Fusion Power and Nuclear Weapons

by Roger Webb

If you’re a conscientious objector to nuclear weapons and a conscientious proponent of fusion power, can you work on power but not the weapons at the same time? A look at the science involved may give us an answer.

It turns out there are radioactive byproducts in a purely deuterium (1 neutron + 1 proton) fusion reaction. Two deuterons fuse to form tritium (2 neutrons + 1 proton) and an energetic proton in one reaction pathway, and helium and an energetic neutron in the second reaction pathway.

The tritium atom is the radioactive byproduct. It has a half-life of about 12 years, which is not bad considering the half-lives of fission byproducts. The energetic neutron is problematic, because it can be absorbed by other nuclei, which could then become unstable.

Magnetic fusion reactors could make use of the extra neutron by surrounding the core with a shield of liquid lithium. The lithium atom absorbs the neutron and breaks up into a helium atom and a tritium atom. The tritium can be reclaimed and used as fuel for the reactor.

It turns out that the ideal materials for fusion reactions are deuterium and helium-3, which fuse to form helium-4 (regular helium) and regular hydrogen. There are no radioactive byproducts and no neutrons formed. However, the only available helium-3 on earth is a byproduct of nuclear weapons production.

The good (?) news is there is plenty of helium-3 ready to be strip-mined on the Moon, where it is deposited by the solar winds. At least strip mining has only the primary effects of soil erosion on the Moon...

So, if the Moon ever joins the U.N., its principal trading material would be He-3, which would be a clean and virtually inexhaustible supply of fuel for Earth’s fusion reactors.

Just wanted to get the science right.