Fusion reactors could allow a country to accelerate its development of nuclear weapons, producing the necessary radioactive ingredients in as little as a few weeks.
Nuclear weapons need specific radioactive isotopes, normally uranium-235 or plutonium-239, that can be easily split and start a chain reaction. This so-called fissile material is rare in nature, but can be produced artificially by a source that produces a lot of neutrons, such as a nuclear fission reactor of the kind in use today.
As such, the construction and use of nuclear power plants can be restricted by international agreements, such as the Joint Comprehensive Plan of Action, a deal designed to prevent Iran developing nuclear weapons.
Advertisement
The risk posed by more advanced nuclear fusion reactors, which are currently in development, isn鈥檛 understood as well. But now at the Massachusetts Institute of Technology and his colleagues have calculated how long it would take for such a reactor to produce enough fissile material for a nuclear weapon, finding that it could be much less than the minimum level of one year generally considered necessary to stop weapon proliferation.
To produce fissile material in this way, a country would need a large quantity of non-fissile uranium-238. It would also have to find a way to place it near the fusion reactor, such as in the breeding blanket, a layer of material that is used to make further fuel for the reactor and to absorb heat.
鈥淚 have all this uranium that I can鈥檛 use for a weapon, but I know if I can put some extra neutrons in there, I鈥檒l get my weapons material. I just need to make some neutrons,鈥� says Ball. 鈥淲ell, here鈥檚 my fancy new fusion reactor that makes an incredible number of neutrons, a truly astounding number of neutrons, that I can use to convert the material.鈥�
Ball and his team built a computer model of a doughnut-shaped tokamak fusion reactor and simulated how billions of neutrons produced in the reactor would breed fissile plutonium from uranium that had been placed in the breeding blanket.
They found that producing a significant amount of fissile material, defined by the International Atomic Energy Agency (IAEA) as 8 kilograms of plutonium, could be achieved in less than a year with 5 tonnes of starting uranium, or in as little as two weeks if you began with 50 tonnes.
Producing fissile material in shorter timescales could be a concern, says at the University of Liverpool, UK, but current fission reactors can already be used to enrich nuclear material as they also produce large amounts of neutrons. This is prevented by international bodies like the IAEA and agreements such as the Treaty on the Non-Proliferation of Nuclear Weapons, which enforce strict monitoring on countries鈥� use of material that could be used to produce fissile material. These processes should also help prevent proliferation in the case of fusion reactors too, says Powell.
Ball and his team suggest one physical measure that could help avoid the threat is to require that nations building fusion reactors use more lithium-6 in their breeding blanket, an isotope that absorbs neutrons. With this in place, the time taken to enrich the uranium will be increased, says Ball.
arxiv
Article amended on 10 May 2024
We have clarified the details of the computer simulation and the potential steps to avoid nuclear weapon proliferation
