DE1542175A1 - Process for the reprocessing of spent nuclear fuel as well as device for carrying out the process - Google Patents

Description

Process for reconditioning used Nuclear fuels and devices for carrying out the process

The invention relates to a method for the reprocessing and disposal of spent nuclear fuel by the spent nuclear fuel is first dissolved with the help of a solvent and then the substances by extraction are obtained from the solution, the invention also relates to devices that are advantageous for performing the Process can be used, but they can also be used for other purposes, such as, for example, generally for the preparation of solutions or have it used for mixing and extraction purposes.

The nuclear fuel from nuclear power plants are after a taken out of the reactor vessel for a certain operating time in order to clean it or the still unused and recover newly formed valuable fissile materials and artificial elements. The recovery takes place in Reprocessing plants in which the fuel and breeding material like uranium, plutonium and thorium on the one hand freed from the fission products and on the other hand separated from each other will.

Process for the reprocessing and purification of nuclear fuel are known in different designs

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According to one of these known processes, known as the "ehop-leach" process is referred to, the rod-shaped fuel assemblies Chopped into small pieces of about 50 to 60 mm, having previously cut the fuel bundle into individual rods have been dismantled. The pieces of fuel rod falling out of the shearing machine are placed in a solvent, in which only the nuclear fuel dissolves and the cladding material remains in solid form. The dissolving the nuclear fuel takes place in a device, the filling and emptying of which is carried out intermittently. The fuel solution flows from this device to a separation column in which the fissile materials are separated from the fission products and from each other. So-called "Mixersettier" are used in the separation process which are the aqueous phase (nuclear fuel solution) and the organic phase (extractant) are in countercurrent. In several stages, the phases are controlled by a stirrer first mixed together in one chamber and then in one under the action of natural gravity separated calming zone separated. Both phases are fed to the column continuously and also continuously derived from this.

A major disadvantage of the known processes is that they only permit continuous operation in individual stages. In addition , the throughput rate of these known processes is relatively low, since the dissolution is discontinuous and the separation takes place under the action of natural gravity. Because of the relatively low throughput rates, large structural units result for such systems. Another disadvantage is the possibility of the fission materials and fission products being deposited in the individual apparatus, as this can lead to nuclear damage and an increase in radioactivity.

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The invention is based on the object of eliminating the mentioned disadvantages of the known methods and a Continuous process for the reprocessing of spent nuclear fuel in all process stages to create, which allows high throughput rates with small devices. The small dimensions the apparatus allow a large tolerance of the degree of enrichment of the fissile materials to be processed, without the to achieve critical mass »Another object of the invention suitable devices for carrying out the process . "

According to the invention, the nuclear fuels are in crushed, preferably in ground form in one continuous form working dissolving tank brought into solution, from which the nuclear fuel solution is continuously withdrawn and is fed to an extraction column consisting of mixing centrifuges in which the in solution Substances are continuously extracted from the solution.

The main advantage hereby is that the nuclear fuel dissolves without any deposits of the same takes place in the individual devices and also the mixture with the extractant and the subsequent Separation of the phases takes place independently of the natural gravity of the same by centrifugal action, whereby considerably higher throughput rates can be achieved than before with small-sized apparatuses. The reprocessing plant can be operated continuously in all stages, which is with regard to the hazard caused by Criticality and radioactivity offer significant advantages.

To carry out the method according to the invention, devices are used in which the substances are initially in

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Solution brought and then separated by means of an extractant.

To produce the solution, a device is expediently used which, according to the invention, consists of a closed rotating container consists of the with supply lines for the solvent and the substance to be dissolved as well as with a derivative is provided for the solution. Mixing and / or stirring devices are preferably in the rotating container arranged. A transport device, preferably one, is expediently located inside the container Conveyor screw arranged, which transports the substances to be dissolved in countercurrent to the solvent through the container. For emptying the container, rotating blades 3 3 in. Can be arranged in the container.

Zv / angular is in particular an arrangement in which two Coaxial cylindrical containers rotating against one another are provided, each having a screw conveyor. The inner container can be used to remove the substances that do not go into solution while the solution of the releasable substances in the space between the inner container and the outer container takes place according to the countercurrent principle.

The substances and the solvent are fed to the container and the solution is discharged continuously Way of working. The solution leaving the container is then fed to an extraction device, in which the substances in solution are obtained separately Extraction is preferably carried out in microfuge that according to the invention are provided with separate inlet and outlet lines for the various liquid phases, their

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The distance from the rotating shaft is different, it is big * The Misoh centrifuges advantageously consist of a preferably conical container in which a rotating centrifugal drum is arranged. The inlets and outlets for the liquid phases are arranged so that the supply of the liquid with the higher specific gravity lies at a point that has a smaller distance from the centrifuge axis of rotation than the The supply of the liquid with the lower specific weight, while the discharge of the liquid with the greater specific weight is arranged at a greater distance from the centrifuge axis than the derivative of the Liquid with the lower specific weight. on In this way it is achieved that the liquid phases fed to the centrifuge are prevented by the centrifugal drum Change their place, whereby an intimate mixing of the liquids is achieved. In addition, the individual Remove the phases from the centrifuge separately from one another. To increase the resistance to resistance, special misoh or stirring elements can be attached to the centrifugal drum, e.g. blades, baffles or the like. be arranged. Such guide elements are useful both on the Arranged inside as well as on the outside of the shell of the centrifugal drum, the arrangement preferably is made in such a way that the guide elements on the outside of the centrifugal drum cause a downward flow and the guide elements on the inside of the centrifugal drum cause a flow close to the top

The devices according to the invention can be used with particular advantage for carrying out the method according to the invention. Xs understands eiob. but that the devices can also be used for other purposes

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and are generally applicable where there is a problem of bringing substances into solutions or chemical reactions or to carry out separations of the phases or an extraction in a continuous procedure.

Advantageous exemplary embodiments of the devices according to the invention are shown in the drawing. Show it:

Fig. 1 a device for the continuous dissolving of substances, especially nuclear fuels}

Fig. 2 shows a centrifuge intended for the extraction of substances, in particular nuclear fuels according to the invention.

The device according to Fig. 1 consists of a closed cylindrical outer container 1, in which a likewise closed cylindrical inner container 2 is arranged coaxially. The outer container 1 is closed on the front sides by means of lids 15 and 15 *, from which at least the deodorant 15 can be easily removed. The outer container 1 is set in rotation via a driven shaft 19 or by means of rollers 22, which also serve to support the container.

The inner container 2 is arranged in a stationary manner in the outer container 1. It is passed through the lid 15 of the outer container and is supported on the outside at a bearing 21. To the weight of the outer container 1, a screw conveyor 3 is mounted on the inside, so that it rotates with the external container 3 · The spiral of Sohnek- ke consists of a sheet metal which with perforations 3 ''

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is provided. Rod-shaped ones serve to strengthen the spiral Spacer 20.

In the interior of the inner container 2, a second screw conveyor 7 is arranged, which sits on an axis 16, which is rotatably coupled to the shaft 19 by means of a square bolt 18, so that the worm 7 together with the storage container 1 and the screw 3 rotates. To the One end of the inner container 2 has a funnel-shaped opening 5 which forms the inlet of the inner container. The outlet 8 of the inner container is located at the other end located outside the outer container 1.

In the interior of the outer container, perforated blades are arranged, which rotate with the outer container and thereby take up any undissolved material lying on the bottom of the outer container and, as it rotates, into the Throw funnel 5 so that it is conveyed by screw 7 to outlet 8.

Four connection lines 6, 9, 11 and 14 are arranged on the cover 15 of the outer container 1. Via the connecting cable 6 is the crushed nuclear fuel with or without construction material and casing in the space inserted between the outer and inner container, so that it is from the screw 5 in the direction of arrow P to the other end of the Container is transported. The dissolving liquid is supplied via a pipe 9 which is located in the hollow axis 16 lies. The hollow shaft 16 is on the opposite one Side with cross bores 17 or the like. provided, through which the dissolving liquid enters the outer container 1. The dissolving liquid then flows against the transport direction of the

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Screw 3 (opposite to arrow P) through the container and dissolves the nuclear fuel. The nuclear fuel solution leaves the outer container 1 on the opposite side via the drainage pipe 11, which leads to a funnel on the inside is expanded. There are shovels inside the outer container

10 and 13 placed the nuclear fuel when rotating Take up the solution and put it in the funnel of the drainpipe

11 promote.

A perforated ring plate 12 is expediently arranged between the screw 3 and the blades 10, which prevents that still undissolved substances are shoveled out with the nuclear fuel solution.

The gases produced in the outer container 1 when the nuclear fuel is dissolved are sucked off through the opening 14.

The outer container 1 is filled during operation only up to a height below the inner container, so that the dissolving liquid cannot flow out of the outer container. The screw 3 expediently consists of a material which consists of boron or boron alloys, which have a high lieutron absorption capacity.

The blades 10 and 13 fixedly mounted on the inner wall of the cover 15 are dimensioned so that their delivery capacity is greater than the length of the supplied dissolving liquid.

As can be seen, all of the openings or connections 6, 8, 9, 11 and 14 are at one end of the outer container 1 arranged. The lid 15 can be removed from the outer container 1. After removing the cover 15, the parts that are located in the outer container 1 can be pulled out of this will.

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If necessary, the arrangement can also be made in such a way that the inner container 2 together with the ">>■". nck "1 Ii ^r T is iarehung added, while the outer container 1 and the screw 7 are fixedly arranged. The directions of transport of the substances through the container are the same in this case.

The nuclear fuel solution leaving the container via the opening 11 is fed to an extraction system which consists of several mixing or extraction centrifuges connected in series. In Fig. 2 is such a Centrifuge shown in which the fissile materials from the fission products and these from each other with the help of an extractant separated from each other.

The device consists of a stationary sedimentation tank 100, which widens conically downwards and is airtight on the top by means of a cover 102 is locked. Those resulting from the extraction. Gases can escape through a tube 112 on the cover * be sucked. In the container 100, a rotating centrifugal drum 103 is arranged, which is driven on a Shaft 104 is mounted, which lies in a fixed outer axis 105. The outer axle 105 is used for fastening of the container 100. It has an interruption 120 at the bearing point of the centrifugal drum and is at one storage point 114 between two consecutive Centrifuge is screwed tight.

Two connection lines 106 and 107 are arranged on the cover 102, whose mouths are inside the container at different distances from the axis 4/5. The pipeline 106 opens into the space between the centrifugal drum and container jacket, while the pipe 107 into the The interior of the centrifugal drum opens.

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The centrifugal drum has a jacket with openings, like sieve openings or the like. is provided. she can from a wire mesh or the like. be made.

A drain pipe 109 is arranged on the outside of the bottom of the container 100. Furthermore, a drain pipe 108 is arranged in the vicinity of the outer axis 105> immediately below the interruption 120 and is covered by a bell-like deflector plate 115 so that a siphon-like overflow is formed. Furthermore, a tube 116 joined reasonable ψ, which opens approximately at the bottom of the shell of the centrifugal drum to the overflow.

The device works as follows. The specific gravity Phase, d. H. the nuclear fuel solution is through the pipe 107 in the space between the outer axis 105 and the centrifugal drum 103 introduced, while the specific light phase, i.e. H. the extraction liquid, via the tube is fed at a point outside of the centrifugal drum which is located at a greater distance from the axis 105. the two phases are therefore under the action of the centrifugal forces that are established by the rotation of the centrifugal drum change places, d. H. it becomes the specific heavy phase through the jacket of the centrifugal drum outwards to the outer surface of the conical container 100 and the specifically light phase in the opposite direction migrate from the outside of the centrifugal drum into its interior, producing an extremely intense mixture or chemical reaction of these two phases takes place. The liquid in the container 100 rotates with the centrifugal drum 103, with its speed

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however, is smaller than that of the centrifugal drum.

This further increases the mixing effect.

To aid the rotation of the fluid are on The outer and inner surface of the shell of the centrifugal drum blades 110 are arranged. Further are at these two Areas of small guide vanes 111 or the like. attached that a flow of circulating liquid in the way cause there is a downward and inward flow of liquid in the outside of the centrifugal drum the liquid inside the centrifugal drum

adjusts an upward flow. This current forces " the easy phase down and the heavy phase up. This will ensure a quick separation of the phases the desired chemical reaction slowed down

The inside of the centrifugal drum is located via the drain pipe 108 adjusting specific light phase withdrawn and to that forming the next stage of the process Mixing centrifuge conveyed. The baffle 115 seated over the drain pipe 108 prevents the inflow of the heavy phase into the pipe 108. The heavy phase which is established on the outside of the centrifugal drum is on Bottom of the container discharged via the drain pipe 109 and i promoted to the previous level.

If the amount of liquid in the centrifuge is so small that a drainage via the drainage pipe 108 is not possible, the light phase separating under the centrifugal effect will pass through the curved channel 116 fed to the drain pipe 108.

Patent claims:

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Claims (1)

Claims Process for the reprocessing and cleaning of spent nuclear fuel by removing the spent nuclear fuel first dissolved with the help of a solvent and then the substances are obtained by extraction from the solution, thereby characterized in that the nuclear fuel in comminuted, preferably ground up, in a continuous working dissolving container (1) brought into solution and the substances in solution then in a Mixing centrifuges (100) existing jixtraction column are continuously separated from the solution. Device for dissolving a substance by means of a solvent, especially for the continuous dissolving of nuclear fuels in a method according to claim 1, characterized in that it consists of a closed rotating Container (1) exists, der.mit feed lines (9> 6) for the solvent and the substance to be dissolved as well as with a Derivation (11) is provided for the solution. 3. Apparatus according to claim 2, characterized in that mixing and / or stirring devices are arranged in the rotating container (1). 4. Apparatus according to claim 2 or 3, characterized by a transport device, preferably a screw conveyor (3) »which transports the material to be dissolved through the container in countercurrent to the solvent. - 13 -009823 / U37 5. Device according to one of claims 2 to 4, characterized in that that the supply and discharge lines (6, 8, 9 »11» H) are arranged on the same end wall (15) of the container (1) are. 6. Device according to one of claims 2 to 5, characterized by rotating blades (10, 13) arranged in the container for emptying the container (1). Device according to one of Claims 2 to 6, characterized by two counter-rotating, coaxial cylindrical containers (1, 2), each with a screw conveyor (3, 7). 8. Device according to one of claims 2 to 7 »characterized in that that the transport screw or screws (3, 7) made of a material with high neutron absorption capacity exist. 9. Apparatus according to claim 4 or 8, characterized in that that the screw flights of the screw conveyor (3) of the outer container (1) are perforated. 10. Device according to one of claims 2 to 9 »characterized in that that at both ends of the cylindrical container (1) rotating blades (4, 10, 13) are arranged are, the blades (10, 13) arranged at one end for discharging the solution from the container (1) and -H-009823/1437 the soils (4) arranged at the other end for Feed the undissolved material into the inner container (2). 11. Device for chemical conversion, e.g. for the extraction of substances in solution by means of an extraction means, in particular for the extraction of the fissile materials in a method according to claim 1, characterized by the Use of at least one mixing centrifuge, which is provided with separate inlet and outlet lines for the liquid phases is whose mouths in the centrifuge a different distance from the axis of rotation of the centrifuge to have. 12 * Device according to claim 11, characterized in that the misoh centrifuge consists of a preferably conical container (100) in which a rotating centrifugal drum (103) arranged iet Device according to claim 11 or 12, characterized in that the supply line (107) for the liquid with the higher specific gravity is at a point that is closer to the centrifuge rotating shaft than the Inlet (106) of the liquid with the lower specific weight, while the outlet (108) of the liquid is arranged with the lower specific weight at a smaller distance from the centrifuge axis than the Derivation (109) of the liquid with the greater specific weight. - 15 -009823 / U37 14. Door direction according to claim 13, characterized in that the feed line (107) for the liquid with the higher specific weight on the inside of the centrifugal drum (103) and the supply line (106) for the liquid with the lower specific weight on the outside of the Centrifugal drum 103 is arranged, while the discharge line (108) for the liquid with the lower specific Weight on the inside and the discharge (109) for the liquid with the higher specific weight on the Outside of the centrifugal drum (103) is arranged. 15 · Device according to one of claims 11 to 14, characterized characterized in that the mixing centrifuge has a double axis (4, 5), the centrifugal drum (103) on the rotating inner axis (104) and the container (100) forming the housing is arranged on the outer axis (105). 16. Device according to one of claims 11 to 15, characterized characterized in that the centrifugal drum (103) is provided with jacket openings, preferably one in the form of a network having trained coat. 17. Device according to one of claims 11 to 16, characterized characterized that on the centrifugal drum mixing · or Stirrer elements such as blades (110) are arranged, the support the liquid phases in their rotational movement. - 16 - 0-9 823/1437 18. Device according to one of claims 11 to 17, characterized in that that on the outer surface of the centrifugal drum (103) guide elements such as strips, guide plates (111) or the like. are arranged, the on the outside of the centrifugal drum a downward flow and on the inside of the Centrifugal drum cause an upward flow or vice versa. 19. Device according to one of claims 11 to 18, characterized characterized in that the drain pipe (108) for the specifically light phase in the vicinity of the axis of rotation (104) of the centrifugal drum (103) is arranged and is protected against the inflow of the heavy phase by a deflector (115). 20. Device according to one of claims 11 to 19, characterized characterized in that several mixing centrifuges are arranged from a common axis (104) and from one common motor are driven. 009823 / U37 Blank page