GB2244171A - Waste disposal - Google Patents

Abstract

Waste material is disposed inland and above a permanent zone of saline water. Horizontal tunnels 10 may connect to a flow connection 14 to a soakaway 18 in the sea-bed below low tide level 17. Passages 12 connect to waste disposal zones above and/or below the tunnels 10. The waste may be in a covered trench with the connection 14 leading to below the waste, or in shallow burial with the connection 14 leading to above the waste. <IMAGE>

Description

WASTE DISPOSAL This invention relates to the disposal of toxic or hazardous waste for example radioactive waste.

According to one aspect of the invention a method comprises disposing waste material inland and above a permanent zone of saline water.

The saline water may be stagnant.

The material may be below ground and surrounded by the saline water.

From another aspect of the invention a method comprises disposing waste material above the adjacent water table and establishing a zone of substantially stagnant saline water beneath the material for receipt of percolating ground water.

The waste material may be below ground.

From a further aspect of the invention a method comprises disposing waste material below ground and establishing a permanent connection for saline water to infiltrate to a region landward of the material, The invention also provides a waste material disposal arrangement with a flow connection to below sea level leading to an inland zone so that saline water is permanently below the material.

The saline water may surround the material and may be essentially stagnant.

The waste may be low level radioactive waste (L or intermediate level (ILW).

The invention may be performed in various ways and some specific embodiments with possible modifications will now be described by way of example with reference to the accompanying schematic drawings, in which: Fig. 1 is a plan view of a saline water connection; Fig. 2 is a side view of Fig. 1; and Figs. 3 to 7 show possible waste disposal arrangements.

A hazard from buried radioactive waste arises from leaching into ground waters and eventual passage to Man.

One way of reducing the hazard is to inhibit ground waters from reaching the waste by burying the waste above the local water table - Figs. 3 and 5. Another way is to arrange that the eventual emergence of such ground water is in a non-potable form as occurs after dilution in saline water - Figs. 3 to 6.

In the present arrangement waste is disposed beneath land and has a connection to below the sea bed.

The waste zone may be 'dry' i.e. above the level of the adjacent water table or 'wet' i.e. below the level of the adjacent water table. The waste is inland of the high tide boundary.

One form of connection to the sea bed is shown in Figs. 1 and 2. A number of connected horizontal tunnels 10 are shown in the form of a rectangle although other forms are possible. Access to the tunnels 10 may be by shafts 11. Further shafts 12 at the landward side lead from the tunnels 10 either upwards at 12a,or downwards at 12b,to the zone of waste disposal. The waste is disposed by transport through shafts 11, tunnels 10 and shafts 12.

Borehole or other connections 14 connect the tunnels 10 to below the sea bed 16, preferably to below low tide boundary 17. The connections 14 may lead to a soakaway zone 18. Water flowing through rock fissures in the sea bed should be thus filtered reducing the possibility of clogging by fines. If desired, a sump or catchpot could be excavated below the drilling entry points, e.g. at 20, to collect possible migrating fines.

The tunnels 10 are shown below low tide level 21 so that with a fairly free flow to and from the soakaway 18 the tunnels 10 would effectively always contain sea water. The tunnels 10 are pumped out as needed during disposal of the waste.

Auxiliary drain off round the sea bed connection for example through rubble trenches to local streams or the shore could reduce the required net soakaway flow.

The maintenance of acceptable soakaway flows should be related to the period stipulated for the decay of disposed waste e.g. a few hundred years for LLfl and short-lived ILi.

The tunnels 10 bring about a general levelling of the water table such that horizontal differences in hydraulic heads at deep disposal positions may then be slight with consequently little driving force for water to pass through the wastes.

Fig. 3 shows one form of waste disposal zone 30.

Here the zone 30 is above the local water table 31 which has been drawn down by the existence of the tunnels 10..

The waste is lifted up shafts 12a into tunnels 34.

Only water percolating more or less vertically e.g.

at 35 will reach zone 30 and then merely as slow seepage at occasional points in the walls OfthetBmels34 if unlined.

The tunnels 34 would be inclined so as to drain down to the tunnels 10. Several levels of zone 30 could be used.

Zone 30 is shown beneath a hillside 36. Backfill, possibly with waste nuclide sorption materials, is possible.

Fig. 4 shows a form of 'wet' trench burial appropriate particularly for large items of waste of low radioactivity e.g. from decommissioning.

Large volume cells 40 e.g. of concrete are sited below the sea connection 14. The waste 41 is in the cells 40.

The cells 40 are surrounded by impermeable backfill 42 and capped with permeable backfill 43 and an impermeable cover 44. Because seawater is denser than percolating rainwater, the seawater would gradually permeate the region round the waste cells creating stagnant conditions.

The waste would then be surrounded by essentially stagnant saline water.

In Fig. 5 the arrangement is similar to Fig. 4 but the waste 50 is in a shallow trench above the connection 14 and has an impermeable cover 51 and rests on permeable backfill 52. The water table is drawn down as at 53 to the level of connection 14.

Saline water thus fills the backfill 52 and gives assurance against flooding and/or pollution of potable water.

In another arrangement a disposal structure is built partly or wholly above ground level and landscaped over with earth to last hundreds of years. The consequences of defects developing which allow leaching of waste nuclides is reduced by siting the structure within a sea bed connection area e.g. above the region 55 between the tunnels 10 in Fig. 1. The leachate would thus pass into saline water.

In Fig. 6 the sea bed connection 14 connects to one or more vertical shafts 60 leading to one or more horizontal tunnels 61 providing a disposal zone 62 which may have impermeable backfill 63. Permeable backfill 64 may be in shaft 60. A cross connection 65 may connect to other shafts 60. The backfill 64 forms a stagnant saline water environment to the zone 62. The saline/fresh water interface would be at 66 so that saline water is brought to the landward side of the zone 62. This arrangement may be suitable for long-lived wastes.

The various disposal zones could have surface facilities in common.

The shafts could be adits or inclined shafts.

The saline connection could discharge at an outlet at the sea bed e.g. a pipe.

The saline connection outlet could be between high and low tide levels so that the connection drains out between tides, i.e. between 17a and 17.

There could alternatively or additionally be bore.

holes in the sides of the shafts 60 to improve drainage.

In a further arrangement shown in Fig. 7, the repository of waste is at 80, the ground at 81, the sea bed at 82, the mean tide level at 83. A ring drain 84 is provided with a drain e.g. a pipe 85 to the sea or the sea bed. The water table is indicated at 86. The probable interface between a saline water region 87 and a fresh water region 88 Is at 89. Thus if the ring drain 84 is e.g. 5 metres above mean tide level 83 the interface 89 may be 200 metres below mean tide level 83 and the repository 80 is in stagnant saline water; the waste is thus above a permanent zone of saline water because it is surrounded by such water.

Claims (13)

ClAIMS

1. A method comprising disposing waste material inland and above a permanent zone of saline water.

2. -A method as claimed in claim 1, in which the saline water is stagnant.

3. A method as claimed in claim 1 or claim 2, in which the waste material is below ground and surrounded by the saline water.

4. A method comprising disposing waste material above the adjacent water table and establishing a zone of substantially stagnant saline water beneath the material for receipt of percolating ground water.

5. A method as claimed in claim 4, in which the waste material is below ground.

6. A method comprising disposing waste-material below ground and establishing a permanent connection for saline water to infiltrate to a region landward of the material.

7. A method as claimed in claim 1, including forming a drain above mean tide level with a flow connection from the drain to an outlet beneath the sea or sea bed.

8. A waste material disposal arrangement with a flow connection to below sea level leading to an inland zone so that saline water is permanently below the material.

9. An arrangement as claimed in claim 8, in which the saline water surrounds the waste material.

10. An arrangement as claimed in claim 8 or claim 9, in which the saline water is essentially stagnant.

11. A method or arrangement as claimed in any preceding claim, in which the waste material comprises low level radioactive waste.

12. A method or arrangement as claimed in any preceding claim, in which the waste material comprises intermediate level radioactive waste.

13. A method substantially as hereinbefore described with reference to the accompanying drawings.