Fissile Material Cut-off Treaty

Fissile Material Cut-off Treaty (FMCT) is also a proposed international treaty to prohibit the further production of fissile material for nuclear weapons or other explosive devices. Neither this treaty has been negotiated nor have its terms been defined.

A proposal has been made by United States that fissile material includes high-enriched uranium and plutonium (except plutonium that is over 80% Pu-238). According to a proposal by Russia, fissile material would be limited to weapons-grade uranium (with more than 90% U-235) and plutonium (with more than 90% Pu-239). Neither proposal would prohibit the production of fissile material for non-weapons purposes, including use in civil or naval nuclear reactors.

What is Fissile Material?

Any material which can be used to create a Nuclear Bomb is a fissile material. However the different draft FMCT documents define the fissile material differently.  The definition of fissile material in the U.S. draft FMCT is close to the definition adopted by the IAEA for weapon-usable or “direct-use” material: uranium enriched to more than 20% in U-235 or U-233 and plutonium containing less than 80% Pu-238.

Its worth note that U-238 is non fissile and U-235 is fissile.  Plutonium-239 is the isotope most useful for nuclear weapons. Plutonium-239 and 241 are fissile, meaning the nuclei of their atoms can break apart by being bombarded by slow moving thermal neutrons, releasing energy, gamma radiation and more neutrons.

Russia has proposed an alternative definition which bans only “weapon-grade” plutonium (Pu-239 and Pu-241) and uranium containing more than about 90 percent of the isotopes Pu-239 and U-235 respectively.