London, June 26: A design flaw in Britain’s nuclear arsenal means that warheads could set off a chain reaction “like popcorn” if they were accidentally dropped, according to ministry of defence documents.

More than 1,700 warheads are affected by the problem which would cause them to explode one after another, an effect known as “popcorning”.

A typical Trident nuclear missile contains three to six warheads, and some submarines carry up to 24 missiles, meaning the potential for disaster could be huge.

Defence companies try to prevent accidental explosions of warheads by designing them to be “singlepoint safe” which means that a sudden knock at a single point should not detonate the plutonium core.

The typical scenario would see the weapon being dropped from a crane while being loaded on or off a submarine.

However, a nuclear-weapons safety manual drawn up by the MoD’s internal nuclear-weapons regulator, and declassified last month, argues that this standard single-point design might not be enough to prevent “popcorning”.

The manual, seen by the New Scientist, says that warheads should be capable of resisting multiple simultaneous impacts which “would contribute to the prevention of popcorning and should be a design objective”.

It also recommends replacing the highly sensitive explosive that surrounds the warheads’ plutonium cores because a single knock may not detonate the core, but could set off the explosive.

Less-sensitive explosives are available but they are heavier and bulkier than those currently in use so the warheads would have to be redesigned.