EP0169440B1 - Closing method for a radioactive-material container, and container for carrying out this method - Google Patents

Description

The invention relates to a method for closing a container made of metallic material for receiving radioactive material, in particular radioactive material introduced into an inner container, in which a closure lid is at least partially inserted into a front receiving opening of a basic container body under radial guidance, the closure lid under a predetermined Contact force that significantly exceeds the weight of the closure lid is held in contact with a contact surface of the container base body formed in the region of the front receiving opening and is welded to the container base body in this position. The invention further relates to a container suitable for carrying out this method.

From GB-A-2106442 a method of the generic type is known, in which the basic container body is provided with an outwardly flared conical receiving opening and the closure cover has a correspondingly conically turned jacket. When closing, the closure lid is pressed axially into the front opening, the co-conical cooperating surfaces forming a radial guide. Then the The cover is welded to the receiving opening of the container body by a circumferential melt flow connection. From EP-A2-77 955 a method is known in which, on the one hand, a flat lid with an outwardly extending edge flange is introduced into the front receiving opening of a container base body and the front side of the container base body is welded to the front side of the flange of the closure lid and for another, a flat cover is placed on an annular flange extending at the front end of the container and is welded to the container body along a circumferential weld joint.

In the known container with a cylinder-like cover, FIG. 1 of EP-A2 77 955), no contact pressure is applied in the joining area, whereas in the container with a plate-like cover (FIG. 2 of EP-A2 77 955), the contact pressure is only determined by the weight of the cover .

As a result of a missing or insufficient contact pressure, the thermal loading during welding can lead to bulging or opening in both cover configurations, which corresponds to a stress load on the weld seam.

If such a container is placed in a final deposit and the closure cap through a geological formation, such as. B. salt or granite, the weld seam is loaded with corrosion-critical shear and tensile stresses caused by deformation of the flat cover plate. Such a stress load on the weld seam deteriorates its corrosion behavior considerably.

The invention has for its object to improve the method of the generic type and the container suitable for carrying out this method so that the welded seam with the container base body of corrosion-critical shear, shear and tensile stresses, in particular under the considerable mechanical long-term loads, with a high load capacity of the closure lid is largely exempt from final storage.

This object is achieved procedurally in that an at least on its inner surface domed closure cap is used and that the predetermined contact pressure between a radially extending bearing surface of the closure cover and a radially extending contact surface of the container body is made effective.

By pressing the sealing cover against the radially running contact surface of the container body, a surface contact is maintained during welding, which avoids bulges or gaps as a result of thermal stress during welding. As a result of the dome-like arched inner surface of the cover, when it is loaded under the rock pressure during final storage, practically no corrosion-critical loads and tensions are introduced into the weld seam, because the cover, which is curved at least on the inside, largely resists bulging inwards and to avoid corrosion-critical loads and tensions in the welded connection between the closure lid and the container base body in the repository, it is important to press the closure lid against the contact surface of the container base body with a contact force that significantly exceeds the weight of the closure lid during the construction of the welded connection. The contact pressure is preferably selected in the amount of the external load expected in the final deposit.

A particularly simple procedure when closing the container in the hot cell can be achieved in a further development of the invention in that the contact pressure is built up by means of a pressing device acting on the cover from the outside and the pressing device is removed after the welding. After the pressing device has been removed, the weld itself bears the contact pressure or preload force until an external pressure builds up in the repository. In the repository, however, the welded connection becomes stress-free again, so that stress corrosion cracking is avoided.

This contact pressure is preferably removed by a positive or non-positive engagement between the closure lid and the container body, that is to say not at least not only by the welded connection. For this purpose, the invention provides in a further development that the contact pressure is built up by means of a positive engagement between the closure lid and the container body, preferably by means of a thread engagement between an external thread of the closure lid and an internal thread of the container body. In this case, the flank load of the positive engagement is relieved in the case of the external pressure load on the closure cover. Instead of a thread engagement as A bayonet lock or the like can also be provided in a form-fitting manner.

Furthermore, it is expedient to shrink the closure lid into the front opening of the container base body under the action of the pressing force applied by a pressing device, the pressing force being maintained until the lid is held immovably in the container base body by shrinking engagement after temperature compensation.

The container made of metallic material suitable for carrying out the method according to the invention, which is provided with a container base body with an end-side receiving opening and a contact surface formed in the region of the end-side receiving opening and a radially guided sealing cover, wherein the sealing cover is welded to the front receiving opening of the basic container body and is held in contact with the contact surface of the basic container body under the action of a predetermined contact pressure, is characterized in that the closure lid is domed at least on its inner surface and is provided with a radially extending bearing surface which can be placed on the radially extending bearing surface.

The closure cover is preferably provided with an external thread which engages with an internal thread formed in the region of the front receiving opening. This results in a particularly simple application of the contact pressure and there is no stress on the weld seam when transport aids are attacked on the cover.

However, it is also possible for the closure cover to be provided with an external shrink engagement surface, which has an area in the region of the front-side receiving opening provided internal shrink engagement surface is in shrink engagement. In this embodiment of the container, the production of external and internal threads or other positive engagement means can be dispensed with.

In a container with a shrink-fit lid, a diffusion weld can be built up between the shrink engagement surfaces, as z. B. is described in patent application P 33 34 660.7-33 from 09/24/1983.

The outer surface of the closure lid can, for. B. be a radially extending flat surface. However, it is preferred that the lid is also domed on its outer surface.

There are a number of options for the location of the weld. However, it is preferred that the cover is provided on its dome-like curved outer surface with a ring-like projection, the outer diameter of which is adapted to the inner diameter of the front receiving opening at its free end. Such a construction is from EP-A2 77 955 (FIG. 2) and from the older publication KfK 3000, September 1980 - "Comparison of the Different Disposal Alternatives and Assessment of Their Realizability" -, Study "Disposal Alternatives" - Kernforschungszentrum Karlsruhe, ISSN 0303- 4003, Page 4-69, Figure 4.9 - "Double-shell fuel element container" -, known. The last-mentioned literature reference relates to a double-shell fuel element container, in which the outer container shell is welded to an outer closure cover shaped in accordance with FIG. 2 of EP-A2 77 955.

However, it is also possible to provide the lid with a circumferential flange which rests and / or rests on a corresponding annular surface of the basic container body.

When using a ring-like approach, a transport mushroom can advantageously be screwed into this.

• Figur 1
  einen Schnitt durch eine erste Ausführungsform,
• Figuren 2 und 3
  Teilschnitte durch weitere Ausführungsformen mit Gewindeeingriff zwischen Verschlußdeckel und Behältergrundkörper und
• Figur 4
  eine Ausführungsform mit Schrumpfeingriff zwischen Verschlußdeckel und Behältergrundkörper.

The invention will now be explained in more detail with reference to the accompanying figures. It shows:

• Figure 1
  2 shows a section through a first embodiment,
• Figures 2 and 3
  Partial sections through further embodiments with threaded engagement between the closure lid and the container body and
• Figure 4
  an embodiment with shrink engagement between the closure lid and container body.

A mold 2 with highly radioactive waste is introduced into a container base body 1, which consists of a double-domed base 1a, a straight-cylindrical jacket 1b and a receiving opening area 1c, a gap remaining with the inner surface 3 of the jacket 1b. A relief groove 4 and a radially extending ring-like contact surface 5 are provided in the transition region between the casing 1b and the receiving opening region 1c (cf. FIG. 1). Adjacent to the contact surface 5 are an axially extending guide surface 6, an internal thread 7, a shorter guide surface 6 'and a joining surface 8. The internal thread 7 is preferably designed as a conical thread. In the receiving opening area 1c, a cover 9 is screwed, which rests on the contact surface 5 with an annular bearing surface 10. Furthermore, it is guided with guide sections 11 and 11 'on the guide surface 6 or 6' and is in threaded engagement with the internal thread 7 with an external thread 12.

The inner surface 13 enclosed by the bearing surface 10 and the outer surface 14 of the cover 9 are domed like a dome. On the outer surface, the cover 9 is provided with a ring-like extension 15 which has a joint surface 16 corresponding to the joint surface 8.

To close the container, the lid 9 is screwed in between the surfaces 5 and 10 until a predetermined contact pressure is reached. Then a sealing weld 17 is built up between the two joining surfaces 8 and 16.

The weld seam can be built up by introducing welding aids or by welding without a welding wire.

When the closure cover 9 is loaded in the end bearing, no stresses due to the deformation of the cover are transferred into the weld seam 17, so that stress corrosion cracking can essentially not occur in it.

The dome-like design of the bottom 1 a and the cover 9 enables additional shields 18 and 19 to be introduced, the additional cover shield 19 being secured in the cover by a ring 20.

When an internal thread is formed on its inner surface engaging the outer dome 14, the ring extension 15 enables the screwing in of a transport mushroom shown in broken lines in FIG. 1, which can be unscrewed in the deposit.

The depth of the corrosion path is determined by the depth of the weld joint 17 and can be extended by a corresponding extension of the ring extension 15 and the container body.

As can be seen from the above description and in particular from FIG. 1, to which reference is expressly made here, the wall thicknesses of the container bottom 1a and lid 9 are made thinner than the wall thickness of the jacket 1b. As a result, the different radial deformation of the dome-shaped cover or the dome-like curved base is compensated for within certain limits.

As can be seen from Figure 1, the dome-like outer surface of the additional lid shield 19 is arranged at a certain distance from the inner surface 13 of the lid, so that the inner additional shield 19 is radially displaceable to a certain extent, so that the container jacket in the lid area is free under the external pressure load can deform without the shield 19 and thus the retaining ring 20 are loaded. The additional shielding 18 is also designed relative to the floor 1a in such a way that it can be moved radially.

In the embodiment according to FIG. 2, a peripheral flange 21a is provided on a closure cover 21, the underside 21b of which is welded to the free end face of the receiving opening area 1c. In this embodiment, the guide surface 6 'between the thread 7 and the free end face is designed to fit tightly in order to avoid a radial displacement of the cover 21.

In the embodiment according to FIG. 3, a peripheral flange 23 is provided on a cover 22, the substantially axially extending outer surface 23a of which is welded to a partial surface of the receiving opening region 1c that extends in the circumferential direction.

In the embodiment according to FIG. 4, the contact surface 5 of the basic container body 1 is followed by a smooth-faced, straight-cylindrical and axially extending engagement surface 24, which is followed by the joining surface 8; these areas together determine the receiving opening area 1c.

In this a closure cover 25 is shrunk, which rests with its ring-like contact surface 10 on the contact surface 5 under a predetermined contact force that exceeds the weight of the closure cover. The closure cover 25, like the cover 9, has domed surfaces 13 and 14 and an annular extension 15 with a joint surface 16 corresponding to the joint surface 8. In addition, the lid is provided with a shrink engagement surface 26 which is in shrink engagement with the surface 24.

In the container, the mold 2 is centered at its upper end with respect to the container and secured against axial displacement in the repository container by means of a fastening ring 27 with a welded-on slotted spring element 28, which rests on the securing ring 20. This measure can also be used with advantage in the embodiments according to FIGS. 1-3. The securing ring 27, which is conically shaped in accordance with the mold shape, contributes to shielding against scattered radiation in the axial direction.

To close the container body with the closure lid 25 after inserting and centering the mold, the receiving opening area 1c is heated, preferably inductively from the outside. Then the lid, previously cooled to ambient temperature, is inserted into the receptacle and, while maintaining a force applied to the lid 25 from the outside by means of a pressing device, is held in abutment on the contact surface 5 until there is temperature compensation between the lid and the container body. The geometry and fit of the lid and the receiving area are selected so that after the temperature has been equalized, the lid is held immovably in the base body of the container due to the adhesive forces caused by the compressive stress such that even after the forces acting from outside have been reduced (symbolically in FIG attacking arrows K) the predetermined contact pressure between the surfaces 5 and 10 is maintained. To build up the shrink engagement, it may only be necessary to heat or cool one of the components.

After shrink-fitting the lid, the subsequent preheating of the lid and container body in the area of the joining surfaces 8 and 16 and the construction of the weld seam 17 uniformly heats both components and thus deforms them in such a way that the radially directed compressive stress and the axially directed predetermined contact force are retained. It is also possible, instead of a continuous smooth fit in the area of the surfaces 24 and 26, a graduated fit, for. B. to use a graded fit with approximately the same length of seat and different tolerance zones. You can e.g. B. to the weld 17 subsequent fit with a larger diameter than a press fit and the fit below and adjacent to the contact surface 5 of a smaller diameter can be designed as a transition fit. This ensures that even with the most unfavorable actual dimensions of the two fits, the smallest excess of the upper fit is approximately the same size as the largest excess of the lower fit. Thus there is always a sufficient shrinkage pressure between the joining surfaces of the lid and the container body in the upper fit adjoining the weld seam 17.

In the case of the cover configurations according to FIGS. 2 and 3, a shrinking engagement can be provided instead of a threaded engagement to hold the contact pressure.

Finally, in the case of smooth-walled shrink engagement, it is also possible to build up a diffusion weld between the shrink engagement surfaces, as described in the pending patent application F 33 34 660 by the applicant on September 24, 1983. The diffusion welding can be the entire engagement surface or part of the z. B. cover like a ring, as indicated in Figure 4 by the reference character D. The diffusion welding can at least partially relieve the external weld 17 or possibly completely replace it. For safety reasons, however, the construction of an externally controllable weld seam is always preferred.

Non-alloyed or low-alloyed steels or cast materials are preferably used as the metallic material for container base body 1 and cover 9, 21, 22 and 26. Between the contact surfaces 5 and 10, a seal can also be built, for. B. by Introducing a silver ring or foil or by diffusion welding according to P 33 34 660.

The weld can be built up by known methods, e.g. B. electron beam or inductive. The embodiment according to FIG. 1 is preferred in terms of welding technology because in this embodiment relatively small masses of material have to be heated in order to build up the weld seam 17.

It is important that as a result of the contact pressure on the contact surfaces of the container body and lid, the weld seam is not subjected to tensile or shear stresses, and that when the high operating pressure is applied to the container body and lid as a result of the system and the dome-like design, at least the inner surface of the lid is stress-induced Corrosion in the weld seam is avoided. When using a cover with thread engagement or a comparable positive engagement or with shrink engagement, the weld seam essentially only has to act as a sealing seam, since transport forces acting on the cover are absorbed by the positive engagement or shrink engagement. It should be pointed out that the welded connection, be it as an external weld seam or internal diffusion welded connection, contributes in a targeted manner to corrosion protection and / or to fastening the cover. In the embodiment with the cover shrunk in, the shrink engagement increases the corrosion resistance, so that the axial length of the weld seam 17 can possibly be reduced to a corresponding extent.

The term "welding" chosen in the claims and in the description also includes soldering, unless explicit reference is made to "diffusion welding".

An annular surface 1d is formed between the container bottom 1a and the casing 1b (see FIG. 1), which corresponds to the annular end face of the opening area 1c and thus enables the containers to be stacked.

Claims (11)

1. A method for closing a container of metallic material for accommodating radioactive material, in particular radioactive material introduced into an inner container (2), in which a closure cap is inserted, with radical guidance, at least partially into a frontal location opening of a basic container body (1), the closure cap is held in contact, under a predetermined contact force which substantially exceeds the weight of the closure cap, with a contact face (5) of the basic container body, the said contact face being formed in the region of the frontal location opening, and is welded in this position to the basic container body, characterised in that a closure cap (9; 21; 22; 25) which is arched like a dome at least on its inner face (13) is used and in that the predetermined contact force is brought into effect between a radially extending bearing face (10) of the closure cap (9; 21; 22; 25) and a radially extending contact face (5) of the basic container body (1).
2. A method according to claim 1, characterised in that the contact force (K) is built up by means of a pressing device acting on the outside of the cap (9; 25) and the pressing device is removed after welding.
3. A method according to claim 1, characterised in that the contact force is built up by means of positive engagement between closure cap (9; 21; 22) and basic container body (1), preferably by means of a thread engagement between an external thread (12) of the closure cap and an internal thread (7) of the basic container body (1).
4. A method according to claim 1, characterised in that the closure cap (25) is shrunk into the frontal opening of the basic container body (1) under the action of the contact force (K) applied by a pressing device, the contact force being maintained until, following temperature equalisation, the cap is held immovably in the basic container body by shrink-fit engagement.
5. A container of metallic material, the said container being suitable for carrying out the method according to any of claims 1 to 4, with a basic container body (1) having a frontal location opening and a contact face (5) formed in the region of the frontal location opening (1c) and having a radially guided closure cap, the closure cap being welded to the frontal location opening of the basic container body and held in contact with the contact face of the basic container body under the action of a predetermined contact force, characterised in that the closure cap (9; 21; 22; 25) is designed with a dome-like arch at least on its inner face (13) and is provided with a radially extending bearing face (10) which can be placed on the radially extending contact face (5).
6. A container according to claim 5, characterised in that the closure cap (9; 21; 22) is provided with an external thread (12) which is in engagement with on internal thread (7) formed in the region of the frontal location opening (1c).
7. A container according to claim 5, characterised in that the closure cap (25) is provided with an external shrink-fit face (26) which is in shrink-fit engagement with an internal shrink-fit face (24) provided in the region of the frontal location opening (1c).
8. A container according to claim 7, characterised in that a diffusion weld (D) is built up between the shrink-fit faces (24, 26).
9. A container according to any of claims 5 to 8, characterised in that the cap (9) is also arched like a dome on an outer face (14).
10. A container according to claim 9, characterised in that, on its outer face (14) arched like a dome, the cap (9) is provided with an annular projection (15), the outside diameter of which is matched to the inside diameter of the frontal location opening (1c) at the free end of the latter.
11. A container according to any of claims 5 to 8, characterised in that the cap (21, 22) is provided with a circumferential flange (21a; 23a) which rests on and/or against a corresponding annular face of the basic container body (1).

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