American researchers have shown that prospective magnetic fusion power systems would pose a much lower risk of being used for the production of weapon-usable materials than nuclear fission reactors and their associated fuel cycle.

The researchers, from Princeton University, found that if nuclear fusion power plants are designed to accommodate appropriate safeguards, there is little risk of fissile materials being produced for weapons, either secretly or overtly.

Their results have been published today, 29 March, by IOP Publishing in the journal Nuclear Fusion.

In the study, the researchers undertook a quantitative assessment of the risks of proliferation – the spreading of nuclear materials for use in weapons – that could be associated with future magnetic fusion energy power systems in three different scenarios and compared them to the risks associated with nuclear fission.

Co-author of the study Alex Glaser summarizes: "We found that the proliferation risks from fusion are low compared with fission, assuming that IAEA safeguards are applied in both cases."

The three scenarios were: the clandestine production of weapon-usable material in an undeclared facility; the covert production of such material in a declared facility; and the production of material in a breakout scenario where the effort is not concealed.

Firstly, their findings showed that it is highly implausible that a small-scale nuclear fusion system could be built, and then operated, in a clandestine fashion to produce material for even one weapon in two years, due to the large size and power consumption of the facility that would be required; it would be clearly visible by, for example, the continuous power it would consume and ultimately have to dissipate – at least some 40 MW.

In comparison, first-generation centrifuge plants used to produce highly enriched uranium for fission power plants are much less conspicuous and can be operated to produce material for one weapon per year with less than 0.5 MW of power, similar to many industrial operations.

The researchers then used a set of supercomputer simulations to determine the quantities of weapons materials that could be produced with a commercial-size fusion power plant. While the production potential is significant in principle, it would be easy for inspectors to detect the covert production of weapon-usable material in a declared nuclear fusion power plant.

The final scenario examined was breakout, where weapon-usable material is produced as quickly as possible and without concealment. The researchers estimate that the minimum period that would be required after breakout to produce any weapon-usable material in a fusion power plant would be one to two months. They also note that fusion power plants require many supporting facilities, such as power inputs and cooling towers, which could potentially be shut down without risk of nuclear contamination, and therefore prevent material from being produced.