GB2146831A - Decontamination of radioactively soiled metal sections - Google Patents

Abstract

Revolving metallic wire brushes are used for decontaminating radioactive metal sections. The impurities removed from the sections are entrained in an air stream and drawn through a two-stage dust separation unit. The low-volume waste material is bagged at the separators for subsequent disposal.

Description

SPECIFICATION Decontamination of radioactively soiled metal sec tions The present invention relates to a process and an apparatus for the decontamination of radioactively soiled metal sections, including tubular sections.

Metal sections, such as aluminium frame members used in nuclear power stations, must be thoroughly decontaminated before leaving the area ofthe power station. This is particularly difficult if the contamination consists of adhering masses such as splashes of chalkorcement.

Such deposits are generally removed using an acid (sulphuric acid) which is usually sprayed on to the metal surface under pressure. This obviously gives rise to large volumes of contaminated acid which have to disposed of in a complex and expensive manner.

The object of the present invention is therefore to provide a simple and less expensive method of decontaminating these metal surfaces, without in creasingthevolume of impurities and without damaging the surface ofthe sections.

In accordance with the invention we have found that metal sections can be completely decontaminated by mechanical scrubbing, the scrubbing preferably being performed by metallic wire brushes revolving at a controlled rate. It is to be understood that the metal sections include, interalia,tubular metal sections.

The metal surfaces ofthe sections can be scrubbed without being scratched by the wires of the brushes, and the sections have a bright decontaminated surface. The brushes preferably revolve at a circumferential speed of 15to 60 m/sec and at least one brush should be pressed on or againstthe surface with a force ofabout 100 kp. The sections can be moved forward relative to the brushes at a preferred rate of about 3 m/min.

With substantially flat sections, it is sufficient to use roller brushes with a continuous cylindrical surface, these brushes acting on both sides ofthe sections and laterally on the edges. The brushes can be built-up of roller or disc segments to provide an adjustable width.

This also has the advantage of providing stepped cross-sections if roller or disc segments of differing diameter are mounted nexttoeach otheron a common axis. It is then possible to simultaneously clean parts of a section lying at different depths.

With sections having grooves, flanges or rails,the horizontal areas of the section are treated with brushes revolving about horizontal axes, while the vertical areas are treated with brushes revolving about vertical axes. Angled orT-shaped rails or flanges can also be cleaned.

Pipes ortubes can be treated in an analogous manner. At the same time the inner wall of the tube can be treated by a rotating brush arranged at the head of a spindle, the spindle being pushed into the tube. In this manner atube of about 3 meters can be decontaminated. The withdrawal of the dust from inside the tube is then effected by a suction device pushed into the tube.

The dust produced is preferably sucked away and collected using separators. To this end, it is proposed thatthe dust is firstly conveyed into a cyclonic separator and then into a dust filter with filter pockets so thatthe separated dust can be bagged in a convenient manner.

The suction device is preferably arranged downstream ofthefilter(s) and sucks the dustfair mixture through the filter plant. The dust can also be wetted with water before being sucked away.

In one embodiment of the invention,the cleaning device is located in a housing which is hermetically sealed, and the quantity of air required for extracting the dust and dirt particles is drawn through inlet and outlet openings of the housing through which the sections are conveyed. The rotating brushes produce an adequate quantity ofvorticesfor spinning the entrained dust and dirt particles upfromthe base of the housing and feeding them to a discharge opening in the roof ofthe housing which communicates with the suction device. Air slits can also be left in the base ofthe housing.

Finally, the dust-free air leaving the suction unit is conveyed to stations which measure, for example, the level of activity and asbestos dust to checkthatthe prevailing anti-pollution regulations are being observed.

Acleaning apparatus embodying the invention will now be described by way of example only with reference to the attached drawings, in which: Fig. 1 shows the apparatus being used for cleaning reinforced metal sections; Fig. 2 shows two such sections; and Fig. 3 shows the entire plant.

The illustrated cleaning apparatus is arranged in an hermetically sealed housing 1. It consists of a framework 15 carrying walls 16. Two of the opposed sidewalls include an inletopening 2 and an outlet opening 3 through which the sections Sto be cleaned are conveyed by a feed table 17 and adeliverytable 18 each with rollers 19.

Electric motors 10, 11, 12 rest on the framework 15 within the housing and drive brushes 6, 7, 8, 9, by means of belts. Ifthesections are substantiallyflat on both sides, one upper brush roller and one lower brush roller are sufficient. However, the illustrated apparatus is for cleaning a section with a substantially smooth underside (see Fig. 2) but with longitudinal rails orflanges 23 on the top. Brush rollers 9 driven by motor 12 are provided to clean the vertical faces ofthe rails orflanges, and these brushes 9 are arranged next to the inlet opening 2.The brushes 9 are arranged on a holder 20 which is connected via a pivotal leverto a hydraulically or pneumatically driven pistonicylinder pair 22so that the brushes can be raised or lowered for exampletoaccommodate materials of differing thicknesses and, above all, to produce the necessary pressure againstthe vertical faces. The upper horizontal surfaces of the rails orflanges are cleaned by the roller brush 8which can also be raised and lowered.

The roller 8 may include a combination of roller brush segments and spacer members respectively aligned with the rails orflanges and with the intermediate spaces between the rails or flanges.

In the forward feed direction ofthe work-piece, the roller brush 6, driven bythe motor 10, cieans the underside ofthe workpiece and the roller brush 7 which is driven in common with the brush 8 by the moto 11 cleans the upper side. The brush 7 is divided by means of spacer members into individual roller segments which dip into the intermediate spaces between the rails orflanges 23. The brush 7 can be raised and lowered, and pressure on the brush can be adjusted, by means ofthe piston/cylinder24.

In the present example, each internal rail flank is cleaned by a separate brush 9 (three grooves, six brushes). in principle, however, itis also possible for two flanks to be cleaned simultaneously by one brush.

An additional driving means 13 finally sets the brush 24 into rotation in order to clean the outermost flanks 25 ofthe sections.

A separate driving means for advancing the sectionsthrough the plant can be dispensed with by using instead the friction effect ofthe brushes on the sections. In this case, decelerating friction rollers (not shown) may also be used.

If the brushes rotate in opposing directions, the deceleration effect can also originatefromthe rotating brushes directed againstthe forward feed. In this case, it may be necessaryto adaptthe circumferential speed.

Deposits removed from the sections are sucked through a discharge opening 14, a single (upper) suction motor and opening generally being sufficient.

It is possible to operate the cleaning device alone and then to collect the contaminated entrained dust after a few cleaning operations. Generally, however, the process involves continuously sucking away the dust produced.

The performance ofthe suction motor can be used to regulate the quantity of air. Alternativelythe quantity is advantageously regulated by adjusting the size ofthe inlet and outlet openings 2,3. It is then possible, for example, to produce periodic pressure pulses by rapid opening and closure of the openings 2, 3.

Fig. 2 shows aluminium sections 5 of the type used, for example, in frame construction. The cross-members 23 reinforce their strength. The brushes 9 mounted on the plate 26 are shown schematically in this Figure.

Figure 3 is a schematic representation of the entire plant. By means ofthetables 17,18, as mentioned above, the sections are supplied to the decontamination apparatus 27 and cleaned there by means of revolving metallicwire brushes. Air is drawn through the openings 2 and 3 by the suction unlit 28. A screw-type compressorwith an output of 1800 m3 of air/h is preferably used here. The dust/air mixture sucked away passes through the pipe 29 into the preliminaryseparatorwhich is a cyclonicseparator30.

A bagging arrangement31 can be connected to its foot Thegmatly diluted dust/airmixtureisfed through pipe 32 to a dustfilter33 which has a vibrating device for the periodic removal of the filtrate. The dust filter 33 is connected via the pipe 34 to the screw-type compressor 28. The loss of pressure in the pipes 29, 32,34 and the separators 30 and 33 is sufficiently low to enable all dustto be sucked away from the decontamination apparatus 28.

Claims (24)

1. Aprocessforthe decontamination of a radioactively soiled metal section wherein the sections are mechanically scrubbed.

2. A process according to Claim 1 whereinthe mechanical scrubbing is performed by metallic wire brushes.

3. A process according to Claim 2 wherein the wire brushes are revolving at a controlled rate.

4. A process according to Claim 3, wherein the revolving brushes rotate at a circumferential speed of 15 to 60 m/s.

5. A process according to Claim 3 or Claim 4 wherein at least one ofthe revolving brushes are urgedagainstthesectionwitha predetermined force.

6. A process according to any one of the preceding claims where the section is advanced relative to the scrubbing means at a predetermined feed rate.

7. A process according to Claim 6 in which the predetermined feed rate is approximately 3m/min.

8. A process according to any one ofthe preceding claims where the scrubbing is performed in a chamber and particles removed from the sections are extracted through a suction device.

9. A process according to Claim 8 wherein the particles are firstly conveyed into a main cyclonic separator and then filtered.

10. A process according to Claim 9 wherein the suction device is arranged downstream ofthe particle filters.

11. A process according to any one ofthe Claims 8 to 10 wherein the particles are wetted before being sucked away.

12. Apparatus for carrying out a process according to any one ofthe preceding claims, the apparatus comprising a hermetically sealed housing with an inlet opening and an outlet opening, means for supporting the section to be decontaminated, and a plurality of revolving wire brushes so arranged that substantially the entire surface of the section is scrubbed by the brushes as the section is advanced from the inlet opening to the outlet opening.

13. Apparatus according to Claim 12furthercomprising driving means for driving the section through the housing art a controlled rate.

14. Apparatus according to Claim 12 or Claim 13 further comprising a suction device for extracting particles removed from the section by the wire brushes.

15. Apparatus according to any one ofthe Claims 12to 14wherein the size of the inlet and outlet openings is adjustable.

16. Apparatus according to Claim 14 wherein the particles are extracted through a discharge opening at the top ofthe housing.

17. Apparatus according to any one ofthe Claims 12 to 16 wherein at least one ofthe brushes comprises a roller Brush composed of discrete roller or disc segments.

18. Apparatus according to any one of the Claims 12to 17 wherein at least one ofthe brushesis movable toward and away from the section.

19. Apparatus according to Claim 16 wherein a dust separator is disposed between the suction device and the discharge opening.

20. Apparatus according to Claim 19 wherein the dust separator consists of cyclonic main separator and a subsequentfilter.

21. Apparatus according to Claim 14wherein the suction device is a screw-type compressor.

22. Apparatus according to any one ofthe Claims 1 2to 21 wherein at least one brush rotates about a horizontal axis and at least one other brush rotates about a vertical axis.

23. A processforthe decontamination of radioac tivelysoiled metal sections, the process being substantially as herein described with reference to the accompanying drawings.

24. Apparatus according to Claim 12 and substantially as herein described with reference to the accompanying drawings.