Report: Nuclear warheads could explode, release radiation while in transit

Nuclear warheads must be inspected regularly to make sure that the materials used in constructing them do not become unstable and unreliable as a result of aging and the intense radiation to which they are exposed. In the United Kingdom, for example, Trident nuclear warheads are taken off the submarine and trucked to a Ministry of Defense (MoD) lab to be inspected. The MoD has always insisted that an accidental nuclear explosion could not happen in transit because a warhead’s plutonium core must be compressed symmetrically by conventional explosives to create an implosion. Bombs are designed to be “single point safe,” so a knock at a single point should not trigger all the explosives around the core.

A new study prepared form MoD says this is not the case. Nuclear warheads damaged in a vehicle pile-up or a plane crash could partially detonate, to say nothing of deliver a lethal radiation dose. As if this were not enough, the study also says that an attack by terrorists on a nuclear weapons convoy could produce an even more disastrous outcome.

The study concludes that extreme accidents could result in a nuclear explosion because it could lead to the weapon not remaining single-point safe. The report puts the overall yearly risk of an “inadvertent yield” in the United Kingdom at 2.4 in a billion, mainly owing to the possibility of an aircraft crashing onto a convoy. Inadvertent yield suggests a partial nuclear explosion, also called fizzle yield, smaller than the full yield of up to 100 kilotons.

The MoD has drawn up contingency plans for responding to a fizzle yield event. The study says that radiation doses in such an event could range from 1 to 10 sieverts. According to the U.K. Health Protection Agency, people exposed to 4 sieverts have a 50 percent chance of dying from acute radiation poisoning, while 6 sieverts or more will kill everyone exposed.

The MoD report does conclude that emergency arrangements are adequate, and the MoD itself said in a statement that neither a terrorist attack nor an accident could trigger a full nuclear explosion because each warhead is transported with “vital parts of its final configuration removed.” Scientists do not accept the MoD’s reassurances at face value. Frank Barnaby, a nuclear physicist who worked on the U.K. nuclear weapons program and is now a consultant with the independent Oxford Research Group, told the New Scientist that “The MoD report confirms what many scientists have long suspected — that nuclear bombs can go off by accident….They have also effectively admitted that a terrorist attack could cause a nuclear explosion. A Trident warhead exploded in a densely populated area could kill hundreds of thousands of people. However small the risk, that is too horrifying to contemplate.”