Weapons-grade uranium

Weapons-grade uranium refers to uranium that has been enriched to a very high concentration of the fissile isotope uranium-235 (U-235), typically 90% or more. This level of enrichment is necessary to build an efficient and compact nuclear weapon.

Key Points:

• Natural uranium contains about 0.7% U-235 (the rest is mostly U-238).

• Low-enriched uranium (LEU) used in nuclear power reactors is enriched to 3–5% U-235.

• Highly enriched uranium (HEU) is enriched above 20% U-235.

• Weapons-grade uranium is enriched to ≥90% U-235, which enables:

• A fast, uncontrolled chain reaction needed for a nuclear explosion.

• A smaller, lighter, and more powerful warhead design.

Why is it dangerous?

Weapons-grade uranium allows a country to:

• Build a nuclear bomb with much shorter preparation time (“breakout time”).

• Evade international safeguards if diverted from peaceful uses.

• Pose a major non-proliferation threat.

In the Iran context, their 60% enriched uranium stockpile is not yet weapons-grade, but it's very close—only a short enrichment step away. That’s why the global concern is so high.

HEU (Highly Enriched Uranium) – Uses & Characteristics

• Definition: Uranium enriched to above 20% U-235  (60% enriched uranium stockpile in Iran case)

• . Weapons-grade is typically 90%+.

• Pilot enrichment & naval use:

  • Can be used in pilot enrichment cascades to develop or study nuclear reactors for naval propulsion (e.g., submarines).

  • Advantage: At 60% enrichment, the same amount of energy can be stored in a smaller volume, so fewer cylinders are needed for storage and transport.

• Strategic military implication:

  • HEU is a short step away from weapons-grade, making it a sensitive material for non-proliferation.

LEU (Low Enriched Uranium) – Uses & Practicality

• Definition: Uranium enriched to below 20%, commonly 3–5% for civilian reactors.

• Main use: Fuel for nuclear power plants (like pressurized water reactors).

• Down-blending HEU to LEU:

  • Technically possible to dilute HEU (like 60%) to get 19.75%, 5%, or 3% for various reactor uses.

  • But economically irrational because:

    • Requires prior energy-intensive enrichment just to dilute it later.

    • LEU can be more efficiently produced directly from natural uranium using conventional centrifuge methods.

Why Down-Blending HEU is Inefficient

• It’s more practical and cheaper to:

  • Enrich natural uranium to LEU levels using centrifuges, or

  • Mix 20% uranium with natural/depleted uranium for lower grades.

• Thus, HEU stockpiles are not preferred for civilian energy due to:

  • Cost,

  • Proliferation risk, and

  • Security/storage issues.