U-235 Concentration needed for:

Power reactor:

  • 3-5% of U-235
  • This level of uranium is called Low Enriched Uranium (LEU)

Nuclear weapon:

  • 90% of U-235
  • Referred to as Weapons Grade or Highly Enriched Uranium (HEU)

All of the uranium isotopes are fissionable materials that can undergo nuclear fission reactions (see http://paducahvision.org/nuclearenergy.html).  Uranium-235 is a “fissile” material meaning that it is capable of undergoing a self-generated and self-sustained nuclear fission reaction.  Uranium-234 and U-238 are capable of a fission reaction only when their fission reaction is initiated by an outside energy source such as bombardment by neutrons.

Use of uranium as a reactor fuel or weapons component requires the U-235 isotope to be “enriched” until the U-235 abundance exceeds that of natural uranium (see http://paducahvision.org/uranium-enrichment.html).  Typical U-235 enrichment abundance for use as a nuclear fuel is 2 – 5%.  One kilogram of enriched uranium-235 has the capacity to produce as much energy as 1,500,000 kilograms (1,500 tons) of coal.