GB2109984A

GB2109984A - Disposing of radioactive materials

Info

Publication number: GB2109984A
Application number: GB08228754A
Authority: GB
Inventors: Rainer Koster; Werner Schwarzkopf
Original assignee: Kernforschungszentrum Karlsruhe GmbH
Current assignee: Forschungszentrum Karlsruhe GmbH
Priority date: 1981-10-08
Filing date: 1982-10-07
Publication date: 1983-06-08
Also published as: DE3140020A1; GB2109984B; FR2514545A1; DE3140020C2; FR2514545B1; JPS5872100A

Abstract

In disposing of sealed drums of highly radioactive materials, a leakproof metallic jacket is formed round the drum by inserting the drum (6) into a casting mould (7, 8, 10) and suspending it therein by a suitable suspension device (20, 21) having a rupture point (23), pouring casting material (12) into the mould (7, 8, 10) to at least the level of the rupture point, rotating and/or withdrawing the suspension device (20, 21) from the cast material (12) to cause rupture of the suspension device at the rupture point (23), completely cooling and hardening the casting and removing the casting, with the drum (6) of radioactive material located therein, from the mould. An apparatus for carrying out such a method is also provided. <IMAGE>

Description

SPECIFICATION Method and apparatus for producing a leakproof homogeneous sealing jacket for radioactive material The present invention relates to a method and apparatus for producing a leakproof, homogeneous, metallic sealing jacket for a drum containing highly radioactive material. Atypical example of such a drum is a steel chill mould containing highly radioactive wastes which have been fused into glass.

Radioactive wastes are sometimes stored permanently in deep salt formations, the wastes being isolated from the biosphere by a plurality of barriers connected in series with one another. The product, the salt formation and the surrounding overhead rocks form the essential barriers. Previously, the waste container has not served as a barrier.

Previously known packs have not exhibited homogeneous sealing and were, in principle, liable to suffer corrosion. In consequence, it has only been possible to determine, in advance, the storage period for such packs to a limited extent.

The present invention seeks to provide a method for producing a seal, in the form of a jacket, which is homogeneous on all sides, which is capable of containing environmentally destructive substances, such as highly radioactive wastes fused into chill moulds, by using castable materials. The present invention also seeks to provide an apparatus which is suitable for carrying out such a method.

According to the present invention, there is provided a method of producing a leakproof, homogeneous, metallic, sealing jacket for a tightly sealed drum containing highly radioactive material, such as a steel chill mould containing highly radioactive wastes which have been fused into glass, or spent fuel elements, the method comprising introducing the sealed drum into a mould of greater dimension, positioning the drum in the mould so that it is spaced from the walls thereof, by using a suspension means which has a predetermined breaking point, pouring a casting material into the mould around the drum at least until the predetermined breaking point is completely covered, rupturing the suspension at the predetermined breaking point by pulling and/or rotating the suspension means, completely cooling or hardening the cast material, and removing the hardened cast material, together with the integrally cast chill mould from the mould.

Desirably, the present invention includes the further operational steps of cooling, and thereby hardening, the cast material from, up to and around the predetermined breaking point.

It is advantageous if cooling is controlled from below, in an upward direction, by a cooling or heating device whilst the cast material hardens.

It is preferred if the rupturing of the predetermined breaking point is actuated by a casting material level indicating device or by a time-dependent control command.

Other desirable aspects of the present invention are that the further cooling and hardening are also controlled by a cooling or heating device and that the cast body, after the casting material has com pletely hardened, is then tempered.

Also according to the present invention, there is provided an apparatus suitable for carrying out such a method, the apparatus comprising a mould formed from a vertically disposed cylinder having a base member, the cylinder being surrounded by a mould ing box or case, the height of the moulding box being at least equal to the height of the casting to be produced in the mould, the base of the mould having an inlet aperture extending towards the interior of the mould and being connected to an inlet gate for the casting material located in the upper region of the moulding box by means of an ascending tube or riser, the mould being provided with a detachable cover which has air ducts or ventilation channels formed therethrough, a lifting rod, forming part of a lifting device, extending through the detachable cover and protruding into the mould, the lower end of the lifting rod being provided with a retaining device for gripping a drum or chill mould to be jacketed, the lifting rod being longitudinally displaceable and being capable of being arrested at different desired levels and/or being rotatable about its longitudinal axis, a predetermined breaking point being provided in the lifting rod above the retaining device, the mould cylinder being surrounded a single-or multiple-stage cooling and/or heating means located within the moulding box, the mould cylinder, the mould base and the cast body being separable from one another when the casting is complete and a heating device, accommodated in the lower end of the lifting rod, the heating zone of the heating device being located, in use beneath the surface, of the casting material in the cylinder.

Packs produced by the method of the present invention have optimum mechanical stability and anti-corrosion properties.

It is also possible to determine, in advance, the storage period of a pack by effecting corrosion tests on a sample of the material and applying the results to the pack itself. The pack can be made thick-walled so as to overcome any surface wear caused by corrosion. Moreover, thick-walled packs permit the use of relatively thin shielding or screening walls for transportation containers, thereby simplifying storage and transport procedures. Still further, the final storage medium is protected from irradiation.

One embodiment of the present invention will be further described, by way of example, with reference to the accompanying drawings, in which: Figure lisa vertical section through a chill mould containing highly radioactive waste; Figure 2 is a vertical section through an apparatus in accordance with the present invention employed for producing a cast jacket around the chill mould shown in Figure 1.

In Figure 1, there is shown a chill mould 6 which comprises a stainless steel container 2 filled with highly radioactive waste 1 fused in borosilicate glass. The container 2 is sealed by means of a welded cover 3. The cover 3 is provided with a mushroom-shaped knob 4 by means of which the chill mould may be handled. A counter-weight 5 may be additionally provided on the base of the container 2. This is used for calibration purposes during a subsequent casting process. A protective layer 13 in the form of, for example, ceramic wool may also be fused onto the chill mould 6so as to be located therearound, as shown in Figure 2. This layer 13 protects against shrinkage stresses.

A fused or cast mass is then provided around the chill mould, or a calibrated waste drum, and an apparatus suitable for achieving this is shown in Figure 2. In this Figure, the chill mould, or calibrated waste drum 6 is shown located in a casting mould.

The casting mould comprises a cylindrical steel tube 7 and a base box 8 which seals the bottom end of the mould. The mould is provided with the knob-shaped contour 9, by means of which a carrying knob is formed on the subsequently cast body.

A moulding box 10 is provided around the tube 7 and has an inlet gate 11 through which the casting material passes into the casting mould. Obviously, the upper end of the gate 11 or the moulding box 10 must be at least as high as the desired height of the upper edge of the subsequently cast body 12 in the mould. A riser tube 14, which is downwardly inclined from the inlet gate 11 for the casting material and which leads into the interior of the mould or tube 7, acts as the passage through the box 10. The riser tube 14 is connected to an aperture 15 which is provided in the base box 8, the aperture 15 thus forming the inlet into the mould. A slag collector 16 may be provided in the lowermost region of the riser tube 14 in the base 8 or, indeed, at any other suitable location.

A heating or cooling means 17 is provided in the moulding box 10 around the steel tube 7 and permits the cooling or hardening of the casting material 12 to be controlled both in a height direction and a depth direction. The heating or cooling means 17 may be of a single-or multiple-stage construction, so that the casting material can be caused to harden gradually on a step-wise manner or, if desired, continuously.

Spheroidal graphite iron/cast silicon, Ni resist or any other suitable material may be used as the casting material for forming the cast body 12.

The steel tube 8 is sealed by means of a detachable cover 18 which has air ducts or ventilation channels 19 formed therein. A lifting rod 20, which is both longitudinally displaceable and rotatable and forms part of a lifting device 21, extends through the detachable cover 18. A retaining device for holding the chill mould 6 is mounted on the lower end 22 of the lifting rod 20, and, as shown, comprises a bolt or pin 25 which is screw-threadedly fitted into the mushroom-like handling knob 24 of the chill mould 6.

A heating device is provided in the lower portion 22 of the lifting rod 20, the heating zone produced by the heating device being substantially located be neath the surface 28 of the casting material so as to influence the desired hardening in this region. A pre-determined breaking point 23 is provided be tween the lower end 22 of the rod and bolt or pin 25, which breaking point 23 has less tensile strength than the lifting rod 20. The predetermined breaking point 23 may be formed, from, for example, a material having a low melting point, whilst the remaining part of the suspension device may be formed of a material having a high melting point.

The operational steps to be followed for producing a cast body: (a) assembling the base box 8 with the moulding box 10 and the steel tube 7; (b) connecting the waste drum, or the chill mould 6, to the suspension means 25 for suspension by the lifting rod 20; (c) introducing the suspension means 25, together with the waste drum 6 and the cover 18, into the lifting device 21, e.g. from the side; (d) setting the desired spacing 26 of the top of the mould 6 from the underside of the cover 18 and arresting the lifting rod 20 in such position; (e) positioning the cover 18, together with the lifting means 21, the suspension means 25 and the waste drum 6, onto the steel tube 7; (f) pouring in the molten material through inlet gate 11 whilst observing the filling level or height;; (g) after the casting process has ended, the lifting means 21 is actuated by a control command dependent upon the filling level or time, and the Ifiting rod 20 is raised and removed from the casting, thereby rupturing the predetermined breaking point 23; (h) after the desired hardening or tempering has been achieved by the cooling or heating means 17, the cast residues may be removed from the mould and separated out; although the extension process can only be carried out when the fused mass has hardened to a predetermined and desired level and/or depth.

To sum up, therefore, the characterising features of the method of the present invention which is used to achieve the all-round, homogeneous sealing of drums are taring or calibrating the waste drums together with the molted material, providing suspension means having a predetermined breaking point for carrying the drum and locating it so that it can be sealed on all sides, providing lifting means for extracting the suspension means from the cast material; providing control means, eithertimedependent or filling level-dependent for actuating the separation and removal of the suspension means; and providing cooling or heating means for controlling the hardening of the cast material.

Claims

1. A method of producing a leakproof, homogeneous, metallic sealing jacket for a tightly sealed drum containing highly radioactive material, such as a steel chill mould containing highly radioactive wastes which have been fused into glass, or spent fuel elements, the method comprising introducing the sealed drum into a mould of greater dimensions positioning the drum in the mould so that it is spaced from the walls thereof, by, using a suspension means which has a predetermined breaking point, pouring a casting material into the mould around the drum at least until the predeter mined breaking point is completely covered, ruptur ing the suspension at the predetermined breaking point by pulling and/or rotating the suspension means, completely cooling or hardening the cast material, and removing the hardened cast material, together with the integrally cast chill mould from the mould.

2. A method as claimed in claim 1, comprising the additional step of cooling, and thereby harden ing, the cast material as far as and around the predetermined breaking point.

3. A method as claimed in claim 1 or 2, in which cooling is controlled from below, in an upward direction, by a cooling or heating device whilst the cast material hardens.

4. A method as claimed in any of claims 1 to 3, in which the rupturing of the predetermined breaking point is actuated by a casting material level indicating device or by a time-dependent control command.

5. A method as claimed in any one of claims 1 to 4, in which the further cooling and hardening is also controlled by a cooling on heating device.

6. A method as claimed in any one of claims 1 to 5, in which the cast body, after the casting material has completely hardened, is then tempered.

7. A method as claimed in any one of claims 1 to 6, in which the chill mould is tared or calibrated with the casting material when the chill mould and fused mass have different densities.

8. A method of producing a sealing jacket as claimed in claim 1 substantially as hereinbefore described.

9. An apparatus for carrying out the method as claimed in any one of claims 1 to 8, comprising a mould formed from a vertically disposed cylinder having a base member, the cylinder being surrounded buy a moulding box or case, the height of the moulding box being at least equal to the height of the casting to be produced in the mould, the base of the mould having an inlet aperture extending towards the interior of the mould and being connected to an inlet gate for the casting material located in the upper region of the moulding box by means of an ascending tube or riser, the mould being provided with a detachable cover which has air ducts or ventilation channels formed therethrough, a lifting rod, forming part of a lifting device, extending through the detachable cover and protruding into the mould, the lower end of the lifting rod being provided with a retaining device for gripping a drum or chill mould to be jacketed, the lifting rod being longitudinally displaceable and being capable of being arrested at different desired levels and/or being rotatable about its longitudinal axis, a predetermined breaking point being provided in the lifting rod above the retaining device, the mould cylinder being surrounded by a single-or multiple-stage cooling and/or heating means located within the moulding box, the mould cylinder, the mould base and the cast body being separable from one another when the casting is complete and a heating device, accommodated in the lower end of the lifting rod, the heating zone of the heating device being located, in use beneath the surface, of the casting material in the cylinder.

10. An apparatus as claimed in claim 9 addi tionallycomprising a slag collector formed in the base of the mould beneath the inlet aperture extending into the mould, the slag collector being disposed between the ascending tube or riser and the inlet aperture.

11. An apparatus as claimed in claim 9 constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.