FR2638559A1 - Handling plant for a fast-neutron nuclear reactor - Google Patents

Abstract

The plant comprises, inside the vessel 10 of a fast-neutron nuclear reactor, a beam 54 capable of pivoting about a vertical axis offset in relation to the reactor core, and a trolley 60 movable on the beam and carrying a guide tube 62. A handling passage 36 situated above the slabs 12, 34 overhanging the vessel 10 and the neighbouring cells 30, 32 contains a stationary beam 66 on which a trolley 68 travels carrying a guide tube 70. This passage 36 is in communication with the vessel and the cells via passages 38, 40, 42. The transfer of an assembly 26 between the reactor core 14 and one of the cells 30, 32 is thus performed with the aid of a single grapnel 64 suspended from a cable 72 which is wound on a winch 74 placed at the end of the passage 36.

Description

Handling installation for a fast neutron nuclear reactor
DESCRIPTION
The invention relates to an installation for handling nuclear fuel assemblies, designed to be used in a fast neutron nuclear reactor.

 In fast neutron nuclear reactors, the reactor core is generally placed in a vessel with a vertical axis, closed at its upper end by a horizontal closing slab. This tank is usually filled with a liquid metal usually consisting of sodium, used to transfer the heat released in the reactor core to the intermediate heat exchangers which are placed either directly in the tank or outside of this, depending on whether it is an integrated type or a goat type reactor. The flow of Liquid metaL between the reactor core and the exchangers is ensured by pumps which can also be placed inside or outside the reactor vessel.

In known reactors, in particular of the integrated type, the handling of assemblies inside
The tank is generally ensured by means of a handling device such as a nerdy. This device is mounted in a small rotating plug, capable of turning in a large rotating plug rotatably supported by the closure slab of the tank, in the part of the latter overhanging the core of the reactor. The axes of the two rotating plugs are eccentric relative to each other, so that their combined rotation enables the handling equipment to be brought vertically to each of the nuclear fuel assemblies constituting the core and Vertical to an unloading station usually outside the latter.

 In these known integrated type reactors, the transfer of the assemblies between the unloading station and a cell located outside the reactor vessel is usually ensured by placing the assemblies in a transfer pot filled with sodium. This pot is suspended from a winch placed in an airlock overlapping both the tank and the cell, on inclined ramps plunging into the tank and into the cell from the airlock.

 In such a handling installation, the use of two nested and eccentric rotating plugs imposes a relatively large minimum diameter of the tank, in particular in the case of an integrated type reactor, by repelling the various components such as pumps and the exchangers beyond the periphery of the large rotating plug. The cost of the reactor is penalized appreciably.

 Furthermore, the transfer of assemblies between the core and the outer cell requires the use of a large number of components, which again penalizes the cost of the reactor.

 The subject of the invention is precisely a handling installation of a new type, designed so as to reduce the cost of the reactor both through a reduction in the diameter of the tank authorized by the elimination of rotating plugs and through a reduction the number of components involved in handling.

 According to the invention, this result is obtained by means of an installation for handling nuclear fuel assemblies, in a fast neutron nuclear reactor comprising a vessel closed by a horizontal closing slab and containing juxtaposed juxtaposed assemblies forming the core. of the reactor, this installation being characterized by the fact that it comprises a movable horizontal beam mounted in the tank, immediately under the slab, means for pivoting this beam around a vertical axis offset relative to the reactor core, a first carriage mounted on the mobile beam and carrying a first vertical guide tube, means for moving the first carriage along the mobile beam, a gripping gripper of an assembly, capable of moving inside the first tube guide, and means for moving this grapple inside the first guide tube.

In an installation thus designed, the components which must be present in the tank can be suspended from the closing slab in the immediate vicinity of the core, in particular in the zones situated on the sides of the zone swept by the mobile beam. The diameter of
The tank can thus be reduced compared to conventional installations using rotating plugs. In addition, the removal of these plugs is in itself an appreciable simplification.

 According to a particularly advantageous improvement of the invention, the installation further comprises at least one cell external to the tank and surmounted by a second horizontal slab extending said closing slab; a handling corridor connecting a first zone located above a handling channel centered on said vertical axis and passing through the closure slab, and a second zone located above a channel for access to said cell , crossing the second slab; a fixed horizontal beam mounted in the handling corridor; a second carriage mounted. on the fixed beam and carrying a second vertical guide tube; and means for moving the second carriage along the fixed beam; said means for moving The grapple for moving the latter also in the second guide tube and comprising a winch placed near an end of the handling corridor adjacent to the second zone, and a flexible member connecting the grapple to the winch.

 Thanks to this improvement, a single winch is used to transfer each assembly between the reactor core and the outer cell. In addition, the transfer lock, the ramps and the unloading station located in the tank to ensure the installation of the assembly in the transfer pot are eliminated. The handling installation is therefore significantly simpler and less expensive.

 Advantageously, the handling corridor provides access to both a washing cell for irradiated assemblies and to an arrival cell for new assemblies by two access channels.

 Usually, a fast neutron reactor comprises a plug-cover-core suspended from the closure slab, above the reactor core, and containing in particular the reactor control bars as well as thermocouples used to measure the temperature at the outlet. of the heart. In this case, the handling installation according to the invention further comprises a removable hood capable of being fixed in a sealed manner on the closing slab and comprising a lifting means making it possible to retract the plug-cover-core at the inside of this hood during handling.

 According to a preferred embodiment of the invention, the mobile beam is fixed, near one of its ends, on a vertical structure tube centered on the pivot axis of the beam and rotatably mounted in your closing slab, The means for rotating the mobile beam acting on a part of the structural tube located above The closing slab, the other end of the mobile beam being supported by an arcuate track fixed circle under this slab.

A preferred embodiment of the invention comprising different variants will now be described, by way of nonlimiting example, with reference to the appended drawings in which:
- Figure 1 is a side view, showing in section and schematically a handling installation according to the invention;
- Figure 2 is a top view schematically showing the part of the installation located inside the reactor vessel;
- Figure 3 is a top view comparable to Figure 2, showing a larger scale the control of the different movements of the carriage placed in the reactor vessel;
- Figure 4 is a vertical sectional view showing, according to a first variant of the embodiment illustrated in the figures, the part of the installation making it possible to transfer the assemblies from the interior of the tank to the corridor handling overhanging the slab;
- Figure 5 is a sectional view comparable to Figure 4 illustrating in more detail the control of the various movements of the carriage, the beam and the guide tube placed in the reactor vessel, according to the first variant;
- Figure 6 is a sectional view comparable to Figure 5 illustrating a second alternative embodiment of the invention; and
- Figure 7 is a sectional view schematically showing the retraction of the cap-cover louver in a removable hood placed on the cover slab of the reactor vessel.

 FIG. 1 shows diagrammatically the whole of a handling installation according to the invention, located in a nuclear reactor with fast neutrons of the integrated type. This reactor comprises, in known manner, a tank 10 of vertical axis closed at its upper end by a horizontal closing slab 12. it is important to note that in order to facilitate the exposure, the tank 10 and the closing slab 12 have been illustrated exploded in FIG. 1.

 The main components located inside the vessel 10 are identical to the components usually found in fast neutron nuclear reactors. This is the reason why these components are shown very schematically and will now be described only very briefly.

 These main components include the reactor core 14, usually centered on the vertical axis of the tank 10, and an internal tank 16 delimiting inside the tank 10 a hot collector 18 situated mainly above the heart 14 and a cold collector 20 located mainly below and around the core of the reactor. The tank 10 is filled with a liquid metal generally consisting of sodium, up to the proximity of the closing slab 12. In the space formed around the core 14 inside the tank 10 are placed primary pumps 22 and heat exchangers 24 suspended from the closure slab 12 and agencies so that, under the impulse of the pumps 22, the hot liquid metal leaving the core 14 through the neck Warm reader 18 passes through the exchangers 24, then comes out in the cold collector 20 before being reinjected into the lower part of the heart 14.

 To complete this brief description of the integrated fast nuclear neutron reactor illustrated very schematically in FIG. 1, it is recalled that the core 14 of this reactor is formed by a number of nuclear fuel assemblies 26 arranged side by side in a vertical position.

 In addition, the core 14 is usually surmounted by an assembly 28, called a plug-cover-core, one of the functions of which is to allow the displacement control and the guidance of the control rods used to control and stop the reactor. . The heart-cover cap 28 also serves to support, in the immediate vicinity of the upper end of the heart 14, measurement systems such as thermocouples. it is suspended from the closing slab 12 of the reactor and occupies, during the operation of the reactor, the zone of the hot collector 18 situated between the core 14 and the closing slab 12, vertical to the central part of the core. In FIG. 1, the plug-cover-core 28 is shown in the position it occupies during the handling of the assemblies 26.

 A facility for handling nuclear fuel assemblies 26 equipping such a reactor will now be described.

 The handling installation according to the invention makes it possible, in the usual way, to transfer the nuclear fuel assemblies 26 irradiated in the core 14 of the reactor from this core 14 to a cell 30 external to the vessel 10 of the reactor and constituted, for example, by a washing cell. Conversely, it also makes it possible to transfer new assemblies into the core 14 of the reactor from a cell 32 also located outside of the tank 10 and being for example in the form of a corridor located entered the building containing the tank 10 and the washing cell 30. The cells 30 and 32 are surmounted by a horizontal slab 34, the upper face of which is approximately at the same level as the upper face of the closing slab 12 of the tank 10 of the reactor.

In order to allow the transfer of the assemblies between the interior of the reactor vessel 10 and one or
The other of cells 30 and 32, a handling corridor 36 is formed above the slabs 12 and 34. The corridor 36 thus connects an area located above a handling channel 38 crossing the closing slab 12 of the reactor with an area located above an access channel 40 crossing the slab 34 and opening into the washing cell 30, passing through an area located above an access channel 42 also crossing the slab 34 and opening into the corridor 32. The handling channel 38 passes through the closing slab 12, in a peripheral part thereof situated between two of the components such as the pumps 22 and the exchangers 24 suspended from the wall 12 in this zone .

 The handling corridor 36 is preferably rectilinear and it contains a controlled atmosphere, at a reduced oxygen rate, as do the cells 30 and 32.

 In order to ensure satisfactory biological protection above the closing slab 12 during the operation of the reactor, a steel plug 44 is normally placed in the handling channel 38. This plug is retracted inside the corridor 36 during handling using a suitable lifting device of any type, shown diagrammatically at 46 in FIG. 1. Furthermore, the tightness of the handling channel 38 is guaranteed during the operation of the reactor, thus - that during handling by a valve 48 such as a slide valve placed in the corridor 36.

 Valves 50 and 52 such as slide valves, also placed in the corridor 36, make it possible to close, respectively, the access channels 40 and 42 respectively when the reactor is in operation, and during certain phases of handling.

 The handling devices which constitute the main part of the installation according to the invention will now be described always with reference to FIG. 1.

 These devices firstly include, inside the vessel 10 of the reactor, a movable horizontal beam 54 which is located immediately below the closure slab 12, in the sky of neutral gas overhanging the liquid metal contained in the tank 10. This beam 54 is fixed, near one of its ends, to a vertical structure tube 56 passing through the closure slab 12 and by which the beam 54 is suspended from this slab so that it can pivot around the vertical axis of this tube 56. The structure tube 56 is itself traversed along its axis by the handling channel 38. The structure tube 56 is supported by the slab 12, in the corridor 36, by a crown with balls, and sealing is ensured by inflatable or lip seals.

 In order to ensure its support and its guidance, the opposite end of the movable beam 54 is equipped with rollers 54b (FIG. 2) which roll on a raceway 58 in an arc centered on the vertical axis of the structural tube 56 and fixed under the closing slab 12. The center of the raceway 58 is located at a location approximately diametrically opposite to the structural tube 56, relative to the vertical axis of the tank 10. In addition, the movement of the movable beam 54 around its vertical pivot axis is chosen so that a carriage 60 able to move along this beam can be placed vertically with any of the assemblies 26 constituting the core 14 of the reactor.

A total deflection of around 45 allows, for example, to achieve this result.

 The carriage 60 supports a guide tube 62, of vertical axis, which projects downwards to a level slightly higher than that of the upper end of the core 14. A grapple 64 designed to grip one of the assemblies 26 can be received in the guide tube 62 and move out of it, in a manner which will be described later.

 To these handling instruments located in the reactor vessel 10 are added handling instruments located in the handling corridor 36. These instruments include a fixed horizontal beam 66 passing vertically from each of the channels 38, 40 and 42, near the ceiling of the corridor 36. A carriage 68 is mounted on the fixed beam 66 so that it can move along the latter. The carriage 68 supports a guide tube 70, of vertical axis, which projects downwards to a level slightly higher than the upper face of the valves 48, 50 and 52. Like the guide tube 62, the guide tube 70 has a length allowing it to receive the gripping grapple 64 and an assembly 26 suspended from this grapple. The movements of the carriage 68 make it possible to bring the guide tube 70 in the extension of the handling channel 38 and in the extension of the access channels 40 and 42.

According to a particularly economical characteristic, the same grapple 64 is used in the guide tubes 62 and 70, which ensures all of the transfer of the irradiated assemblies from the core 14 of the reactor to the washing cell 30 as well as the transfer of new assemblies from lane 32 to core 14 using this single grapple. To this end,
The grapple 64 is suspended from a cable 72, the opposite end of which is wound on the drum of a winch 74 mounted at the end of the handling passage 36 overhanging the washing cell 30. This winch 74 is located more precisely. in the extension of the beam 66, so that its drum is placed inside the corridor 36 and that the geared motor controlling the rotation of the drum is placed outside this corridor, in the external atmosphere. The control shaft by which the gear motor actuates the drum crosses the wall of the corridor 36, by means of a system of rotating joints.

 From the winch drum 74, the cable 72 runs horizontally along the beam 66 to a deflection pulley 76 carried by the carriage 68. The cable 72 then travels vertically inside the guide tube 70. When the grapple 64 is placed in the guide tube 62 and when the latter is not placed in the extension of the handling channel 38, as illustrated in FIG. 1, the cable 72 descends inside this latter channel up to to a return pulley 78 mounted on the movable rail 54. The cable 72 then travels horizontally along the latter to a return pulley 80 carried by the carriage 60, beyond which the cable 72 descends into the tube guide 62 to grapple 64.

 In the embodiment shown in the figures, the gripping of an assembly 26 by the grapple 64 is carried out by means of a bayonet type system requiring rotation of the grapple. In this case, the cable 72 is a simple cable and the gripping is ensured by a rotation of the guide tubes 62 and 70 relative to the carriages 60 and 68 which support them. This solution is not, however, limiting, the grapple 64 can also include an electromagnet ensuring gripping. In this case, the cable 72 includes electrical conductors.

 To control the movement of the carriage 68 along the fixed beam 66, any suitable means can be used. By way of example, the beam 66 can support over its entire length an endless screw, engaged on a nut mounted in the carriage 68. Any rotation of the endless screw, controlled by a geared motor preferably located outside of the corridor 36, then makes it possible to move the carriage 68 at will in one and the other direction along the fixed beam 66.

 In practice, the fixed beam 66 may in particular be formed of two parallel rails on which rest the wheels fitted to the carriage 68.

 As illustrated in FIGS. 2 and 3, the structures of the movable beam 54 and of the carriage 60 are essentially comparable to those of the beam 66 and of the carriage 68. Thus, it can be seen in FIG. 2 that the beam 54 is formed by two parallel horizontal rails 54a on which two pairs of wheels 60a of the carriage 60 roll. Also seen in this figure are the rollers 54b mounted at the end of the beam 54 and resting on the path of the bearings 58.

 As illustrated in particular in FIGS. 2 and 3, one of the rails 54a supports an endless screw 82 which is engaged on a nut 84 fixed on the carriage 60. By controlling the rotation of the endless screw 82 according to the one or the other of two variant embodiments which will be described later, the carriage 60 is therefore moved along the movable beam 54.

 The other rail 54a also supports over its entire length a drive square 86 along which a nut 88 can slide freely secured in rotation with the drive square 86. The nut 88 is immobilized in translation relative to the carriage 60 and has on its outer surface the shape of an endless screw on which is meshed a toothed wheel 90 whose axis is mounted on the carriage 60. A rotation of the toothed wheel 90 is transmitted to the guide tube 62, so supported rotating by the carriage 60, by a pinion system 92. Thanks to this arrangement, when the entrainment square 86 is driven in rotation in one or the other direction from control means produced according to the either of two variants which will be described later, a rotation of the guide tube 62 about its axis is ensured. Given that the grapple 64 is immobilized in rotation in the guide tube 62, the gripping or on the contrary the release of an assembly 26 is achieved by this grapple when it is in the guide tube 62. On the other hand, this arrangement prevents a movement of the carriage 60 along the beam 54 resulting in a rotation of the guide tube 62.

According to a first alternative embodiment of the invention illustrated in particular by FIGS. 4 and 5,
The controls for rotation of the worm 82 and of the drive square 86 are placed above the handling corridor 36, vertical to the structure tube 56.

 In this first variant, the upper partition of the corridor 36 comprises a rotating plug 94 situated vertically from the structural tube 56. This rotating plug 94 is secured in rotation to the tube 56 by a connecting piece 95 and supports, outside of the corridor 36, two geared motors 96 and 98 used to respectively control the rotationally entrainment of the worm 82 and the entrainment square 86. For this purpose, the output shaft of each of the geared motors 96, 98 is in taken by bevel gears 97, 99 on a tree. vertical 100, 102 passing tightly through the plug 94 and the support tube 56 by systems of rotating joints. Conical pinions 101, 103 (FIGS. 3 and 4) ensure below the structure tube 56 the transmission of the rotational movements of the shafts 100 and 102 respectively with the worm 82 and the drive square 86. Since these two sets are identical, only one of them has been shown in FIGS. 4 and 5.

 In the variant embodiment shown in FIGS. 4 and 5, the rotary plug 94 supports a third geared motor 104 used to control the slide valve 48 mounted on the structural tube 56. This control is carried out by means of a vertical shaft 106 sealingly passing through the plug 94 and the ends of which are meshed respectively on the output shaft of the gearmotor 104 and on the control shaft of the slide valve 48 by bevel gears 105 and 107.

 In addition (FIG. 5), a fourth geared motor 108 is mounted outside the passage 36, on the upper partition thereof, in order to control, by means of the plug 94 and the structural tube 56, the rotation of the movable beam 54 around its vertical pivot axis which corrides with the axis of the plug and the tube. To this end, the output shaft of the gearmotor 108 carries a pinion 110 meshed with a rack 112 formed on the periphery of the plug 94.

 In an alternative embodiment not shown, the plug 94 and the structural tube 56 may have no connecting structure. In this case, the output shaft of the gearmotor 108 sealingly crosses the upper partition of the handling corridor 36 and comprises at its lower end a second pinion similar to the pinion 110 and meshing on a rack similar to the rack 112, formed at the periphery of the structural tube 56, above the slab 12.

 In a second variant embodiment of the invention illustrated in FIG. 6, all of the controls which are placed outside the handling corridor 36 in the first variant are placed inside the corridor and supported directly by the structural tube 56.

 Thus, this structural tube 56 supports on its upper face two geared motors 96 'and 98' which directly control the rotations of the worm 82 and of the drive square 86 by vertical shafts 100 'and 102' passing tightly the tube 56 whose ends are respectively engaged on the output shafts of the gearmotors and on the worm and the drive square by means of bevel gears 97 ′, 99 ′ and 101, 103.

 The structural tube 56 also supports on its upper face a geared motor 104 ′ directly controlling the slide valve 48.

 Finally, in this second variant embodiment, the rotation of the movable beam 54 is ensured by a fourth geared motor 108 ′ also mounted on the upper face of the structural tube 56 and whose output shaft carries a pinion 110 ′ which s meshes with a crack in an arc 112 'mounted on the slab 12 around the tube 56.

 In this case, the geared motors 96 ', 98', 104 'and 108' can be placed in a sealed and ventilated casing 113.

 In the usual case described above with reference to Figure 1 or the reactor comprises a cover-core plug 28 occupying the space located immediately above the core 14 inside the tank 10, the presence of this cover cap - heart prevents any handling. Consequently, as illustrated in FIGS. 1 and 7, it is then necessary to retract the plug-cover-core 28 upward to clear the abovementioned space, when a handling campaign is to take place.

 For this purpose, there is then placed above the closing slab 12, in the central zone thereof comprising the plug-cover-core 28, a removable hood 114. This hood is equipped at its upper part with a attachment piece 114a allowing its handling using the traveling crane usually located in the reactor building. Its lower end can be fixed in a leaktight manner on the closure plate 12 by any suitable means.

In its upper part, the hood 114 is equipped with a winch 116 making it possible to hoist the hood in a position illustrated in FIG. 7, in which
The lower end of the plug-cover-core is located approximately at the same level as the lower face of the closure slab 12. The handling of the plug-cover-core 28 using the winch 116 is facilitated by placing on the upper face of the plug 28 a removable attachment piece 118.

The hood 114 is internally equipped, in the immediate vicinity of its lower mouth, with inflatable seals 120 whose swelling bring them into leaktight abutment against the outer surface of the core-cap 28. Other inflatable seals 122 are also placed inside of the hood 114 at a level slightly higher than the trace 124 left by the liquid metal on the plug-cover-core during the operation of the reactor, when the plug-cover-core is fully retracted in the hood. These inflatable seals 122 can also be brought into tight contact with
The outer surface of the cap-cover-core. Appropriate means allow a neutral gas such as argon to circulate in the two zones of the hood separated by the inflatable seals 122.

 In order to reduce the height of the removable hood 114 as much as possible, the control bar mechanisms, the thermocouple outlets and the other equipment located on the plug-cover-core 28 are of the buried type.

 Furthermore, the hood 114 can be used, thanks to the addition of an airlock, to dismantle the plug-cover when necessary.

 In the light of the above description, the implementation of the handling installation according to the invention will now be described.

 When a handling campaign has to be carried out, the plug-cover-core 28 is initially retracted inside the hood 114, previously fixed on the closing slab 12.

 The plug 44 is then removed using the devices 46 and the valve 48 open. Under these conditions, each of the guide tubes 70 and 62 is placed vertical to the handling channel 36 and the grapple 64 which was previously inside the guide tube 70 is lowered into the guide tube 62 by means of the winch 74.

 By the combination of the rotational movements of the beam 54 around its vertical axis and of translation of the carriage 60 along this beam, the guide tube 62 containing the grapple 64 can be brought to the vertical of any of the assemblies 26 of the heart to evacuate.

After a descent of the grapple to this assembly, a rotation of the guide tube and, consequently, of the grapple ensures the gripping of this assembly. The grapple 64 is then raised in the guide tube 62, as well as
The assembly 26 which it supports, still thanks to the winch 74.

 The carriage 60 is then brought again to the vertical of the handling channel 38 in order to allow the grapple 64 raising the assembly 26 to be evacuated into the guide tube 70. By bringing the guide tube 70 to the vertical of the access 40 by a translation of the carriage 68 along the beam 66, the assembly 26 can be lowered suspended from the grapple 64 in the washing cell 30, always by actuating the winch 74. The complete transfer of the assembly is thus carried out from the heart to the washing cell using a single grapple and winch.

 The transfer of a new assembly from the corridor 32 to the core 14 of the reactor is carried out in a comparable manner, by carrying out the operations described above in reverse order. This transfer is therefore also carried out using the same grapple 64 and the same winch 74.

 Of course, during the various movements of the carriages 60 and 68, the grapple 64 must remain fixed relative to the guide tube 62 or 70 in which it is located.

To this end, different techniques can be used. One can in particular use a winch whose cable has a constant tension thanks to mechanical means such as a spring or a counterweight. The winch can also be controlled by cable tension. Finally, it is possible to program the movements of the winch according to the location of the assembly whose transfer is carried out.

 To allow, if necessary, an intervention on the delicate parts of the installation located inside the vessel 10 of the reactor, the structural tube 56 is preferably removable and its outer envelope is greater than that of the carriage 60, teLle so that the latter can be evacuated with the tube 62 above the slab 12. In addition, removable plugs (not shown) can be provided in the slab 12.

In the event of a major incident, the removal of the plug-cover-core 28 would allow easier intervention.

 The above description clearly shows that the handling installation according to the invention comprises a reduced number of components appreciably limiting the cost of the installation. In addition, the use of a pivoting movable arm 54 inside the vessel 10 of the reactor makes it possible to eliminate the system of revolving plugs usually used and, consequently, to place the components such as the exchangers 24 and the pumps 22 in the immediate vicinity of the reactor core 14 (see FIG. 2). The diameter of your tank 10 can therefore be reduced, which also significantly reduces the cost of the reactor.

 Of course, the invention is not limited to the embodiment which has just been described by way of example, but covers all the variants thereof. In particular, it is clear that the devices making it possible to control the various movements of the carriages, the guide tubes and the movable arm may be different from those which have been described (for example, of the pinion-rack or chain-pinion type). Furthermore, the use of a grapple comprising an electromagnet makes it possible to use a guide tube 62 integral with the carriage 60. In addition, it is clear that a handling installation in accordance with the invention can be used on a reactor with fast neutrons of the loop type in which the exchangers at least are killed outside of the vessel 10 containing the reactor core. Finally, it should be noted that the handling installation according to the invention can be used to serve two reactors, by extending the handling corridor 36, on the side of the winch 74, up above the handling channel 56 of a second reactor.

Claims (10)

 1. Installation for handling nuclear fuel assemblies, in a fast neutron nuclear reactor comprising a tank (10) closed by a horizontal closure slab (12) and containing juxtaposed assemblies forming the core (14) of the reactor, this installation being characterized by the fact that it comprises a movable horizontal beam (54) mounted in the tank, immediately under the slab, means (108, 108 ') for pivoting this beam around a vertical axis offset from the reactor core, a first carriage (60) mounted on the mobile beam and carrying a first vertical guide tube (62), means (96.96 ') for moving the first carriage along the mobile beam, a gripping grapple (64) of an assembly, capable of moving inside the first guide tube, and means (74) for moving this grapple inside the first guide tube.  2. Installation according to claim 1, characterized in that it further comprises at least one cell (30,32) external to the tank and surmounted by a second horizontal slab (34) extending said closing slab; a handling corridor (36) connecting a first zone located above a handling channel (38) centered on said vertical axis and passing through the closure slab, and a second zone located above a channel access (40,42) to said cell, crossing the second slab; a fixed horizontal beam (66) mounted in the handling corridor; a second carriage (68) mounted on the fixed beam and carrying a second vertical guide tube (70); and means for moving the second carriage along the fixed beam; said means for moving the grapple (64) making it possible to move the latter also in the second guide tube and comprising a winch (74) placed near an end of the handling corridor adjacent to the second zone, and a flexible member (72 ) connecting the grapple to the winch.  3. Installation according to claim Z, charac terized in that it comprises closing means (44,48,50,52) of the handling channel (38) and the access channel (40,42).  4. Installation according to any one of claims 2 and 3, characterized in that the handling corridor (36) provides access to a washing cell (30) of irradiated assemblies and to an inlet cell ( 32) of new assemblies by two access channels (40,42).  5. Installation according to any one of claims 2 to 4, characterized in that the winch (74) comprises a gearmotor placed outside the handling corridor (36), a drum placed in the corridor and a shaft control unit connecting the gearmotor to the drum and crossing a wall of the corridor in a sealed manner.  6. Installation according to any one of claims 1 to 5, characterized in that, the reactor comprising a plug-cover-core (28) normally placed in the tank (10) above the reactor core, this installation further comprises a removable hood (114) capable of being fixed in a sealed manner on the closing slab, this hood comprising a lifting means (116) making it possible to retract the plug-cover-core inside the hood During handling.  7. Installation according to claim 6, characterized in that the hood (114) is internally equipped with inflatable seals (120,122) at a level located immediately above a lower opening of the hood and at a level located immediately at -above an immersed part of the plug-cover-core, when the latter is retracted into the hood.  8. Installation according to any one of the preceding claims, characterized in that the soft beam (54) is fixed, near one of its ends, on a vertical structure tube (56) centered on said vertical axis, and rotatably mounted in the closing slab (12), the means (108,108 ') for pivoting the mobile beam around said axis acting on a part of the structural tube situated above the closing slab, the other end of the movable beam (54) being supported by a raceway (58) in an arc fixed under the closing slab.  9. Installation according to claim 8, characterized in that the structural tube (56) is removable and has an outer casing greater than that of the first carriage (60), so that the latter can be dismantled with the vertical tube , when placed below it.  10. Installation according to any one of the preceding claims, characterized in that the gripping gripper (64) is immobilized in rotation in the first guide tube (62), means (98.98 ') being provided for controlling a rotation of the latter about its vertical axis.