EP0465283A1 - Process and device for dismantling an irradiated component of a nuclear reactor by machining the casing - Google Patents

Abstract

The tubular wall (1) of the irradiated component is machined with the formation of chips (44), on its upper annular surface, using a machining machine (30) bearing on this upper surface and moving in rotation around the axis (6) of the wall (1) of the component. The shavings (44) formed by the machining machine (30) which moves in the vertical direction and downwards, during the progress of the machining, in the axial direction (6) are continuously collected and removed. ) of the wall (1) of the component. The machining machine (30) can be produced in the form of a milling head. The device comprises fixing means on the upper part of the tubular casing (1) comprising arms (7a, 7b) provided with jacks allowing the clamping of the device (4) on the wall (1) of the component and of the devices d support (12) comprising arms (13) pivotally mounted about a horizontal axis, between a low support position and a high erasing position (13 '). The support arms (13) pass from their low position to their high position, when the machining tool (31) passes. <IMAGE>

Description

The invention relates to a method and a device for dismantling an irradiated component of a nuclear reactor and in particular of a vessel of a nuclear reactor cooled by pressurized water, by machining its wall with removal of shavings.

Water-cooled nuclear reactors and in particular pressurized water nuclear reactors comprise a vessel which is intended to contain the core of the nuclear reactor and which is connected to the cooling circuit of the reactor in which the cooling water circulates.

The wall of the reactor vessel which is in contact with the cooling fluid and exposed to the radiation emitted by the reactor core can be highly contaminated after a certain period of operation of the reactor.

In the case of nuclear power plants which have reached the end of their life and which require a complete shutdown, so far, the solution chosen has been to leave these power stations in the state they were in and to allow the activity of the constituent materials to decrease. their components, in order to dismantle them later, in more satisfactory conditions than at the time of shutdown, without having to use complex tools controlled remotely.

In the future, the number of plants that will be put out of industrial operation will increase significantly, so that it is necessary to consider a dismantling of these plants, in order to restore in its original state, the site where they are established.

The dismantling of the conventional part of the power plant does not pose any particular problem but on the other hand, the dismantling of the part of the power station constituting the nuclear reactor proper poses problems difficult to solve, due to the radioactive emissions of the materials constituting the components of the reactor.

In particular, the tank of water-cooled nuclear reactors which contains the fuel assemblies and which is in contact with the cooling water of the reactor during its operation is very highly contaminated, in the case of reactors reaching the end of their life .

In the case of pressurized water nuclear reactors currently in operation, the reactor vessel is in the form of a generally cylindrical body closed by domed bottoms, of large dimension and having a large wall thickness.

The tank which has a very high mass is disposed inside a tank well formed in a concrete structure which also delimits one or more swimming pools located above the upper level of the tank.

The tank which contains, in addition to the fuel assemblies, various internal structures is connected, by tubes, to pipes of the primary circuit of the reactor.

The core assemblies and certain components of the internal structures can be disassembled and taken out of the tank, so as to ensure their evacuation and, possibly, their elimination, when the reactor is put out of service.

Up to now, no process and device have been known for dismantling the vessel of a pressurized water nuclear reactor, under very good safety conditions and making it possible in particular to avoid the risks of radio contamination. -active in the intervention area, while using means of machining and handling of a structure relatively simple to carry out the evacuation and elimination of material from the tank.

The object of the invention is therefore to propose a method for dismantling an irradiated component of a nuclear reactor comprising at least one wall of tubular shape arranged with its axis in the vertical direction, this method making it possible to carry out in very good safety conditions and in a simple manner elimination by machining with removal of chips from the material of the wall of the component and evacuation of the chips obtained.

• on usine la paroi tubulaire avec formation de copeaux sur sa surface annulaire supérieure, en utilisant une machine d'usinage en appui sur cette surface supérieure et se déplaçant en rotation autour de l'axe du composant,
• et on recueille et on évacue en continu les copeaux formés par la machine d'usinage qui se déplace dans la direction verticale et vers le bas, au cours de la progression de l'usinage, suivant la direction axiale du composant.

For this reason :

• the tubular wall is machined with the formation of chips on its upper annular surface, using a machining machine resting on this upper surface and moving in rotation around the axis of the component,
• and continuously collecting and removing the chips formed by the machining machine which moves in the vertical direction and downwards, during the progress of the machining, in the axial direction of the component.

The invention also relates to a device implementing the dismantling method according to the invention.

In order to clearly understand the invention, a description will now be given, by way of nonlimiting example, of an embodiment of the dismantling process according to the invention and the device making it possible to implement this process, in the case of dismantling. a tank of a pressurized water nuclear reactor.

The single figure is a vertical sectional view in elevation of the upper part of a vessel of a pressurized water nuclear reactor and of a device ensuring the dismantling of this tank by the process according to the invention.

In the figure, we see the upper part of the vessel 1 of a pressurized water nuclear reactor which is constituted by a casing of tubular shape having a large wall thickness arranged with its vertical axis inside a well. tank formed in a concrete structure not shown.

The tubular tank has, at its upper part, a flange 2 whose thickness is greater than the thickness of the wall of the tank in its current part. The flange 2 is intended to receive the tank cover ensuring a tight closure of the interior volume of the tank during the operation of the reactor.

The tank 1 also comprises, in the vicinity of its upper part, pipes such as 3 allowing the connection of the tank to the pipes of the primary circuit.

There is shown in the figure a device for carrying out the dismantling of the tank by machining its wall with removal of shavings.

After a definitive shutdown of the nuclear reactor, the primary circuit and the tank are cooled and the tank cover is removed, the reactor pool located above the tank being filled with water.

The core assemblies are unloaded and evacuated as well as the internal equipment of the tank.

The reactor pool is then drained as well as the tank which can nevertheless be partially filled with water during the implementation of dismantling.

A dismantling device for implementing the method according to the invention is installed on the upper part of the tank 1, using from the central unit's polar bridge or by another suitable lifting and handling means.

In the figure, there is shown such a device generally designated by the reference 4, in the service position on the upper part of the tank 1.

The device 4 comprises a tubular support 5 placed, in the service position, with its axis coinciding with the axis 6 of the tank 1.

Four arms of large section such as the arms 7a and 7b are rigidly fixed on the lower part of the support 5, by means of fixing lugs 8, in radial directions perpendicular to the axis 6 arranged at 90 ° from one another, around the axis 6 of the support 5.

The arms such as 7a and 7b are machined internally in their axial direction to form actuator chambers in which rods 9 move carrying at their ends support pads 10 on the internal wall of the tank 1.

The arms such as 7a and 7b secure and center the device 4 by clamping inside the tank, when the jack rods 9 are in their extracted position.

On the upper part of each of the arms such as 7a and 7b is fixed a support device 12 making it possible to rest the whole of the device 4 on the annular upper surface of the tank 1, to ensure its maintenance, independently of the clamping ensured by the set of radial steering arms such as 7a and 7b.

Each of the support devices 12 comprises an arm 13 pivotally mounted by means of a joint 14 with a horizontal axis, on the corresponding arm. The pivoting arm 13 comprises, at its end opposite to the articulation 14, a support piece 15 coming to rest on the annular upper surface of the tank 1, when the arm 13 is in its low position as shown in the left part of the figure, above the arm 7a.

The position of the support surface 15 in the direction of an axis 17 perpendicular to this support surface can be adjusted by a compensation device 16 whose operation will be explained in the following text.

An actuating cylinder 18 of the arm 13 is articulated on the external surface of the tubular support 5. The rod 19 of the cylinder 18 is connected, also articulated, to the arm 13.

The axes of articulation of the jack 18 and of the rod 19 are placed in a horizontal direction.

By actuating the double-acting cylinder 18, in one direction or the other, it is possible to place the arm 13 in a low support position, as shown on the left of the figure, or on the contrary in a raised position 13 ′, As shown in the right part of the figure, the movement of the arm 13 by pivoting between these two positions being represented symbolically by the arrow 21.

The tubular support 5 carries, in the vicinity of its upper part, a rotary bearing 20 having as axis the axis 6 common to the support 5 and to the tank 1.

The bearing 20, constituted in the form of a roller bearing, comprises a fixed internal barye integral with the support 5 and an external ring movable in rotation on which is fixed a support 24.

A radial direction arm 25 is movably mounted inside the support 24, in a direction 26 corresponding to its longitudinal direction.

A geared motor 27 ensuring the drive of a pinion-rack assembly mounted in the support 24 makes it possible to move the arm 25 in the direction 26, in one direction and in the other, as shown diagrammatically by the arrow 28.

The arm 25 carries, at its end opposite to the support 24, a milling head 30 constituting the tool for removing by machining the irradiated material from the wall of the tank 1. The milling head 30 comprises a milling cutter 31 mounted at the end of a vertical steering spindle rotated by a motor 32.

The support 5 carries at its upper end, above the bearing 20, a fixed toothed crown 34. A geared motor 35, fixed on the mobile external barye of the bearing 20, carries, at the end of its output shaft, a pinion drive 36 meshing with the fixed ring gear 34.

The rotation of the gear motor 35 and the pinion 36 allows to drive the outer ring of the bearing 20, the support 24 and the milling head 30 in rotation about the axis 6 of the tank.

The arms such as 7a and 7b carry, by means of flexible fixing devices 38, a collecting hopper 39 of frustoconical shape and comprising a peripheral seal 40 along its upper edge whose diameter is substantially equal to the inside diameter of the tank 1. The seal 40 ensures a tight connection between the upper external edge of the collecting hopper 39 and the internal surface of the tank 1.

A conveyor 41 of vertical direction connected, at its lower part, to an extension 5a of the support 5, is mounted, in the vertical direction, inside the support 5, so as to open, at its upper part, into a conduit 42 of flared shape.

The milling machining of the upper surface of the tank 1, according to the procedure which will be described below, results in the formation of chips and metal particles 44 which are directed by a deflector 45 in the direction of the collecting hopper 39. The chips and particles 44 coming into contact with the internal surface of the hopper 39 are directed by gravity towards the bottom of the hopper, this movement of the chips and particles being facilitated by the presence of a vibrator 47 in contact with the external surface hopper 39.

The chips and particles which collect at the lower central part of the hopper 39 are taken up by the conveyor 41 and transported inside the support 5, up to its upper part to be discharged onto a handling device or into a hopper allowing to feed an induction furnace ensuring the reflow of the chips and particles of irradiated material from the wall of the tank. The flared conduit 42 ensures complete recovery of the chips and particles at the top of the conveyor 41, some of these chips or particles being able to be projected outside their normal transport path, which would cause contamination of the milling device. by these particles of radioactive material.

To carry out a dismantling operation of a tank 1 of a pressurized water nuclear reactor, the device 4 is placed in its operating position on the upper part 2 of the tank constituted by the cover fixing flange. The support devices 12 whose arms 13 are placed in the low position come to rest by their support pieces 15 on the upper surface of the flange 2.

The device is clamped and fixed by feeding the cylinders provided in the arms such as 7a and 7b. The pads 10 come into contact with the inner surface of the tank to ensure the clamping.

The milling cutter 31 which is, at the start of operation, in a position of withdrawal towards the inside of the tank is rotated and the arm 25 is moved outwards, so that the milling cutter, the position of which is in height is adjusted by the compensation devices 16 of the support pieces 15 of the arms 13 can engage in the metal of the wall of the tank 1 to a thickness corresponding to the thickness of a machining pass.

The movable outer ring of the bearing 20, the support 24, the arm 25 and the milling head 30 are rotated about the axis 6 of the tank, by feeding the gearmotor 35.

The milling head 30 rotating around the axis 6 performs a machining pass on the annular upper surface of the tank.

When the cutter reaches the vicinity of a support device 12 whose arm 13 is in the low position, a detector makes it possible to control the corresponding jack 18, by means of a servovalve. The arm 13 is moved by pivoting to come into a raised position such as position 13 ′.

The compensation device 16 moves the support piece 15 outward over a distance corresponding to the thickness of the pass.

When the cutter has carried out the machining on the part of the upper surface of the tank on which the part 15 of the arm 13 comes to bear, a detector controls the displacement of the jack 18 in the direction causing the arm 13 to fold down. , the support piece 15 coming into contact with the surface of the wall of the freshly machined tank. Position adjustment of the support piece 15 ensures perfect contacting of this support piece with the upper surface of the tank, when the pivoting arm 13 is folded down and held in position by the rod 19 of the jack 18 in its deployed position.

The machining pass is carried out during a complete revolution of the milling head 30 around the axis 6 of the tank, the arms 13 of the support devices 12 being moved in their high position, at the time of passage strawberry at their level.

In the thickest parts of the tank, for example at the level of the tank flange 2 and the pipes 3, the complete machining of the upper surface of the tank according to the thickness of a pass may require a radial displacement of the cutter and carrying out several machining passes.

When the upper part of the tank 1 has been machined to the thickness corresponding to a machining pass, the milling head 30 is returned to its initial position and the rods 9 of the jacks associated with the arms such as 7a and 7b are placed in their retracted position, so as to release the clamping pads 10 of the device 4 inside the tank.

The device 4 rests on the support devices 12 whose maintenance in the low position is ensured by the jacks 18.

The compensation devices 16 are then reset, so as to be able to make the adjustments, at the time of the passage of the cutter, during the next machining pass.

The jacks associated with the arms such as 7a and 7b are actuated so as to clamp the device 4 inside the tank.

Then, as before, a new machining pass is carried out.

The chips and particles formed by the cutter 31 are continuously recovered by the hopper 39 and the vertical conveyor 41, so as to be continuously introduced into an induction reflow oven.

The dismantling of the tank is ensured by removing the metal from its wall, during successive milling passes.

All the operations described above are controlled automatically, so that the dismantling of the tank is carried out inside the concrete structure in which the tank well is formed, without any human intervention. This avoids exposing operators in a highly contaminated area.

In addition, automatic control and monitoring of the cutting condition of the cutter is carried out, so as to carry out an automatic change of this cutter, when its condition is considered to be defective. It is also possible to provide programmed tool change sequences after a certain period of operation of the dismantling device by machining.

The tool change is carried out in a conventional manner thanks to a robotic auxiliary arm which supports the cutter on the milling head to introduce it into a barrel or a display and to proceed with the installation of a new cutter having a satisfactory cutting condition.

The dismantling process and device according to the invention therefore make it possible to dismantle a nuclear reactor vessel completely automatically, so that the time required to carry out the machining is only of secondary importance.

It is possible to use the same dismantling device by machining to successively dismantle all of the tanks of a fleet of nuclear reactors.

In addition, the recovered irradiated material can be easily shaped by reflow and by casting to form blocks of irradiated material whose mass and shape make it possible to facilitate long-term storage.

The invention is not limited to the embodiment which has been described.

This is how the machining of the wall of the tank can be carried out using a device different from that which has been described.

This device can include a different machining machine from a milling head.

The means for moving, holding and centering the machining machine may be different from those which have been described. These means may include any number of arms, greater than two, to ensure the clamping of the machine on the tubular wall.

All the handling means allowing the recovery of the chips or particles and their transport to a melting or recovery device can also be different from those which have been described.

Finally, the invention applies to the dismantling of any component of a nuclear reactor comprising at least one part of tubular shape arranged with its vertical axis.

Claims (10)

1.- Method for dismantling an irradiated component of a nuclear reactor comprising at least one wall (1) of tubular shape arranged with its axis in the vertical direction, characterized by the fact: - that the tubular wall is machined with the formation of chips, on its upper annular surface, using a machining machine (4) resting on this upper surface and moving in rotation around the axis of the component, - and that the shavings formed by the machining machine which moves in the vertical direction and downwards are continuously collected and removed, during the progress of the machining, in the axial direction of the tubular wall (1) of the component. 2.- Method according to claim 1, characterized in that the chips (44) collected and continuously discharged are remelted to form blocks of irradiated materials, for long-term storage of these blocks. 3.- Method according to any one of claims 1 and 2, characterized in that the machining of the tubular wall (1) of the component is carried out by milling. 4.- Device for dismantling an irradiated component of a nuclear reactor comprising at least one tubular wall (1) arranged with its axis (6) in the vertical direction, characterized in that it comprises a support ( 5), fixing means (7a, 7b, 12) of the support (5) on the upper part of the wall (1) of tubular shape, a machine tool (30) for the upper surface of the shape wall tubular (1), support means (24, 25) of the machining machine (30) rotatably mounted on the support (5) around the axis (6) of the tubular wall (1), means for driving in rotation (34, 35, 36) of the machining machine (30) around the axis (6) of the tubular wall (1) of the component and means for collecting and evacuation (39, 41) of the chips or particles formed by machining the tubular wall (1). 5.- Device according to claim 4, characterized in that the fixing means (7a, 7b, 12) of the support (5) of the dismantling device (4) are constituted by at least two arms integral with the support (5) , arranged in radial directions inside the tubular wall (1) in the service position of the dismantling device (4) comprising support and clamping cylinders (9, 10) movable in their longitudinal direction, their outer end and support devices (12) each associated with an arm (7a, 7b) comprising a support arm (13) pivotally mounted about a horizontal axis on the corresponding clamping arm (7a) movable between a low support position and a high erase position, thanks to an actuating device (18, 19). 6.- Device according to claim 5, characterized in that each of the support arms (13) comprises a support piece (15) on the upper surface of the tubular wall (1) having a substantially support surface flat, the position of the support piece (15), in a direction perpendicular to its support surface, being adjustable by means of a compensation device (16). 7.- Device according to any one of claims 5 and 6, characterized in that the machining machine (30) is fixed to the end of a support arm (25) movable in its longitudinal direction relative to the support (5) of the dismantling device (4), the arm (25) being arranged in a radial direction relative to the tubular wall (1) of the component in the service position of the dismantling device (4). 8.- Device according to any one of claims 5 to 7, characterized in that the means of recovery and evacuation (39, 41) of the chips or particles of irradiated material obtained by machining comprise a hopper of frustoconical shape ( 39) fixed inside the tubular wall (1), below the machining machine (30), so as to recover the chips or particles (44) obtained by machining and to collect them at its central part, and a conveyor (41) arranged in a substantially vertical direction, the lower part of which is arranged in the vicinity of the central part of the hopper (39) in which the chips or particles (44) are collected. 9.- Device according to claim 8, characterized in that a vibrator (47) is placed in contact with the wall of the hopper (39), to promote movement towards the central part of the hopper of the chips or particles ( 44) obtained by machining. 10.- Device according to any one of claims 8 and 9, characterized in that the support (5) of the dismantling device is made in tubular form and placed with its axis in a vertical arrangement coinciding with the axis of the tank (6) when the device (4) is in its service position
and that the conveyor (41) for transporting the chips or particles (44) is placed inside the tubular support (5) and in a vertical arrangement.

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