CHAPTER 3: SOME OPTIONS AND
THEIR ADVOCATES
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
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.
Synroc
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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