Material from various parts of the nuclear fuel cycle could be stolen by terrorists and used to make nuclear weapons.
This particular dastardly plot suffers from a couple of problems. First off, the terrorists attempting to steal nuclear material must get past the rigorous security and accounting of all of it. By virtue of the small quantities required for the nuclear fuel cycle, the opportunities and means to steal any significant amount of material are seriously limited.
Second off, everything else that is horribly wrong with the idea of using fuel cycle material in a nuclear bomb!
Stealing from the front end
Nuclear weapons depend on the extreme supercriticality of the fuel to make most of the material fission within a fraction of a second. Any delay and the weapon will blow itself apart before any significant release of energy. Such supercriticality cannot be produced in uranium that is not enriched to at least 90% uranium-235, so-called weapons grade uranium because the uranium-238 will absorb neutrons and poison the reaction. It is possible to achieve supercriticality from a very large mass of low enriched uranium (which is somewhat unsuitable for terrorist useage anyway since covert transportability is important) but it will not be able to explode like a nuclear bomb as it cannot be suitably compressed to achieve the necessary rate of reaction. Natural uranium is 0.7% uranium-235 and uranium used in reactor is commonly enriched to less than 5%. At no point in the fuel cycle is uranium anywhere near close to sufficiently enriched to be useable in a nuclear weapon.
Stealing from the back end
Trying to steal nuclear material from the back end of the nuclear fuel cycle presents one very obvious problem: it is highly radioactive. This means it is behind large amount of shielding make it hard to access, but it also means it will kill the terrorist the moment he gets close to it. But, if he was able to bring in all the professional equipment required to safely steal back end material, it would still be useless. The only significant quantity of fissile material in spent fuel is plutonium. But plutonium is a particularly awkward fuel to use in a bomb. It requires the use of an implosion device to rapidly compress the sphere in order to trigger the explosion. Any imperfection and the sphere will flatten rather detonate.
Moreover, in order to workable at all, plutonium needs to be more than 90% plutonium-239, while the kind found in spent fuel is a mix of various isotopes with typically no more than 55% plutonium-239. These isotopes make it more radioactive damaging the electronics of a bomb and making it more dangerous to handle. They also have a higher rate of spontaneous fission exacerbating the problem of pre-ignition, whereby the bomb blows itself apart before a large amount of energy is released.
The IAEA does efine an isotopic composition of plutonium with less than 80% plutonium-238 as "weapons useable" though this term is not well defined and no-one has successfully been able to manufacture a nuclear weapon using less than 90% plutonium-239.
Separating the isotopes of plutonium is difficult because of the similarities in their atomic masses. When a certain composition of plutonium is desired it is bred directly in specially designed reactors, with special reprocessing methods.
In short, nothing in the civil nuclear fuel cycle is particularly useful for terrorists to steal with the goal of making nuclear weapons.
Terrorists could still use stolen material for use in a "dirty bomb".
A "dirty bomb", more technically known as a radiological dispersal device, probably has highest the highest bark to bite ratio of any weapon. It suffers from the terminal problem that small scale dispersal is easy to clean up, while a large scale dispersal renders the radioactivity too diffuse to cause any harm to anyone.
Successfully stealing radioactive material is no simple matter. Materials from the fuel cycle are heavily guarded so access is difficult from the outset. Uranium is not very radioactive and so too ineffective to be at all useful. Spent fuel is too radioactive that it would kill anyone trying to steal some. Plutonium, which is the most valuable of all and hence the most secure, is also too unworkable. It is fairly radioactive making it awkward to handle, but not radioactive enough to render it a particularly potent fuel for an RDD. All these also would need to be ground down to powder to be effectively dispersed. Large chunks are too easy to clean up.
The best materials for use in an RDD are from industry or hospitals. They are more highly radioactive than nuclear fuels like uranium and plutonium and easier to access. However, they are not that much easier. They are heavily shielded and so inconvenient to steal. Removing the shielding for a more covert theft would be likely to kill the thieves quickly.
But if a terrorist was able to successfully construct an RDD without killing himself in the process, its potential is severely limited. Radioactive materials are very easy to detect. Moving around with an unshielded RDD is like carrying a locator beacon on you. A shielded RDD on the other hand would be too bulky to be practical.
If successfully detonated at its target, the dispersal would dilute the radioactivity to levels of ineffectiveness. The dosage to the population in the area would not amount to more than a chest x-ray for the likely isotopes to be used. The only way it could be more significant is if the material remains confined to a small area. Not only does that somewhat mute "mass destruction" label, but is also makes it very easy to clean up, no more difficult than a spill of toxic chemicals.
So the implausibility of the threat of a dirty bomb is based on multiple factors.
- Stealing suitable radioactive material is very problematic.
- Manufacturing the weapon is likely to kill the terrorist first (and if it does not, then the weapon is not even worthy of the label "radiological").
- Transporting the bomb to the target will likely lead to detection and interception.
- Once detonated, wide dispersal renders the effectiveness negligible, and poor dispersal renders the fallout easily cleaned up.
The power of a dirty bomb is in the reaction of fear it would provoke, made possible thanks to the sensationalist scaremongering of the media and anti-nuclear activists. It is they, through the malicious use of FUD, who can turn a weapon, nor more harmful than a conventional explosive, into a major catastrophe. The best way to fight it is the reject the Radiation Boogey Man.
A dirty bomb is a weapon of mass panic, not mass destruction.
The much larger quantity of radioactive material in a nuclear reactor could be unleashed by terrorists flying an airliner into it.
Figure 1- the steel reinforced concrete containment structure of Sizewell B can resist the impact of a large airliner.
What a waste of a perfectly good hijacked airliner! With all the skyscrapers and other public spaces lying around, attacking a nuclear reactor is probably the most ineffective way of causing mass destruction imaginable. Attacking the public areas directly guarantees instead death by the hundreds or even thousands. Flying the aircraft into the containment structure of a nuclear reactor will merely pose the risk of scratching the paintwork. These structures are specifically designed to resist such impacts. The fragments of the shattered aircraft will simply reflect off the structure. Nuclear reactors are not like the Twin Towers, they are close to the ground and smaller than the aircraft themselves meaning a sharp localised impact is not possible.
Even though even the best impacts are highly unlikely to breach containment, even in the event of the structure cracking, the steel containment and other emergency systems still pose a barrier to the dispersal of material, let alone significant enough material to pose a threat to public health beyond appeals to FUD.
So the problems with this are:
- Getting hold of a large aircraft is more difficult than before 9/11 since passengers will no longer simply remain passive in the hope that the negotiators will solve the problem.
- Being able to hit the reactor hard enough is a very difficult task and the probability of success is low.
- The hardest impacts are unlikely to breach the containment structure.
- Even if it was breached, there are still barriers to the dispersal of material.
- We have already seen a worst case scenario dispersal disaster and its effects were significantly less than feared.
The same applies to spent fuel pool and dry cask storage areas, which are significantly smaller than large aircraft at any rate and so could not possibly absorb even a fraction of the energy. In some cases, these are even below ground level offering greater protection. A study by the Electric Power Research Institute (pdf) corroborated this for current installations. With 9/11 engrained on everyone's minds in this age, newer designs will be even more robust.
Storage of highly toxic chemicals is significantly less robust and less well protected and so offers a more tempting target.
Terrorists could release spent fuel by bombing spent fuel shipments.
The containers used to carry spent fuel are built to withstand all manner of stresses. Homemade explosive that could be placed on the train hardly represent a threat to their integrity. Any explosive that could pose such a threat could easily level a large building, taking the occupants with it, doing greater harm instantly than the radioactive leak could.
Fallout
In every scenario cooked up for terrorists dispersing radioactive material, a common theme is apparent: despite the extremely large amount of effort and resources required to produce any dispersal, the risks to the population remain disproportionately low. We have already seen the worst nuclear power has to offer and the terrorists in Iraq cause worst carnage on a daily basis than Chernobyl has over twenty years. If the terrorists directed the energy they would invest towards a nuclear attack to conventional attacks on city centres and public spaces, as they tend to do, they could cause far worse. It should also be remembered that if this type of complicated terrorism appeals, there are vast stores of highly toxic chemicals, which are far, far more vulnerable.
The risk of terrorist success is extremely low and the risk to public health even if they were successful is not much greater when compared to what could be done with a conventional attack. These nuclear terrorist threats are pure FUD; turning relatively negligible risks, as compared to conventional attacks or attacks involving toxic chemicals in some form, into full blown potential disasters.