GB2146166A - Equipment for reclaiming radioactive metallic components from spent nuclear power plants - Google Patents

Abstract

In reclaiming radioactive and/or radioactively contaminated metallic material by comminuting, melting and casting it, the necessary equipment, i.e. the mill, 1, the electric furnace 3 and the horizontal continuous killet casting and parting equipment 7, 8 and 9, is accommodated in a shielded low- pressure chamber 15, above and outside of which a crane unit 2 travels with its hook and cable passing through a sealing slit 18 in the roof 19. The slit is adapted to permit the crane to transport a container 4 from the mill 1 where it is filled with the comminuted material, to the furnace 3 where it delivers the material at the top of the furnace. The chamber is equipped with extractor units 27 and 28 which remove emissions from the furnace and container during use and which maintain the chamber at sub-atmospheric pressure, and with 8 unit 5 which assembles cut billet lengths for transport. <IMAGE>

Description

SPECIFICATION Equipment for reclaiming radioactive metallic components from spent nuclear power plants This invention relates to equipment for the reclamation of radioactive and/or radioactively contaminated metallic components from spent nuclear power plant units, such as arise when nuclear power plants are dismantled, the equipment having means for comminuting the metallic components, means for transporting the comminuted material, a melting furnace for the comminuted material, means for processing the melted material to the solidified state, and means for offloading the solidified material, the transporting means being used to charge the comminuted material into the melting furnace.

In known equipment of this type (DE-OS 30 02 695), the comminuting means deliver the material into a charging unit of the transporting means, integrated with the melting furnace. The melting furnace is a plasma-gun melting furnace having a special melting crucible, and its plasma gun is aimed into the melting crucible. The melting crucible functions simultaneously as, on the one hand, the means for processing the melted material to the solidified state and, on the other hand the transporting means for offloading the material that has solidified inside it. The melting furnace is encapsulated together with the integrated transporting means, and furthermore the equipment as whole is contained in a hot cell the construction of which requires the application of shielding techniques. The entire system is costly.The plasma-gun unit of the plasma-gun melting furance generates extremely high temperatures, which necessitates either cooling the melting crucible or introducing a separate preliminary melting chamber into which the plasma-gun unit is aimed. The melting crucible is raised into the melting furnace from below, which necessitates additional complicated systems for raising and lowering the melting crucible. In consequence, it is necessarily very costly to automate the known equipment completely, with its special melting crucible system.

The primary object of the invention is to provide equipment whereby the special melting crucible system referred to and the associated costly manipulations can be elminated and complete automation can be effected without any difficulty, the equipment as a whole thus functioning as it were as a robot for the reclamation of metallic components, and shielding becoming a simple matter. A secondary object is for the equipment to be constructed as a portable unit.

According to the present invention, equipment for the reclamation of radioactive and/or radioactively contaminated metallic components from spent nuclear power plant units comprises means for comminuting the metallic components, at least one container for the reception of the comminuted material, an electric melting furnace having top charging means, a unit for processing the melted material to the solidified state, in the form of a horizontal continuous casting machine having a billet extraction device, and a parting machine to cut the continuous billet into easily handled lengths, the container having a top charging mouth closable by means of at least one flap or slide, a bottom dischaging device and an extractor unit connected near the charging mouth, and being adapted as a charging container for the melting furnace by being transportable with the aid of a crane unit to set its bottom discharging device on the top charging means of the electric melting furnace, which top charging means are provided with an extractor unit, the container together with the electric melting furnace, the horizontal continuous casting machine, the parting machine and a unit for taking up the billet lengths ready for transport being accommodated in a shielding low-pressure bay outside and above which the crane unit travels, and which low-pressure bay has a sealing slit in its roof for a cable and hook only of the crane unit.

The invention arises from the realisation that an electric melting furnace integrated with a horizontal continuous casting machine delivers the solidified material in an aggregated state, viz., in the form of a continuous billet which can easily be parted into billet lengths, while the continuous billet and the billet lengths can be manipulated without any difficulty. In this respect, the electric melting furnace and the horizontal continuous casting machine integrated therewith combine functionally to effect a first step towards achieving the object of the invention, with the added contribution to its achievement of a further functional combination of the container, with its special construction and function, with the transporting crane unit.In this situation, the low-pressure bay provides simple shielding means and the crane unit in general is not subject to damaging contamination, since in its functional combination with the low-pressure bay it operates outside the low-pressure bay and the crane cable and hook alone are introduced into the low-pressure bay. Equipment in accordance with the invention can, moreover, be constructed as a readily transportable system.

The bottom discharging device of the container is preferably a vertically moving bottom lock of the throat-lock type, which can be operated by means of an actuating lever.

However, it is adequate in most applications to provide the top charging means of the electric melting furnace with at least one closure slide, the latter being closed during the melting process so that the container is free to pick up more comminuted material while melting is in progress.

The low-pressure bay is preferably a steel frame structure, fabricated from steel tubes for example, and is provided with a plastics foil casing and/or covering. The sealing slit in the roof of the bay is preferably a labyrinth seal, for example a bristle labyrinth seal through which the crane cable is introduced.In order to rationalise the various processing steps and provide the basis for simple automation, the low-pressure bay preferably has an entry lock followed by a working compartment, the container with the comminuted material being adapted to be filled at the centre of the entry lock, and the electric melting furnance, the horizontal continuous casting machine, the billet extraction device, the parting machine and the unit for taking up the billet lengths ready for transport being disposed along the longitudinal axis of the working compartment, while the sealing slit is disposed on the axis of the working compartment from the entry lock forwards, for example in the ridge of a ridgeshaped bay roof.

The extractor units ensure freedom from radioactive contamination. Bearing in mind that the extracted gases will contain variable amounts of radioactive substances, it is preferred to adopt an arrangement such that the extractor unit serving the container in its functional position over the melting furnance, together with the extractor unit for the top charging device on the melting furnace, are connected to a common vacuum source having a filter unit, while the low-pressure bay is served by an extractor unit having its own vacuum source and filter unit.The entry lock to the low-pressure bay is preferably adapted to function also as an exit lock, so that the crane unit can take into the exit lock a container full of billet lengths picked up within the working bay, this container being adapted to carry the billet lengths, and the billet lengths can be taken from the exit lock as their radioactivity fades or even disappears, for further treatment or processing.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a plan view showing the layout of equipment in accordance with the invention, Figure 2 is a scrap section, on a larger scale, taken on the line A-A of Fig. 1; and Figure 3 is a vertical section through the melting furnace and the horizontal continuous casting machine of Fig. 1, on a larger scale.

The equipment shown in the drawing is intended for the reclamation of radioactive and/or radioactively contaminated metallic components from spent nuclear power plant units, such as arise when nuclear power plants are dismantled. Its basic construction includes: means 1 for comminuting the metallic components, means 2 for transporting the comminuted material, a melting furnace 3 for the comminuted material, means for processing the melted material to the solidified state, and means for offloading the solidified material. The transporting means 2 are used to charge the comminuted material into the melting furance 3.

In accordance with the invention, the equipment has at least one container 4 for the reception of the comminuted material, the furnace 3 is an electric melting furnace having top charging means 6, a unit for processing the melted material to the solidified state is in the form of a horizontal continuous casting machine 7 having a billet extraction device 8, and a parting machine 9 is provided to cut the continuous billet into easily handled lengths.

Referring more particularly to Fig. 3, the container 4 has a top charging mouth 11 closable by means of a flap or slide 10, a bottom discharging device 1 2 and an extractor unit connected at 1 3 near the charging mouth 11, and is adapted as a charging container 4 for the melting furnace 3. Accordingly, the container 4 can be brought with the aid of a crane unit 2 to set its bottom discharging device 1 2 on the top charging means 6 of the electric melting furance 3, which top charging means 6 are fitted with an additional extractor unit connected at 1 4.

The container 4, the electric melting furnace 3, the horizontal continuous casting machine 7, the parting machine 9 and the unit 5 for taking up the billet lengths ready for transport are accommodated in a shielding low-pressure bay 15, which is held below atmospheric pressure as will be described later in more detail. The crane unit 2 travels outside and above the low-pressure bay 15, and, as can be seen in Fig. 2, the cable 1 6 and the hook 1 7 alone are introduced into the low-pressure bay 1 5 through a sealing slit 1 8 in its roof 19.

The bottom discharing device 1 2 of the container 4 is a vertically moving bottom lock of the throat-lock type, which can be operated by means of an actuating lever 20. Fig. 3 shows the closed position of this bottom lock 1 2 in full lines and its open position in broken lines. The container 4 could be adapted as a closure for the electric melting furnace 3 and remain set thereon during melting operations.

However, the drawing shows a preferred embodiment in which the top charging device 6 of the electric melting furnace 3 has a closure slide 21, which can be closed during melting operations so that the container 4 can be taken away and refilled while the melting operations continue.

As simply indicated in Figs. 1 and 2, the low-pressure bay 1 5 is a steel frame structure, fabricated from steel tubes, and has a plastics foil casing 22 and/or covering. The sealing slit 1 8 in its roof 1 9 is a labyrinth seal in the form of a bristle labyrinth seal 23, through which the crane cable 1 6 and hook 1 7 are introduced. The low-pressure bay 1 5 has an entry lock 24 followed by a working comparment 25, and the comminution means 1 are accommodated in the entry lock 24. The container 4 is arranged to be filled with com- minuted material at the cenre of the entry lock 24.The electric melting furnace 3, the horizonal continuous casting machine 7, the billet extraction device 8, the parting machine 9 and the unit 5 for taking up the billet lengths ready for transport are set in line on the longitudinal axis 26 of the working compartment 25. The sealing slit 1 8 is also set on the axis 26, extending in a straight line from the entry lock 24 forwards, being disposed in the ridge of the ridge-shaped bay roof 19.

The extractor unit connected at 1 3 to the container 4 to serve it in its functional position over the melting furnace 3, together with the extractor unit connected at 14 to the top charging device 6 on the melting furnace 3, are connected to a common vacuum source 27 and filter unit, either or both of which can be preceded by a device for cooling the waste gases, though this is not shown. The lowpressure bay 1 5 has an extractor unit 28 with its own vacuum source 29 and filter unit. The entry lock 24 can also function as an exit lock. To enable the equipment to be transported to another site, the plastics foil casing 22 and the filters serving the vacuum sources 27 and 29 are discarded and replaced by new elements.

Claims (11)

1. Equipment for the reclamation of radioactive and/or radioactively contaminated metallic components from spent nuclear power plant units, the equipment comprising means for comminuting the metallic components, at least one container for the reception of the comminuted material, an electric melting furnace having top charging means, a unit for processing the melted material to the solidified state, in the form of a horizontal continuous casting machine having a billet extraction device, and a parting machine to cut the continuous billet into easily handled lengths, the container having a top charging mouth closable by means of at least one flap or slide, a bottom discharging device and an extractor unit connected near the charging mouth, and being adapted as a charging container for the melting furnace by being transportable with the aid of a crane unit to set its bottom discharging means on the top charging means of the electric melting furnace, which top charging means are provided with an extractor unit, the container together with the electric melting furnace, the horizontal continuous casting machine, the parting machine and a unit for taking up the billet lengths ready for transport being accommodated in a shielding low-pressure bay outside and above which the crane unit travels, and which pressure bay has a sealing slit in its roof for a cable and hook only of the crane unit.

2. Equipment as in Claim 1, wherein the bottom discharging device of the container is a vertically moving bottom lock of the throatlock type, which can be operated by means of an actuating lever.

3. Equipment as in either of Claims 1 and 2, wherein the container is adapted as a closure for the electric melting furnace, on which it sits during melting operations.

4. Equipment as in either of Claims 1 and 2, wherein the top charging means of the electric melting furnace has at least one closure slide.

5. Equipment as in any one of Claims 1 to 4, wherein the low-pressure bay is a steel frame structure and is provided with a plastics foil casing and/or covering.

6. Equipment as in Claim 5, wherein the sealing slit in the bay roof is a labyringth seal through which the crane cable and hook are introduced.

7. Equipment as in any one of Claims 1 to 6, wherein the low-pressure bay has an entry lock followed by a working compartment, the container being adapted to be filled with the comminuted material at the centre of the entry lock, and the electric melting furnace, the horizontal continuous casting machine, the billet extraction device, the parting machine and the unit for taking up the billet lengths ready for transport being disclosed along the longitudinal axis of the working compartment, while the sealing slit is disposed on the axis of the working compartment from the entry lock forwards.

8. Equipment as in any one of Claims 1 to 7, wherein the extractor unit serving the container in its functional position over the melting furnace, together with the extractor unit for the top charging device on the melting furance are connected to a common vacuum source having a filter unit.

9. Equipment as in any one of Claims 1 to 8, wherein the low-pressure bay is served by an extractor unit having its own vacuum source and filter unit.

10. Equipment as in Claim 7 or Claim 9, characterised in that the entry lock to the lowpressure bay is adapted to function also as an exit lock.

11. Equipment for the reclamation of radioactive and/or radioactively contaminated metallic components from spent nuclear power plant units substantially as hereinbefore described with reference to the accompanying drawings.