What are High Enriched Uranium (HEU) and Low Enriched Uranium (LEU)?
The International Atomic Energy Agency defines HEU as uranium with a concentration of the isotope 235U of 20% or more. Ninety percent 235U is considered weapons grade, but all HEU is usable in nuclear weapons. LEU is Uranium with a 235U concentration below 20% and cannot sustain the chain reaction necessary for a nuclear explosion. Approximately 2/3 of the total services necessary to produce weapons-grade uranium goes into enriching it from natural uranium (usually .7% 235U) to LEU (3.6% 235U for power generation).
