NUCLEAR warheads stored on submarines could explode one after another in a nightmarish accident scenario known as "popcorning", it was claimed yesterday.
A newly declassified Ministry of Defence (MoD) safety manual is said to draw attention to the danger.
And it has once again raised concerns about the presence of nuclear weapons at Faslane on the Clyde, only 25 miles from Glasgow.
The document
points to design flaws that could undermine safety measures intended to prevent accidental detonation.
Nuclear warheads are supposed to be "single-point safe", meaning that a sudden knock at a single point – for instance as a result of being dropped from a crane – should not set off the plutonium core.
But the MoD manual argues that the standard single-point design may not be enough to prevent "popcorning" – a disastrous chain reaction of explosions that could occur as a result of warheads being stacked closely together.
It says warheads should be capable of resisting multiple simultaneous impacts, New Scientist magazine has reported.
This "would contribute to the prevention of popcorning and should be a design objective".
The manual also recommends replacing the highly sensitive explosive material that surrounds the warheads' cores. A single knock may not detonate the core, but could set off the conventional explosive.
Less sensitive explosives are heavier and bulkier than those currently in use.
A typical submarine-borne Trident nuclear missile contains between three and six warheads, and a United States submarine might carry up to 24 missiles.
The New Scientist report said: "The effects of a popcorning accident would be dire. According to the manual, in the worst case scenario, people a kilometre away would receive a radiation dose of 100 sieverts – that's 16 times the lethal dose."
The seriousness of the accident would depend on the pattern of warhead explosions, the magazine said.
An MoD spokeswoman told New Scientist that, while popcorning was a "theoretical possibility" it was "a scenario that is not credible".
She added that any risk was mitigated by the way missiles were handled, transported and stored.
Dr Stefan Michalowski, a senior scientist at the Organisation for Economic Co-operation and Development in Paris, who studied warhead safety at Stanford University in California in the 1990s, said that he was worried about the risk of an "extreme event".
An example might be a gun battle that caused a warhead to be hit by stray bullets and detonated, he said. "The explosion of a boatload of missiles in a port would be an unimaginable catastrophe," he said. "It's a very, very scary thought."
Recently, the churches in Scotland got together to campaign against the renewal of Britain's nuclear weapons, and Alex Salmond, the First Minister, has made it clear that he and his party, the SNP, do not want "weapons of mass destruction in Scotland".
Even though defence is an issue reserved to Westminster, the Scottish Government has set up a working party, under the chairmanship of Bruce Crawford, the parliamentary business minister, to look at the future of nuclear weapons in Scotland. Among its remits is to examine how to provide alternative work for people at Faslane.
