Geologists explore nuclear storage

Materials World magazine
,
1 Dec 2008
Nuclear repository in Dopravni, Czech Republic

The UK is again considering underground nuclear waste storage. However, the process of identifying locations for geological disposal has been complicated by the UK Government’s invitation to local authorities to come forward as potential candidates for sites.

Delegates at an event at the Geological Society in London, UK, on 24 October, heard that site selection should be about meeting a risk target. Professor Stuart Haszeldine of the University of Edinburgh, UK, emphasised the need to explore the geological and engineering case for a project rather than being swayed by public opinion. The Government request for expressions of interest from communities wishing to host a waste site ‘has a fundamental flaw’, he said, as it excludes places where no one lives.

The geology in the UK has not changed since the last round of investigation in the 1980s, but non-invasive technologies to assess rock formations have undergone ‘enormous advances’ thanks to oil and gas exploration, according to Professor Bruce Yardley of the University of Leeds, UK. Techniques to investigate a potential site could include geophysical methods such as seismic reflection, ground penetrating radar and resitivity, which would then be supported by selective drilling. Computer modelling can manipulate data and build up images of the subsurface structure.

Factors to consider include the chemical environment around the repository, the
permeability structure and the history of geological activity in the area. ‘We need to distinguish how [the rock formations] behaved in the past from how they behave now,’ says Yardley.

French connection – underground nuclear disposal in France

Dr Patrick Landais from the French National Agency for Radioactive Waste Management (ANDRA) gave an overview of the progress made towards underground disposal in France. In 1999, the French Government approved an underground laboratory on a clay site in Bure (Meuse/Haute-Marne), managed by ANDRA.

In the clay-rich area, which is around 155MA old, 130m-thick material was selected due to its low permeability of 10-14-10-12m/s and a pore size of 20-30nm. It is located in the sedimentary Paris Basin, which has a flat structural strata.

The team has studied various scenarios and their effect on the site/waste, including container/overpackaging/seal failure, and intrusive borehole drilling. Further experiments are planned to examine gas migration, bacterial populations, oxidation, desaturation, self-sealing of fractures in the clay and the behaviour of materials in situ.

The group is working towards commissioning a deep repository in 2025, and a site is expected to be selected in 2013. France is also examining the possibility of a separate site for graphite and radium-bearing waste. Sub-surface disposal under an intact clay layer is being considered.

Haszeldine highlighted the need for similar work in the UK, saying, ‘Initial choices are vital’. But he warned, ‘geology is not in our culture’ and cautioned that geological science faces a skills shortage. ‘[It] has rival employers, why should people come to work in nuclear storage?’

Ultimately, the drive for nuclear power in the UK may make people consider the sector as a long-term employer and speed up decisions on an underground repository site. But this, says Haszeldine, is dependent on reaching the required level of safety assurance.

Further information: Geological Society