FR2710181A1 - Method and device for induction cutting of elements of a nuclear installation. - Google Patents

Abstract

The invention relates to the induction cutting of an element entering into the constitution of a nuclear installation with a view to its dismantling. The induction is generated by the passage of an electric current in an induction coil (20) flat and arranged vis-à-vis the part of the element to be cut.

Description

METHOD AND DEVICE FOR INDUCTION CUTTING OF ELEMENTS

OF A NUCLEAR INSTALLATION.

DESCRIPTION

  The present invention relates to the induction cutting of elements entering into the constitution

  of a nuclear installation. It applies particularly

  especially when cutting the melting pots.

  Dismantling of nuclear installations

  is a problem of particular concern to self-employed

  rites responsible for nuclear safety and protection as well as nuclear operators. Since

  a few decades, many ways of asking

  have been implemented and experience has shown that there is a need to improve

  dismantling existing ones or even creating new ones.

  Many countries have, moreover, started programs

  my research and development on this.

  Since nuclear installations are of different types and sizes, it is necessary to have

  of a wide variety of means to carry out the operations-

  dismantling operations. These are generally carried out

  by cutting using one of the many methods

  existing: thermal, electrothermal, pyrotechnic

ques, mechanical, etc.

  The choice of a cutting process is based on many criteria: cutting efficiency, cost, implementation constraints, degree

  nuisance, the material to be cut.

  It is known to practice mechanical cutting by circular saw, reciprocating saw, disc, cable and abrasive wheel, high pressure water jet with or without abrasive, tools for cutting by bore. The weight and size of these tools make them difficult to manipulate.

  Certain components of nuclear installations

  are particularly difficult to discover

  per. This may be due to the nature of the material from which they are made, their thickness and their condition. This is particularly the case of fusion pots made of nickel, chromium and iron alloy, such as the Inconel 601, which have a thickness of around 10 mm. In addition, used melting pots have a residual deposit of glass on their inner wall which increases the difficulty of cutting. This makes it currently practically impossible to cut these pots. Tests with a reciprocating saw have shown that it takes approximately two months

to cut such a pot.

  Thermal cutting processes are generally very efficient and allow the cutting of large thicknesses of steels. However, they generate significant amounts of slag, smoke and aerosols,

  which forces them to associate ventilation devices

  tion, filtration and containment.

  Document FR-A-2 667 533 discloses a process allowing the separation of irradiated fuels from their metallic sheath. It consists of induction heating the metal sheath to cause the fusion of a weak point of the sheath and propagating the fusion to create a slit. Induction is generated by passing an electric current through a solenoid surrounding the metal sheath. This process makes it possible to correctly separate irradiated fuels from their sheath without contaminating the fuels with metal

in fusion.

  Document FR-A-2 080 952 also discloses a method for treating irradiated ceramic nuclear fuel cartridges. The metal cladding surrounding the fuel is subjected to local heating by induction generated by a coil arranged around the cartridge. When a part of the cartridge placed in the induction coil is exposed to an appropriate high-frequency magnetic field,

  the metal sheath eventually breaks.

  These induction cutting processes apply

  quent particularly well for cutting relatively small diameter tubes since they require the placement of tubes in solenoids. They

  cannot be applied to cutting large pieces

  its, bulky or of any shape.

  In another field, that of welding, there are known induction heating devices allowing the preheating of parts to be welded. An inductor comprising a flat coil is used for this.

  which is passed an electric current. The heating

  fe is obtained by placing the coil near the

parts to be welded.

  To achieve rapid cutting of the parts particularly resistant to mechanical cutting, such as used melting pots, the inventor of the present invention has thought of cutting these parts by induction, the induction not being conventionally generated from a solenoid surrounding the room but using an inductor of the type used to simply heat

parts to be welded.

  The subject of the invention is therefore a method of induction cutting of an element forming part of a nuclear installation with a view to its dismantling, the induction being generated by the

  passage of an electric current in a coil of induc-

  tion, characterized in that the induction is produced by a flat coil arranged opposite the part

of the element to be cut.

  The invention also relates to an induction cutting device for an element forming part of a nuclear installation with a view to its dismantling, comprising an induction coil and means for electrical connection of each end.

  from this coil to an electrical supply,

  that the coil is a flat coil.

  For better efficiency, the coil has

  preferably two turns. Also for better efficiency, the

  reel preferably has an elongated shape.

  The device advantageously comprises means for cooling the coil by circulation

coolant.

  The coil can be hollow to allow the passage of the cooling fluid between its two ends. The electrical connection means may consist of two parts per coil end, one part serving for the electrical connection with this

  coil end and a part used for circulation

tion of the coolant.

  They can consist of two sets, each

  assembly consisting of a first electric conductor

  that, tubular and connected by one of its ends to one end of the coil ensuring the continuity of the cooling circuit and by its other end to a cooling fluid circulation duct,

  and a second electrical conductor connected to the power supply

  electrical and electrical and thermal contact

with the first driver.

  The two assemblies can be fixed to each other by clamping means between the second conductors with the interposition of an insulator between these

second conductors.

  The invention will be better understood and other characteristics and particularities will appear on

  reading of the description which will follow, given as

  of nonlimiting example, accompanied by the appended drawings among which: FIG. 1 represents a cutting equipment provided with an inductor according to the invention disposed at the end of a manipulator arm; - Figure 2 shows an inductor according to the invention isolated from the equipment to which it is assigned; - Figure 3 shows the flow of current in the inductor coil at a given time; - Figure 4 shows the currents induced in the workpiece when the current in the coil flows in the direction shown in Figure 3; - Figure 5 illustrates the thermal effect generated in the workpiece by an inductor with two turns according to the invention; and - Figure 6 illustrates the thermal effect generated in the part to be cut by an inductor with a turn

according to the invention.

  FIG. 1 represents a cutting equipment according to the invention ready to cut an element 1 used in the constitution of a nuclear installation. This element 1 is for example a melting pot. The inductor 2, shown in isolation in Figure 2, is supported

  by a transformer attached to the end of a remote arm

  manipulator 3. This end of the arm 3 supports, in addition to the transformer, the electrical connections and the cooling water circuit of the inductor,

  the assembly bearing the global reference 4.

  As shown in FIG. 1, the cutting is done inside a dismantling cell 5 provided with a table 6 serving as support for the element to be cut. One of the walls 7 delimiting the cell 5 maintains the remote manipulator 8 and is provided with a porthole 9 allowing the observation of the part to be cut. A sheet of cables 10, passing through the wall 7, makes it possible to convey the supply current and the cooling water from the generator 11 located in the control zone of the device to the inductor 2. equipment may include

  an ELVA generator of the Maximinac type with 50 kW of power

  this maximum output. This is a device that is usually

  used during soldering operations and

  hard, forging small parts, super quenching

  and preheating. It is connected to the three-phase 380 V, 50/60 Hz mains. The mains voltage is first rectified, then converted into an inverter to obtain an alternating current with a frequency between 10 and 30 kHz. This alternating current should be adapted to the inductor coil. The generator output is connected to the inductor coil via the mechanically attached transformer

  at the end of the manipulator arm.

  Figure 2 provides a detailed view of the

  conductor 2. This inductor is produced by assembling and welding several elements. It comprises a flat coil 20 comprising, in the example shown here, two turns. The coil is hollow to allow the

  circulation of a cooling fluid. The extremi-

  tees of the coil 20 are connected by welding to hollow and conductive branches 21 and 22. The connection between the coil 20 and the branches 21 and 22 is made so as to ensure not only the electrical connection but also the continuity of the cooling circuit between the end 23 of the branch 21 and the end 24 of the branch 22. Quick couplings ensure the hydraulic connection between the ends 23 and 24 and the connections of the cooling circuit carried

  by the end of the manipulator arm.

  The electrical connection with the secondary of

  transformer carried by the end of the remote control arm

  reader is done via electrical terminals

  and 26. These are two plates folded at right angles.

  The first parts 27, 28 of these plates are fixed by screwing on the output terminals of the transformer to ensure an electrical and mechanical connection of the inductor. The second parts 29, 30 are solidly fixed to each other by an insulating bolt, for example in teflon, with the interposition of an insulating plate 31.

  The branches 21 and 22 are welded respectively-

  on terminals 25 and 26 to ensure continuity

electric to coil 20.

  Figures 3 and 4 are to be considered together.

  The flow of current is shown in Figure 3

  alternating traversing the coil with two turns of the induc-

  tor at a given instant, the coil being placed opposite and at a short distance from the element 1 to be cut. It is then created in element 1, in the regions located opposite the turns of the coil, induced currents flowing as shown

in figure 4.

  To illustrate the thermal effect generated in the element 1 to be cut, there is shown in the figure a diagram of the temperature T to which is subjected the part of the element located opposite the coil in service for a cross section such than

  that indicated by the arrows in FIG. 3. We note

  that the turns of the coil used have sections of different shapes. The outer coil has a rectangular section whose sides parallel to the element 1 are longer than the sides perpendicular to this

  element 1. The inner coil has a rectangular section

  laire whose sides parallel to the element 1 are shorter than the sides perpendicular to this element 1. The magnetic induction produced by the traveling current has been shown around the turns of the coil 20

  the coil. 5 The diagram in FIG. 5 shows the evolution of the temperature in element 1 following the cuts.

  induced rants. This passes through a maximum located in the longitudinal axis of the coil to descend rapidly on each side of this maximum and with small lifts at the level of the external coil. It is understood that the elongated shape given to the coil promotes an accumulation

  heat energy along the longitudinal axis of this coil. The induction produces, in the heated zones of element 1, forces exerted in the directions indicated in FIG. 5. In the zone located opposite

  from the longitudinal axis of the coil, a force F is created which forces the molten metal back to create the initiation of a slit which will continue. The forces f1 and f2.20 due to the outer turn, have the consequence of avoiding a rise of the molten material on the sides.

  This gives a fairly clear cut of the element 1.

  A coil with a single turn does not achieve such a result. This is what the coil shows

  which has only one turn and for which the temperature curve is wider.

  All the elements constituting the inductor are preferably made of copper.

  Tests carried out have shown that the invention has a certain interest. They were conducted for a frequent

  ce of the voltage applied to the coil in the order of 12 kHz. Continuous output power was approximately

  46.2 kW. The generator supplied the primary with trans-

  trainer located at the end of the manipulator arm, an alternating voltage of 420 V peak to peak for a current intensity of 110 A peak to peak. The voltage across the inductor was 40 V maximum for an intensity between 1500 and 6000 A. The coil consisted of a copper tube 7 x 10 mm by 1 mm thick. The cooling consisted of a water flow of 12 1 / min for a pressure of 5 bars. Under these conditions, we cut

  complete with a melting pot, including handling, in 76 hours instead of 2 months with the reciprocating saw.

  The glass stuck inside the pot poses no constraints.

Claims (9)

  1. Induction cutting process of an element   ment (1) entering into the constitution of a nuclear installation with a view to its dismantling, the induction being generated by the passage of an electric current in an induction coil, characterized in that the induction   is produced by a flat coil (20) arranged opposite   opposite the part of the element to be cut.   2. Device for induction cutting of an element forming part of a nuclear installation with a view to its dismantling, comprising a   induction coil (20) and electrical connection means   stick from each end of this coil to a supply   electrical ration, characterized in that the coil is a flat coil.   3. Device according to claim 2, charac-   terized in that the coil (20) has two turns.   4. Device according to any one of the res-   dications 2 or 3, characterized in that the coil has an elongated shape.   5. Device according to any one of the res-   dications 2 to 4, characterized in that it comprises means for cooling the coil by circulation coolant.   6. Device according to claim 5, charac-   terized in that the coil is hollow to allow the passage of the coolant between its two ends.   7. Device according to claim 6, charac-   terized in that the electrical connection means consist of two parts per coil end, one part serving for the electrical connection with this   coil end and a part used for circulation tion of the coolant.   8. Device according to claim 7, characterized in that the electrical connection means comprise two assemblies, each assembly being made up of a first electrical conductor (21, 22), tubular 5 and connected by one of its ends at one end of the coil (20) ensuring continuity of the cooling circuit and by its other end (23,24) to a coolant circulation duct, and a second electrical conductor (25,26 ) connected to the power supply and in electrical contact   and thermal with the first conductor.   9. Device according to claim 8, charac-   terized in that the two assemblies are fixed to each other by clamping means between the second conductors (25,26) with the interposition of an insulator   (31) between these second conductors.