Most LLW is typically sent to land-based disposal immediately following its packaging for long-term management (See the table below for details). This means that for the majority (~90% by volume) of all of the waste types, a satisfactory disposal means has been developed and is being implemented around the world.
Concentrating on ILW and HLW, many long-term waste management options have been investigated world-wide which seek to provide publicly acceptable, safe and environmentally sound solutions to the management of radioactive waste. Some countries are at the preliminary stages of their investigations whilst others such as Finland, Sweden and the USA have made good progress in their investigations to select publicly acceptable sites for the future disposal of waste. The USA also has an operational disposal facility for L/ILW in Carlsbad, New Mexico, underground in a salt formation called the Waste Isolation Pilot Plant (WIPP).
The table below sets out the commonly accepted management options. For each option, examples are given of actual investigations, pending decisions and/or implementations within the various countries that have radioactive wastes. Additional ideas that have also been considered and discounted in the past can be viewed here.
The options and ideas discussed should not be considered as providing an exhaustive list of all those investigated world-wide, but do include:
- options and ideas that have been investigated by national waste management companies and;
- options and ideas that have been the subject of research and development by research institutes, such as universities.
When considering these, it should be noted that the suitability of an option or idea can be dependent on the wasteform, volume and radioactivity of the waste. As such, waste management options and ideas described in this section are not all applicable to different types of waste.
Commonly Accepted Management Options
|
| Option |
Examples |
| Near-surface disposal at ground level, or in caverns below ground level (at depths of 10m's) |
- implemented for LLW in many countries, including Czech Republic, Finland, France, Japan, Netherlands, Spain, Sweden, UK and USA
- implemented in Finland and Sweden for LLW and short-lived ILW
|
| |
Deep geological disposal
(at depths between 250m and 1000m) (suitable for long-lived wastes) |
- most countries with high-level and long-lived radioactive waste have investigated deep geological disposal and it is official policy in various countries (variations also include multinational facilities)
- implemented in USA for ILW
- preferred sites for HLW/Spent fuel selected in Finland and USA
- site selection taking place in Sweden for HLW/spent fuel
- decision to be taken in France in 2006
- Canadian and UK disposal policies under review
|
Near Surface
Description
The IAEA definition of this option is the disposal of waste, with or without engineered barriers in:
- Near-surface disposal facilities at ground level. These facilities are on or below the surface where the protective covering is of the order of a few metres thick. Waste containers are placed in constructed vaults and when full the vaults are backfilled. Eventually they will be covered and capped with an impermeable membrane and topsoil. These facilities may incorporate some form of drainage and possibly a gas venting system.
- Near-surface disposal facilities in caverns below ground level. Unlike near-surface disposal at ground level where the excavations are conducted from the surface, shallow disposal requires underground excavation of caverns but the facility is at a depth of several tens of metres below the Earth's surface and accessed through a drift.
The term near-surface disposal replaces the terms 'shallow land and ground disposal', but these older terms are still sometimes used when referring to this option.
These facilities will be affected by long-term climate changes (e.g. glaciation) and this effect must be taken into account when considering safety as such changes could cause disruption of these facilities. This type of facility is therefore typically used for LLW and ILW with a radionuclide content of short half-life (up to about 30 years).
Near-surface disposal at ground level
Near-surface disposal in caverns below ground level
Examples
Near-surface disposal facilities at ground level currently in operation:
- UK - Drigg in Cumbria operated by BNFL (for LLW only).
- Spain - El Cabril operated by ENRESA.
- France - Centre de l'Aube operated by Andra.
- Japan - Rokkasho Mura operated by JNFL.
Near-surface disposal facilities in caverns below ground level currently in operation:
- Sweden - Forsmark, where the depth of the facility is 50m under the Baltic seabed.
- Finland - Olkiluoto and Loviisa power stations where the depth of the facilities are each at about 100 metres.
Further reading: BNFL, ENRESA, ANDRA, JNFL, Forsmark (Sweden), TVO - Olkiluoto (Finland) (external sites)
Deep Geological Disposal
Description
The long timescales over which some of the waste remains radioactive led to the idea of deep geological disposal in underground repositories in stable geological formations. Isolation is provided by a combination of engineered and natural barriers (rock, salt, clay) and no obligation to actively maintain the facility is passed on to future generations. This is often termed a multi-barrier concept , with the waste packaging, the engineered repository and the geology all providing barriers to prevent the radionuclides from reaching humans and the environment.
A repository is comprised of mined tunnels or caverns into which packaged waste would be placed. In some cases (e.g. wet rock) the waste containers are then surrounded by a material such as cement or clay (usually bentonite) to provide another barrier (called buffer and/or backfill). The choice of waste container materials and design and buffer/backfill material varies depending on the type of waste to be contained and the nature of the host rock-type available.
Excavation of a deep underground repository using standard mining or civil engineering technology is limited to accessible locations (e.g. under land or nearshore), to rock units that are reasonably stable and without major groundwater flow, and to depths of between 250m and 1000m. At a depth greater than 1000m, excavations become increasingly technically difficult and correspondingly expensive.
Examples
Deep geological disposal remains the preferred option for waste management of long-lived radioactive waste in several countries, including Argentina, Australia, Belgium, Czech Republic, Finland, Japan, Netherlands, Republic of Korea, Russia, Spain, Sweden, Switzerland and USA. Hence, there is much information available on different disposal concepts; a few examples are given here. The only purpose-built deep geological repository for long-lived ILW that is currently licensed for disposal operations is in the USA. Plans for disposal of spent fuel are well advanced in Finland, Sweden and the USA, with the first facility scheduled for operation by 2010. In Canada and the UK, the policy of deep disposal is currently undergoing review.
Sweden: the disposal concept for spent fuel and other long-lived radioactive waste in strong fractured rocks.
The Swedish proposed disposal concept uses a copper container with a steel insert to contain the spent fuel. After placement in the repository, the container would be surrounded by a bentonite clay buffer to provide a very high level of containment of the radioactivity in the wastes over a very long time period. Similar concepts have been developed in other countries for use with spent fuel, such as Finland.
The deposits of pure copper in the world have proven that the copper also used in the final disposal container can remain unchanged inside the bedrock for extremely long periods of time, if the geochemical conditions are appropriate (reducing groundwaters). The findings of ancient copper tools, many thousands of years old, also demonstrate the long-term corrosion resistance of copper, making it a credible container material for long-term radioactive waste storage.
Further reading: Swedish Management Agency - SKB, Finnish Management Agency - Posiva (external sites)
Belgium, France, Netherlands and Switzerland: disposal of spent fuel and vitrified HLW in clay
The Belgian disposal concept proposes that spent fuel and HLW is placed in high integrity steel containers and then emplaced in excavated tunnels within a ductile (self-sealing) clay. The very low permeability of the clay leads to virtually no groundwater flow over long time periods. Waste would be backfilled with excavated clay or, alternatively, could be emplaced into unlined secondary tunnels where the clay would be allowed to creep into contact with the waste containers. Similar systems have been proposed in the Netherlands and, using less plastic clays, in France and Switzerland.
Further reading: Belgian Management Agency - ONDRAF/NIRAS, French Management Agency - ANDRA, Dutch Management Agency - COVRA, Swiss Management Agency - NAGRA (external sites)
United States: disposal of defence derived transuranic waste (similar to long-lived ILW) in layered salt strata.
The Waste Isolation Pilot Plant (WIPP) for defence wastes has been operational since 1999. For this repository natural rock salt is excavated from a several metres thick layer, sandwiched between other types of rock, 650 metres below ground level. The wastes placed in these excavations contain large volumes of long-lived ILW, usually in steel containers. The steel containers are then placed in concrete overpacks. A backfill material is then used to surround the overpacks. The primary purpose of the backfill is to provide control of the chemical environment. Containment of the radionuclides in the wasteform mostly relies on the almost complete absence of water flow in the salt.
Further reading: WIPP homepage (external site)
United States: disposal of spent fuel and high level waste at Yucca Mountain
Yucca Mountain, located in the remote Nevada desert, is the proposed site for the construction of a US national repository to store spent fuel and high level waste from nuclear power and military defense programs. The repository will exist 300 metres underground in an unsaturated layer of volcanic tuff rock (see also: Factsheet on " Volcanoes and Yucca Mountain " (external site)).
Waste will be stored in highly corrosion-resistant double-shelled metal containers, with the outer layer made of a highly corrosion-resistant metal alloy, and a structurally strong inner layer of stainless steel. Drip shields made of corrosion-resistant titanium will cover the waste containers to divert moisture and provide protection from possible falling rock or debris. Containment relies on the extremely low waste table, which lies approximately 300 metres below the repository and the long-term durability of the engineered barriers.
The site is currently preparing a license application to proceed with construction of the repository. The repository is scheduled for operation in 2010. An illustration of the proposed repository can be viewed here (external site).
Further reading: The Yucca Mountain Project website ( external site )
Germany and the Netherlands: Salt domes
Salt environments are also available in northern Germany and the Netherlands although these are salt domes rather than bedded formations. In Germany, the former salt mines at ASSE and Morsleben have been used for LLW and ILW disposal though this has now been suspended. The decommissioning process is now being investigated to determine the method for backfilling and sealing the repository. It has been proposed that salt domes could be used for the disposal of heat-generating HLW and spent fuel. The site at Gorleben was selected in the 1970s for this purpose, but there is currently a moratorium on further exploratory work there. A feature of salt environments is the very low rate of (perhaps even absence of) groundwater flow and the gradual self-sealing of the excavations due to creep of the salt.
Further reading: German Management Authority - Federal Ministry (BMU), Dutch Management Agency - COVRA (external sites)
United Kingdom: Nirex Phased Disposal Concept
The Nirex Phased Disposal Concept has been developed for relatively large volumes of ILW and LLW, usually cemented into stainless steel containers. These containers would be emplaced into a repository in a host rock environment below the water table. The waste would be monitored and remain retrievable and the groundwater managed to prevent contact with the wastes, until such a time that the repository is sealed. When this happens, the waste will be surrounded (backfilled) by specially formulated cement and the repository allowed to resaturate. The cement would provide a long lasting alkaline environment that contributes to containment of the waste by preventing many radionuclides from dissolving in the groundwater. Similar cement-based schemes for ILW disposal have been proposed in France, Japan, Sweden and Switzerland.
Further reading: Nirex website (external site)
Multinational Repositories
Not all countries are adequately equipped to store or dispose of their own radioactive waste. Some countries are limited in area, or have unfavourable geology and therefore siting a repository and demonstrating its safety could be challenging. Some smaller countries may not have the resources to take the proper measures on their own to assure adequate safety and security, or they may not have enough radioactive waste to make construction and operation of their own repositories economically feasible. It has been suggested that there could be multinational repositories located in a willing host country that would accept waste from several countries. Other terms for such shared repositories include "international" and "regional". They could include, for example use by others of a national repository operating within a host country, or a fully international facility owned by a private company operated by a consortium of nations or even an international organisation. However, for the time being, many countries would not accept under their national law nuclear waste from other countries.
Further reading: Association for Regional and International Underground Storage (ARIUS) (external site)
See also: National Policies
Interim Waste Storage
Specially designed interim surface or sub surface storage waste facilities are currently used in many countries to ensure the safe storage of radioactive waste pending the availability of a long-term management/disposal option. It must be noted that interim storage, whether short-term or long-term, is not a final solution, something will still remain to be done with the waste. Interim storage facilities are generally used for Intermediate Level Waste (ILW) and High Level Waste (HLW), although some countries, namely Finland, Sweden and the USA, now have disposal facilities for ILW in operation. Similar arrangements exist for the storage of spent nuclear fuel from reactors.
The figure below illustrates a typical storage container used for spent fuel. The multi-layer approach to containment is designed to ensure that the most penetrating forms of radiation cannot enter the outer environment.
Some countries, including Australia, Belgium, Netherlands, Germany, Italy and Switzerland also place Low Level Waste (LLW) in interim storage, although most LLW is typically sent directly to land-based near-surface disposal facilities.
Recognising that long-term management options, specifically for ILW and HLW, may require significant time to be achieved, interim storage arrangements may need to be extended beyond the time periods originally envisaged.
Nuclear Waste Management - Other Ideas for Disposal
Numerous options for long-term nuclear waste management have been considered in the past. The table below highlights a number of these.
| Ideas |
Examples |
| Long-term above ground storage |
- investigated in France, Netherlands, Switzerland, UK and USA
- not currently planned to be implemented anywhere
|
| Disposal in outer space (proposed for wastes that are highly concentrated) |
- investigated by USA
- investigations now abandoned due to cost and potential risks of launch failure
|
Deep boreholes
(at depths of a few km's) |
- investigated by Australia, Denmark, Italy, Russia, Sweden, Switzerland, UK and USA
- not implemented anywhere
|
Rock-melting
(proposed for wastes that are heat-generating) |
- investigated by Russia, UK and USA
- not implemented anywhere
- laboratory studies performed in the UK
|
| Disposal at subduction zones |
- investigated by USA
- not implemented anywhere
- not permitted by International agreements
|
| Sea disposal |
- implemented by Belgium, France, Federal Republic of Germany, Italy, Japan, Netherlands, Russia, South Korea, Switzerland, UK and USA
- not permitted by International agreement
|
| Sub seabed disposal |
- investigated by Sweden and UK (and organisations such as NEA/OECD)
- not implemented anywhere
- not permitted by International agreement
|
| Disposal in ice sheets (proposed for wastes that are heat-generating) |
- investigated by USA
- rejected by countries that have signed the Antarctic Treaty or committed to providing solutions within national boundaries
|
Direct injection
(only suitable for liquid wastes) |
- investigated by Russia and USA
- implemented in Russia for 40 years and in USA (grouts)
- investigations abandoned in USA in favour of deep geological disposal of solid wastes
|
Above Ground Storage
Above ground storage is normally considered an interim measure for the management of radioactive waste. France investigated it within the framework of the 1991 law on waste for HLW, but not as a means of final disposal. ZWILAG in Switzerland and Ahaus and Gorleben in Germany are examples of operating interim long-term above ground storage for HLW. However, controlled surface storage over longer time periods (greater than a couple of hundred of years) has also been suggested as a long-term waste management option.
Long-term above ground storage involves specially constructed facilities at the earth's surface that would be neither backfilled nor permanently sealed. Hence, this option would allow monitoring and retrieval at any time without excessive expenditure.
Suggestions for long-term above ground storage broadly fall into two categories:
- Conventional stores of the type currently used for interim storage, which would require replacement and repackaging of waste every two hundred years or so;
- Permanent stores that would be expected to remain intact for tens of thousands of years. These structures are often referred to as 'Monolith' stores or 'Mausoleums'.
The latter category of store is derived from the principle of "guardianship", where future generations continue to monitor and supervise the waste.
Both suggestions would require information to be passed on to future generations, leading to the question of whether the stability of future societies could be ensured to the extent necessary to continue the required monitoring and supervision.
Examples
No country is currently planning to implement long-term (i.e. greater than a few hundred years) above ground storage. However, France is investigating long term interim storage, but not necessarily above ground.
Long-term above ground storage has been considered as part of the range of management concepts in Switzerland by EKRA (Expert Group on Disposal Concepts for Radioactive Waste). The expert group (EKRA) observed that it was unclear what additional steps would be necessary to show how the long-term above ground storage concept could be brought to the state of development, which is comparable with that of geological disposal and they recommended geological disposal as the preferred option.
Further reading: ANDRA - French Waste Management Agency
Disposal in Outer Space
The objective of this option is to remove the radioactive waste from the Earth, for all time, by ejecting it into outer space. The waste would be packaged so that it would be likely to remain intact under most conceivable accident scenarios. A rocket or space shuttle would be used to launch the packaged waste into space. There are several ultimate destinations for the waste which have been considered including directing it into the Sun, leaving it in an orbit around the Sun between Earth and Venus and ejecting it from the solar system altogether. This would be necessary as placing the waste in space in a near Earth orbit would not be sufficient due to the possibility of the waste returning to Earth.
The high cost of this option means that such a method of waste disposal might be appropriate for high level waste (HLW) or spent fuel (i.e. long-lived highly radioactive material that is relatively small in volume). Reprocessing of the waste might be required to separate out only the most radioactive material for space disposal and hence reduce the volume.
Examples
This option has not been implemented and further studies have not been performed because of the high cost of this option and the safety aspects associated with the potential risk of launch failure.
The most detailed studies of this option were performed in the United States by NASA in the late 1970's and early 1980's. Today only Radioisotope Thermal Generators (TRGs) containing a few kilograms of Pu-238 are launched by NASA.
Deep Boreholes
For the deep borehole option solid packaged wastes would be placed in deep boreholes drilled from the surface to depths of several kilometres with diameters of typically less than 1 metre. The waste containers would be separated from each other by a layer of bentonite or cement. The borehole would not be completely filled with wastes. The top 2 kilometres would be sealed with materials such as bentonite, asphalt or concrete.
Boreholes can be readily drilled offshore (as described in the section on Sub Seabed Disposal) as well as onshore in host rocks both crystalline and sedimentary. This capability significantly expands the range of locations that can be considered for the disposal of radioactive waste.
Examples
Deep borehole concepts have been developed (but not implemented) in several countries, including: Denmark, Sweden, Switzerland and USA for HLW and spent fuel.
Compared with deep geological disposal in an underground repository, placement in deep boreholes is considered to be more expensive for large volumes of waste. This option was discounted from further development in countries such as Finland and USA. The feasibility of disposal of spent fuel in deep boreholes has been studied in Sweden, in order to check whether deep geological disposal remains the preferred option . The borehole concept remains an attractive proposition under investigation for the disposal of sealed radioactive sources from medical and industrial applications.
Rock Melting
The deep rock-melting option involves the melting of wastes in the adjacent rock. The idea is to either produce a stable, solid mass that incorporates the waste or encases the waste in a diluted form (i.e. dispersed throughout a large volume of rock) that cannot easily be leached and transported back to the surface. This technique has been mainly suggested for heat generating wastes such as vitrified HLW and host rocks with suitable characteristics to reduce heat loss.
The HLW in liquid or solid form could be placed in an excavated cavity or a deep borehole. The heat generated by the wastes would then accumulate resulting in temperatures great enough to melt the surrounding rock and dissolve the radionuclides in a growing sphere of molten material. As the rock cools it would crystallise and incorporate the radionuclides in the rock matrix, thus dispersing the waste throughout a larger volume of rock.
There are some variations of this option in which the heat generating waste would be placed in containers and the rock around the container melted. Alternatively, if insufficient heat is generated the waste would be immobilised in the rock matrix by conventional or nuclear explosion.
Examples
Rock melting has not been implemented anywhere for radioactive waste. There have been no practical demonstrations or in situ demonstrations of the feasibility of this option, apart from laboratory studies of rock melting. Some examples of this option and variations are described below.
In the late 1970's and early 1980's, the rock melting option at depth was taken forward to the engineering design stage. This design involved a shaft or borehole which led to an excavated cavity at a depth of 2.5 kilometres. It was estimated, but not demonstrated, that the waste would be immobilised in a volume of rock one thousand times larger than the original volume of waste.
Another early proposal was the design of weighted, heat-resistant containers of heat generating wastes such that they would continue to melt the underlying rock, and allow them to move downwards to greater depths with the molten rock solidifying above it. This alternative resembles similar self-burial methods proposed for disposal of HLW in ice sheets.
In the 1990's, there was renewed interest in this option, particularly for the disposal of limited volumes of specialised HLW, particularly plutonium, in Russia and in the UK. A scheme was proposed in which the waste content of the container, the container composition and the placement layout would be designed to preserve the container and prevent the wastes becoming incorporated in the molten rock. The host rock would be only partially melted and the container would not move to greater depths.
Russian Scientists have proposed that HLW, particularly excess plutonium, could be placed in a deep shaft and immobilised by nuclear explosion. However, the major disturbance to the rock mass and groundwater by the use of nuclear explosions, as well as arms control considerations, has led to the general rejection of this option.
Disposal at a Subduction Zone
Subduction zones are areas where one denser section of the Earth's crust is moving towards and underneath another lighter section. The movement of one section of the Earth's crust below another is marked by an offshore trench, and earthquakes occur adjacent to the inclined contact between the two plates. The edge of the overriding plate is crumpled and uplifted to form a mountain chain parallel to the trench. Deep sea sediments may be scraped off the descending slab and incorporated into the adjacent mountains. As the oceanic plate descends into the hot mantle parts of it may begin to melt. The magma thus formed migrates upwards, some of it reaching the surface as lava erupting from volcanic vents. The idea for this option would be to dispose of wastes in the trench region such that they would be drawn deep into the Earth.
Examples
Although subduction zones are present at a number of locations across the Earth's surface they are geographically very restricted. Not every waste-producing country would be able to consider disposal to deep-sea trenches, unless international solutions were sought. However, this option has not been implemented anywhere and as it is a form of sea disposal it is therefore not permitted by international agreements
Disposal at Sea
Disposal at sea involves radioactive waste being shipped out to sea and dropped into the sea in packaging designed to either:
- implode at depth, resulting in direct release and dispersion of radioactive material into the sea; or
- sink to the seabed intact.
Over time the physical containment of containers would fail, and radionuclides would be dispersed and diluted in the sea. Further dilution would occur as the radionuclides migrated from the disposal site, carried by currents.
The amount of radionuclides remaining in the sea water would be further reduced both by natural radioactive decay, and by the removal of radionuclides to seabed sediments by the process of sorption.
This method is not permitted by international agreements.
Examples
The application of the sea disposal of LLW and ILW has evolved over time from being a disposal method that was actually implemented by a number of countries, to one that is now banned by international agreements. Countries that have at one time or another undertaken sea disposal using the above techniques include Belgium, France, Federal Republic of Germany, Italy, Netherlands, Sweden and Switzerland, as well as Japan, South Korea and the USA. This option has not been implemented for HLW.
Sub Seabed Disposal
For the sub seabed disposal option radioactive waste containers would be buried in suitable geological setting beneath the deep ocean floor. This option has been suggested for LLW, ILW and HLW. Variations of this option include:
- A repository located beneath the seabed. The repository would be accessed from land, a small uninhabited island or from an offshore structure.
- Burial of radioactive waste in deep ocean sediments.
This method is not permitted by international agreements.
Examples
Sub seabed disposal has not been implemented anywhere and is not permitted by international agreements.
The disposal of radioactive wastes in a repository constructed below the seabed has been considered by Sweden and the UK. In comparison to disposal in deep ocean sediments, if it were desirable the repository design concept could be developed so as to ensure that future retrieval of the waste remained possible. The monitoring of wastes in such a repository would also be less problematic than for other forms of sea disposal.
In the 1980's, the feasibility of the disposal of HLW in deep ocean sediments was investigated and reported by the Organisation for Economic Co-operation and Development. For this concept radioactive waste would be packaged in corrosion-resistant containers or glass, which would be placed beneath at least 4000 metres of water in a stable deep seabed geology chosen both for its slow water flow and for its ability to retard the movement of radionuclides. Radionuclides that are transported through the geological media, to emerge at the bottom of the seawater volume, would then be subjected to the same processes of dilution, dispersion, diffusion and sorption that affect radioactive waste disposed of at sea (see section on Disposal at Sea ). This method of disposal therefore provides additional containment of radionuclides when compared with the disposal of wastes directly to the seabed.
Burial of radioactive waste in deep ocean sediments could be made by two different techniques: penetrators or drilling placement. The burial depth of waste containers below the seabed can vary between the two methods. In the case of penetrators, waste containers could be placed about 50 metres into the sediments. Penetrators weighing a few tons would fall through the water, gaining enough momentum to embed themselves into the sediments. A key aspect of the disposal of waste to seabed sediments is that the waste is isolated from the seabed by a thickness of sediments. In 1986, some confidence in this process was obtained from experiments undertaken at a water depth of approximately 250 metres in the Mediterranean Sea.
The experiments provided evidence that the entry paths created by penetrators were closed and filled with remoulded sediments of about the same density as the surrounding undisturbed sediments.
Wastes could also be placed using drilling equipment based on the techniques in use in the deep sea for about 30 years. By this method, stacks of packaged waste would be placed in holes drilled to a depth of 800 metres below the seabed, with the uppermost container about 300 metres below the seabed.
Disposal in Ice Sheets
For this option containers of heat-generating waste would be placed in stable ice sheets such as those found in Greenland and Antarctica. The containers would melt the surrounding ice and be drawn deep into the ice sheet, where the ice would refreeze above the wastes creating a thick barrier.
Although disposal in ice sheets could be technically considered for all types of radioactive wastes, it has only been seriously investigated for HLW, where the heat generated by the wastes could be used to advantage to self-bury the wastes within the ice by melting.
It has been rejected by countries that have signed the Antarctic Treaty (1959) or have committed to providing a solution to their radioactive waste management within their national boundaries.
Examples
The option of disposal in ice sheets has not been implemented anywhere. It has been rejected by countries that have signed the Antartic Treaty, or have committed to providing a solution to their radioacitve waste management within their national boundaries. Since 1980 there has been no significant consideration of this option.
Further reading: Scientific Committee on Antarctic Research - Antartic Treaty (external site)
Direct Injection
Description
This approach involves the injection of liquid radioactive waste directly into a layer of rock deep underground that has been chosen because of its suitable characteristics to trap the waste (i.e. minimise any further movement following injection).
In order to achieve this a number of geological pre-requisites are required. There must be a layer of rock (injection layer) with sufficient porosity to accommodate the waste and with sufficient permeability to allow easy injection (i.e. act like a sponge). Above and below the injection layer there must be impermeable layers that act as a natural seal. Additional benefits could be provided from geological features that limit horizontal or vertical migration. For example, injection into layers of rock containing natural brine groundwater. This is because the high density of brine (salt water) would reduce the potential for upward movement.
Direct injection could in principle be used on any type of radioactive waste provided that it could be transformed into a solution or slurry (very fine particles in water). Slurries containing a cement grout that would set as a solid when underground could also be used to help minimise movement of radioactive waste.
Examples
Direct injection has been implemented in Russia and the USA as described below.
In 1957 extensive geological investigations started in Russia for suitable injection layers for radioactive waste. Three sites were found, all in sedimentary rocks. At Krasnoyarsk-26 and Tomsk-7 injection takes place into two porous sandstone beds capped by clays at depths up to 400 metres. Whereas at Dimitrovgrad injection has now stopped, but took place into a sandstone and limestone at a depth of 1400 metres. In total, some tens of millions of cubic metres of low, intermediate and high-level radioactive wastes have been injected.
In the United States, direct injection of about 7500 cubic metres of low-level radioactive wastes as cement slurries was undertaken during the 1970's at a depth of about 300 metres over a period of 10 years at the Oak Ridge National Laboratory, Tennessee. It was abandoned because of uncertainties over the migration of the grout in the surrounding fractured rocks (shales). In addition a scheme involving high-level waste injection into crystalline bedrock beneath the Savannah River site in South Carolina was abandoned before it was implemented due to public concerns.
Radioactive material is produced as a waste product from the oil and gas industry and generally referred to as "Technologically-Enhanced Naturally-Occurring Radioactive Materials - TENORM". In the UK, much of these wastes are exempt from the need for their disposal to be authorised under the UK's Radioactive Substances Act 1993 because of their low levels of radioactivity. However, some of the wastes are of higher activity and there are currently a limited number of disposal routes available , this includes re-injection back into the borehole (i.e. well-head), which is authorised by the UK's Environment Agency.