Consequently, the proponents of fusion reactors claim that when they are developed, fusion reactors will constitute a “perfect” energy source that will share none of the significant drawbacks of the much-maligned fission reactors.īut unlike what happens in solar fusion-which uses ordinary hydrogen-Earth-bound fusion reactors that burn neutron-rich isotopes have byproducts that are anything but harmless: Energetic neutron streams comprise 80 percent of the fusion energy output of deuterium-tritium reactions and 35 percent of deuterium-deuterium reactions. (Think of the numeral one with 24 zeroes after it.) This gargantuan advantage in fusion reactivity allows human-made fusion assemblies to be workable with a billion times lower particle density and a trillion times poorer energy confinement than the levels that the sun enjoys. Artificial (terrestrial) fusion schemes, on the other hand, are restricted to much lower particle densities and much more fleeting energy confinement, and are therefore compelled to use the heavier neutron-rich isotopes of hydrogen known as deuterium and tritium-which are 24 orders of magnitude more reactive than ordinary hydrogen.

Scaling down the sun. As noted above, fusion reactions in the sun burn ordinary hydrogen at enormous density and temperature, sustained by an effectively infinite confinement time, and the reaction products are benign helium isotopes.

I concluded that a fusion reactor would be far from perfect, and in some ways close to the opposite. In experiments to date, the energy input required to produce the temperatures and pressures that enable significant fusion reactions in hydrogen isotopes has far exceeded the fusion energy generated.Īs we move closer to our goal, however, it is time to ask: Is fusion really a “perfect” energy source? After having worked on nuclear fusion experiments for 25 years at the Princeton Plasma Physics Lab, I began to look at the fusion enterprise more dispassionately in my retirement. But to replicate that process of fusion here on Earth-where we don’t have the intense pressure created by the gravity of the sun’s core-we would need a temperature of at least 100 million degrees Celsius, or about six times hotter than the sun. Our sun constantly does fusion reactions all the time, burning ordinary hydrogen at enormous densities and temperatures. These pro-fusion advocates also say that fusion reactors would be incapable of generating the dangerous runaway chain reactions that lead to a meltdown-all drawbacks to the current fission schemes in nuclear power plants.Īnd, like fission, a fusion-powered nuclear reactor would have the enormous benefit of producing energy without emitting any carbon to warm up our planet’s atmosphere.īut there is a hitch: While it is, relatively speaking, rather straightforward to split an atom to produce energy (which is what happens in fission), it is a “grand scientific challenge” to fuse two hydrogen nuclei together to create helium isotopes (as occurs in fusion). Proponents claim that when useful commercial fusion reactors are developed, they would produce vast amounts of energy with little radioactive waste, forming little or no plutonium byproducts that could be used for nuclear weapons. Fusion reactors have long been touted as the “perfect” energy source.

Big reactor meltdown