GB2167599A

GB2167599A - Repositories for waste disposal and methods of disposing waste

Info

Publication number: GB2167599A
Application number: GB08528515A
Authority: GB
Inventors: William Robert Burton
Original assignee: NUCLEAR TECHNOLOGY
Current assignee: NUCLEAR TECHNOLOGY
Priority date: 1984-11-20
Filing date: 1985-11-20
Publication date: 1986-05-29
Also published as: GB8429241D0; GB2167599B; GB8528515D0

Abstract

Waste is placed in a below-ground repository and is provided with means restraining convective flow of water from the repository to the biosphere. Thus a filled access shaft 13A has an undulation to trap convected water 12A or has an upwardly concave U-bend for the same purpose. The rock surrounding the waste may be grouted with a solution containing solutes at least some of which remain in solution after the grout is set to make the water density greater than that in material above the grouted rock. The material in the shaft may also be thus grouted. The repository may be located where surrounding ground water is at a greater density, even after being heated by the waste, than in a region further above the repository. <IMAGE>

Description

SPECIFICATION Repositories for waste material and methods of disposing waste This invention relates to repositories for waste material for example radioactive waste and methods of disposing waste.

According to one aspect of the invention there is provided a below-ground disposal repository for waste material having means restraining convective flow of water from the repository from reaching the biosphere.

The invention also provides a below-ground disposal repository for waste material having means restraining convective flow of water from the repository.

A shaft may lead from the ground to the repository, the shaft including a U-bend which is concave upwards.

The shaft may have an inverted bend.

Conveniently material around the repository is treated to have a water density greater than that in the material above the treated material. The treatment may be an aqueous phase containing solutes.

The material may be treated with grout having an additive which contains solutes which remain in solution after setting of the grout. Material in the shaft may include such grout or aqueous phase.

The repository waste may be disposed in a chamber surrounded by material having naturally occuring ground water of a density which, even after receiving heat from the waste, is always greater than water in a region above said material.

The invention further provides a method of disposing waste in a below-ground repository comprising restraining convective flow of water from the repository from reaching the biosphere.

The invention also provides a method of disposing waste in a below-ground repository comprising restraining convective flow of water from the repository.

The invention may be performed in various ways and some specific embodiments will now be described further by way of example with reference to the accompanying drawings in which: Figure 1 shows diagrammatically in section a repository for radioactive waste; Figure 2 shows one means for restraining convective flow of water from the repository of Figure 1; and Figure 3 shows another means.

In disposing of waste in the ground there is a commitment to attempt to observe that the disposed material, or anything arising from it, cannot find its way back into the biosphere. British patent specifications Nos. 2 128 800 and 2 128 801 are examples.

The present invention has arisen from considering the possibility of heat generated from the disposed material causing a density reduction in the interstitial water in the ground surrounding the waste such that a flow is created counter-acting against recognised steps taken to contain the dis posed material so that disposal arrangements which are otherwise safe could have a route to the biosphere.

In Figure 1 there is shown a below-ground radio active waste disposal repository chamber 10 sur rounded by rock 11 with water 12 in the interstices of the rock (the rock and the interstices are exag gerated for illustrative purposes). The rock 11 is se lected to have low permeability to water flow and free from cracks. An access shaft 13 exists to the surface 14 of the ground. This shaft is sealed with backfill material when the repository is closed. Material in the repository is nominally excluded from reaching the biosphere as, typically, the access shaft is sealed with local rock or cement. Over the very long period for which the radioactivity should be excluded from the biosphere, however, it is difficult to ensure that one or more cracks do not form in the access shaft seal.

The disposed waste will give rise to heat and this heat will be taken into the rock 11 and water 12. This water will fall in density relative to water further away from repository. Thus a convection system will be set up which could induce migration of radioactivity from the waste, such as along any cracks that may have developed in the sealing of the shaft 13, so that radioactivity could reach the biosphere from which it had hopefully been excluded. The repository can be regarded as the chamber and the surrounding material which is subject to significant Thermal effects. Material outside the repository is subject to substantially no significant Thermal effects.

In Figure 2, in accordance with the invention, the access shaft 13A is made of undulating form so as to have bends which are concave upwards and concave downwards so that water 12A rendered buoyant by heating is trapped at an inverted bend 15A in the shaft 13A. That part of the shaft which is beyond the bend 15A is sufficiently removed from the repository to receive no significant thermal effects. The convected water in the shaft is prevented from reaching the biosphere.

In Figure 3, and also in accordance with the invention, the access shaft 13B is made of concaveupwards U-bend form with a U-bend 15B located below the repository so that water 14B rendered buoyant by heating is trapped above the U-bend.

That part of the shaft 13B which is beyond the bend 15B is again sufficiently removed from the repository to receive no significant thermal effects.

The convected water in the shaft does not reach the biosphere.

In an alternative inventive arrangement, the material or rocks surrounding the repository chamber 10 of Figure 1 are force-filled with an aqueous phase containing solutes, at least some of which solutes remain in solution so that, even with a temperature rise, the density of the aqueous phase exceeds that of the ground water around said surrounding material or rocks. A similar type of procedure in the material in shaft 13 would inhibit convection in that direction. The aqueous phase may form part of grout at least some of the solutes remaining in solution after setting of the grout.

This aqueous phase procedure could additionally be used in the arrangements of Figure 2 and 3.

In another arrangement the repository chamber is sited in a first below-ground zone, selected to have the naturally occurring ground water surrounding the zone of a greater density than naturally occurring ground water at a second zone at iesser depth above the first zone so that even with a temperature rise the ground water in the first zone will not migrate to the second zone.

The grouting and aqueous phase procedures mentioned above could also be used in these arrangements and also the U-bend or undulating shaft.

The repository site would be selected with the intention that the temperature rise would not lead to boiling.

In a further arrangement the repository chamber or repository is sited such that water permeability of material above the repository is less than that of material to the side so that convected water is deflected laterally. There may be several strata e.g. as at 20 above the repository where horizontal permeability is greater than upward permeability, leading to lateral deflection or successive lateral deflections of convected water to restrain or prevent convected water from reaching the biosphere. This arrangement can apply also to any of the arrangements described above.

Claims

1. A below-ground disposal repository for waste material having means restraining convective flow of water from the repository from reaching the biosphere.

2. A below-ground disposal repository for waste material having means restraining convective flow of water from the repository.

3. A repository as claimed in Claim 1 or Claim 2, in which a shaft leads from the ground to the repository, the shaft including a U-bend which is concave upwards.

4. A repository as claimed in Claim 3, in which the shaft has an inverted bend.

5. A repository as claimed in any preceding claim, in which material around a repository chamber is treated to have a water density greater than that in the material above the treated material, for example treated with an aqueous phase containing so lutes.

6. A repository as claimed in Claim 5, in which the material is treated with grout having an additive which contains so lutes which remain in solution after setting of the grout.

7. A repository as claimed in any of Claims 3 to 6, in which material in the shaft includes such grout or aqueous phase.

8. A repository as claimed in any preceding claim, comprising a chamber surrounded by material having naturally occurring ground water of a greater density, even after being heated by the waste, than water in a region above said material.

9. A below-ground disposal repository for waste substantially as hereinbefore described with reference to and as shown in Figure 1, or Figure 2, or Figure 3, of the accompanying drawings.

10. A method of disposing waste in a belowground repository comprising restraining convective flow of water from the repository from reaching the biosphere.

11. A method of disposing waste in a belowground repository comprising restraining convective flow of water from the repository.

12. A repository as claimed in any of claims 3 to 9, in which the shaft leads to a repository chamber.

13. A below-ground repository for waste material having means for preventing convective flow of water from the repository from reaching the biosphere.

14. A method of disposing waste in a belowground repository comprising preventing convective flow of water from the repository from reaching the biosphere.

15. A method of disposing waste, and a belowground waste repository, however defined.