FR2472250A1 - METHOD AND APPARATUS FOR EXTINGUISHING NUCLEAR COMBUSTIBLE MATERIALS FROM THEIR SOLDERING TUBES - Google Patents

Abstract

A. THE PROCESS IS INTENDED TO EMPTY THE DUCTS CONTAINING IRRADIATED NUCLEAR FUEL COMING FROM DIFFERENT TYPES OF REACTORS. B. THE INSTALLATION ALLOWS TO SLIT THE DUCTS 5 ON A HELICAL LINE AND TO OPEN A SLOT WIDE ENOUGH TO ALLOW THE FUEL TO FALL INTO A HOPPER. C. THIS INSTALLATION ALLOWS THE EMPTYING OF NUCLEAR FUEL DUCTS WITH A HIGH FLOW AND A MINIMUM OF POLLUTION.

Description

1.- 2472250

  The invention relates to a method and a

  device for emptying the sheaths of nuclear fuel rods

  areas for boiling water reactors, pressurized water

  regenerators, by mechanical cut of the fuel sheath

  nuclear weapons, in particular of combustible

  nuclear weapons they contain.

  After their implementation in the reactions

  nuclear power plants, irradiated fuel elements, ie

  say burned, are stored then retired. Uranium and plutonium, most often present as dioxides, are here separated from the fission products and then converted back into fuel elements. The fission products and the remains of the cladding tubes are conditioned and sent to a final depot.

  Several methods are known for

  irradiated fuel elements, that is to say burned.

  A process has been presented ("Entsorgung der Kerntechnik", Proceedings of the 19 May 20, 1876, Mainz, edition of Deutschen Atomforum eV, Bonn), according to which the elements or fuel rods are brought perpendicular to a hydraulic shear at beams. This cutter cuts

  fuel rods in short segments about 5 cm long.

  These bar segments containing the irradiated nuclear fuel material fall into a dissolving basket, where the irradiated nuclear fuel material of the cladding tubes is dissolved with hot nitric acid. Dissolved nuclear fuel

  is then treated by the extraction processes.

  This process has significant disadvantages. The availability of very expensive beam shears is low because the dissolution process must be

  to proceed in a discontinuous manner as a result of the regular evacuation

  empty fuel sheaths. In addition, the shearing speed of the shears is relatively low because it is controlled by the amount of radioactive waste gas released during the dissolution. This command is needed by

  compulsory feeding of the filter device

  waste gas. The costly conformation dictated by the perpendicular supply of the fuel elements also makes the shear extremely fragile, so that one has to dispose of

  at least one other reserve shear. The dissolu-

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  The necessary removal of the solution, which must be able to evacuate, further complicates the construction of the dissolution device and renders it fragile, and furthermore prevents the continuous operation of the dissolution operation. Another disadvantage is that during the dissolving operation in hot nitric acid,

  radioactive tritium is released by the sheaths, and its removal

  nation poses problems. It is also unfavorable that in each case the sheaths must be washed after their expulsion from the dissolution device, before being packaged and

stored permanently.

  Another reprocessing process is known as "Vol-oxidation". In this process, the bar segments with the irradiated nuclear fuel are heated in an oven, in a stream of air, at 400-5000 C, and oxidized. The uranium dioxide pellets are then decomposed into pulverulent U308, and the fission products also oxidize as far as possible. The pulverulent mixture is mechanically separated from the sheaths and is then introduced into the dissolver which thus no longer contains a dissolving basket. A continuous dissolution process is therefore possible, but it has considerable disadvantages. The oxidation process in the oven changes the

  structure of the uranium network and other elements

  cipants. As a result, large quantities of radioactive isotopes

  Gaseous assets of iodine and krypton elements are released, which implies an expensive filtration facility. It is

  even for tritium, which is released by the sheaths in proportion

  high temperatures at oven temperature. Since, during the subsequent dissolution, other quantities of this radioactive gas are released, provision must be made in at least two places for the complex treatment of the radioactive waste gases. The use of furnaces for the oxidation of highly radioactive materials is also linked to difficulties, and mechanical separation

  ducts also means an expensive step.

  There are also proposals for methods of removing cladding tubes surrounding the fuel, other than by cutting off the elements or

  fuel rods with a beam shear. -

  Thus, DE-1 042 777 discloses a device, which allows to cut and remove the sheaths under water and then grind the fuel. The operation of this device, however, requires that the fuel constitutes a coherent piece, in the form of a bar, and is therefore not suitable

  to empty the sheaths filled with pellets. Another incon-

  venient is constituted by the considerable expense entailed by

  the construction of moving and fragile parts, which excludes

  the implementation for industrial processing,

  irradiated fuel elements, in hot cells.

  US Pat. No. 2,880,636 discloses a device which makes it possible to obtain longitudinal slots in the sheath and to fold it into two strips by means of wedges. The disadvantage here lies primarily in the high wear of cutting tools, which leads to downtime for repairs. In addition, the precise fixing of fuel rods, necessary for

  to practice a proper cleft, raises problems ..

  DE 1,280,427 also describes

  a device that allows, with specially shaped sheaths-

  rigid, such as cladding tubes provided with cooling profiles, to separate the sheath of the nuclear fuel by longitudinal slots. By a complicated system of pushers, the combustible material is pushed through a

  perforated plate at the same time as the longitudinal slot is

  However, this device is not suitable for the irradiated fuel elements of boiling water or pressurized water reactors because these elements are long and their shape is not rigid. Another disadvantage is that one must separate at least the first end cap before operating,

  and that the device has many moving parts.

  The outer sheath of a fuel element of a liquid sodium cooled reactor can be separated by means of a sheath-eliminating machine described in DE 2 108 041. Fuel ducts

  properly so called are not concerned.

  Accordingly, the invention aims to provide a method and a device for emptying the sheaths of nuclear fuel rods for pressurized water boiling water reactors or breeder reactors by mechanical notch of the nuclear fuel sheath, in particular of 4l .. - 2472250 irradiated nuclear fuel materials contained therein, which can operate without a complicated mechanical device, which requires little repair and is easily repaired, which provides high efficiency and immediately provides a powder of nuclear combustible material usable directly for reprocessing. For this purpose the invention proposes that the sheath is cut in a helical pattern and that the notch is widened by folding and / or twisting the notched part of the sheath. The opening operation is preferably performed by means of a cutting operation. If the sheaths are made of stainless steel, it has proved especially advantageous to first cut the sheath along a helical line and then, by printing a tension with the helical cuts, to blow them. The advantage of this method is that the notch tool does not wear on the ceramic fuel. In addition, the obtained metal chips can be kept separate

fuel.

  By untwisting the helical band obtained by the cuts, the fuel is completely released by folding and / or twisting the notched portion of the sheath, so that it can flow and be collected in a suitable container. The sheath will preferably be folded

at an angle of 10 to 400.

  The method according to the invention is preferably implemented in a device which essentially consists of a casing, where are housed the supply, evacuation and guiding of the sheaths, a transport device and a member intended to cut the sheaths, a device characterized in that

  the transport device and the element for the cut

  feel in the form of a pair of separately driven rollers arranged coaxially one beside the other, that this pair of rollers composed of a transport roll and a notch roll and the two support rollers for guiding the cladding tubes, are directly opposite and shifted each time 1200, the axis of the rollers still forming an angle of 30 to 600 with the axis of the sheaths, and that the supply ducts form an angle

with their evacuation.

  The invention will be better understood with the aid of the single appended figure, schematically showing, at

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  As an example, an embodiment of the device according to the invention. The fuel rods 2, for example from intermediate storage, consist of a sheath 1i which contains the "pellets" or pellets of combustible material 3 (hereinafter referred to as "pellets") consumed, prepared normally from The fuel rods 2 are transported on a suitable base, such as a profile plate, horizontally with respect to the slotting device 4, and introduced into the duct supply 5. By means of the driven conveyor roller 7, which has on its periphery, the teeth 6 spaced 2 mm for example, and having a steep side in the direction of transport, the sheath 1 is driven with the fuel pellets 3, in the axial direction between the untrained support rollers 9 and the roller notch 8 trained. These rollers are directly opposite and they are shifted each time by 1200, the axis of

  rollers forming an angle of 30 to 600 with the axis of the sheath.

  The sheath introduced thus describes a helical movement. The

  transport rollers 7 and the notch roll 8 are preferably

  carried separately by orientable wings 10, 11.

  The radius of curvature of the teeth 6 of the transport roller 7 is adapted to the radius of the fuel rods, variations of 10 to 15% of the diameter of the bars being easily compensated. The pressures exerted by the transport roller 7 and the notch roller 8, on the sheath 1 are separately adjustable from the outside by tensioning elements

12, 13.

  The fuel pellets 3 are

  greased into powder and pieces, and the sheath 1 is notched

  following a helical pattern by the notch and advance forces

  cement. The notch roller 8 comprises for example a diameter of about 100 mm-for fuel rod diameters of 11 to 13 mm. The large circumference or length of the resulting cut for the knife ensures very little wear. The notch roller 8 and the transport roller 7 are entrained

  preferably at different speeds, and is particularly

  favorably to drive the notch roller 8 about 30%

  faster than the transport roller 7. The helicopter belt

  4o dale of the sheath 14 obtained is slightly diverted from a

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  angle 10 to 40, on a deflection plate 16, for example connected to the evacuation of the sheath 15, the notch 17 is thus widened, and the sheath then going into a duct debris store. The disintegrated fuel 17 flows through the slit of the helical wrapping belt, for example into a fuel store 20. LaIfente 17 has a width of 6 to 15 mm, depending on the size of the sheath at the start. The notch device 4 is surrounded by a housing 19, which provides the necessary drive

  with the transport rollers 7 and the notch 8, the

  size 4 according to the invention, which may optionally be filled with inert gas, performs for example the complete emptying of at least 6 m of fuel rod per minute. For example, the complete emptying of 4.5 m long fuel rods with zircaloy sheaths, the dimensions of which are 11.7 x 0.4 mm, with welded plugs on both sides, and filled with pellets of Sintered uranium dioxide, compacted to 95%, is carried out. in 40 seconds, the peMets being crushed into powder or crumbs. The material used for the notch roller 8 is

hardened tool steel.

  The notch device has a weak structure and is unlikely to fail, due to

  that the rollers, which are the only moving parts, are easily

  Replaceable because they are connected to the box only by card links. The support rollers 9 are preferably adapted, on the peripheral surface of the rollers, to the diameter of the sheath, and they are adjustable and exchangeable from the outside.

  of the housing 19, by means of fasteners 21.

  The empty spiral tubes 14, however containing almost all of the tritium, are transported from the tube debris store to a compaction device and /

  or packaging, where a reduction may be

  volume of bulky debris before incorporation into a non-leachable matrix and their packaging for

subsequent final storage.

  The empty spiral tubes 14 can be cleaned before compaction and conditioning. As the notch device operates at ambient temperature, it hardly escapes from tritium, and because of the

  mechanical grinding, practically no radioactive release gas.

  The housing 19 of the notch device 4

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  according to the invention preferably has the shape of a hopper, and it is directly connected to a powder magazine 20 for the nuclear fuel, which comprises an evacuation and dosing device 22 for transferring the nuclear fuel into the container dissolution for reprocessing. The irradiated nuclear fuel is subjected to a continuous dissolving, without cladding, in hot nitric acid, the assay being carried out in such a way that the released radioactive gases and the nitrogen oxides formed reach the gas filter

rejection in optimal quantity.

  The method and the device according to the invention

  are suitable for all fuel rods of boiling water, pressurized water or fast breeder reactors, irrespective of the material of the sheaths, such as steel or zircaloy, and whatever the form of the fuel

  content, such as oxides or carbides.

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Claims (7)

  1. A method for emptying sheaths of nuclear fuel rods for boiling water reactors, pressurized water reactors or breeder reactors, by mechanical notch of the nuclear fuel sheath, in particular of irradiated nuclear fuel materials, which they contain, characterized in that that the sheath (1) is entailed in a helical pattern and that the notch is widened by folding and / or   twist of the notched part of. the sheath (1).   2. Method according to claim 1, characterized in that the notch is made by an operation cutting.   3. A process according to claim 1, characterized in that the notch is performed, if the sheaths are stainless steel, by notching and subsequent application   a tensile stress on the helical cut.   4. Process according to any one of   Claims 1 to 3, characterized in that the notched sheath   is bent directly after the notch operation on an angle from 10 to 400.   5.- Arrangement for implementing the   process according to any one of claims 1 to 4,   constituted by a casing, are accommodated the supply, evacuation and guiding of the ducts, a transport device and a member intended to cut the ducts, characterized in that the transport device (7) and the element for the notch (8) are in the form of a pair of separately driven rollers arranged coaxially with each other, that this pair of rollers comprises a transport roller (7) and a notch roll (8) and the two support rollers (9) serving to guide the cladding tubes, are directly opposed and offset each time by 1200, the axis of the rollers always forming an angle of 30 to 600 with axis of the ducts, and that the supply (5) of the ducts forms an angle with their evacuation (15).   6.- Device according to claim 5, characterized in that the transport roller (7) and the notch roller (8) are placed separately on wings (10, 11) hinged. 7) Device according to any one   Claims 5 and 6, characterized in that the roller of   transport (7) and the notch roller (8) are driven to different speeds.   o8) Device according to any one of   Claims 5 to 7, characterized in that the vacuation of the   sheath (15) is provided with a deflection plate (16) forming   an angle of 10 to 40O with the supply of the sheath (5).   9) Device according to any one of   Claims 5 to 8, characterized in that the support rollers   (9) are fitted to the peripheral surface of the rollers, to the diameter of the sheaths, and are adjustable and exchangeable   from outside the housing (19) by means of fasteners (21).   ) Device according to any one of   Claims 5 to 9, characterized in that the pressure of   transport rollers (7) and notch (8) is adjustable   separately from the outside, by means of tensioning elements (12, 13).   11) Device according to any one of   Claims 5 to 10, characterized in that the housing (19) has   the shape of a hopper and is connected to a powder magazine (20) for the nuclear fuel, provided with an evacuation device and dosage (22).