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 generally relates to the maintenance of steam generators of nuclear reactors.

[0002] More specifically, the invention relates to a method for maintaining a tube of a nuclear reactor steam generator, the tube being secured to an external casing of the steam generator, the tube comprising an external end connected to an external conduit for circulating 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 further 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 tubing. Thus, the internal passage of the tubing is in fluid communication with the internal conduit through the thermal sleeve.

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

[0006] The external conduit 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 conduit is in this case the ARE torus, distributing the secondary heat transfer fluid in the upper part of the steam generator, at the periphery thereof.

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

[0008] It has been observed that the annular area of ​​the inner surface of the tubing against which the distal end of the thermal sleeve was arranged could exhibit wear. This area thus has a hollow surface.

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

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

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

[0012] Such a method is however very restrictive, because it requires cutting the external conduit for circulation of the secondary heat transfer fluid to access the interior of the tubing.

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

[0014] To this end, the invention relates to a method for repairing a tubing of a steam generator of a nuclear reactor, the tubing 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 tubing 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 tubing, such that the internal passage is in fluid communication with the internal conduit through the thermal sleeve, the distal end extending against or in the immediate vicinity of an annular zone (of the internal surface of the tubing,the method comprising a step of introducing a protective sleeve into the internal passage, the protective sleeve being pressed against the internal surface and covering the annular area.

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

[0016] It can be easily introduced from inside the steam generator, the repair method therefore not requiring the removal of the external circulation conduit.

[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 introduced from the inside of the steam generator, without separating the outer end of the tubing from the external conduit;

[0019] - the method comprises, before the introduction step, a step of dismantling 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 provided 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 comprises a sealing ring surrounding the protective sleeve and in pressing 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 cuff has a central axis, the protective cuff having a slot extending over an entire axial length of the protective sleeve, 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 the external face, the lower edge having a lower recessed area hollowed out in the external face and the upper edge having an upper recessed area hollowed out in the internal face resting against the lower recessed area;

[0026] - the lower hollow 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 cuff is a helical spring, made of a wire having preferably a rectangular section;

[0028] - the protective sleeve has a central axis and comprises: - an outer split tube bearing against the inner surface of the tubing, the outer split tube having an outer slot extending over an entire axial length of the outer split tube, and

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

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

[0031] - the protective sleeve comprises a ring closing the gap between the tube external slot and the internal slotted tube and closing one end of the external slot;

[0032] - the protective sleeve comprises an anti-rotation lock, locking in rotation the inner split tube and the outer split tube relative to each other.

[0033] According to a second aspect, the invention relates to a steam generator of a nuclear reactor, the steam generator comprising an outer casing and a tube secured 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 fluid communication with the internal conduit through the thermal sleeve, the distal end extending against or in the immediate vicinity of an annular zone of the internal surface of the tube,the steam generator comprising a protective sleeve placed in the internal passage, the protective sleeve being pressed against the internal surface and covering the annular zone, the protective sleeve creating a seal between the distal end of the thermal sleeve and the internal surface.

[0034] Other characteristics and advantages of the invention will emerge from the detailed description given below, for information purposes only and in no way limiting, with reference to the appended figures, among which: - [Fig.l] [Fig.l] is an axial sectional view of the upper part of a steam generator; - [Fig.2] [Fig.2] is a sectional view of the steam generator of [Fig.l], taken according to the incidence of arrows II, only part of the internal duct being represented; - [Fig.3] [Fig.3] is an enlarged sectional view of the tubing and thermal sleeve of the steam generator of Figures 1 and 2, taken along the incidence of arrows III; - [Fig.4] [Fig.4] is a section of an upper part of the tubing and the thermal sleeve of [Fig.3], after fitting the protective sleeve; - [Fig.5] [Fig.5] is a top view of the protective sleeve of [Fig.4]; - [Fig.6] [Fig.6] is a sectional view of the protective sleeve of the [Fig.5], taken according to the incidence of arrows VI; - [Fig.7] [Fig.7] is a view similar to that of [Fig.4], showing a thermal sleeve used as a replacement for the original thermal sleeve, and showing a variant of the stop provided in [Fig.4] to block the protective sleeve in translation; - [Fig.8] [Fig.8] is a view similar to that of [Fig.4], showing a protective cuff according to a second embodiment of the invention; - [Fig.9] [Fig.9] is a perspective view of a protective sleeve according to a third embodiment of the invention; - [Fig. 10] [Fig. 10] is a top view of the protective sleeve of [Fig.9]; and - [Fig.l 1] [Fig.l 1] is a sectional view of a detail of the protective sleeve of figures 9 and 10, taken according to the incidence of arrows XI of [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 pressurized water nuclear reactor, conventionally, 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 into contact with the fuel assemblies of the core, then is directed to each of the steam generators. In each steam generator, it gives up part of its heat energy to the secondary heat transfer fluid.

[0039] The secondary heat transfer fluid is brought to the steam generator by a feed water supply pipe, designated by the acronym ARE. The secondary heat transfer fluid enters the steam generator in the liquid state and is vaporized under the effect of the heat energy received from the primary heat transfer fluid. It leaves the steam generator in the vapor state. The steam is then directed to a turbine in order to produce 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 external casing 3 and a tube 5 ([Fig.2]) integral with the external 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 is understood to mean an accessory by means of which the external conduit 9 is connected to the external casing 3. The tubing can also be designated by the term “piquage” in French or “nozzle” in English.

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

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

[0045] The steam generator 1 also comprises 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 an ARE torus.

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

[0048] The steam generator 1 also comprises 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 fluid 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 bundle envelope 11 delimits with the external 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, make it possible to distribute the secondary heat transfer fluid from the internal conduit 13 over the entire periphery of the annular passage 25. The secondary heat transfer fluid circulates downwards in the annular passage 25, and rises upwards inside the bundle envelope 11, in contact with the bundle of tubes.

[0052] The secondary heat transfer fluid escapes from the bundle casing 11 upwards, and passes inside a set of separators 29 and dryers 31, occupying the entire upper part of the external casing 3. The dry steam leaves the steam generator 1 through an outlet 33 provided at the top of the external casing 3, then circulates in the turbine, in the condenser before being returned to the steam generator 1 by 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 zone 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 portion 37 of the internal conduit 13 known as a T-connector.

[0055] This T-connector 37 comprises a branch 39 substantially radial with respect to the axis A, to which the proximal end 21 of the thermal sleeve is connected. It also comprises two circumferential branches 41 and 43. The circumferential branches 41 and 43 extend circumferentially around the 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 annular zone 35 and the distal end 23 of the thermal sleeve 19. This wear results in the formation of a hollow 44 in the annular zone 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 comprises 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 zone 35.

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

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

[0061] - a step of 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 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.

[0063] As illustrated in [Fig. 3], the thermal sleeve 19 is typically fixed to the internal conduit 13 by a removable fastener 49, for example a collar. The disassembly step comprises the following sub-steps: - Cutting of the T-fitting 37; - Separation of the thermal sleeve 19 and the T-fitting 37; - Moving the T-fitting 37 and storing it inside the ge 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 neighboring sections of the internal conduit 13, by cutting in two planes L shown in [Fig.2],

[0065] The thermal sleeve 19 is separated from the T-fitting 37 using the fastener mountable 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 from the tubing 5 on the inside of the steam generator 1, taking advantage of the volume released due to the evacuation of the T-connection 37.

[0067] The thermal sleeve 19 is evacuated from the steam generator 1 through a manhole in the case where it is not reused. In the case where it is reused, it is stored inside the steam generator 1, at 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 external casing 3 of the steam generator through a manhole, and put in place by taking advantage of the volume released due to the evacuation of the T-connection 37.

[0070] The protective cuff 45 is elastically compressible.

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

[0072] The section here is the cross 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 constrain the protective sleeve 45 and make it pass elastically from a rest section to a reduced section, smaller than the rest section. When the constraint is released, the protective sleeve 45 spontaneously returns to its rest 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 visible 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 over the entire length of the protective sleeve 45. Similarly, the upper edge 53 extends axially over the entire length of the protective sleeve 45. The edges 51 and 53 are free with respect 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 constitutes, circumferentially, one end of the tube. In the same way, the upper edge 53 constitutes circumferentially another end of the tube. These two ends partially overlap.

[0080] The lower edge 51 has a lower recessed area 59 hollowed out in the external face 55 of the cuff. This recessed area 59 is circumferentially delimited on one side by a side 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 comprises an upper recessed area 63 hollowed out in 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 side 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 has a slightly longer axial length than the upper edge 53. The lower hollow area 59 is closed at one axial end by an end wall 67. The lower hollow area 59 is open axially at its opposite end. The edge of the protective sleeve 45, at the upper edge 53, is pressed against the end wall 67.

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

[0084] In the example shown, the lower hollow zone 59 and the upper hollow zone 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 comprises a cover closing an axial end of the gap 69.

[0088] This cover is constituted 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 tube 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. [Fig. 6] shows the protective sleeve 45 in its resting state, in the absence of stress. The upper edge 53 is circumferentially spaced from the side wall 61. The lower edge 51 is circumferentially spaced from the side wall 65. When stress is exerted to reduce the 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 recessed area 59 and the upper recessed area 63 are hollowed out each about 50% of the thickness of the split tube.

[0091] Thus, the lower edge 51 and the upper edge 53 stacked on top of each 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 environment of the medium. It is made of a material having sufficient elasticity so that the sleeve can be stressed to a reduced section, and can return to its resting section elastically.

[0093] To place the protective sleeve 45 in the internal passage 15, this sleeve is forced to its reduced section, introduced into the internal passage 15, then the force is released, so that the protective sleeve 45 returns to its rest section. In doing so, the protective sleeve 45 comes to bear against the internal surface 17 of the tube 5.

[0094] As visible in [Fig.4], the protective sleeve 45 extends axially from the annular zone 35 to the end of the internal passage 15 opening into the interior of the steam generator.

[0095] The protective sleeve 45 completely covers the annular zone 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 casing 3 of the steam generator.

[0097] This surface S1 has a general shape in the form of a portion of a torus, and is particularly thermally fragile. It is protected by the protective sleeve 45.

[0098] When the original thermal sleeve 19 is reused, at the reassembly step, the thermal sleeve 19 is engaged inside the protective sleeve 45. Its distal end 23 comes to bear against the internal face 57 of the protective sleeve, at 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 zone 35. This makes it possible to create a seal between the thermal sleeve 19 and the internal surface 17 of the tubing 5.

[0099] Then, the T-connector 37 is reassembled on the internal conduit 13.

[0100] The tubular sections 41, 43 are re-welded onto the neighboring 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 fixing 49.

[0101] When the original thermal sleeve 19 is replaced by a replacement protective sleeve 47, the design thereof 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 its proximal end 72.

[0103] This proximal end 72 is designed to be welded onto the radial section 39 of the T-connector 37. This makes it possible to increase the rigidity of the connection, and to limit the vibratory instabilities of the thermal sleeve.

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

[0105] Then, the T-connector 37 is reassembled onto 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 in abutment against the stop 73, the opposite end 71 covers the annular zone 35 and the hollow 44.

[0108] The stop 73 is constituted by a relief projecting radially towards the outside of 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] The stop 73 extends circumferentially around the entire periphery of the cuff 19, 47.

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

[0112] Advantageously, the stop 73 comprises 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 comes to bear 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 tubing or towards the SI surface.

[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. Elements that are identical or provide the same function will be designated by the same references.

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

[0117] This helical spring is formed by a wire of rectangular section.

[0118] The helical spring has contiguous turns.

[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 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. Elements that are identical or provide the same function will be designated by the same references.

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

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

[0124] - 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 along an entire axial length of the internal split tube 89.

[0125] As 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 external split tube 85 has two rectilinear edges 93, parallel to each other, delimiting between them the external slot 87. The external slot 87 is therefore also rectilinear.

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

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

[0129] In the example shown, the recessed areas 95 form two parallel bands, extending circumferentially all around the outer split tube. When the cuff protection is in place in the tubing 5, the areas 97 of the external surface which are not hollowed out are in abutment against the internal surface 17 of the tubing. On the other hand, the hollow areas 95 are filled with a layer of water, thermally protective, 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 internal slotted tube. The edge 99 is rectilinear over most of its length, but forms a circumferentially projecting tab 103 at one axial end of the internal slot 91. The edge 101 is also rectilinear over 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 internal split tube 89 carries two circular beads 107. The beads 107 are formed at the two axial ends of the internal split tube 89. The external split tube 85 is arranged between the two beads 107, and is axially blocked in translation by the two beads 107.

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

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

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

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

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

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

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

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

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

[0141] It is also applicable to the tubing 115 visible in [Fig.2]. The tubing 115 makes it possible to connect the ASG circuit 118 to the internal conduit 117. The ASG circuit makes it possible the supply of emergency feedwater to the steam generator in the event of loss of the main power 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 in [Fig.2], arranged like the thermal sleeve 19.

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

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

[0145] It comprises 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 zone 35.

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

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

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

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

[0150] The repair method has multiple advantages.

[0151] Because the protective sleeve is introduced from the inside of the steam generator, it is not necessary to separate the external end of the tubing from the external conduit. This method is minimally intrusive and allows intervention exclusively from the inside of the steam generator.

[0152] The repair method is flexible, as 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 on 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 likely to be damaged or gouged, remains covered by the protective sleeve.

[0154] When the stop comprises a sealing ring surrounding the protective sleeve and bearing on the protective sleeve, the secondary heat transfer fluid which could be introduced between the protective sleeve and the thermal sleeve is blocked at the stop, and cannot flow towards the inside of the tubing.

[0155] Because the protective sleeve is elastically compressible, its application place 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 slot delimited between a lower edge and an upper edge covering the lower edge makes it possible to limit the leakage zone 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, the lower edge having a lower recessed area at the outer face and the upper edge having a higher recessed area at the lower face resting against the recessed area of ​​the lower edge, it is possible to give the protective sleeve a substantially constant thickness over its entire periphery. This makes it possible to guarantee a minimum leakage level 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, leakage along the gap is controlled.

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

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

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

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

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

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

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

[0167] When the protective sleeve includes an anti-rotation lock, the inner split tube and the outer split tube are locked in rotation relative to each other, which prevents the outer slot and the inner slot from coming into position alongside each other, which would have the effect of increasing leaks.

[0168] The repair method can have multiple variations.

[0169] The method has been described with the protective sleeve introduced from the inside of the steam generator. However, it would be possible to provide for the protective sleeve to be introduced from the outside of the steam generator, after separation of the external end of the tubing and the external conduit. In this case, it would not be necessary to dismantle the T-connector.

Claims

Claims

1. Method for repairing a tubing (5, 115) of a steam generator (1) of a nuclear reactor, the tubing (5, 115) being integral with an external casing (3) of the steam generator (1) and comprising an external end (7) connected to an external conduit (9, 118) for circulating a secondary heat transfer fluid, the tubing (5, 115) having an internal passage (15) delimited by an internal surface (17), the steam generator (1) comprising an internal conduit (13, 117) housed inside the external 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 tubing (5, 115), such that the internal passage (15) is in fluid communication with the internal conduit (13, 117) through the thermal sleeve (19, 119),the distal end (23) extending against or in close proximity to an annular zone (35) of the internal surface (17) of the tubing (5, 115), the method comprising a step of introducing a protective sleeve (45) into the internal passage (15), the protective sleeve (45) being pressed against the internal surface (17) and covering the annular zone (35).,

2. Method according to claim 1, in which the protective sleeve (45) is introduced from the inside of the steam generator (1), without separating the external end (7) of the tubing (5, 115) from the external conduit (9, 118).

3. A method according to claim 1 or 2, wherein the method comprises, before 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 inner 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 inner surface (17).

4. Method according to claim 3, in which 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).

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

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

7. A method according to any preceding claim, wherein the protective sleeve (45) is a split tube.

8. A method according to claim 7, 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).

9. A method according to claim 8, 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).

10. A method according to claim 9, 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).

11. Method according to any one of claims 1 to 6, in which the protective sleeve (45) is a helical spring, made of a wire preferably having a rectangular section.

12. A method according to any one of claims 1 to 6, wherein the protective sleeve (45) has a central axis (C) and comprises: - an outer split tube (85) bearing against the inner surface (17) of the tubing (5, 115), the outer split tube (85) having an outer slot (87) extending over an entire axial length of the outer split tube (85), and - an inner split tube (89) pressed against an inner side of the outer split tube (85), the inner split tube (89) having an inner slot (91) extending over an entire axial length of the inner split tube (89); the outer slot (87) and the inner slot (89) being circumferentially offset from each other around the central axis (C).

13. A method according to claim 12, wherein the protective sleeve (45) comprises a ring (107) closing the gap between the outer split tube (85) and the inner split tube (89) and closing one end of the outer slot (87).

14. A method according to claim 12 or 13, wherein the protective sleeve (45) comprises an anti-rotation lock (109), locking the inner split tube (89) and the outer split tube (85) in rotation relative to each other.

15. 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 outer end (7) connected to an outer conduit (9, 118) for circulating 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 inside 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 that the internal passage (5, 115) is in fluid 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 zone (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 zone (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).,

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