FR2675616A1 - METHOD AND DEVICE FOR CONTROLLING THE CUTTING OF A SPACER THREAD OF NEEDLES OF NUCLEAR FUELS. - Google Patents

Abstract

The device makes it possible to detect whether the cutting of the spacer wire (1) of a fuel needle (20) has actually taken place, in particular if the cutting of the spacer wire (1) is carried out by means of a cassette with electrodes (25). The device uses a contact cone (10) on which the spacer wire (1) rubs after cutting. If the cut has not actually taken place, the section to be cut is still brought to its cutting potential (VC). Detection of the latter makes it possible to detect the absence of the cut of the spacer wire section. The contact piece (10) being rotating, in correspondence with the advance of the spacer wire (1), the connection to the comparison means (22) is made by means of a connection track (8) and of a collecting brush (12). Application to the control of the cutting of the spacer wire of irradiated nuclear fuel pins in fast neutron reactors.

Description

CONTROL METHOD AND DEVICE

OF THE CUTTING OF A SPACER THREAD

  NUCLEAR FUEL NEEDLES

DESCRIPTION

FIELD OF THE INVENTION

  The invention relates to the reprocessing of irradiated fuels and in particular the reprocessing of needles used in nuclear reactors

fast neutrons.

PRIOR ART

  In the context of the reprocessing of irradiated fuels and coming from fast neutron nuclear reactors, it is necessary to remove the spacer wire which is wound in a helix around each of the fuel needles, before shearing each of them L ' operation is performed

  by an automatic machine, in a reduced time.

  It is necessary to monitor this operation in order not to disturb the processing cycle of these

nuclear fuels.

  A cutting detection device is already known which uses two mustache-shaped parts closing on the fuel needle downstream of a discharge cutting device.

  electric, called "multi-electrode cassette".

  This type of operation makes it possible to establish contact with the spacer wire. The operation is as follows. If an electrical charge is detected in the mustache pieces, this means that the section of spacer wire has not been cut, because it has continuity between the uncut wire and the mustache which is electrically insulated This device is composed of an electromagnet and rods The assembly consists of around twenty parts The reliability of this device is not very good indeed, the cut wire detection function implements too many moving parts, these being requested ten times per treatment cycle of a fuel needle. A wear phenomenon therefore inevitably appears, because any mechanical lubricant is prescribed. by the environment in which the system operates. Drawbacks and technical problems ensue; here are the main ones: blocking of the piston of this device; rupture of flexible arms (whiskers);

poor wire detection.

  Of course, this defect involves major interventions on the manipulator and especially involves the intervention of personnel in the corridors where access requires special clothing.

and a mask.

  The object of the invention is to remedy these drawbacks by proposing another type of detection of the cutting of the spacer wire for the

  nuclear fuel needles.

SUMMARY OF THE INVENTION

  A first main object of the invention is a method for controlling the cutting of a nuclear fuel needle spacer wire, this wire being brought before cutting to a potential.

  different from that of a reference part.

  According to the invention, the method consists in measuring the potential difference between the wire and the reference part in order to detect an absence of wire cut when the potential difference

  between the wire and this piece persists.

  The method is particularly well suited when the wire cutting has been carried out by means of a multi-electrode cassette. In fact, electric charges are thus brought into play in the spacer wire using such a cutting means. It turns out to be very advantageous if the control is interrupted When the cutting takes place, in order to avoid losses by Joule effect in the machine and to avoid excessive heating of

rooms.

  A second main object of the invention is a device for controlling the cutting of a spacer wire for nuclear fuel needles, this spacer wire being brought to an electrical voltage different from that of a reference part of the machine. According to the invention, the device comprises: a contact part intended to be in contact with the spacer wire; means for measuring the potential difference

  between the contact part and the reference part.

  Preferably, the contact piece is a hollow conical piece, called a contact cone, which is placed coaxially around the needle moving along an axis of movement, downstream of the cutting device and on the external surface of which the spacer wire comes to rub In the case where the assembly rotates during the cutting of the spacer wire, the device according to the invention comprises: grippers for gripping the needle, coaxial and integral in rotation with the contact cone; means for driving the contact cone in rotation to maintain the contact of the spacer wire on the cone at any location; a coaxial track mechanically and electrically secured to the contact cone; a fixed collecting brush, connected to the means

measuring and rubbing on the track.

  This type of device is advantageously completed by an electromagnet placed inside the body, coaxially and around the axis of movement of the needle to control the opening and closing of the clamps, during handling.

of the needle.

LIST OF FIGURES

  The invention and its various characteristics will be better understood on reading

  of the following description of the invention, which is

  appended to two figures representing respectively: FIG. 1, schematically, the location of the control of the cutting of the spacer wire according to the invention in the treatment of irradiated fuels; Figure 2, the control device

  cutting the spacer wire according to the invention.

DETAILED DESCRIPTION OF A MODE OF

PRODUCTION

  FIG. 1 therefore represents a link in the processing chain for irradiated fuel needles. One of these needles 20 is shown horizontally surrounded by its spacer wire 1. This assembly is subjected, by a displacement along a horizontal axis 4, to a series of operations thanks to an installation of several devices fixed on a

bench 30.

  First of all, the assembly of the needle and its spacer thread 1 is driven in rotation by any drive means symbolized by drive wheels, identified 13 The first main operation of the treatment consists in cutting the thread spacer 1 A wire cutting device 24 is therefore installed in the path of the needle 20 to cut the spacer wire I again

attached to it.

  A receptacle 26 is preferably placed

  below the cutting device 24 for the spacer wire 1.

  It is specified that the system for controlling the cutting of the spacer wire according to the invention is only applicable in the case where there is a potential difference between the spacer wire 1 and a part.

  of reference of the machine, for example the bench 30.

  This is in particular the case when the device 24 for cutting the spacer wire 1 is a system of the "electrode cassette" type, that is to say acting by

electric arcs.

  The control device according to the invention

  is therefore placed downstream of the cutting device 24.

  It has been symbolized by a contact piece 10 placed around the needle 20 and around the longitudinal axis 4, by means of rotation drive 28 of this contact piece and by control means 22 of the operations of control This contact piece 10 is preferably conical in shape, since its initial function is to separate the spacer wire 1 from the needle. It is also also called contact cone. It is in any case placed coaxially with the axis. main 4 and fuel needle

20.

  Once the spacer wire 1 has been cut, the needle 20 then being freed from the latter can be cut into sections to be subjected to subsequent treatment operations

  used fuel, including dissolutions.

  The device according to the invention has been represented in two parts in FIG. 2 for reasons of layout, it is understood of course that the two lower and upper parts of this FIG. 2 are in reality one next to the other. We find in this FIG. 2, the main elements of FIG. 1, that is to say the needle, the spacer wire 1, the contact device 10 and the control means 22 We have also shown in phantom, the cutting device 24 of the

Figure 1 by two electrodes 25.

  Given that the spacer wire 1 is brought to a determined cutting potential VC, preferably by means of the cutting electrodes 25, the concept of the control method according to the invention consists in detecting the presence of a potential difference between this spacer wire 1 and a determined reference potential V Indeed, the cutting device, by its operation, brings the spacer wire 1 and the fuel rod 20 to a determined cutting potential VC In addition, it is very useful to use a contact device 10 which separates the spacer wire from the needle 20 Indeed, the concept of the invention is based on the fact that once cut, the section of spacer wire I is no longer kept at potential of cutting VC like the rest of the spacer wire I and the fuel needle 20 The section of spacer wire 1 cut being always in contact with the contact piece 10, it is then immediately brought to the reference potential V of this piece

contact 10.

  Consequently, the main operation of the method according to the invention consists in continuously measuring the potential of the contact piece 10

  and compare it to the determined reference potential.

  In this way, if the spacer wire 1 is cut, the potential of this contact piece 10 will remain the same. In this case, it can be chosen equal to a determined reference potential V The reference potential V can be provided by n ' any part and can be in particular that of the frame 36 of the device according to the invention On the other hand, if the spacer wire 1 has not been cut, the contact part 10 will be brought to the cutting potential VC By continuously comparing the potential of the contact piece with the reference potential V, it is thus easy to determine whether the cutting of the spacer wire 1 was effective or not by the presence of a difference between the potential of the contact piece 10 and the potential of reference V. In the case where the spacer wire 1 is cut using an electrode cassette, and in order not to damage the parts in electrical contact with the spacer wire 1, it is preferable to interrupt contact while cutting the spacer wire 1 takes place Indeed, in the case where the spacer wire 1 is not cut, the large current load delivered by the electrodes will tend to be distributed in these parts of the machine which are in contact with the spacer wire 1 These parts could therefore be damaged by

  excessive heating due to the Joule effect.

  Originally, the contact piece 10 is conical in order to separate the spacer wire 1 from the fuel needle 20. According to the invention, it may have a complementary shape ensuring permanent contact with the spacer wire 1 As 2 shows it, this shape can consist of a radial extension of taper greater than the cone and constituting a sort of fin along the spacer wire 1, if it is rotated,

  during the angular displacements of the latter.

  Indeed, the fuel rod 20 advances between two consecutive cuts and the spacer wire 1 has an angular position which therefore evolves. In the case where this contact piece 10 has a protrusion, it is rotatably mounted around the axis 4 of the machine, in order to follow the angular position of the spacer wire 1 The speed of rotation of the contact piece 10 must be greater than the speed of movement of the angular position of the spacer wire 1 in a given plane, perpendicular to the axis horizontal 4 The spacer wire 1 will therefore have any angular position with respect to the contact piece 10. In the embodiment described in these figures, the control device has clamps 2 placed just upstream of the contact piece 10 These clamps 2 are integral in rotation with this contact piece and serve to pull the fuel needle 20, horizontally along the axis 4, between two successive cuts of the spacer wire 1 Their opening and closure can be controlled by an electromagnet 26 The frame 36 of the device according to the invention is mounted movable in translation along the main axis 4 to allow the displacement of the fuel needle 20 by means of the clamps 2. L electromagnet 26 can be mounted coaxially with the main axis 4, around the trajectory of the fuel needle 20 which passes through the middle of the device according to the invention By means of a spacer 28, it can thus be controlled by a slight translation of the opening of the clamps 2 thanks to slightly inclined and corresponding surfaces 29, machined both at the end of the spacer 28 and inside the clamps 2 A return spring 30, having a fixed end relative to to the electromagnet allows the removal of this spacer 28 and the closing of the clamps 2: The rotational drive of the contact piece 10 can be ensured by means of the housing 32 with which the contact piece 10 is ground ideal by means of a toothed wheel 34 fixedly mounted on this body 32 This toothed wheel 34 can be driven by means of a corresponding toothed wheel not shown in a rotational movement provided by any motor. This assembly is therefore mounted rotating relative to a frame 36 of the device via at least two rolling bearings 38. The potential of the spacer wire 1 and therefore of the contact piece 10 must be transmitted to the measuring means 22 For this purpose, uses an electrical conductor 9 connecting the contact piece with a track 8 placed at the periphery of the housing 32 This track 8 is a cylindrical surface coaxial with the horizontal main axis 4 It is itself conductive A collecting brush is placed in correspondence with this track 8 and rubs on it It is held by a brush holder 14 to which is connected a transmission wire 18 connected on the other hand to the measurement means 22 A relay 16

  can possibly complete this installation.

  The electrical potential of the spacer wire 1, which is the theoretical cutting potential VC, can be constantly compared with the reference potential V,

  preferably outside cutting times.

  The detection sequence can consist of the following successive operations: cutting the wire by means of the electrodes 25; advancing one step of the needle 20 by means of the clamps 2; detection by means of the contact piece and the connecting pieces of the potential of the spacer wire 1; comparison with the reference potential V; 1) if the wire is cut; advance of an additional step of the fuel needle 20;

new spacer wire cut 1.

  2) if the wire is not cut, second cut of the spacer wire 1 by means of the electrodes 25; second detection of the VC cutting potential; new comparison with the reference potential V; and so on

ADVANTAGES OF THE INVENTION

  It can therefore be seen that the control device according to the invention requires very few new elements compared to the already existing installation, when the cutting is carried out by means of electrodes. Indeed, the friction of the wire

  spacer I on a contact piece 10 already exists.

  The latter is therefore automatically at the cutting potential VC The elements for transmitting this electrical voltage to the measuring devices are the only important new elements in the device

according to the invention.

  1 1 A simple absence of difference between the reference potential V and the cutting potential VC indicates that the spacer wire 1 has not been

completely cut.

  All of these cutting and checking operations can be combined using a PLC.

Claims (6)

  1 Method for controlling the cutting of a spacer wire (1) of a nuclear fuel needle (20), the spacer wire (1) being brought before cutting to a potential (VC) different from that (V) d '' a reference piece, characterized in that it consists in measuring the difference between the potential of the spacer wire (1) and that (V) of the reference piece in order to detect an absence of cutting of the spacer wire (1), when this potential difference is effective.   2 Method according to claim 1, characterized in that the control of the cutting of the spacer wire (1) is interrupted for the moment   o the cutting of this spacer wire (1) takes place.   3 Method according to claim I or 2, applied to an installation for processing a fuel needle (20) in which the cutting of the spacer wire (1) is carried out by means of a multi-electrode cassette (25).   4 Device for controlling the cutting of a spacer wire (1) of a fuel needle (20), the spacer wire (1) being brought during cutting to a cutting potential (VC) different from that (V) a reference part, characterized in that it comprises: a contact part (10) intended to be in contact with the spacer wire (1); means for measuring (22) the difference between the potential of the contact piece (10) and   that (V) of the reference part.   Device according to claim 4, characterized in that the contact piece (10) is a conical, hollow piece, in the form of a cone, and placed around the needle (20), moving along an axis of movement (4) downstream of the cutting device (25) and on the external surface of which the wire spacer (1) rubs.   6 Device according to claim 5, the spacer wire (1) being wound in a spiral around the needle (20), characterized in that it comprises grippers (2) of the fuel needle (20), integral and coaxial in rotation with the contact piece (10); means for driving in rotation (34) the contact piece (10) to maintain the contact of the spacer wire (1) on the contact piece (10) at the same angular location; a connection track (8) coaxial and mechanically and electrically secured to the contact piece (10); a fixed collecting brush (12), connected to the measuring means (22) and rubbing on the track connection (8).   7 Device according to claim 6, characterized in that it comprises an electromagnet (26) placed inside the casing (32), coaxially and around the axis of movement (4) of the needles (20), to control the opening and closing of the pliers (2), when handling the needle fuel (20).