BBC News 24 investigates Dounreay's missing uranium

Enough uranium to make a dozen atomic bombs has apparently not been accounted for.

The government has been urged to look into the disappearance of 170kg of enriched uranium from the nuclear plant.

One nuclear expert said the material could be enough to make a dozen atomic bombs.

The Scottish Nationalists demanded an immediate inquiry to find out what had happened to the uranium.

The worst case scenario being presented is that the material could have been taken for a nuclear arms programme.

But the UK Atomic Energy Authority is trying to calm fears, denying the suggestion that any of the material ended up in weapons.

Instead, the missing uranium could be due to an "accounting uncertainty".

'We are not being told the whole story' - SNP

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The uranium went missing between 1965 and 1968, according to a report by the Authority.

The extent of the loss was discovered during a study of one of the plant's waste shafts, which had been used as a dump.

The SNP's environment spokeswoman Roseanna Cunningham said a commission should be established to uncover the truth about the latest in a series of embarrassing episodes at the Dounreay plant in Caithness, in northern Scotland.

"How on earth can material as deadly as this just go missing?" she said.

"As usual one gets the feeling that we are not being told the whole story.

"Either that or Dounreay's incompetence down the years has been even worse than anyone imagined.

"We are now in the ludicrous situation where we are hoping that the uranium was used to make British atom bombs because the alternatives are even harder to stomach."

'Worst-case estimate'

Dounreay said the estimate of 170kg of missing uranium made in a recently-published inventory was "a worst-case estimate" of the content of the waste shaft.

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The uncertainty arose because Dounreay processed material from a range of sources in the 1960s, a spokesman said.

Inquiries in both 1963 and 1973 concluded the missing material was probably due to uncertainty in estimates of the uranium brought to the plant.

"This reflected the imprecision of the analytical techniques available at that time, coupled with the difficult nature of the input material," the spokesman added.

String of embarrassments

The clean-up operation on the shaft began at the end of March, when the government confirmed it was leaking radioactivity. The work is expected to take 25 years.

Then in April the government announced it was taking 5kg of uranium from the former Soviet republic of Georgia to prevent it from falling into the wrong hands.

On May 16, the Health and Safety Executive revealed a sweeping safety review of the Dounreay plant.

The inquiry followed an incident when a digger cut through electrical cables, paralysing the plant after the emergency supply also failed, prompting concerns about the control of the plant.