Fossilised rat dung helps find nuclear waste sites

Fossilised dung hills formed by rodents over thousands of years are helping scientists to locate underground sites for storing high-level nuclear waste.

Certain rodents produce rubbish heaps, known as middens, composed of waste piles of organic material mixed with faeces and cemented with urine.

Scientists plan to use them to determine the precise changes in climate more than 10,000 years ago which are crucial in determining the long-term stability of a nuclear waste repository.

American nuclear authorities, like those in Britain, are keen to demonstrate the safety of storing high-level nuclear waste in underground stores. A key factor is proving that radioactive materials will not leach into rock and enter the groundwater supply.

The US Geological Survey has recruited experts to study the middens of the North American packrat, a rodent responsible for dung heaps that are up to 40,000 years old, to shed light on rainfall levels in previous millenia.

Geoffrey Spaulding, a senior research scientist at Dames and Moore environmental consultancy in Las Vegas, said high- level waste has to be isolated for between 10,000 and 100,000 years.

Packrats are noted for depositing objects in their middens which can contain perfectly preserved seeds, leaves, twigs and fruit, Dr Spaulding said.

'Because the material was collected immediately around the packrats' den . . . the data they yield are very precise,' Dr Spaulding writes in the current issue of Nuclear Engineering International. 'One of the only ways to judge what the next 10,000 years might bring is to look at what has happened over the last 20,000 years.'

Packrat middens near to the proposed site for the US's high- level repository in Nevada indicate that if another ice age were to hit the area, groundwater levels would not endanger a nuclear store, Dr Spaulding said.