Select Committee on Science and Technology Third Report


Options studied World-Wide

3.1 Over the approximately three decades since the start of major research and development (R&D) programmes world-wide, a variety of options have been suggested for the long-term management of long-lived radioactive wastes. These are outlined in Box 2.

3.2 Several of the options were only seriously considered for high level wastes (vitrified reprocessing HLW and spent fuel). R&D initially focused on these wastes because it was felt that they would be the most difficult to deal with, and if a long-term management option could be developed for HLW one for other long-lived wastes would follow. It was then recognised that the diversity and larger volume of ILW presented its own difficulties, and that some of the options which could be appropriate for HLW would not be so for ILW. Present international views on the options are as follows.

Box 2: Management Options for Long-Lived Radioactive Wastes

The main options

Emplacement in Geological Formations on Land

The types of geological formations considered for waste emplacement are all those in which there is likely to be low or no groundwater flow: evaporites (salt domes, bedded salt); sedimentary rocks (clays and shales); hard rocks (granite, tuff).

The emplacement geometries studied include mined caverns and tunnels, both entirely on land and under the bed of coastal seas with access from land, at depths of 300-800m; very deep boreholes (kilometres) drilled from the surface, boreholes drilled from caverns and tunnels. All repository designs include "engineered barriers", particularly backfilling and sealing materials.

The option is suitable for all long-lived wastes.

It relies on the predictable stability of geological and hydrogeological conditions over millions of years.

Indefinite Storage on or near the Surface

This is storage on or near the surface pending technological advances to render the waste harmless or to develop better disposal methods than those thought of so far.

It is applicable to all long-lived wastes.

It relies on supervision by humans and could imply repeated rebuilding of stores and repackaging of wastes.

Disposal options which are no longer being considered

Placing Wastes on the Bed of the Deep Ocean

The water depths at sites used in the 1970s and 1980s, and proposed for the future, were several kilometres, in parts of the ocean away from boundaries of tectonic plates and hundreds of kilometres from shore.

For LLW and ILW the method used was to drop canisters of waste from a ship (sea dumping).

For HLW there were suggestions to construct some kind of concrete structure on the ocean floor, as well as to use sea dumping (but with much longer lived canisters than for LLW and ILW).

Emplacement in the Sediments of the Deep Ocean

The main emplacement method studied was the use of 'penetrators': torpedo-shaped outer canisters which would embed themselves a few metres below the ocean floor, but drilling into the ocean floor was also looked at.

The characteristics of proposed sites were as for sea dumping, and for penetrators sediments had to be sufficiently plastic to close over the wastes.

The option was primarily considered for HLW.

Emplacement in the Rock beneath the Deep Ocean

This option consists of placing canisters of waste in boreholes drilled in the ocean floor. The suggested borehole depths were kilometres below the ocean floor, at sites where ocean depths are kilometres.

The option was only considered for HLW, because of its relatively small volume.

Subduction Zones

These are zones in the ocean floor where one section of the earth's crust is moving under another section. Canisters of wastes would be placed in the zone and, in principle, they would move towards the centre of the earth and would not re-emerge for hundreds of millions of years.

The option was considered mainly for HLW.

Placing Wastes in Antarctic Ice Sheets

The canisters of waste would be placed in holes drilled in the ice sheet, where they would move downwards by melting the ice, which would refreeze over them.

The option was considered for HLW only, because of its heat generation.

It relies on ice sheets being stable for millions of years.

Ejection into Space

In this option canisters of waste would be loaded into a spacecraft which would travel out of the earth's orbit.

It was considered for low volumes of waste, mainly HLW, only.

It would only be feasible with very reliable space craft, because an accident at launch or shortly after could release large amounts of radioactive material into the atmosphere, with huge health and environmental consequences.

Other options

Partitioning and Nuclear Transmutation

Partitioning means separation of long-lived radionuclides from wastes (typically by chemical means), transmutation is transforming these radionuclides into short-lived ones, or stable elements, in a reactor or using a particle accelerator.

The option is not feasible for ILW and existing HLW.

The physics of transmutation has been studied extensively, the technology less so (especially accelerators). Problem areas are partitioning, processes for making radionuclides into suitable physical and chemical forms for transmutation, and waste management processes (chemical engineering). The option would require major nuclear programmes and technological advances if it were to be used on a large scale in future.


Synroc is a synthetic rock material which is made by mixing waste constituents with minerals; radionuclides are held within crystal lattices so would be released very slowly into any water that came into contact with the waste after disposal.

It could be used to immobilise HLW arising from reprocessing, and other HLW such as surplus plutonium.

Immobilisation of wastes in Synroc has not yet been carried out on a commercial scale. In the future it could become an alternative to vitrification for reprocessing HLW. It may be used in the US for surplus weapons grade plutonium and in the former Soviet Union for various types of HLW.

Geological Disposal

3.3 From a technical point of view, emplacement in geological formations on land always has been and still is the 'front-runner'. In some countries it is the only option which has ever been considered. Some research has been carried out into placing wastes in very deep boreholes drilled down from the earth's surface but it was concluded that this would not be practicable for substantial volumes of HLW and ILW. R&D is now focused on deep repositories, ie mined tunnels and caverns, in some instances with boreholes drilled into their floors. In most countries' R&D programmes it is envisaged that a deep repository will become operational during the latter half of the next century and may not be closed and sealed until the century after that. Meanwhile, wastes are stored on or just under the surface.

Indefinite surface Storage

3.4 This option is favoured by those who reject geological disposal as unsound or unproven, and who wish to leave future generations the freedom to develop better methods for managing wastes in the very long term. Indefinite surface storage has not been the subject of much R&D and no countries with major nuclear programmes have adopted indefinite storage as a policy.

Seabed Disposal

3.5 Emplacement on the bed of the deep ocean was considered primarily for some types of ILW but the United Kingdom also evaluated the option for vitrified HLW. In several nuclear nations it is still thought of as, technically, an excellent option for some wastes, particularly large volume items. The option is unacceptable to non-nuclear nations, especially those whose economies depend on the sea (eg Pacific island states). It is now prohibited by international agreements.

Sub-seabed Disposal

3.6 This option was only considered for HLW because of the logistics and costs of emplacing the larger volume ILW in the sediments or rocks beneath 3-4 km of water. The international R&D programme on sub-seabed disposal, set up by the Nuclear Energy Agency of OECD[18], concluded that it would be technically feasible, given sufficient R&D, and that its radiological impact on human health and the environment could be kept low. The option was always politically and socially unacceptable to many nations, in the same way as seabed disposal, and it is now prohibited by international agreements.

Subduction Zones

3.7 Placing wastes in subduction zones was also only considered for HLW because of logistics and costs. R&D on the option was confined to paper studies, from which it was concluded that, for the foreseeable future, there would not be enough confidence in predictions about the fate of the wastes. The option also suffers from the same political and social objections as seabed and sub-seabed disposal.

Ice Sheets

3.8 This option relies on heat from wastes to melt the ice and achieve the required disposal depths. It was thus only considered for HLW. From preliminary paper studies it was concluded that there would never be enough confidence in predictions of the fate of wastes, and that there was the potential for releases of radioactive materials into the ocean. Subsequently, concern about the preservation of the Antarctic environment became another strong reason for rejecting this option. It is now ruled out by international treaties.

Ejection into Space

3.9 Initially this option was suggested for HLW but it was also thought about for low volume residual wastes from partitioning and transmutation. It was never included in major R&D programmes because the radiological consequences of an accident in which waste became dispersed in the atmosphere would be so large. The Challenger disaster reinforced opposition to the option.

Partitioning and Nuclear Transmutation

3.10 Partitioning and transmutation (P&T) was first suggested over thirty years ago as a means of reducing the long term toxicity of radioactive wastes. This would be achieved by transmuting long-lived radionuclides into shorter-lived radionuclides, or stable elements, by irradiation with neutrons. The transmutation could take place in a nuclear reactor or in the target of a particle accelerator. Partition is the process of physically or chemically separating the long-lived radionuclides and would be needed prior to transmutation. Initially P&T was considered for HLW and particular constituents of spent fuel (eg iodine-129). Latterly, transmutation has been proposed to deal with surplus military plutonium in the former Soviet Union and the US.

3.11 R&D on P&T began in the 1970s and continues in several countries, particularly France and Japan. Despite the effort devoted to it, P&T is still at the experimental stage and use of it on a large scale would require significant technological developments. For example, in France it is anticipated that the development and introduction of the technology would take between twenty and forty years. This technology is for use of P&T as an intrinsic part of nuclear fuel cycles: there is now general agreement that it is not feasible to use P&T to deal with existing HLW or spent fuel. It is also impractical to use P&T for ILW and LLW, in which the radionuclides of interest are dispersed throughout large volumes of material.[19] P&T is thus not a solution for the waste legacy, nor for wastes that will arise in future from present nuclear programmes.


3.12 We heard evidence from the Earl of Shannon and other representatives of Synroc International about the potential of this synthetic rock material to immobilise HLW and other wastes (QQ 1083-1140). The Synroc process was invented in the late 1970s by Professor Ted Ringwood of the Australian National University and consists of mixing waste constituents with minerals to produce a solid in which the radionuclides are held within the lattices of crystals. The process has not been demonstrated on a commercial scale but may be applied soon in the US to immobilise weapons grade plutonium prior to its disposal[20]. BNFL is examining the technology and we support the continuation of this work.

18   OECD: Organisation for Economic Co-operation and Development Back

19   R. Cummings, R P Bush et al, An assessment of partition and transmutation against UK requirements for radioactive waste management. Report DoE/RAS/96.007 for the UK Department of the Environment, 1996. See also QQ 1141-1211. Back

20   Sunday Times, 4 October 1998. Back

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