and the upper edge, the protective sleeve having a cover closing an axial end of the gap, leaks along the gap are controlled.

[0160] When the protective sleeve is made in the form of a helical spring, consisting of a wire preferably having a rectangular cross-section, the protective sleeve is made in a simple, inexpensive and easy-to-install form.

[0161] When the protective cuff has a central axis and comprises:

[0162] - an externally split tube bearing against the internal surface of the tubing, the tube externally split tube having an external split extending along the entire axial length of the externally split tube and

[0163] - an internally split tube pressed against an inner side of the externally split tube, the tube internally split having an internal split extending along an entire axial length of the internally split tube;

[0164] - the external slit and the internal slit being circumferentially offset from one another by relation to the other around the central axis,

[0165] it can be made more easily than the protective sleeve of the first embodiment. The protective sleeve of the first embodiment has hollow areas at both ends, which are difficult to make in a thin sheet of metal.

[0166] When the protective sleeve includes a ring sealing the gap between the outer split tube and the inner split tube, and sealing one end of the outer split, leaks of secondary heat transfer fluid between the thermal sleeve and the inner surface of the tubing are strictly limited.

[0167] When the protective sleeve includes an anti-rotation block, the internal split tube and the external split tube are blocked from rotating relative to each other, which prevents the external and internal splits from coming to rest alongside each other, which would increase leakage.

[0168] The repair method may have multiple variations.

[0169] The method has been described with the protective sleeve inserted from inside the steam generator. However, it would be possible to insert the protective sleeve from outside the steam generator, after separating the external end of the tubing and the external conduit. In this case, it would not be necessary to disassemble the T-fitting.

Claims

Demands

1. A method for repairing a pipe (5, 115) of a steam generator (1) of a nuclear reactor, the pipe (5, 115) being integral with an outer casing (3) of the steam generator (1) and comprising an external end (7) connected to an external conduit (9, 118) for the circulation of a secondary heat transfer fluid, the pipe (5, 115) having an internal passage (15) delimited by an internal surface (17), the steam generator (1) comprising an internal conduit (13, 117) housed within the outer casing (3) and a thermal sleeve (19, 119) having a proximal end (21) connected to the internal conduit (13, 117) and a distal end (23) engaged in the internal passage (15) of the pipe (5, 115), such that the internal passage (15) is in fluidic communication with the internal conduit (13, 117) through the thermal sleeve (19, 119),the distal end (23) extending against or in the immediate vicinity of an annular area (35) of the inner surface (17) of the tubing (5, 115), the method comprising a step of introducing a protective sleeve (45) into the inner passage (15), the protective sleeve (45) being pressed against the inner surface (17) and covering the annular area (35), the protective sleeve (45) being introduced from inside the steam generator (1), without separating the outer end (7) of the tubing (5, 115) from the outer conduit (9, 118).

2. Method according to claim 1, wherein the method comprises, prior to the introduction step, a step of dismantling the thermal sleeve (19, 119), and after the introduction step: - a step of reassembling the thermal sleeve (19, 119), the protective sleeve (45) creating a seal between the distal end (23) of the thermal sleeve (19, 119) and the internal surface (17); or - a step of reassembling a replacement thermal sleeve (47), the protective sleeve (45) creating a seal between a distal end (48) of the replacement thermal sleeve (47) and the internal surface (17).

3. Method according to claim 2, wherein a stop (73) is provided on the thermal sleeve (19, 119) or on the replacement thermal sleeve (47), blocking in translation the protective sleeve (45) towards the inside of the steam generator (1).

4. Method according to claim 3, wherein the stop (73) comprises a sealing ring (83) surrounding the protective sleeve (45) and bearing on the protective sleeve (45).

5. Method according to any one of the preceding claims, wherein the protective sleeve (45) is elastically compressible and has at rest a rest section greater than an internal section of the internal passage (15).

6. Method according to any one of the preceding claims, wherein the protective sleeve (45) is a split tube.

7. Method according to claim 6, wherein the protective sleeve (45) has a central axis (C), the protective sleeve (45) having a slot (50) extending over an entire axial length of the protective sleeve (45), delimited between a lower edge (51) and an upper edge (53) covering the lower edge (51).

8. Method according to claim 7, wherein the protective sleeve (45) has an outer face (55) bearing against the inner surface (17) of the tubing (5, 115) and an inner face (57) opposite the outer face (55), the lower edge (51) having a lower recessed area (59) hollowed out in the outer face (55) and the upper edge (53) having an upper recessed area (63) hollowed out in the inner face (57) resting against the lower recessed area (59).

9. Method according to claim 8, wherein the lower recessed area (59) is circumferentially delimited opposite the upper edge (53) by a side wall (61), a gap (69) being delimited between the side wall (61) and the upper edge (53), the protective sleeve (45) having a cover (67) closing an axial end of the gap (69).

10. Method according to any one of claims 1 to 5, wherein the protective sleeve (45) is a helical spring, made of a wire preferably having a rectangular cross-section.

11. A method according to any one of claims 1 to 5, wherein the protective sleeve (45) has a central axis (C) and comprises: - an external slotted tube (85) bearing against the internal surface (17) of the tubing (5, 115), the external slotted tube (85) having a slot external (87) extending over an entire axial length of the external split tube (85), and - an internal split tube (89) pressed against an inner side of the external split tube (85), the internal split tube (89) having an internal slot (91) extending over an entire axial length of the internal split tube (89); the external slot (87) and the internal slot (89) being circumferentially offset from each other around the central axis (C).

12. Method according to claim 11, wherein the protective sleeve (45) includes a ring (107) sealing the gap between the external split tube (85) and the internal split tube (89) and sealing one end of the external slot (87).

13. Method according to claim 11 or 12, wherein the protective sleeve (45) includes an anti-rotation block (109), blocking the internal split tube (89) and the external split tube (85) from rotating relative to each other.

14. Steam generator of a nuclear reactor, the steam generator (1) comprising an outer casing (3) and a tube (5, 115) integral with the outer casing (3), the tube (5, 115) comprising an external end (7) connected to an external conduit (9, 118) for the circulation of a secondary heat transfer fluid, the tube (5, 115) having an internal passage (15) delimited by an internal surface (17), the steam generator (1) comprising an internal conduit (13, 117) housed within the outer casing (3) and a thermal sleeve (19, 47, 119) having a proximal end (21, 72) connected to the internal conduit (13, 117) and a distal end (23, 48) engaged in the internal passage (15) of the tube (5, 115), such so that the internal passage (5, 115) is in fluidic communication with the internal conduit (13, 117) through the thermal sleeve (19, 47, 119), the distal end (23,48) extending against or in the immediate vicinity of an annular area (35) of the inner surface (17) of the tubing (5, 115), the steam generator (1) comprising a protective sleeve (45) placed in the inner passage (15), the protective sleeve (45) being pressed against the inner surface (17) and covering the annular area (35), the protective sleeve (45) creating a seal between the distal end (23, 48) of the thermal sleeve (19, 47, 119) and, the inner surface (17), the protective sleeve (45) being adapted to be introduced from inside the steam generator (1), without separating the outer end (7) of the tubing (5, 115) from the outer conduit (9, 118).

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