ZA200906977B

ZA200906977B - Method for recovering at least one fuel assembly which has remained engaged below an upper plate of a core of a pressurized water nuclear reactor

Info

Publication number: ZA200906977B
Application number: ZA200906977A
Authority: ZA
Inventors: Laurent Cahouet; Steve Eschalier; Frederic Buchot; Jean-Yves Ginda; Christophe Parize
Original assignee: Areva Np
Priority date: 2008-10-16
Filing date: 2009-10-07
Publication date: 2010-07-28
Also published as: FR2937457B1; FR2937457A1

Description

1 conser oo 1

Method for recovering at least one fuel assembly which has remained engaged below an upper plate of a core of a pressurised water nuclear reactor

The present invention relates to a method for recovering at least one fuel assembly which has remained engaged below an upper plate of a core of a pressurised water nuclear reactor during handling of the upper internal pieces of equipment of the reactor.

The pressurised water nuclear reactor comprises, inside the building of the reactor, a vessel which contains the core of the nuclear reactor constituted by fuel assemblies, which are generally of regular prismatic form and which are arranged in a vertical and juxtapositioned manner.

There are arranged inside the vessel of the nuclear reactor internal pieces of equipment which particularly ensure the support and retention of the fuel assemblies of the core of the nuclear reactor.

A first group of internal pieces of equipment ensuring the support and lateral retention of the fuel assemblies constitutes the lower internal pieces of equipment and a second group ensuring the retention of the fuel assemblies in the vertical direction, that is to say, in the axial direction of those assemblies, and the guiding of the control rods for the reactivity of the core, constitutes the upper internal pieces of equipment.

The upper internal pieces of equipment comprise in particular, at the lower portion thereof, a plate which is intended to be supported on the upper portions of the fuel assemblies, the plate being referred to as the upper core plate.

The upper core plate comprises, projecting relative to its lower face which is intended to be supported on the upper portions of the fuel assemblies, that is to say, on the upper nozzles of those fuel assemblies, centring and positioning pins which are intended to become engaged in the openings of the upper nozzles of the fuel assemblies.

Generally, the upper core plate comprises two facing pins for guiding each of the fuel assemblies, which pins are intended to be introduced into two generally square openings of the upper nozzle, arranged along a diagonal of the nozzle.

During operation of the nuclear reactor, the fuel of the assemblies of the core is subject to given wear so that it is necessary to periodically replace the assemblies of the core of the nuclear reactor.

Therefore, operations are periodically carried out for recharging a portion of the core of the nuclear reactor. To that end, a cold shutdown of the reactor is carried out and the cover which closes the upper end portion of the vessel, in which the core of the nuclear reactor is positioned, is disassembled. The end portion of the vessel covered by the cover opens into the bottom of the cavity of the nuclear reactor, which is filled with water so that it is possible to carry out the operations for recharging the core below a depth of water sufficient to protect operators.

In order to be able to access the fuel assemblies of the core, after the cover of the vessel has been opened, it is necessary to remove the upper internal pieces of equipment which cover the upper portion of the core. The upper internal pieces of equipment of the nuclear reactor are fixed to a support which can be taken up by a handling means, such as the polar crane of the nuclear reactor, for its lifting and handling. It is thereby possible to position the upper internal pieces of equipment on a stand for storing those pieces of equipment that is located in the cavity of the nuclear reactor.

During an operation for lifting and handling the internal pieces of equipment of the pressurised water nuclear reactor, it may be the case that at least one fuel assembly of the core accidentally remains engaged with the upper core plate of the upper internal pieces of equipment so that it is not possible to continue the operation for handling the upper internal pileces of equipment as far as an operation for positioning the pieces of equipment on a storage stand at the bottom of the cavity.

Accidental engagement of at least one fuel assembly below the upper core plate of the upper internal pieces of equipment may occur when one of the pins for centring the upper core plate has been deformed, for example, during a preceding operation for handling the upper internal pieces of equipment. In that case, the centring pin may become blocked inside the opening of the nozzle of the fuel assembly whose positioning it ensures.

An object of the invention is to provide a method which allows recovery of at least one fuel assembly which has remained engaged below the upper core plate in order, on the one hand, to prevent the at least one assembly from falling into the vessel of the reactor when it is separated from the upper internal pieces of equipment, and, on the other hand, to be able to remove it for storage in a storage rack.

Therefore, the invention relates to a method for recovering at least one fuel assembly which has remained engaged below an upper plate of a core of a pressurised water nuclear reactor, the reactor comprising, in a cavity containing water, a vessel which is provided at its upper portion with a flange and which contains the core of the reactor constituted by vertical, juxtapositioned fuel assemblies, upper internal pieces of equipment which are provided so as to be supported on the upper portion of the core by the upper core plate and which comprise centring pins which are intended each to engage in an opening which is provided at the upper portion of a fuel assembly, and means for lifting and handling the upper internal pieces of equipment, characterised in that, after the presence of the at least one fuel assembly which has remained engaged below the upper core plate has been detected, when the upper internal pieces of equipment are lifted, a) the at least one fuel assembly is secured and retained under water by means of a group of securing tools in abutment against the flange of the vessel, and at least the following main steps are carried out under water: b) the remote disengagement of the at least one fuel assembly from the upper core plate is carried out by means of at least one unblocking tool jack, c) the upper internal pieces of equipment are transferred and they are positioned on a receiving stand which is provided in the water-filled cavity, d) the at least one spent fuel assembly is removed towards a storage zone in order to position it in a suitable receiving device, and e) the securing tools are removed after they have been separated from the at least one fuel assembly.

According to other features of the invention: - after the steps a), b) and c) have been carried out: - a handling tool is moved above the at least one fuel assembly and the handling tool is locked to the at least one fuel assembly, - the at least one fuel assembly is lifted by a few millimetres by means of the handling tool, ~ the securing tools are disconnected from the at least one fuel assembly, - the at least one fuel assembly is lifted vertically, and - the steps d) and e) are carried out, - after the steps a), b) and c) have been carried out: - a handling tool is moved above the at least one fuel assembly and the handling tool is locked to the at least one fuel assembly, - the at least one fuel assembly and the securing tools are lifted, ~- the step d) is carried out with the securing tools which are fixedly joined to the at least one fuel assembly, ~ the securing tools are disconnected from the at least one fuel assembly, and - the step e) is carried out, - after the step a) has been carried out: - the step c¢) is carried out with the securing tools and the at least one fuel assembly, - the at least one fuel assembly is lowered and engaged in a suitable receiving device, and - the steps b) and e) are carried out,

- for two fuel assemblies which have remained engaged below the upper core plate: + = each fuel assembly is disengaged, remotely and successively, from the upper core plate by means of the at least one unblocking tool jack, - the first fuel assembly is lifted by a few millimetres by means of the handling tool, - the first fuel assembly is disconnected from the securing tools, - the first fuel assembly is lifted and removed, - the second fuel assembly is lifted by a few millimetres by means of the handling tool, - the second fuel assembly 1s disconnected from the securing tools, - the second fuel assembly is lifted and removed, and - the securing tools are removed.

The invention and its advantages will be better understood from a reading of the following description which is given by way of example and with reference to the appended drawings, in which: - Figure 1 is a schematic axial section through a vessel of a nuclear reactor containing the core and the internal structures of the reactor, - Figure 2 is a schematic front elevation of a fuel assembly, - Figure 3 is a general view of the cavity of the nuclear reactor, in the initial phase for lifting the upper internal pieces of equipment during a cold shutdown of the reactor, - Figure 4 is a schematic perspective view of part of a group of tools for securing at least one fuel assembly which has remained engaged below the upper core plate of the nuclear reactor, - Figure 5 is a side elevation of a tool which is used for carrying out the separation of the fuel assembly from the upper core plate of the nuclear reactor, and - Figures 6 and 7 are schematic elevations of the cavity of the nuclear reactor and show a variant of the steps for recovering a fuel assembly which has remained engaged below the upper core plate of the nuclear reactor.

Figure 1 illustrates a vessel of a pressurised water nuclear reactor which is generally designated 1.

The vessel 1 which is generally of cylindrical shape is formed at its lower portion by a curved bottom and comprises an upper end which is closed, when the nuclear reactor is operating, by a curved cover la.

The vessel 1 contains the core 2 of the reactor, constituted by the fuel assemblies 7 (Figure 2) which are generally of prismatic shape and which are arranged in a vertical and juxtapositioned manner inside the internal structures which are generally designated 3, the internal structures constituting the lower internal pieces of equipment of the nuclear reactor.

The lower internal pieces of equipment 3 particularly comprise a core support plate 3a, a core casing 3b and a baffle assembly 3c for laterally retaining the core 2 of the nuclear reactor. A second internal structure assembly 4, which is referred to as the upper internal pieces of equipment of the nuclear reactor, is supported on the upper portion of the core 2.

The upper internal pieces of equipment 4 particularly comprise a lower plate 4a, by means of which the upper internal pieces of equipment are supported on the upper portion of the core 2 and which is referred to as the upper core plate. The upper internal pieces of equipment further comprise a very thick upper plate 4b which constitutes the : support plate for the guide tubes of the control rods of the nuclear reactor. Core support columns 4c bring about the assembly and the support of the mutually parallel plates 4a and 4b which are positioned horizontally in the nuclear reactor.

Tubes 5, which are in a vertical arrangement and which are referred to as adaptors which are used to bring about the passage of extension pieces for moving control clusters in some of the core assemblies, extend through the cover la of the vessel 1. The extension pieces and the control clusters of the nuclear reactor are moved inside guiding tubes 6 .which constitute components of the upper internal pieces of equipment 4. The guiding tubes 6 comprise an upper portion 6a which is supported on the upper plate 4b of the upper internal pieces of equipment 4 and a lower portion 6b which is interposed and fixed between the guide tube support plate 4b and the upper core plate 4a of the upper internal pieces of equipment 4.

Figure 2 is a front elevation of a fuel assembly 7 of the core 2 of the nuclear reactor.

The fuel assembly 7 comprises a framework for retaining the fuel rods 9 of the fuel assembly in accordance with a bundle in which the fuel rods 9 are mutually parallel and distributed in such a manner that the cross-sections thereof constitute a regular network in planes which are perpendicular to the longitudinal axis 10 of the fuel assembly.

The framework of the fuel assembly comprises grids 8 which are distributed over the length of the fuel assembly in the direction of the axis 10, guide tubes 9a being substituted for some of the fuel rods 9 inside the bundle of rods, and an upper nozzle 12a and a lower nozzle 12b which are fixed to end portions of the guide tubes 9a which project relative to the axial ends of the bundle of fuel rods 9. The upper nozzle 12a provides, with the axial ends ¢f the bundle of rods 9, a peripheral housing which is generally designated 11.

The lower nozzle 12b of the fuel assembly comprises feet by means of which the fuel assembly is positioned on the core support plate 3a, inside the vessel 1 of the nuclear reactor.

The upper nozzle 12a particularly comprises leaf springs 13 for retaining the fuel assembly, on which the upper core plate 4a is supported when the upper internal pieces of equipment are positioned in the vessel of the reactor, after the core 2 has been charged with fuel assemblies 7.

As shown in Figure 1, the upper core plate 4a comprises centring pins 14 which are intended each to become engaged in an opening of the upper nozzle 12a of a fuel assembly 7.

In this manner, the upper internal pieces of equipment 4 bring about the retention of the upper portions of the fuel assemblies 7 which are juxtapositioned in the core 2 in order to constitute an assembly network, generally in a square grid. The cross-sections of the fuel assemblies 7 and the nozzles 12a and 12b are generally square and comprise

3 i : — - F2000e/06977 two centring openings in two corners of the nozzle located on a diagonal.

The presence of the springs 13 interposed between the upper core plate and the fuel assembly 7 allows retention of the fuel assemblies counter to the vertical forces which are applied to those assemblies, for example, owing to the flow of cooling water from the reactor at high speed in the vertical direction 10, whilst still allowing differential expansion of the fuel assemblies relative to the internal structures of the nuclear reactor. :

In order to carry out recharging of the core 2 of the nuclear reactor with fuel assemblies 7, after the nuclear reactor has been shut down and cooled, the cover la is disassembled from the vessel 1, then the cover is lifted and handled in order to position it on a stand for receiving it inside the building of the reactor.

Subsequently, the lifting and handling of the upper internal pieces of equipment 4 of the nuclear reactor are carried out so as to position the upper internal pieces of equipment on a storage stand which is arranged in the cavity of the reactor.

It is then possible to gain access to the upper portion of the fuel assemblies 7 inside the vessel in order to carry out recharging of the core using the mechanical device for charging the nuclear reactor.

The recharging operations are carried out under water, the cavity of the reactor being filled with water.

! hog 22066/n4075

Figure 3 illustrates an internal portion of the building of the reactor comprising the cavity 16 of the reactor delimited by concrete walls.

The vessel 1 of the nuclear reactor which contains the core 2 constituted by the fuel assemblies 7 opens at the upper end portion thereof into the bottom 19 of the cavity 16.

In Figure 3, the cavity 16 and the vessel 1 are shown during a cold shutdown of the nuclear reactor for recharging the core. The cover la of the opening of the upper end of the vessel 1 has been disassembled and positioned on a storage stand and the cavity of the reactor has been filled with water up to the level 17.

The upper internal pieces of equipment 4 comprising the upper core plate 4a have been fixed to a very tall support structure 18 which is referred to as a tripod support. The tripod support is suspended on the polar crane of the building of the nuclear reactor (not illustrated) which allows the tripod support 18, to which the upper internal pieces of equipment 4 are fixed, to be lifted.

Whilst the upper internal pieces of equipment 4 are being lifted in the vertical direction of the axis 21 of the vessel 1, that operation being controlled, for example, by video cameras which are lowered to the bottom of the cavity, the presence of at least one fuel assembly 7a which has remained engaged with the upper core plate 4a of the upper internal pieces of equipment 4 has been detected.

The presence of the at least one fuel assembly 7a was detected as soon as the upper portion of the fuel assembly lq reached a location above the bottom 19 of the cavity 16, in which the upper end portion of the vessel 1 opens.

The operation for lifting the upper internal pieces of equipment 4 is then stopped.

The lower portion of the fuel assembly 7a which has remained engaged is still engaged over a given length inside the core 2 of the nuclear reactor, that is to say, between fuel assemblies 7 which are adjacent to the assembly 7a, in the core of the nuclear reactor.

In order to prevent the at least one fuel assembly 7a from falling on the other fuel elements 7 of the core, the at least one fuel assembly 7a is secured in order to ensure retention in this position during separation from the upper core plate 4a.

In this manner, after the presence of at least one fuel assembly 7a which has remained engaged below the upper core plate 4a when the upper internal pieces of equipment are lifted has been detected, the various steps of the recovery method of the at least one fuel assembly 7a are carried out under water.

The first step of this method involves securing and retaining the fuel assembly 7a by means of a group of securing tools 20 in abutment against the flange 1b of the vessel 1. The upper face of the flange 1b is covered by a suitable protective means lc (Figure 4) of known type.

The positioning of the various elements of the group of securing tools 20 is carried out by operators positioned above the cavity 16, in particular in at least one platform

{® (Figure 3) which is movable above the vessel 1 on rails 26 of the mechanical charging device of the reactor (not illustrated).

Figure 4 illustrates a side of the securing tools 20 that is arranged on the edge of the flange 1b, the other side of the securing tools being identical and symmetrical.

As shown in Figure 4, the securing tools 20 comprise: - two levelling tables 30, - two beams 40 and - means 50 for moving together and locking the two beams 40.

The levelling tables 30 which are intended to be positioned on the flange lb and on the edge of the bottom 19 of the cavity 16 are each constituted by a plate 31 which is provided with three feet 32, each of which is formed by an adjustable screw jack.

The adjustment of each foot 32 is carried out remotely from the platform 25 by means of a pole 35.

Each of the beams 40 has a length greater than the diameter of the vessel 1 and carries two locking plates 45 which are arranged opposite each other when the beams 40 are positioned on the levelling tables 30, in a manner parallel with each other.

Each beam 40 is also provided with a stop 49, the object of which is to limit the movement together of the beams 40, as will be seen below.

In order to secure the fuel assembly 7a which has remained engaged below the core plate 4a, the operators lower into

406 9ra697y; the cavity 16 the two levelling tables 30 and position them at the bottom 19 of the cavity 16 in such a manner that two feet 32 are in abutment against the collar of the flange 1b of the vessel 1 and a foot 32 is in abutment against the bottom 19 of the cavity 16.

The two levelling tables 30 are positioned opposite each other relative to the fuel assembly 7a which is intended to be secured.

Subsequently, the operators, for example, from the platform 25, successively introduce in the cavity 16 each of the beams 40 and position the ends of each of the beams 40 on each levelling table 30, as shown in Figure 4.

By means of poles 35, the levelling tables 30 are adjusted by acting on the feet 32 so as to ensure correct positioning of the locking plates 45 which are carried by the beams 40 relative to the housing 11 which is provided in the upper portion of the fuel assembly 7a. The levelling operation is carried out by adjusting the two levelling tables 30 practically at the same time.

Subsequently, each locking fork 50 for movement together is lowered into the cavity 16 and is positioned on the corresponding levelling table 30. Each locking fork 50 comprises two fingers 52 and the fingers 52 are positioned at one side and the other of the ends of the two beams 40.

Each locking fork 50 further comprises a bevel gear 53 which is actuated by means of a pole 35 and which allows the fingers 52 to be moved together in order to move together the beams 40 as far as contact with the stops 49. During the movement together, the locking plates 45 are introduced into the housing 11 of the fuel assembly 7a in order to lock the fuel assembly and thereby to secure it, as shown in Figure

The following step of the method for recovery according to the invention involves separating the fuel assembly 7a which has remained engaged with the upper core plate 4a.

To that end, as illustrated in Figure 5, the operators lower, inside the cavity 16, a tool 60 below the upper core plate 4a in order to apply a separation force between the upper portion of the fuel assembly 7a and the upper core plate 4a.

The tool 60 used to apply a separation force between the fuel assembly 7a and the upper core plate 4a, which is referred to as the unblocking tool jack, is illustrated in

Figure 5 in a service position under the upper core plate 4a.

The tool jack 60 comprises a tool body 61 which is rectilinear and elongate and which comprises, in a zone near a first end, means for fixing a handling pole 35.

A counterweight 62 is fixed to the first end of the body 61.

The counterweight 62 is constituted, for example, by metal discs stacked on top of each other and fitted on a rod which is fixedly joined to the first end of the body 61 of the tool 60. In a second end portion opposite the first, the body 61 of the tool 60 has a longitudinal nesting, in which a lever 64 is mounted so as to pivot about a journal 63 of transverse direction parallel with the upper planar face of abutment of the body 61 and engaged in an axial hole of an articulation tab 62 which is fixedly joined to the body 61.

*£009/06977

The body of a jack 65 is engaged and fixed in a through-hole of the lever 64, the shank of the jack 65 being in abutment against the internal face of the body 61 parallel with the upper abutment face of the body 61 of the tool 60.

In order to apply, by means of a lever effect, a separation force between the upper core plate 4a and the fuel assembly 7a, in the upper nozzle of which a centring pin 14 has remained engaged, as shown in Figure 5, the tool 60 is positioned below the upper core plate 4a using the handling pole 35.

The end 64a of the lever 64 which has a thickness less than the thickness of the linear portion of the lever is introduced between the upper nozzle of the fuel assembly 7a and the lower face of the upper core plate 4a, then the upper planar face of abutment of the body 61 of the tocol jack 60 is brought into abutment against the lower face of the upper core plate 4a.

The operators remotely actuate the jack 65 so as to pivot the lever 64 downwards, as shown by the arrow F. In this manner, by means of a lever effect, a separation force is applied to the upper portion of the fuel assembly 7a which can thereby be separated with respect to the upper core plate 4a. The fuel assembly 7a which is separated in this manner remains and is retained in this position owing to the securing tools 20.

The effort applied by the jack 65 is relaxed and the tool jack 60 is moved so as to separate it from the upper core plate 4a. The tool 60 can be mounted at a higher level of the cavity 16. The internal pieces of equipment 4 are lifted by a few millimetres or a few centimetres in order to

Br Tot] . P200:9/06 977 establish whether the fuel assembly 7a has effectively become separated from the upper core plate 4a.

Once the disengaging operation has been carried out, the upper internal pieces of equipment 4 can be transferred to their storage stand.

Subsequently, the operators move, above the fuel assembly 7a, a handling tool of known type (not illustrated) and lock the handling tool to the fuel assembly 7a.

The fuel assembly 7a is lifted by a few millimetres by the handling tool which is connected to the mechanical device for charging the core of the reactor.

This action of lifting by a few millimetres allows the securing tool 20 to be disconnected from the fuel assembly

Ta.

The spent fuel assembly 7a is removed towards a storage zone and 1s positioned in a suitable receiving device. The securing tools 20 are subsequently removed.

If two fuel assemblies 7a have remained engaged below the upper core plate 4a, the following steps are carried out.

Firstly, the operators carry out the disengagement, remotely and successively, of each fuel assembly 7a from the upper core plate 4a by means of at least one unblocking tool jack 60, as illustrated in Figure 5.

When the disengagement of the two fuel assemblies 7a has been carried out, a handling tool (not illustrated) which is connected to the mechanical device for charging the core is na - 2d009/0697 7 engaged with the first fuel assembly 7a and the fuel assembly 7a is disengaged by a few millimetres. The securing tools 20 are disconnected from the first fuel assembly 7a then the first fuel assembly 7a is lifted and removed towards a storage zone in order to position it in a suitable receiving device.

The handling tool connected to the mechanical device for charging the core of the reactor is positioned perpendicularly relative to the second fuel assembly 7a and locked thereto.

The second fuel assembly 7a is lifted by a few millimetres so as to disconnect the second fuel assembly 7a from the securing tools 20.

The second fuel assembly 7a is lifted and removed towards the storage zone where it is positioned in a suitable receiving device.

According to a variant, after the fuel assembly 7a has been disconnected from the upper core plate 4a, the fuel assembly 7a can be lifted with the securing tools 20 and the assembly constituted in this manner can be removed towards a storage zone in order to position the fuel assembly 7a in a suitable receiving device 15.

Subsequently, the securing tools 20 are disconnected from the fuel assembly 7a. © If two fuel assemblies 7a have remained engaged below the upper core plate 4a, it is possible to carry out identical steps in order to remove the two fuel assemblies 7a and the securing tool 20 towards the storage zone.

If the fuel assembly 7a cannot be disengaged from the upper core plate 4a by means of the unblocking tool jack 60, the operators can carry out different operations.

After the fuel assembly 7a has been secured and retained by means of the securing tools 20, the operators lift the assembly constituted by the upper internal pieces of equipment 4, the securing tools 20 and the fuel assembly 7a by means of the tripod support 18 (Figure 6) which is suspended on the polar crane of the building of the nuclear reactor (not illustrated).

The assembly is transferred to the receiving stand, as shown in Figure 7.

Subsequently, the fuel assembly 7a is lowered and engaged in a suitable receiving device 15.

The operators carry out the remote operation for disengaging the fuel assembly 7a from the upper core plate 4a by suitable means so that the fuel assembly 7a is supported in the receiving device 15.

The securing tools 20 are disconnected from the fuel assembly 7a which is removed towards a storage zone.

If two fuel assemblies 7a have remained engaged below the upper core plate 4a, it is possible to carry out identical operations in order to remove the assembly which is constituted by the upper internal pieces of equipment 4, the two fuel assemblies 7a and the securing tools 20.

&

The assembly is transferred to the receiving stand and the operators carry out the same remote disengagement operations for each of the fuel assemblies 7a.

Claims

. cL LL Tee 21 Claims

1. Method for recovering at least one fuel assembly (7a) which has remained engaged below an upper plate (4a) of a core (2) of a pressurised water nuclear reactor, the nuclear reactor comprising, in a cavity (16) containing water, a vessel (1) which is provided at its upper portion with a flange (lb) and which contains the core (2) of the reactor constituted by vertical, juxtapositioned fuel assemblies (7), upper internal pieces of equipment (4) which are provided so as to be supported on the upper portion of the core by the upper core plate (4a) and which comprise : centring pins (14) which are intended each to engage in an opening which is provided at the upper portion of a fuel assembly (7), and means (18) for lifting and handling the upper internal pieces of equipment (4), characterised in that, after the presence of the at least one fuel assembly : (7a) which has remained engaged below the upper core plate (4a) has been detected, when the upper internal pieces of equipment (4) are lifted, a) the at least one fuel assembly (7a) is secured and retained under water by means of a group of securing tools (20) in abutment against the flange (1b) of the vessel (1), and at least the following main steps are carried out under : water: b) the remote disengagement of the at least one fuel assembly (7a) from the upper core plate (4a) is carried out : by means of at least one unblocking tool jack (60), c) the upper internal pieces of equipment (4a) are transferred and they are positioned on a receiving stand which is provided in the water-filled cavity (16), d) the at least one spent fuel assembly (7a) is removed towards a storage zone in order to position it in a suitable receiving device (15), and e) the securing tools (20) are removed after they have been separated from the at least one fuel assembly (7a).

2. Method according to claim 1, characterised in that, after the steps a), b) and c) have been carried out: ~- a handling tool is moved above the at least one fuel assembly (7a) and the handling tool is locked to the at least one fuel assembly (7a), - the at least one fuel assembly (7a) is lifted by a few millimetres by means of the handling tool, : - the securing tools (20) are disconnected from the at least one fuel assembly (7a), - the at least one fuel assembly (7a) is lifted vertically, and - the steps d) and e) are carried out.

3. Method according to claim 1, characterised in that, after the steps a), b) and c¢) have been carried out: . - a handling tool is moved above the at least one fuel assembly (7a) and the handling tool is locked to the at least one fuel assembly (7a), - the at least one fuel assembly (7a) is lifted with the securing tools (20), - the step d) is carried out with the securing tools (20) which are fixedly joined to the at least one fuel assembly (7a), - the securing tools (20) are disconnected from the at least one fuel assembly (7a), and - the step e) is carried out.

4. Method according to claim 1, characterised in that, after the step a) has been carried out: : —- the step c¢) is carried out with the securing tools (20) and the at least one fuel assembly (7a),

- the at least one fuel assembly (7a) 1s lowered and engaged in a suitable receiving device (13), and - the steps b) and e) are carried out.

5. Method according to claim 1, characterised in that, for two fuel assemblies (7a) which have remained ‘engaged below the upper core plate (4a): - each fuel assembly (7a) is disengaged, remotely and successively, from the upper core plate (4a) by means of the at least one unblocking tool jack (60), - the first fuel assembly (7a) is lifted by a few millimetres by means of the handling tool, - the first fuel assembly (7a) is disconnected from the securing tools (20), - the first fuel assembly (7a) is lifted and removed, - the second fuel assembly (7a) 1s lifted by a few millimetres by means of the handling tool, - the second fuel assembly (7a) is disconnected from the securing tools (20), - the second fuel assembly (7a) is lifted and removed, and, - the securing tools (20) are removed.

6. Method according to claim 1, substantially as herein described and exemplified and/or described with reference to the accompanying drawings. Dated this ti day of October DOT " MARIUS LE eo Patent Attorney / Agent for the'Applicant ~~ +