Nuclear Safety - Fusion Power

Fusion Power

Fusion power is a developing technology still under research. It relies on fusing rather than fissioning (splitting) atomic nuclei, using very different processes compared to current nuclear power plants. Commercial plants and prototype generators are not anticipated before 2030 - 2050. Fusion has significant safety advantages over current fission methods.

Nuclear fusion uses only tiny amounts of fuel at any time, and requires precisely controlled conditions to generate any net energy. Fusion reaction processes are so delicate that this level of safety is inherent; no elaborate failsafe mechanism is required. The fuel itself is extremely safe at any temperature outside that of a working fusion reactor and only tiny amounts are used. If the reactor were damaged or control impaired, or the fuel supply stops, reactions and heat generation would cease almost immediately. For the same reason, there is also no risk of a thermal runaway or nuclear meltdown, since any significant change will render the reactions unable to produce excess heat. In comparison, a fission reactor is typically loaded with enough fuel for one or several years, enough fuel in a sufficiently small space will always produce thermal runaway or "meltdown", and no additional fuel is necessary to keep the reaction going. In the event of fire, calculations suggest that the total amount of radioactive gases from a typical fusion plant would be so small, about 1 kg, that they would have diluted to legally acceptable limits by the time they blew as far as the plant's perimeter fence.

In general terms, fusion reactors also create less radioactive material than a fission reactor, the material it would create is less damaging biologically, and the radioactivity "falls off" within a time period that is within existing engineering capabilities. The main byproduct is a small amount of helium, which is harmless to life. Of more concern is tritium, which, like other isotopes of hydrogen, is a very light gas, and difficult to retain completely. Although volatile and biologically active, the health risk is lower than most other radioactive contaminants, due to tritium's short half-life (12 years), very low decay energy (~14.95 keV), and the fact that it does not bioaccumulate (instead being cycled out of the body as water, with a biological half-life of 7 to 14 days). However the effect of widespread fusion power may require attention in this area.

Unlike fission reactors, whose used fuel rods and other waste remains highly radioactive for thousands of years, most of the radioactive material in a fusion reactor would be the reactor core itself, which would be dangerous for about 50 years, and low-level waste another 100. Fusion reactors can more easily be designed using "low activation" materials that do not easily become radioactive, such as vanadium or carbon fiber. Although the core of a decommissioned reactor will be considerably more radioactive during those 50 years than fission waste, the relatively short time period makes waste management fairly straightforward. By 300 years it would have the same radioactivity as coal ash.

In some designs, powerful magnets are used. Failure of their support structure could allow the magnets to fly outward. The severity of this event would be similar to any other magnet quench, and can be effectively stopped with a containment building.

The overlap with nuclear weapons technology is limited. Copious neutrons could be used to breed plutonium for an atomic bomb, but not without extensive redesign of the reactor, so that production would be difficult to conceal. The theoretical and computational tools needed for hydrogen bomb design are closely related to those needed for inertial confinement fusion, but have very little in common with the more scientifically developed magnetic confinement fusion. Tritium, if used, is a component of the trigger of hydrogen bombs, but not a major problem in production.