Fusion reactors: Not what they’re cracked up to be | Bulletin of the Atomic Scientists

Long touted as the “perfect” energy source, fusion reactors share many drawbacks with fission—and even add a few new ones of their own.


  • Terrestrial fusion reactors need to use tritium (neutron-rich hydrogen isotope) as fuel.
  • Tritium fuel can only be acquired from fusion and fission reactors, and it cannot be fully replenished from the fusion reactor itself.
  • The power required for a power plant to operate itself is called “parasitic power drain”. Fusion reactors require an enormous amount of power to operate and this parasitic power drain forces fusion reactors be very large in order to be economical. Furthermore, 75 to 100 megawatts of parasitic electric power is used (e.g. for refrigerators) even when the fusion reactor is off (e.g. for maintenance).
  • Deuterium-tritium reactions’ fusion energy output is 80 percent energetic neutron streams (deuterium-deuterium is 35 percent), not usable electricity or heat. These streams lead to radiation damage to structures, radioactive waste, the need for biological shielding, and the potential for the production of weapons-grade plutonium 239.
  • Neutron streams must be cooled to produce usable heat, but this incurs radiation damage to the reaction vessel (swelling and fracturing) and everything that it irradiates (e.g. coolant, the vessel, fuel assemblies,
    non-structural components) will become radioactive waste over time.
  • production of plutonium 239 is possible in a fusion reactor simply by placing natural or depleted uranium oxide at any location where neutrons of any energy are flying about. The ocean of slowing-down neutrons that results from scattering of the streaming fusion neutrons on the reaction vessel permeates every nook and cranny of the reactor interior, including appendages to the reaction vessel. Slower neutrons will be readily soaked up by uranium 238, whose cross section for neutron absorption increases with decreasing neutron energy.

  • Tritium handling is hard and tritium is environmentally hazardous.
  • Deuterium and tritium are themselves usable as boosting/supplemental components to nuclear weapons.
  • a fusion reactor would have the lowest water efficiency of any type of thermal power plant, whether fossil or nuclear.

To sum up, fusion reactors face some unique problems: a lack of natural fuel supply (tritium), and large and irreducible electrical energy drains to offset. Because 80 percent of the energy in any reactor fueled by deuterium and tritium appears in the form of neutron streams, it is inescapable that such reactors share many of the drawbacks of fission reactors—including the production of large masses of radioactive waste and serious radiation damage to reactor components. These problems are endemic to any type of fusion reactor fueled with deuterium-tritium, so abandoning tokamaks for some other confinement concept can provide no relief.

Source: Fusion reactors: Not what they’re cracked up to be | Bulletin of the Atomic Scientists by Daniel Jassby