Å®ÉúСÊÓƵ

(see Graphic) Criticism is mounting over the proposed site of the deep repository for nuclear waste near Sellafield in Cumbria. Geologists from the University of Glasgow have added their voices to doubts expressed last week by government advisers. Patterns of water flow underground are more complex than the repository’s builders, Nirex, first supposed. The government’s Radioactive Waste Management Advisory Committee and the Glasgow group warn that these currents could bring radioactive material to the surface sooner than expected.FIG-mg18741501.jpg

Nirex published a report on the geology and hydrology of the Sellafield area last year. The key information came from boreholes drilled into the Borrowdale volcanic group, the rocks that will contain the repository. At the bottom of the boreholes, Nirex found fluid at higher pressures than anticipated. It was also salty, making it denser than fresh water.

In its annual report, the RWMAC says water could flow up through the repository. The committee is concerned that the salty water may drive the circulation of less-dense fresh water in ways that are not understood. But the report stresses the main problem is uncertainty – there are not yet enough data on flow patterns.

Nirex agrees. The pressure readings suggest that water ‘could’ flow upwards, says Uisdean Michie, a geologist at Nirex. ‘What they do not prove or show is that there is flow upwards.’ The alternative explanation, Michie says, is that the Borrowdale volcanics are sufficiently impermeable to hold water at high pressure. Nirex has plans to drill more boreholes, and to dig a ‘rock characterisation facility’ – a chamber at the same location as the planned repository – where it will measure the rock’s properties in situ.

In Glasgow, university geologists Christopher McKeown, Stuart Haszeldine and Gary Couples have taken debate about the site further. ‘Our work shows that the model Nirex published is much too simple,’ says Haszeldine. ‘Water from the Lake District flows downwards, along and up through the site of the repository.’

The researchers modelled the flow of ground water through a cross section of the repository site using information published by Nirex. They calculate the flow at between 1.1 and 19 metres a year. This is fast in terms of the lifetime of the repository and could mean that water returns to the surface sooner than was expected. ‘If we take 10 000 years as the safety limit,’ says Haszeldine, ‘then the permeabilities that Nirex measured are forty times too great to meet that target.’

Nirex says it will not go ahead until it has all the necessary data. In the worst case, if the site is deemed unsuitable, Nirex would have to find another site and restart investigations from scratch.