GB2246660A - Rapid determination of radioactivity level in bulk quantities of soil material - Google Patents

Abstract

A framework of steel beams and columns into which an ISO container of potentially radioactive waste soil can be inserted. The framework supports a series of geiger counters which are brought up close to the sides, top and bottom of the container, which measure the extent of radioactivity coming from the waste. The geiger counters feed the activity levels to a computer which analyses activity levels in relation to position.

Description

SPECIFICATION A METHOD FOR THE RAPID DETERMINATION OF RADIOACTIVITY LEVEL IN BULK QUANTITIES OF SOIL MATERIAL BULK QUANTITIES OF SOIL MATERIAL This invention relates to the the decontamination of polluted land.

There are a large number of sites throughout UK which previous industrial activity has rendered environmentally unsafe which restricts current and future uses. Many of these sites are contaminated with radioactive residues mixed in with the soil and the resulting mix is of varying activity. It is essential to be able to sort the soils, which will be treated or disposed of by different methods dependent on the level of activity.

In the past this sorting has been achieved on a small scale, by operatives digging up the soil by hand, spreading it out over a defined area to a minimal thickness, and scanning the resulting layer of soil with geiger counters to determine the general level of activity and the presence of any lumps of soil of higher activity. These lumps could be removed and tested in greater detail. In other words the sorting divided the waste into two streams. Later developments of hand sorting included the use of moving conveyor belts with directional baffles which directed the different levels of waste into 2 different hoppers. This enabled the geiger counter operator to remain in one position.

With development land becoming ever more scarce, and therefore more valuable, there are financial incentives to rehabilitate contaminated land. There are also political incentives to improve the environment and to remove contamination which blights the countryside, to safer locations, where the sites are properly organised, and disposal properly controlled.

Hand methods of sorting are no longer viable, and for large sites with extensive areas of contamination, previous methods of sorting would be inordinately expensive, time consuming, and possibly dangerous for operatives. Additionally, much of the radioctive waste is of low level of activity, and the only sorting operation necessary is to determine the difference between soils of such low activity as to be effectively uncontaminated, and soils of slightly higher activity which would need a special disposal regime.

This invention permits the automatic scanning of standard containers of contaminated soil, by a special array of geiger counters, positioned upon a structural framework in such a way as to give a profile of the general activity and to detect the presence of any higher than general concentrations of activity in the body of the waste. The structural framework, or gantry, is constructed in such a way as to permit the easy insertion of the container into the array of counters and its easy removal once scanning is complete. In this way a series of containers can have their contents rapidly analysed, and this rapid throughput justifies the use of mechanical equipment to fill the containers, thus enabling large volumes to be handled, and large areas of site to be decontaminated in a short time.

The gantry and associated mechanical dig operation may or may not take place inside a protective temporary enclosure.

One embodiment of the invention is shown on sketch A attached, and is described in detail below.

A framework of stractural steel (F) supports two lifting hoists (H) and an array of geiger counters (G), in this embodiment 36 No.

arranged as 12 upper, 12 lower, and 6 on either side. The counters are collimated, which means that they are lead sheathed to receive directional radioactivity. The lower 12 are attached to a removable part of the frame, which is supported on rails so that the array can be slid in and out of the main framework. The counters feed their readings to a central controlling computer, which is programmed to analyse the readings to a predetermined format, depending on the nature of the waste and the chosen trigger levels of activity.

A typical procedure for the testing of activity level of the waste is as follows: A standard half ISO container filled with waste to be tested is driven into the framework on a transporter. Operatives attach the two hoists to the container and lift it free of the vehicles wich moves off. The operatives push the lower frame along the rails into position beneath the container. The array is then activated for a pre-determined period, typically 300 seconds, and the results analysed in the preprogrammed manner. The reverse of the above operations is then applied and the container lowered onto the transporter which removes it to locations where the waste can be treated, further analysed or simply disposed of. A new container can be then tested.

Claims (3)

1. An array of gieger counters positioned on a structural frame with a fixed orientation and in sufficient numbers and with predetermined collimation as to give a detailed analysis of radioactivity coming from a volume of contaminated waste contained within the array, so that an assessment of the uniformity of the waste, or the presence of hotspots of activity can be determined for the entire bulk of the waste.

2. An array of counters as 1 specifically orientated on a framework to test and analyse radioactive waste contained within standard size ISO or half ISO Containers

3. An array of counters as 1 and 2 mounted on a framework with openings at the fromt and rear which allows the rapid throughput of said containers.