EP0042882B1 - Device for the receipt, the transportation and the ultimate storage of spent reactor fuel elements - Google Patents

Abstract

The invention relates to a device for holding, transporting and final storing burned-out reactor fuel elements comprising a hollow-cylindrical container that can be closed with a cover. On its sealing surface which is opposite the cover, the container is provided with projections which are of dovetail profile. The cover is cast onto the container around the dovetail projections by means of a casting mold whereby an intimate and firm connection between the container jacket and the cover can be produced. The cover can also be prefabricated with filler channels for directing metal casting material into recesses provided in the sealing surface of the cover. When the metal hardens in the recesses the cover is securely locked to the container. The container may have a shielding cover beneath the top cover.

Description

The invention relates to a device according to the preamble of claim 1.

Containers in cylindrical form are known which accommodate several fuel elements and can be closed with a lid. The loaded containers are introduced individually or in groups in drill holes (vertical or horizontal or inclined drill holes) provided in the repository (e.g. salt mine). For reasons of transport and handling, there are limits to size and weight.

Particular problems in the manufacture, transport and final storage of such containers arise with regard to corrosion, shielding against gamma and neutron radiation, sealing and strength of the connection between the container and the container lid and reusability of the container and parts of the container.

To protect the container against corrosion, it is known to use carbon steel, stainless steel or nodular cast iron (GGG) depending on the environmental conditions. To shield against gamma radiation, it is known to use lead or other radiation-shielding materials with a low melting point, and against neutron radiation, materials made from hydrocarbons, for example polyethylene.

From the publication »Proceedings of the 14th Conference on Remote Systems Technology, Pittsburgh, 1966 (USA), Miller et al:» Fusible Metal Seals in Process Equipment «, pages 213-218, is a seal for process equipment that can be installed and removed remotely known. The seal consists of a circumferential sealing lip, which is arranged on the lid or on the casing of a container, projecting outwards and with a part pointing downwards protrudes into a trough with meltable metal surrounding the container. With such a measure, only a seal can be achieved, but no firm mechanical connection between the lid and the container.

DE-B-2 740 933 shows a transport or storage container for radioactive materials, in particular for irradiated nuclear reactor fuel elements, of a conventional type. The transport or storage container is closed with a cover in the form of a stopper, which has an upper edge flange which the lid is screwed to the jacket of the container. There is also a cover plate that can be screwed to the container jacket above the lid. The closure provided in this known container has a low mechanical strength, and sufficient gas tightness is also unlikely to be provided.

EP-A-0 019 544 also shows a transport container with a rather complicated closure, which consists of several individual parts arranged one above the other. The bottom part has the shape of a plug with an upper edge flange which rests on an annular shoulder formed in the jacket of the container with the interposition of a seal. Above it is a clamping element pressing the stopper on the seal with a clamping screw. The actual lid sits above the clamping element, which also has the shape of a stopper and has an upper edge flange which rests on the end face of the container shell and can be tightened firmly against the container with the aid of a further clamping element which can be screwed to the shell of the container . In addition, the edge flange is welded circumferentially to the container in one embodiment or, in another embodiment, is provided with a hanging annular apron which, similar to the closure according to the publication "Proceedings of the 14th Conference on Remote Systems Technology", is known in one in the end face of the Container-trained trough dipped with meltable metal. This known container closure is very complicated and of insufficient mechanical strength, especially when lifting the lid is provided.

The object of the present invention is to design a container according to the preamble of claim 1 such that, while maintaining a good shielding effect, in addition to an absolutely gas-tight connection, a substantially better mechanical strength of the connection between the container and the container lid can be achieved.

This object is achieved according to the invention by the design features specified in the characterizing part of claim 1.

A gas-tight and mechanically secure connection of the container and the container lid can be achieved by the design according to the invention. The design according to the invention enables the lid to be poured after the container has been loaded, as a result of which a very intimate connection is achieved on the sealing surfaces between the lid and the container, so that perfect shielding is also achieved in the area of the sealing surface. The strength of the connection is so great that the container can be lifted on the lid.

Appropriate and advantageous developments of the solution according to the invention are characterized in the dependent claims.

An advantageous method for producing a cover according to one of claims 5, 8 and 13 or 14 is specified in claim 18.

• Fig. 1 schematisch einen Schnitt durch eine erfindungsgemäße Vorrichtung,
• Fig. 2a, b perspektivische Ansichten zweier Vorrichtungen nach Fig. 1 mit unterschiedlich ausgebildeten Behältern,
• Fig. 3 einen Schnitt durch die Vorrichtung nach Fig. 1 im Deckelbereich des Behälters in einer ersten Ausführungsform,
• Fig.4, 5, 6 und 7 Schnitte durch die erfindungsgemäße Vorrichtung im Deckelbereich bei weiteren Ausführungsformen,
• Fig. bis 11 weitere Ausführungsformen der erfindungsgemäßen Vorrichtung,
• Fig. 12 Ausführungsbeispiele für die verwendeten Erhebungen oder Rippen,
• Fig. 13 eine Ausführungsform einer im Behältermantel angeordneten Ausnehmung,
• Fig. 14 Ausführungsformen von in den Behälter einsetzbaren Innenbehältern.

The invention will now be explained in more detail with reference to the drawing, in which exemplary embodiments are shown. It shows

• 1 schematically shows a section through a device according to the invention,
• 2a, b perspective views of two devices according to FIG. 1 with differently designed containers,
• Fig. 3 shows a section through the device 1 in the lid area of the container in a first embodiment,
• 4, 5, 6 and 7 sections through the device according to the invention in the lid area in further embodiments,
• 11 further embodiments of the device according to the invention,
• 12 exemplary embodiments for the elevations or ribs used,
• 13 shows an embodiment of a recess arranged in the container jacket,
• 14 shows embodiments of inner containers which can be inserted into the container.

In the drawing, the same components are provided with the same reference symbols.

The drawing shows a device 2 with an open on one side 4 hollow cylindrical container 6 for receiving, transporting and for the final storage of fuel elements 8 and 10. The cavity 11 of the container can for example be circular cylindrical (Fig. 2a) or a rectangular or polygonal Have cross section (Fig. 2b).

The container 6 can be closed with a lid 12.

The wall of the container 6 is formed in one piece. But it can also be formed in several parts. It is preferably made of carbon steel or stainless steel for smaller wall thicknesses and preferably made of carbon steel or nodular cast iron for larger wall thicknesses. The wall thickness is chosen so that gamma radiation is absorbed; For example, a thickness of 200 mm is sufficient to fall below the transport limit values of 200 mrem / h on the surface. With large wall thicknesses, nodular cast iron has the advantage of being inexpensive in combination with ductility and a good shielding effect. In special cases the wall thickness depends on the repository formation and the corrosion induced on the container. In addition, of course, economic aspects are also decisive. A recoverable spheroidal cast iron outer shield can also be used for transportation in order to minimize the wall thickness of the lost final storage container.

Such an embodiment can e.g. B. as a double container, consisting of an inner and outer container, which will be described in more detail below with reference to FIG. 14.

The peripheral shape of the container 6 is preferably circular in order to simplify the production of the boreholes into which the containers are inserted for the purpose of final storage.

Around the actual container 6 there is usually a cylindrical shield 13, for example made of a suitable hydrocarbon, such as polyethylene, for absorbing the residual neutron radiation. A wall thickness of 3-4 cm is usually sufficient. This shield is arranged so that it can be removed for reuse after transport to the repository.

The free volume in the cavity of the container can be poured out with a filler material to improve the stability and the shielding of the gamma radiation, for which purpose lead is particularly suitable. The free volume to be filled in this way is approximately 3001 for pressurized water reactor fuel elements per fuel element in the case of a Biblis fuel element and approximately the same amount in the case of four boiling water reactor fuel elements.

The lid 12 is gas-tight and firmly connected to the container 6. For this purpose, as can be seen in FIGS. 3 and 4, the wall of the container in the region of the opening 4 is designed in profile. 3, a dovetail-shaped profile 16 can be formed on the edge 14 of the wall, which consists of one piece with the wall.

The lid 12 encompasses the profile 16 with a complementary recess 18, whereby a very firm and tight connection of the lid and the container can be achieved.

To establish this connection, after the fuel elements have been introduced into the container and the cavity has been closed, a shielding cover 20, for example made of stainless steel (the shielding cover is only shown schematically; its arrangement and special design will be explained in more detail below with reference to FIG. 8 received), a hollow mold placed on the container and poured out with a suitable material, preferably with the same material from which the container itself is made, whereby an intimate connection with the container is made after hardening of the casting compound, which is so firm that it is possible to lift the container, for example with the aid of a hook 22 cast into the lid.

4 to 7 show variants for the design according to FIG. 3, the cover 12 according to FIGS. 6 and 7 being provided with a central attachment 23 which can be inserted into the container 6.

In these embodiments, the cover 12 is already prefabricated. It is provided in the sealing surface 24, 26 with dovetail-shaped recesses 28 and 30 into which channels 32, 34 open. The recesses 28 and 30 lie opposite dovetail-shaped recesses 36, 38 which are formed in the opposite sealing surfaces 40, 42 of the container 6. The channels (channels 48, 50) can also open directly into the sealing surfaces (sealing surfaces 44, 46) of the cover, and only recesses 52, 54 can be provided in the sealing surfaces 56, 58 of the container 6, as shown in FIG. 6 and 7 is removable.

To connect the lid 12 and the container 6, the casting material is filled into the channels, which fills the recesses and the channels and, after curing, results in a firm and gas-tight connection.

Screw connections and sealing elements can also be provided.

The profiles need not be dovetail-shaped; they can also have other suitable shapes.

8 shows a preferred embodiment of the device in the lid area in detail.

The container 6, as in the container according to FIGS. 1 to 7, consists of a jacket 70, a bottom, not shown, and a shielding lid 72. The shielding lid 72 has a projecting edge flange 74 which is in a step recess 76 in the end face of the jacket 70 lies. The shielding cover 72 projects into the cavity 11 of the container 6 with an extension 78.

The edge flange 74 of the shielding cover 72 is screwed to the jacket 70 with the aid of screws 80. Seals 84 are provided to seal the gaps 82 between the shielding cover 72 and the step recess 76. The shielding cover is preferably made of nodular cast iron.

A cover plate 86 is also arranged above the shielding cover 72 and covers both the shielding cover 72 and the screws 80 and the gap 82. The cover plate 86 is welded flush onto the end face of the jacket 70.

Finally, the cover 12 is arranged above the cover plate 86 and, as already described in connection with FIGS. 1 to 7, is cast on with the aid of a suitable casting mold. In addition to the curved shape shown in FIGS. 1 to 7, it can also be flat, as shown in FIG. 8. When the lid 12 is poured, the container 6, including the shielding lid and optionally the cover plate, is heated to a suitable temperature, for example 500 to 600 ° C., in order to achieve a uniform structure at the connection point between the lid and the container jacket and to prevent the formation of a martensitic structure.

The cover plate 86 prevents the cover 12 from being connected to the shielding cover 72 and the screws 80. As a result, the container remains accessible in a simple manner. Namely, only the cover 12 needs to be removed together with the cover plate 86. It is then possible to open the container after loosening the screws and removing the shielding cover.

The jacket 70 is provided on its end face with an elevation 88, for example as shown, in the form of a dovetail-shaped annular rib. Other suitable forms for the surveys are also possible. After the application or pouring of the lid 12, these elevations ensure a firm and secure connection between the container 6 and the lid 12.

For better handling of the container, support pins 90 can be attached to the jacket 70, these support pins preferably being designed to be detachable from the jacket.

The lid 12 can be provided with a hook 92 for handling the container 6, which is also preferably detachably attached.

Instead of elevations in the jacket, it is also possible to provide a recess (94) corresponding to the elevation or elevations (shown in dashed lines), which is then filled with casting compound when the cover is poured.

The lid 12 is preferably produced in such a way that a shape which gives the later lid shape is placed on the container 6 provided with the shielding lid 72 and the cover plate 86, into which the casting compound is then introduced.

9 and 10 show two further variants for covering the container 6. In both embodiments, the casing 110 of the container is provided on the inside with a step recess 112. In this step recess sit a shielding cover 114, which is designed like the shielding cover in the embodiment according to FIG. 8 and can be fastened, and a cover 116 such that the surface of the cover 116 is approximately flush with the end face 118 of the jacket.

The cover 116 is prefabricated in this embodiment and has channels 120 which open into the side surfaces of the cover opposite channels 122 formed in the casing 110. As shown, parts of the channels can be dovetail-shaped, as has already been described in the embodiments according to FIGS. 4 and 6. In these channels and, if necessary, dovetail-shaped recesses 30, after the prefabricated lid has been put on, pouring compounds 124 and 126 are poured in, which after solidification results in a firm connection between the lid and the container.

FIG. 11 shows a further modification in the lid area of the container 6, in which the shielding cover 114 is designed approximately like the shielding cover according to FIG. 8 and is connected to the container 6. The lid 128 is also prefabricated and provided with pouring channels 130 and a filling opening 132, for example according to the embodiment according to FIG. 5, and has an outwardly curved shape, such as the lid according to FIGS. 3 to 5.

In this embodiment, a dovetail-shaped recess 134 is provided in the jacket of the container, into which the channels 130 open, cf. 5 and the associated description.

In FIGS. 12a, b, c, d, some cross-sectional shapes for the elevations on the end face of the container shell are shown by way of example. The forms according to FIGS. 12a and 12d result in the firmer connection because of the undercut design.

FIG. 13 shows that the recesses 136 formed in the casing 70 of the container 6, which can basically have the same shape like the elevations according to FIG. 12, preferably have ventilation channels 138 to ensure that the recess is completely filled with casting compound.

14a and 14b show an inner container 140 for receiving fuel elements. This inner container consists of a jacket 142, a lid 144 and a bottom 146. The lid and bottom are welded to the jacket at 148 and 150. The bottom can also be cast in one piece with the container or subsequently poured on. In addition to welding, the lid can also be applied by casting. The lid and the bottom can be curved inwards (FIG. 14a), curved outwards (FIG. 14b) or even straight (FIG. 14b shown in broken lines). For the purpose of transport, the inner container is inserted into an outer container or transport container which is designed like the container according to FIGS. 1 to 13, cf. 1, 2a and 2b, in which the inner container 140 is shown in broken lines and the outer container is formed by the container 6.

Such a double container has several advantages. Only the inner container is lost during final storage. The outer container can continue to be used; it can be saved at the handover at the well of the final deposit.

Such a double container permits problem-free retrievable final storage. Both the outer and the inner container are fed to final storage. At a later point in time, it is then possible to easily retrieve both containers, that is to say the double container, or only the inner container, for example for the purpose of reprocessing the fuel elements.

The inner and outer container can basically be designed and constructed identically. Stainless steel or cast iron is also preferably used as the material for the inner container. When using carbon steel, ceramic or another corrosion protection layer is applied.

The outer shape of the inner container preferably corresponds to the inner shape of the outer container. But it can also have a different shape.

The material thickness for the inner container is selected so that the minimum requirements for the shielding effect and stability are met. The outer container must be designed in such a way that the relevant conditions for transport are met and additional protection against corrosion is guaranteed.

To protect against corrosion, the container can be provided with a ceramic coating or another corrosion protection layer, which can be done, for example, by spraying on the corresponding material.

For the sake of completeness, it should also be mentioned that a valve arrangement can be provided in the lid area in order to enable sampling from the container and to be able to carry out monitoring tasks (for example leakage test).

Claims (19)

1. A device for the reception, conveyance and final storage of spent reactor fuel elements, having a hollow cylindrical container which rests by contact surfaces gainst contact surfaces on a lid which may be combined with the container, characterized in that the container (6) or the lid (12, 116) exhibits in the contact surfaces (14, 40, 56.42,58; 24,26) an annular recess (36, 52, 38, 54, 94, 134, 136; 18, 28, 30) and the lid (12) or the container (6) exhibits in the contact surfaces an annular elevation (16, 88) which is made complementary to the recess and is arranged in this recess.

2. A device as in claim 1, characterized in that the lid (12, 116) is provided for introduction into the container, with a central projection (23) which exhibits further contact surfaces associated with contact surfaces on the container and the outer diameter of which corresponds approximately with the inner diameter of the container.

3. A device as in claim 1 or 2, characterized in that the container and the lid exhibit in the contact surfaces annular recesses lying opposite one another, which are filled with a thermosetting pourable compound bonding the lid and the container.

4. A device as in claim 1, 2 or 3, characterized in that the lid exhibits at least one channel (32, 34, 48, 50, 120, 130) which opens into the contact surface opposite the annular recess in the container or into the annular recess in the lid and into which termosetting pourable compound may be poured for filling up the annular recesses and the channel.

5. A device as in claim 1 or 2, characterized in that for the direct production of the lid (12) on the container a mould is provided, which may be mounted upon the surface of the container and into which the pourable compound provided for the lid may be delivered.

6. A device as in one of the preceding claims, characterized in that the elevations and recesses in cross-section are made of a dovetail shape, rectangular, halfround or rectangular and undercut.

7. A device as in claim 6, characterized in that the recesses (136) arranged in the container (6) exhibit an airduct (138) let towards the outside.

8. A device as in one of the preceding claims, characterized in that the container (6) is provided with a screening lid (72) which is bolted to the jacket (70) and which is tightly covered by the lid (12).

9. A device as in claim 8, characterized in that the screening lid (72) is arranged to be separate from the lid (12).

10. A device as in claim 9, characterized in that the screening lid (72) is overlaid by a coverplate (86) which is welded flush with the endface of the jacket (70) of the container (6).

11. A device as in one of the claims 8 to 10, characterized in that the screening lid (72) is equipped with a flange (74) running round the edge and is arranged in a stepped recess (76) made in the jacket (70) of the container (6).

12. A device as in claim 11, characterized in that between the screening lid (72) and the container jacket one or more seals (84) are arranged in the stepped recess (76).

13. A device as in one of the preceding claims, characterized in that the lid (12) is made flat or domed outwards (convex).

14. A device as in one of the claims 8 to 13, characterized in that the stepped recess (76) is made so deep that both the screening lid (114) and the lid (116) are arranged in the stepped recess.

15. A device as in one of the preceding claims, characterized in that for receiving the fuel elements (8, 10) an inner container (140) is provided in addition, which may be inserted in the container (6) serving as the outer container.

16. A device as in claim 15, characterized in that the inner container (140) is closed by a lid (144).

17. A device as in claim 16, characterized in that the lid (144) and/or the bottom (146) of the inner container (140) are made straight or domed inwards or outwards.

18. A method of production of the device as in one of the claims 5, 8, 13 or 14, characterized in that during pouring of the lid the container (6) inclusive of the screening lid (72) and coverplate

(86) is heated up to a temperature which prevents the formation of a martensitic structure between the lid and the container jacket.

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