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Nirex, Britain’s radioactive waste agency, confirmed this week that
it believes the geology beneath the Sellafield nuclear complex in northwest
England makes it the best location for the country’s first deep repository.

But the government’s own independent advisers on radioactive waste management
have privately voiced reservations about the plan to bury waste at Sellafield.

Nirex is planning to dispose of low and intermediate level radioactive
waste in a labyrinth of caverns excavated up to 800 metres underground.
About 60 per cent of the waste would be generated by the reprocessing operations
at Sellafield. Nirex expects a public inquiry into the scheme to start in
1993. But the agency has already conceded that it will not be in a position
to provide a full safety case by then.

One senior member of the Radioactive Waste Management Advisory Committee
told New Å®ÉúСÊÓƵ that the agency had not yet carried out enough investigations
to demonstrate to the public that it had made the right choice. Ideally,
he said, information from 15 to 20 boreholes would be required to demonstrate
the suitability of the geology. Nirex will probably have drilled 10 by the
time the inquiry opens. Nirex based its choice on evidence from six boreholes
– four in Cumbria and two at Dounreay in northern Scotland.

Nirex’s choice of Sellafield, rather than Dounreay, was roundly attacked
by environmentalists. Greenpeace claimed the choice was ‘politically expedient’
and not based on geological and technical considerations.

Nirex wants to build its repository in the basement rock underlying
the Sellafield site. This consists of carboniferous sediments known as the
Borrowdale Volcanic Series. According to a detailed critique of the selection
process carried out for Greenpeace by Phil Richardson, a consultant geologist,
faulting in the rock ‘will be extremely difficult to predict and map’.

Richardson argues that because of deformation caused by geological ‘folding’
in the past, the movement of ground water in the area will be ‘extremely
complicated and totally unpredictable’. The most likely route for radionuclides
to escape is by dissolving in any ground water passing through the repository.

Dick Morris, the chairman of Nirex, hinted at such problems at an international
conference last month. ‘Although the geology is quite complex it is within
our capability to model the associated ground water flows, and there are
almost certainly volumes of rock suitable for repository construction,’
he said.

Senior Nirex officials and board members defended their choice. Speaking
in London on Tuesday, Alan Hooper, who heads the burial programme, claimed
there was already evidence that the basement rock was ‘stronger’ than originally
expected and of ‘very low permeability’.

Another key safety issue concerns the generation of gases in the repository.
Methane, radioactive carbon dioxide and hydrogen are produced as organic
waste breaks down and the steel and concrete used in containers and the
underground vaults corrode. A build up of gas could damage the vaults or
open out fissures in the rock. This has proved a problem in the world’s
only underground radioactive store built so far, the Forsmark facility under
the Baltic, in Sweden.

Nirex is currently contesting the government’s safety regulations that
require it to guarantee that the risk of exposure to radiation from the
repository will fall within acceptable levels for up to one billion years.
Nirex wants Britain to adopt the same standards as the US and Sweden, which
guarantee safety for 10 000 years.