Definitions for "Highly enriched uranium"
Keywords:  uranium, heu, isotope, weapons, fissile
Uranium in which the percentage of uranium-235 nuclei has been increased from the natural level of .7 percent to some level greater than 20 percent, usually around 90 percent.
Uranium in which the proportion of the fissile isotope, U-235, has been increased from the naturally occuring 0.71% to a high level, normally taken to be at least 90% for weapons purposes, but defined as anything over 20% for regulatory and safeguards purposes.
Uranium in which the naturally occurring U235 isotope - 0.7 percent in natural uranium, 99.3 percent U238 - is increased to 20 percent U235 or above, but usually to 90 percent or more. HEU is used in nuclear weapons, and in some types of research and submarine propulsion reactors.