GB2199180A

GB2199180A - Disposal of waste material

Info

Publication number: GB2199180A
Application number: GB08730008A
Authority: GB
Inventors: William Robert Burton
Original assignee: NUCLEAR TECHNOLOGY
Current assignee: NUCLEAR TECHNOLOGY
Priority date: 1986-12-23
Filing date: 1987-12-23
Publication date: 1988-06-29
Anticipated expiration: 2007-12-23
Also published as: GB8730008D0; GB2199180B

Abstract

A shallow land-burial repository for radioactive and other waste comprises a concrete container 10 having a domed roof 12 and a peripheral wall 13 and optionally a floor 23. A domed upper concrete roof 16 acts as an intrusion barrier and is covered by a water-impervious layer of clay 20 and earth 21. The outer surfaces of roof 12 and wall 13 are exposed or readily exposable to permit inspection and the space around the container may be such as to permit remedial work. Inspection and remedial work may be by workmen or remotely controlled equipment. The upper roof 16 may be part of the containment vessel of an existing reactor being decommissioned, and the container may be in the form of stacked individual containers which may be removable and whose surfaces can be inspected. <IMAGE>

Description

DISPOSAL OF WASTE MAERIAL This invention relates to the disposal of waste material, particularly but not exclusively radioactive waste material.

The invention is principally for waste whose toxic or hazardous properties have effectively disappeared after 300 to 500 years.

According to the invention a land burial repository of waste material comprises a containment structure for the material, the structure having a roof, and an upper roof above the structure roof, the outer surface of the structure roof being exposed or readily exposable, to permit inspection.

The exposure may be such as to permit inspection of the underface of the upper roof.

The structure may have a peripheral wall.

Preferably the outer surface of the peripheral wall is exposed, or readily exposable, to permit inspection.

The structure may have a floor the underface of which is exposed, or readily exposable, to permit inspection of the underface of the floor.

The inspection may be visual or by remotely controlled equipment.

When exposed the unoccupied space outside the structure roof and, where appropriate, the peripheral wall and/or floor may be such as to permit remedial work to be effected on the structure roof and, where appropriate, the peripheral wall and/or floor.

The work may be done by workmen and/or remotely controlled equipment.

The upper roof may be surmounted by a waterimpervious layer.

The bottom of the waste would be at a level above the level of the immediately adjacent water table0 For example if the waste does not extend to a level below the lower edge of the peripheral wall, the repository may be such that the lower edge of the peripheral wall is at a depth higher than the undisturbed local water table.

The upper roof may be supported on pillars.

At least some of the pillars may act as conduits for water drained off the upper roof.

The pillars may provide access from the upper roof to the exterior of the container.

The structure may comprise stacked individual containers of waste, upper and lower surfaces of the containers being exposed for inspection.

The structure may comprise stacked individual containers of waste and said upper roof be removable to permit removal of the containers.

The repository may form part of a dam or of sea defences or of a causeway or the extension of a cliff.

The structure roof and the upper roof together form an effective intrusion barrier.

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 drawings, in which: Fig. 1 is a schematic perspective view with part omitted of a repository for waste material; Fig. 2 is a plan view of a repository; Fig. 3 is a side view of a modified repository; Big. 4 is a plan view of an access passage; and Figs. 5 to 7 are schematic views of other arrangements.

Waste material, and particularly radioactive waste, may need to be stored for a long time, perhaps hundreds of years. If the waste is in a relatively shallow burial zone, an intrusion barrier may be provided and water is inhibited from flowing through the buried waste.

The present arrangement enables the barrier to be inspected to give reassurance of adequate integrity, and enables remedial work to be done if needed or advisable.

Referring to Figs. 1 and 2, a repository is shown beneath the ground surface 11. The containment structure or unit in the form of a container 10 hasa thick concrete roof 12, for example over 0.5 metre thick, and a peripheral thick concrete wall 13 which as shown has four sides 14 but could take other forms. The roof 12 has an upwardly convex top surface 12a. The waste is shown at 15.

An upper roof 16, of concrete for example 0.5 metre thick, extends over and above and is spaced from the roof 12 and is supported on pillars 17. The number and disposition of the pillars can be selected as appropriate or desired. In some cases the pillars may be short and rest on the structure roof 12.

There is a void 9 outside the peripheral wall 13 and structure roof 12 and preferably there are a number of containers 10 spaced apart forming a single landburial site or repository.

There may be a natural rock wall or earth bank 19 adjacent the containers.

The upper roof 16 is surmounted by an impervious layer 20 e.g. of clay and there may be rubble or earth on top of the impervious layer.

Periodic depressions 21 in the contour of layer 20 enable land drains 22 to lead away percolating groundwater.

The pillars 17 rest on rock 18. The container 10 may have a thick concrete floor 23 resting on the rock 18 or the floor 23 may be omitted, the walls 13 resting on the rock. If a floor 23 is present then preferably as shown in Fig. 3 the floor 23 is supported on pillars 24 so that there is a void 25 on the underside of the floor 23.

Because of voids 9 and 25, the outer surfaces of the roof 12, the wall 13 and where appropriate floor 23 are exposed for inspection and preferably for access for workmen or appropriate remotely controlled equipment or tools to effect any repair deemed necessary or desirable. The inspection may be visual, which could be by a workman or a remotely controlled instrument, depending on the depth of the void away from the respective surface.

Vent ports 40 in the wall of the container are positioned to allow throughflow of air and prevent stagnant regions and the accumulation of hazardous gases e.g.

explosive mixtures. For example the ports 40 could be at the apex of the lower roof 12 and near the drain points at the bottom of the peripheral wall, with any necessary cover to prevent for example drips from the upper roof passing into the container 10.

Suitable means are preferably provided to give access from the ground for personnel and equipment as appropriate.

For example a ladder 26 with guard rail 27 may be attached to each or some pillars 17 and tools and equipment and material can be lowered or taken into the void by suitable means.

Either initially or after an agreed period some or all of the voids 9, 25 may be filled in, for example when inspection and possible remedial work are deemed no longer necessary. Preferably the filling material is such that it could subsequently be readily removed e.g. sand, so that the outer surfaces of roof 12, wall 13, floor 23 and the underface of roof 16 are readily exposable.

Each pillar or column 17 may have an internal passage 28 extending from the upper surface of the upper roof 16 to the rock 18 and enables water which may have breached the layer 20 and drained off the top side of the upper roof 16 and drained through rubble 29 down passage 28 to a catch pot 30 at the foot of the respective pillar0 The rubble 29 can be graded to have larger particles lower, to give good drainage and yet prevent the impermeable layer 20 from blocking the drains 28.

The roof 12 is preferably strong enough to support men and equipment as appropriate for carrying out any necessary or desirable remedial work on the underside of the upper roof 16.

The concrete walls and roof 13, 12 are preferably such as to provide adequate protection for the workmen against radiation even if only for short periods. The roof 12 is preferably domed so as to give improved strength and drainage.

The floor 23 is preferably domed also.

The peripheral wall 13 may be inclined slightly inwards as it extends downwards to inhibit water flowing towards the wall from the region 9. The floor 23 if provided has drains 31 at the edges to release any liquid or water in-leakage or liquid formed during ageing of the waste.

In the case of Fig. 3, there may be access ramps and walkways and the like constructed to assist inspection and remedial work.

The containers 10 can be arranged in many ways e.g.

linearly, parallel to a contour e.g. a coast, or in blocks to provide a base for landfill. The containers 10 could form the core of an embankment or dam or part of sea defences or of the extension of a cliff. They could be built above ground, or fit into depressions or excavations.

Any surrounding water table could be drawn down to a level below the bottom of wall 13 i.e. below the level of the bottom of the waste by providing rubble infill with concrete retaining wall around the side of, and to a level below, the wall 13. The bottom of this rubble could be arranged to connect with natural drainage below it, e.g. on or under the foreshore.

The water table immediately adjacent (i.e. abutting) the peripheral wall is at or below the level of the bottom of the wall although the undisturbed local water table could be, but preferably is not, above that level. The immediately adjacent water level is below the level of the bottom of the waste.

Any drainage of liquid from the repository is preferably to sea, preferably through prepared passages with opportunity for collection and sampling.

With these arrangements the waste is stored in a manner enabling the containment structure to be inspected.

In the case of an existing pit or excavation containing waste, piles could be driven through the waste on to bedrock and a roof 12 constructed on the piles with a spaced upper roof constructed on supports on the roof 12, the box being then covered with the impervious layer and possibly a top layer of rubble and soil with adequate access being left from ground level.

In a modification a concrete roof 12 is placed over the waste and a spaced upper roof 16 is supported from the roof 12. The space between the roofs may be void or filled with readily removable material. The void when present permits access for workmen or equipment to inspect the top surface of the roof and the under-surface of the upper roof and preferably for remedial work to be done. Drainage should be arranged in the rock round the existing repository, by boreholes or otherwise, connected to natural drainage passages thus to ensure that the surrounding water-table is below the level of the bottom of the waste: appropriate drainage along the floor of the waste, e.g. by driving pipes at floor level through the waste, should be arranged to prevent accumulation of water at low points of the floor.

Shallow land-burial would normally be in a trench or by cut and cover excavation but the waste could be above the surrounding ground level but surmounted by an impervious layer as described above. Thus the unit 10 could be located in a hillock or earth bank and be provided with the upper roof and impervious layer as above.

In a modification the container for waste material is placed inside the containment vessel of a reactor which has reached residual stage three of a decommission process.

At such a stage the containment vessel is largely empty and the container 10 can be constructed inside the containment vessel with the roof and peripheral wall of the container 10 being spaced inwards of the inner surface of the containment vessel. The floor of the container 10 could be spaced from the floor of the containment vessel by pillars. The containment vessel provides the upper roof. Access is provided to the space between the container 10 and the containment vessel so that the exterior of the roof and peripheral wall of the container 10 can be inspected and remedial action taken if necessary. The containment vessel thus acts as an intrusion barrier. Preferably the containment vessel is covered with a water-impervious layer e.g.

a suitable clay, and the latter can be further covered with soil and/or rocks, providing landscaping as necessary. The space between the container 10 and the containment vessel could be filled with readily removable material as above.

In some embodiments the waste is packed or stored in separate concrete boxes or containers which may in some cases be removable.

Fig. 5 shows an embodiment in which highly compacted waste is put into concrete containers 40 which are stacked in a concrete container 41. The containers may rest on ledges on wall 13 and may be inserted from the side with subsequent closure of the side by a removable part of wall 13. The roof 12 may be slabs of concrete.

Preferably the upper roof of each container 40' act as a structure roof in which case the roof 12 acts as the upper roof and roof 16 can be omitted.

In Fig. 6 the containers 40' may be stored in a structure like a multi-storey car park having floors 45 and an internal concrete roof 46 is installed to act as the upper roof and which could be of removable slabs, the whole being provided with an over-lying water impervious layer. As an alternative a further concrete roof 47 could be provided and roof 46 omitted.

In some embodiments the separate roof 12 is omitted and the containers 40 are stacked on each other on base plinths 42 and the top and sides of each container in the stacks can be inspected. Each container 40' forms a containment 10. An example is shown in Fig 7. The containers have upstanding (or downstanding) portions 43 providing a space 44 between adjacent containers so that the top and bottom surfaces of the containers can be inspected and if desired repaired as above. In a preferred arrangement the roof 16 rests on the stack or stacks of individual containers, as shown in Fig. 7 and is preferably removable as are the containers.

The container 10 Fig. 1 could be replaced by a stack of individual boxes as in Fig. 7 each provided with lifting lugs.

During a supervisory period i.e. as a store, voids could be left unfilled between roofs and between containers; remedial action could be easily taken.

When finally sealing up, a granular solid (sand plus sorber) could fill the voids; it could be removed by suction later if necessary.

In the various embodiments the stacked boxes could be inserted either by top or side loading with appropriate demountable roof or wall.

In some cases separate wall 13 is omitted and the peripheral wall of the containment is formed by natural rock.

In some cases the immediately adjacent water table may be lowered to a level below the level of the bottom of the waste or the lowest box by pumps which are operated temporarily as required.

The repository will usually be a shallow land burial, which can be constructed by cut and cover as contrasted with tunnelling.

In general, where appropriate or possible, the upper roof could be constructed to be removable and replaceable.

Claims

1. A land-burial repository of waste material comprising a containment structure for the material, the structure having a roof, and an upper roof above the structure roof, the outer surface of the structure roof being exposed or readily exposable to permit inspection.

2. A repository as claimed in claim 1, in which when exposed the space outside the outer surface permits remedial work to be done on the outer surface.

3. A repository as claimed in claim 1 or claim 2, in which the exposure is such as to permit inspection of the underface of the upper roof.

4. A repository as claimed in claim 3, in which when exposed the space beneath the underface of the upper roof permits remedial work to be done on the underface.

5. A repository as claimed in any preceding claim, in which the structure has a peripheral wall.

6. A repository as claimed in claim 5, in which the outer surface of the peripheral wall is exposed or readily exposable to permit inspection.

7. A repository as claimed in claim 6, in which when exposed the space outside the peripheral wall permits remedial work to be done on the outer surface of the peripheral wall.

8. A repository as claimed in any preceding claim, in which the structure has a floor the underface of which is exposed or readily exposable to permit inspection.

9. A repository as claimed in claim 8, in which when exposed the space outside the floor permits remedial work to be done on the underface-of the floor.

10. A repository as claimed in any preceding claim, in which the upper roof is surmounted by a water-impervious layer.

11. A repository as claimed in any preceding claim, in which the upper roof is supported on pillars.

12. A repository as claimed in claim 11, in which at least some of the pillars act as conduits for water drained off the upper roof.

13. A repository as claimed in claim 11, in which the pillars rest on the structure roof.

14. A repository as claimed in any of claims 1 to 10, in which the upper roof is provided by a reactor containment vessel.

15. A repository as claimed in any preceding claim, in wnich the structure comprises stacked individual containers of waste, upper andZsr lower and/or side surfaces of the containers being exposed or readily exposable for inspection.

16. A repository as claimed in claim 15, in which when exposed the space outside the upper and/or lower and/or side surface of a container permits remedial work to be done on that surface.

17. A repository as claimed in any of claims 1 to 10, in which the structure comprises stacked individual containers of waste the outer surface of the top of each container being exposed or exposable to permit inspection.

18. A repository as claimed in claim 17, said upper roof is removable to permit removal of the containers.

19. A repository as claimed in claim 17 or claim 18, in which the upper roof rests on the stack.

20. A repository as claimed in any preceding claim, forming part of a dam.

21. A repository as claimed in any of claims 1 to 19, forming part of sea defences.

22. A repository as claimed in any of claims 1 to 19, forming part of a causeway.

23. A repository as claimed in any of claims 1 to 19, forming part of an extension of a cliff.

24. h land-burial repository of waste material substantially as hereinbefore described with reference to and as shown in Fig. 1, or Fig. 2, or Fig. 3, or Fig. 4, or Fig. 5, or Fig. 6, or Fig. 7, of the accompanying drawings.