GB2226689A

GB2226689A - Final storage arrangement for radioactive waste

Info

Publication number: GB2226689A
Application number: GB8928087A
Authority: GB
Inventors: Werner Schwarzkopf
Original assignee: Kernforschungszentrum Karlsruhe GmbH
Current assignee: Forschungszentrum Karlsruhe GmbH
Priority date: 1988-12-16
Filing date: 1989-12-12
Publication date: 1990-07-04
Anticipated expiration: 2009-12-12
Also published as: JP2854049B2; GB2226689B; GB8928087D0; JPH02195299A; BE1005006A3; FR2640800A1; FR2640800B1; DE3842353C1

Description

1 - 1 1- G:-" 173 FINAL STORAGE ARRANGEMENT FOR RADIOACTIVE WASTE The

present invention relates to a final storage arrangement for radioactive waste. More particularly, the present invention relates to a storage arrangement for containing heat-emitting, highly radioactive waste such as vitrified fission products of reprocessing residues which have been filled into moulds, for sealing by the so-called isostatic hot- pressing (HlP) method.

The present invention is concerned, in general with surrounding radioactive waste or moulded ceramic bodies on all sides using metallic materials in a sealed and cavitY-free mannerg whilst simultaneously compressing the enclosed material in order to reduce its porosity. A solid copper canister having relatively thick walls which is intended to receive spent nuclear fuel rods is known for this purpose. The empty spaces around the rods and in the canister are filled with copper powder. A cover with a plug is inserted therein and the canister is disposed in a thick-walled container. The container arrangement is then subjected to isostatic hot-pressing (HIP), the cover being connected to the container by sintering at the very high pressure.

However, it has been found that the cover may bulge excessively and rupture during the compression process. This effect caused by the cavities which are always present and which can lead to excessive deformation.

The present invention seeks to provide a final storage container arrangement which remains intact or 1 leakproof after such treatment, even when considerable pressure is applied in the HIP method.

According to the present invention, there is provided a final storage arrangement for heat-emitting, highly radioactive waste such as vitrified radioactive fission products and reprocessing residues which have been filled into moulds, which arrangement is suitable for sealing and compressing by hot-isostatic pressing, the arrangement comprising a metal inner container for receiving the waste, a thick-walled metal outer container surrounding the inner container, and a filling within the outer container but externally of the inner container, wherein the outer container comprises a cup-shaped main body portion having a cover member which is mountable thereon and insertable therein, the cover member comprising a plug which projects into the interior of the container, the plug having an axial length greater than the spacing between the upper surfaces of the inner and outer containers, the cover member having an upper, outer rim portion to which a bellows arrangement is fixedly secured in a gas-tight manner, the bellows arrangement at least partially covering or enclosing the plug member; the end of the bellows arrangement facing the interior container being welded to the thick-walled main body of the outer container in a gas-tight manner, the bellows being made from a metallic material and having a high radial strength and being axially deformable, and conduit means for evacuating the interior of the bellows or the interior of the container communicating therewith through the gap between the cover member and the plug.

4 As a result of the construction in accordance with the present invention the container is reliably prevented from leaking, despite relatively long deformation paths, since the bellows can accommodate a longer travel path. The cavities within the container are also minimized in a particularly advantageous manner. However, a certain residual cavity, which has to be filled during the deformation. always remains. The interior is evacuated beforehand by means of a vacuum pipe provided for removing the air contained in the cavity.

The invention will be further described, by way of example, with reference to the accompanying drawings, in which:

Fig. 1 shows a vertical section through a thickwalled outer container forming part of the storage arrangement of the present invention; Fig. 2 shows a vertical section through a mould forming a further part of the storage arrangement of the present invention and which is received in the outer container shown in Fig. 1; and Fig. 3 shows the storage arrangement of the present invention immediately prior to the commencement of an isostatic hot-pressing operation.

In Figure 1, there is shown a thick-walled outer container 4 which comprises a thick-walled cylindrical portion 7, a base 8 and a cover portion 5. In order to minimize the size of cavities in the interior of such container 4, the inner surface 9 of the base 8.has the same configuration as the base of an inner container 1 which is to be located therein. In the embodiment shown, the inner container I is in the form of a. mould. The mould is provided with a cover member 3, which latter has an upper surface 13. The cover portion 5 for the outer container 4 includes a plug portion 10 having an inner or lower surface 20 which is adapted to the shape of the mould cover 3 and an upper rim 11 which projects radially outwardly of the mould cover 3. The plug portion 10 may have a slightly conical construction which tapers towards the inner container 1 in order to predetermine the depth which the plug portion 10 may be inserted into the container 4. The axial length of the plug should be greater than the spacing between the top surface 12 of the container 4 and the upper surface 13 of the inner container or mould 1.

A metal bellows arrangement 14, which acts as a sealing membrane is slipped onto the plug member 10. One. axial end of the bellows is welded to the upper rim 11 in a gas-tight manner, and the other end is welded to a ring 15 which, in turn, is welded to the upper surface 12 of the container. The welds are also gas-tight. Alternatively, this end of the bellows 14 may be directly welded to the upper surface 12 of the container. The term "bellows" is used to denote a longitudinally resilient structural element which combines high radial strength with the capacity for axial and longitudinal deformation. When in its fully deformed state, the folds of the bellows 14 should closely abut one against another in order to minimize cavities in the interior.

1 1 In the welded state, the plug member 10 projects into the interior of the outer cylindrical portion 7. The depth of projection is no greater than that at which it abuts against the upper surface 13 of the mould 1 or the cover 3 therefor, as shown in Figure 3.

The mould 1 in the embodiment shown, has an undercut head portion 16 which acts as a grip portion. Below the head portion, a cavity 17 is defined. A transversely divided, metallic filler member 18 is inserted into the cavity 17, the external configuration of the member 18 corresponding to the shape of the cavity 17. The filling piece is divided transversely in order to make it possible to insert it into the undercut.

As shown by the arrows in Figure 3, the f illed and tightly sealed outer container 4 and its cover are subjected to the isostatic hot-pressing process described hereinafter.

Compression is then effected in two phases:

In the first phase, the cavities which cannot be influenced, and which amount to approximately 5 to 10% of the volume, are compressed. The cover member 5 moves. together with the plug 10, and the bellows 14 is deformed. The entire storage arrangement is compressed in the second phase. With optimum matching of the geometry, the upper surface of the cover lies flush with or forms a seal with the upper surface of the main body of the container. The bellows are then compressed in such a way that the individual folds thereof abut tightly against one another. In other words, the capsule and the bellows now form a closed. compact unit just as they did prior to the deformation.

The container arrangement shown in Figures 1 to 3 is sealed by subjecting it to the -following processing steps:

- 1. Filling the mould 1 which is made of. in this embodiment. chrome nickel steel with waste products 2 such as highly radioactive, vitrified fission products contained in a hot cell.

2. Welding the mould cover 3 onto the mould in situ utilising a suitable welding apparatus.

3. Evacuating the mould 1 to approximately 102 to 10-6 mbar.1 see. by means of an evacuation conduit (not shown) and welding the same.

4. Decontaminating the welded mould 1 and discharging into a packing cell.

5. Inserting the mould into a thick-walled (external diameter: internal diameter > 1.28: 1) outer container 4 made of structural steel and of the type shown in Figure 1.

6. Mounting a thick-walled cover 5 of the same material on the container 4 and welding it thereto by a sealing, welded seam in a manner described hereinafter.

7. Evacuating the interior space by means of an evacuation conduit 6.

8. Introducing the filled container 4, with the cover 5 welded thereon, into an installation for hotisostatic pressing.

9. Effecting hot-isostatic pressing of the container 4 in accordance with Figure 3 at a temperature of from 8500 to 10000C and 100 MPa external pressure (as shown by the arrows 19) for a holding time of 1 hour. During this treatment, the following processes take place:

(a) the steel is normalised; (b) diffusion welding of the thick-walled cover member 5 and of the evacuation bore in the conduit 6; (c) the structure of the steel, with respect to the shrink holes therein, is improved; and (d) the evacuated cavities already minimized by the filling material are eliminated.

10. Removing the container from the HIP plant for further use.

Claims

1. A final storage arrangement for heat-emitting, highly radicactive waste such as vitrif ie"d radioactive fission products and reprocessing residues which have been filled into moulds, which arrangement is suitable for sealing and compressing by hot-isostatic pressing, the arrangement comprising a metal inner container for receiving the waste, a thick-walled metal outer container surrounding the inner container, and a filling within the outer container but externally of the inner containert wherein the outer container comprises a cup-shaped main body portion having a cover member which is mountable thereon and insertable therein, the cover member comprising a plug which projects into the interior of the container, the plug having an axial length greater than the spacing between the upper surfaces of the inner and outer containers, the cover member having an upper, outer rim portion to which a bellows arrangement is fixedly secured in a gas-tight manner, the bellows arrangement at least partially covering or enclosing the plug member; the end of the bellows arrangement facing the interior container being welded to the thick-walled main body of the outer container in a gas-tight manner, the bellows being made from a metallic material and having a high radial strength and being axially deformable, and conduit means for evacuating the interior of the bellows or the interior of the container communicating therewith through the gap between the cover member and the plug.

2. A storage arrangement as claimed in claim 1 wherein the filler material is metallic.

z0, 01

3. A storage arrangement as claimed in claim 1 or 2 wherein the end of the bellows is welded to the main body of the outer container through the intermediary of a ring member.

4. A storage arrangement as claimed in any preceding claim wherein the mould has an undercut grip head, and a metallic filling member having a diameter substantially equal to the internal diameter of the container and a shape corresponding generally to the shape of the cavity formed by the undercut in the grip head is inserted into the cavity, the member being transversely divided to permit the insertion thereof into the cavity.

5. A storage arrangement as claimed in claim 4 wherein the filling member fills in the entire cavity defined between the upper, outer surface of the inner container and the inner surface of the cover plug member.

6. A storage arrangement as claimed in claim 1 constructed and arranged to operate substantially as hereinbefore described with reference to the accompanying drawings.

- - - - - - - - - - - - - - - - - published 1990 atThe Patent Office, State HOuse,66/71 High Ho-,oorn. London WCIR4TP.FUrther copies maybe obtained from The Patent Officen- iotnrl Kent BR5 3RD. Printed bV MultTlUx techniques ltd, St Mary Cray, Kent. Con 1/87 mvn 11-+.A I- IA"M,111-v t-hninllPs Rd St Marv Crav. Kent. L;on. vts'7