GB2350831A

GB2350831A - Excavating equipment with radiation detector

Info

Publication number: GB2350831A
Application number: GB0011663A
Authority: GB
Inventors: Ian Adsley; Andrew Herbert Graham
Original assignee: AEA Technology PLC
Current assignee: Ricardo AEA Ltd
Priority date: 1999-05-19
Filing date: 2000-05-16
Publication date: 2000-12-13
Anticipated expiration: 2020-05-16
Also published as: CA2308607A1; GB9911652D0; GB0011663D0; GB2350831B

Abstract

Excavating equipment (10, Fig 1) for excavating material which may be contaminated with radioactive material incorporates a bucket (12) or grab or clamshell to convey excavated material. The bucket (12) incorporates a gamma ray detector (26) within a hollow projection (24), SO the detector (26) is surrounded by the excavated material when the bucket (12) is full. This enables the radioactive contamination within a bucket-full of material to be assayed straight after it has been excavated, so the operator of the excavating equipment (10) can rapidly decide how each bucket-full should be disposed of. Preferably, the detector 26 is provided inside a wall separating the bucket in two. Preferably, ground shielding 28 is provided. The detector is preferably a scintillator.

Description

2350831 Excavating Equipment This invention relates to excavating

equipment which may be used for excavating material, such as soil, which may be contaminated with radioactive material, and to a method of excavating such materials.

When sites which have been used for processing or working on radioactive material, for example using radium in luminous instrument displays, are to be redeveloped it is desirable to ensure that the soil is not contaminated. For this purpose it is known to survey the sites using a radiation detector, thereby determining which areas of the sites are contaminated. The soil from the contaminated areas can then be excavated and disposed of in a licensed radioactive waste disposal site. While performing this operation it is desirable to check each excavated bucket-full, to see if it contains a significant level of radioactive contamination, so that only contaminated soil is disposed of in the radioactive waste disposal site; checking each bucket-full is not easy because of radiation received from the contaminated ground. Measuring the level of radioactivity in a load of materials is also an issue when excavating radioactive ores, and a way of making such a measurement is described in US 5 015 847 (Rouillon); in this case the detector is on a rod suspended above the bucket of a hydraulic excavator. However such ores are typically in the form of lumps of rock, rather than Soil. Furthermore the levels of radioactivity in such ores are typically fairly uniform, for example about 1 Bq/g, whereas the levels of radioactivity in contaminated soil may vary widely. At one contaminated site, for example, the background value (for uncontaminated soil) is 0.7 Bq/g, and contaminated soil can be as high as 15 or 20 Bq/g; the threshold value at which the soil is considered contaminated might be set at 1.3 Bq/9. Under such circumstances it can be difficult to distinguish between radiation from a sample of soil and radiation from the nearby unexcavated soil.

According to the present invention there is provided excavating equipment for excavating material which may be contaminated with radioactive material, the excavating equipment incorporating a bucket to convey excavated material, in which the bucket incorporates an internal projection, the projection being hollow and enclosing a gamma ray detector.

In this document the term bucket refers to any device used for excavating and conveying excavated material, and so may refer to a simple scoop device, or to a grab with more than one scoop or claw. The projection should be such that the detector is at or near the middle of the bucket, so when the bucket is full of excavated material the detector is surrounded by that material. For example the projection might comprise a spike projecting from the bottom into the middle of the bucket. Alternatively the projection might be a wall dividing the bucket in two. Desirably the bucket also includes radiation shielding material between the detector and the bottom of the bucket, for example a lead shielding plug, to minimise radiation received from the ground beneath the bucket.

The detector is desirably a scintillator.

Alternatively it might be a Geiger-Muller tube, or a high resolution detector such as a germanium diode detector. In each case the detector must be protected from damage due to mechanical shocks, and may itself also be ruggedised.

3 -amination The equipment enables the radioactive cont within a bucket-full of material to be assayed straight after it has been excavated, so the operator of the excavating equipment can rapidly decide how each bucket- full should be disposed of. The detector is surrounded by the excavated material on all sides, and so the excavated material itself shields the detector from any radiation from the ground, so enabling the level of contamination within the material in the bucket to be accurately assayed. This can considerably reduce the time required to excavate and assay contaminated soil and rubble. To reduce the shocks to which the detector is subjected it is desirable to break up any compacted material before excavating it, using conventional equipment.

is The invention will now be further and more particularly described, by way of example only, and with reference to the accompanying drawings, in which:

Figure 1 shows a diagrammatic elevation of a mechanical excavator with a bucket; Figure 2 shows a perspective view of the bucket of the excavator of Figure 1; Figure 3 shows a sectional view of the bucket, on the line III-III of Figure 1; and Figure 4 shows a sectional view on the line IV-1V of Figure 3.

Referring to Figure 1 there is shown a mechanical excavator 10 with a bucket 12 at the end of an arm 14. The arm 14 is supported by a turntable 15 mounted on a tractor 16, the turntable 15 enabling an operator (in a cab 13) to turn the arm 14 about a vertical axis, and the arm 14 incorporating a plurality of links so the bucket 12 can be raised and lowered. All the movements of the arm 14 and the bucket 12 are controlled hydraulically. It should be appreciated that, apart from the bucket 12, the 5 excavator 10 is conventional. The excavator 10 may -e additional hydraulic therefore also incorporat mechanisms, and in particular might incorporate a second, conventional arm and bucket (not shown).

Referring to Figure 2, the bucket 12 is of generally rectangular shape, connected to the arm 14 by lugs 18 at the rear corners of the top, and tiltable by a hydraulic linkage 20 (shown in Figure 1) connected to the rear of the bucket 12 near its bottom. The bucket 12 is of steel, and the front edge of the bucket 12 is provided with projecting steel teeth 22. The bucket 12 is divided in two by a central partition 24 which extends from the front to the rear of the bucket 12.

Referring now to Figures 3 and 4, the partition 24 is shown in section. It is of steel, welded to the bucket 12, generally solid, but defining a generally its M4 cylindrical cavity 25 at in which is located a ruggedised gamma-detecting scintillator and photo- multiplier assembly 26, surrounded by a layer of foam rubber (not shown) to provide shock protection. The cavity 25 extends from an opening at the bottom of the bucket 12, this opening being closed by a lead shielding block 28.

A suitable scintillator crystal and photomultiplier tube for this purpose can be obtained, for example, from Bicron Corp. (of Newbury, Ohio), preferably being enclosed within a single stainless steel tube, and being cushioned by an external sleeve of elastomeric material, such as foam rubber, close fitting within the cavity 25.

As described in US 4 158 773 (Novak) the scintillator crystal may be enclosed within a stainless steel tube, leaving an annular space just large enough to accommodate a sleeve of silicone rubber. The inner surface of the sleeve defines a multiplicity of tapered (e.g. conical) protrusions. At one end of the tube is a rubber compression pad, and a disk of silicone rubber that, like the sleeve, is covered in tapered protrusions.

At the other end of the tube is an optical w-lndow, and a flexible silicone rubber lightpipe that couples the crystal optically to the window; this light-pipe may be over 15 mm thick. The crystal itself may be of sodium iodine activated with thallium (NaI(T1)), and may be a single crystal. It may be maintained under compression within the stainless steel tube to minimise the risk of tensile failure. The scintillator crystal may alternatively be polycrystalline with a randomly oriented mosaic structure; such a scintillator has greater mechanical strength because any fractures are normally blocked at crystal boundaries.

The photomultiplier tube is preferably enclosed in a stainless steel tube integral with that that encloses the scintillator crystal. It may be mounted by means of an elastomeric sleeve, for example of silicone rubber, into a support tube that is itself supported by spaced apart elastomeric rings within the steel tube, for example as described in US 5 070 249 (White).

Such an assembly 26 of a scintillator and a photomultiplier should be able to withstand shocks up to say 100 g (where g represents gravitational acceleration), and may be able to withstand shocks up to 500 g or 1000 g. Preferably an accelerometer (not shown) is mounted on the assembly 26, and is coupled to a display in the operator's cab 13 that indicates if a threshold value of shock acceleration is exceeded, this threshold value being say a third or a half of the maximum shock that the assembly 26 can withstand. 5 Thus in use of the excavator 10 the operator uses -e potentially contaminated the bucket 12 to excavat material. The scintillator 26 is connected to an instrument display (not shown) in the operator's cab 13, so the operator can assay each buCket-full as soon as it has been excavated. For example the criterion might be that if the gamma radiation from the material is g-reater than 10 Bq/g then the material is significantly contaminated with radioactive material (such as radium).

It will be appreciated that it is first necessary to measure the average weight of material in a bucket-full, and also to calibrate the scintillator 26, so the count rate from the scintillator 26 corresponding to that criterion is known. The operator can then rapidly determine whether each bucket-full must be treated as radioactive or not, and can then empty each bucketfull accordingly. The material in the bucket 12 shields the scintillator 26 from any radiation originating outside -or 26 is not affected by the bucket 12, so the scintillat radiation from the surroundings; the time taken to assay each bucket-full of material would typically be 2 or 3 seconds.

If the accelerometer display indicates that the detector assembly 26 is being subjected to excessive shocks, the operator would then use an alternative tool (for example) a second, conventional, hydraulic arm and bucket) to break up and loosen the material that is to be excavated. The broken up and loosened material can then be excavated with the bucket 12 as described above, the 7 - shocks to which the detector assembly 26 is subjected thereby being reduced.

It will be appreciated that an excavator may differ from that described above while remaining within the scope of the invention. For example in the bucket 12 the scintillator 26 might be enclosed within a hollow prong or spike mounted in the bucket 12 and projecting into the middle of it, rather than in a hollow partition.

Furthermore the bucket might be in the form of a grab, such as a clamshell or a multi-claw grab, and in this -end from one of the claws of case the projection may ext the grab, or from a distributor head to which all the claws are hinged.

Claims

Claims

Excavating equipment for excavating material which may be contaminated with radioactive material, the excavating equipment incorporating a bucket to convey excavated material, in which the bucket incorporates an internal projection, the projection being hollow and enclosing a gamma ray detector.
2. Equipment as claimed in claim 1 in which the projection comprises a spike projecting into the middle of the bucket.
3. Equipment as claimed in clai-m 1 in which the projection comprises a wall dividing the bucket in two.
4. EquIpment as claimed in any one of the preceding claims also including radiation shielding material arranged so as to minimise radiation received by the detector from the ground beneath the bucket.
5. Equipment as claimed in any one of the preceding claims wherein the detector is a scintillator.
6. Equipment as claimed in any one of the preceding claims wherein the detector is protected from mechanical shocks by a resilient elastomeric material.
7. Equipment as claimed in any one of the preceding claims incorporating means for monitoring the mechanical shocks to which the detector is subjected.
8. Excavating equipment for excavating material which may be contaminated with radioactive material, substantially as hereinbefore described with reference to, and as shown in, the accompanying drawiigs.