A. Glaser and R.J. Goldston of Princeton University have conducted research into the risks of nuclear materials associated with proposed fusion power plants being used in the productions of nuclear weapons .
The authors identify three main scenarios
- Clandestine production of weapon-usable material in an undeclared facility.
- Covert production of such material in a declared facility.
- Use of a declared facility in a breakout scenario, in which a state begins production of fissile material without concealing the effort.
In the reserach the authors made a quantitative assessment of the risk of nuclear proliferation, that is using the materials produced in fusion plants for weapons.
They show that it is not feasible to build a small-scale nuclear fusion system capable of producing weapons within a couple of years, in a clandestine manner. In essence such a plant could not remain invisible due to the power consumption and dissipation. Such a plant should be quite easy to spot.
This is very different to nuclear fission plants, which can be much smaller in size and use far less power. Such fission plants’ power consumption is similar to lots of industrial processes and so a clandestine fission production of weapons could be hidden in an industrial setting.
The second scenario is more plausible, but it would be very easy for inspectors to identify materials being used for weapon production in any declared open fusion plant. Again, this is not quite so easy in fission plants.
The last scenario proposed is breakout; weapon-usable material is produced very quickly and without concealment. The hope being the producers can get a weapon ready before anyone can stop them. The minimum period to produce any weapon-usable material in a fusion power plant would be one to two months, as estimated by the authors.
It is also easier and safer to stop a fusion plant than a fission plant once in operation. There are lots of other supporting infrastructure needed in fusion like the power input and cooling towers. All these could be interrupted with no risk of nuclear contamination.
In all, fusion power stations would be safer and have less risk for nuclear proliferation than existing fission technologies.
 A. Glaser and R.J. Goldston, Proliferation risks of magnetic fusion energy: clandestine production, covert production and breakout, Nucl. Fusion 52 04, 2012.