GB2294356A - Waste disposal - Google Patents

Abstract

Boreholes 10 contain disposed waste. Liquid, e.g. saline water or nitric acid, is supplied from pump 17 or tank 21 to boreholes 12, 13, between and around the boreholes 10 to create a downwash A to prevent leaked toxic material passing to the biosphere. The liquid may be supplied in response to undesired toxic level detected by detectors 14. Boreholes 10 may have lining 9 above a certain depth. The waste may be radioactive and may be solid or liquid.

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 below ground level, and causing liquid to flow downwards under gravity in the vicinity of the waste to prevent contamination of the biosphere.

According to another aspect of the invention a method comprises disposing waste below ground level, and causing liquid denser than ground water around the waste to flow downwards in the vicinity of the waste to move leaked waste downwards.

The method may comprise monitoring for undesired toxic level adjacent the disposed waste, and causing said liquid flow in response to detected undesired toxic level.

The liquid may be cooled.

The liquid may, for example, be saline water or nitric acid.

The waste material may be disposed in boreholes.

The liquid may be delivered to the vicinity at locations laterally outward of the area containing the boreholes and at locations within the area and above the waste.

Also according to the invention a waste material disposal arrangement comprises a zone for containing disposed waste, and means for providing a downward flow of liquid in the vicinity of the disposed waste to resist migration of toxic material and to prevent undesired toxic effects passing to the biosphere.

The arrangement may comprise means for monitoring for undesired toxic level adjacent disposed waste. the providing means being operable in response to detected undesired toxic level.

The waste material may be disposed in boreholes.

The liquid may be delivered to boreholes.

The invention may be performed in various ways and one specific embodiment with possible modifications will now be described by way of example with reference to the accompanying diagrammatic drawings, in which: Fig. 1 is a side view of a waste disposal site; and Fig. 2 is a plan view of Fig. 1.

Generally speaking, the present arrangement is concerned with creating a downward liquid flow past disposed waste to prevent any escaping hazardous or toxic components of the waste from entering water flowing back to the biosphere, thus creating a hazard to man. The operations involved may or may not be part of establishing a stagnant zone.

The downward wash is denser than surrounding groundwater, so moving or falling down to displace the natural groundwater, eventually encompassing the waste and flowing downwards round and past it.

The waste may be radioactive waste in solid form such as low-level (LLW), Intermediate Level (ILW), High Level (HLW, such as vitrified High Active Liquors), Spent Nuclear Fuel or discarded atomic weapon programme material. There may be packaging round the waste such as metallic containers or concrete.

Alternatively, or additionally, the waste may be liquid such as High Active Liquor (HAL) from reprocessing nuclear fuels.

The liquid may be in containers or transferred by pumping or gravity flow to the bottom of boreholes, which may be lined or unlined.

The downward wash is compatible with the natural rock, not significantly reacting with it and so flowing by gravity through the interstices of the rock, displacing the natural (less dense) water.

Examples of possible combinations are: NATURAL WATER DOWNWARD WASH Fresh Water Seawater Brine (by concentration of seawater) Nitric Acid Saline Water (from, for Brine (by concentration of example, seawater intrusion seawater) caused naturally or by a method as described in British Patent Specification 2244171).

The nitric acid would be especially applicable to disposal of HAL i.e. to keep any escaping waste in solution and washed downwards.

Heat-emitting wastes (HLW, Spent Fuel, discarded weapon material or HAL) could potentially cause buoyancy in adjacent natural waters, possibly creating a flow upwards to the biosphere. The downwards wash prevents this. It can be operated, also, as a secondary control or barrier to flow to the biosphere during a period when the waste is particularly hazardous. For example, if the arrangement for providing downwash flow were maintained for a century or so the heat output and residual content of (say) Sr90 and/or Cs137 would fall dramatically, so that hazards become similar to those from lower level wastes.

The density of the downwards wash can be estimated such that if its temperature is raised by heat-emitting wastes adjacent to it, it will still be greater than the local natural water and continue to sink.

The arrangement could be a very useful secondary method of control; guard boreholes above waste could be monitored, by placing detectors in the guard boreholes for (radio) activity release, then used for injection of liquid if significant activity were shown to be migrating.

In the case of HAL, the density of the downwash could be chosen to be less than that of the HAL, although still denser than local ground water, so that any bulk release of liquor from any HAL borehole would not be buoyant in downflowing wash water. The downwash may also be used down an HAL borehole (as well as outside) to impel the HAL into rock and then downward.

Examples of densities are: Density of Fresh Water is 1.000 at 10"C Density of Brine (7% salt) is 1.007 at 70"C Density of Brine (14% salt) is 1.055 at 70"C Density of Nitric Acid (3N) is 1.060 at 70"C Referring now in more detail to Figs. 1 and 2, waste storage boreholes 10 are drilled to the desired depth and location: they can be as close as desired to the accuracy of drilling and to avoid significant heat interaction between them after loading. The holes 10 may be lined or unlined, as above.

Before loading, sections of holes will be 'packered off' to determine the ease of groundwater flow between holes 10. In the disposal of liquid waste, a 'seep' section 11 will allow outflow of liquor: above this section, the hole 10 will be lined (see 9), for example with stainless steel, to prevent outflow at an undesirable depth. In packering off, inflatable blocking material is located above and below a selected region of a borehole e.g. lOft (300cm) apart.

Liquid flow sensors are located in packered sections of two boreholes to monitor liquid flows between the packered regions of the two boreholes to determine the ease or manner of groundwater flow. A pipe extending through the upper packer could be used to abstract samples in the region for external analysis. The flow sensors and packing devices are removed before loading with waste.

Further boreholes 12, 13 provide respectively sidewash and topwash sections which can be packered at required depths to adjust the height of the downwash A. If a borehole is packered at a certain depth, downwash liquid cannot pass along the borehole to a depth below the packering. The latter will then sweep any activity down, for as long as desired. The boreholes 12 are preferably at least as deep as the boreholes 10. The boreholes 13 extend to a depth less than the depth of the top of the waste in boreholes 10.

One or more boreholes 12 could extend to a depth less than the depth of the top of the waste. Liquid waste may be disposed in batches, each of which is followed with wash down the waste hole with monitoring of the 'wash' holes to verify acceptable operation. For example, a sensor is lowered into the hole to verify a satisfactorily low, preferably zero, level of activity remains.

Further wash down can be done if necessary. After all batches are disposed the downwashing can be continued until an insignificant level of activity remains.

Normally downwash in boreholes 12 would be accompanied by downwash in boreholes 13 to avoid displacement of groundwater upwards between boreholes 10.

Examples of monitor devices are shown at 14 and may for example be radiation detectors. They are connected to a monitor control unit 15 above ground level 16 and this is connected to a pump 17 arranged to deliver downwash liquid e.g. as tabled above to the boreholes 12, 13 when an undesired toxic level is detected by any one or more of the detectors 14. Instead of pump 17 delivering direct to the boreholes the pump or other source may deliver to a header tank 21 arranged to provide a gravity feed of downwash liquid. Typically the detectors 14 would be located in boreholes 14a, one or more per borehole.

Boreholes 12, 13 may contain one or more detectors.

Boreholes 13 can act as guard boreholes.

The natural water downwash interface is shown at 18.

Entrained gas arising from radiolysis may, for example, seep out as at 19. Bubbles rising may cause some mixing with downward wash but the flow of the latter will be adjusted to sweep the mixed zone down.

The downwash liquid delivered by the pump 17 may be cooled e.g. by cooling device 20, to counteract the effects of heat emitting waste.

If boreholes 12, 13 (normally full of downwash liquid) are used as monitors of toxic level, a detector can be located in the respective borehole 12 or 13. Sensors 14 may for example be positioned about 10 metres laterally of boreholes 10 as seen in plan.

The downwash flow is indicated schematically by arrows A.

The waste boreholes may contain a sealant above the disposed waste, for example clay, other sealants can be used in the case of disposed solid waste.

The plan area covered by the downwash is sufficient to encompass any leak.

In a modified arrangement downwash liquid is supplied in the absence of a detected undesired toxic level. For example, after initial loading of the waste into the boreholes, downwash liquid may be supplied at timed intervals as a precaution.

Claims (15)

1. A method comprising disposing waste material below ground level, and causing liquid to flow downwards under gravity in the vicinity of the waste to prevent contamination of the biosphere.

2. A method comprising disposing waste below ground level, and causing liquid denser than ground water around the waste to flow downwards in the vicinity of the waste to move leaked waste downwards.

3. A method as claimed in Claim 1 or Claim 2, comprising monitoring for undesired toxic level adjacent the disposed waste, and causing said liquid flow in response to detected undesired toxic level.

4. A method as claimed in any preceding claim, in which the liquid is cooled.

5. A method as claimed in any preceding claim, in which the liquid is saline water.

6. A method as claimed in any of Claims 1 to 4, in which the liquid is nitric acid.

7. A method as claimed in any preceding claim, in which the waste material is in boreholes.

8. A method as claimed in Claim 7, in which the liquid is delivered to the vicinity at locations laterally outward of the area containing the boreholes and at locations within the area and above the waste.

9. A waste material disposal arrangement comprising a zone for containing disposed waste, and means for providing a downward flow of liquid in the vicinity of the disposed waste to resist migration of toxic material and to prevent undesired toxic effects passing to the biosphere.

10. An arrangement as claimed in Claim 9, comprising means for monitoring for undesired toxic level adjacent disposed waste, the providing means being operable in response to detected undesired toxic level.

11. An arrangement as claimed in Claim 9 or Claim 10, in which the waste is disposed in boreholes.

12. An arrangement as claimed in any of Claims 9 to 11, in which the liquid is delivered to boreholes.

13. A method of disposing waste material substantially as hereinbefore described.

14. A waste material disposal arrangement obtained by a method as claimed in any Oe Claims 1 to 8.

15. A waste material disposal arrangement substantially as hereinbefore described with reference to the accompanying drawings.