Special nuclear material

Special nuclear material is a term used by the Nuclear Regulatory Commission of the United States to classify fissile materials. The NRC divides special nuclear material (SNM) into three main categories, according to the risk and potential for its direct use in a clandestine nuclear weapon or for its use in the production of nuclear material for use in a nuclear weapon.

Highly Enriched Uranium
  1. Strategic SNM (SSNM)
  2. SNM of moderate strategic significance
  3. SNM of low strategic significance

Category I

235U5 kg
233U2 kg
239Pu2 kg
.4×235U+233U+239Pu2 kg

Category I is strategic special nuclear material.

Category I, SSNM means SSNM in any combination in a quantity of

This is often referred to as a formula quantity.

Category II

Category II is special nuclear material of moderate strategic significance.

Category III

Category III is special nuclear material of low strategic significance.

Uranium-235

Uranium-235 has different rules because it often is not in a pure form. Plutonium-239 is made in nuclear reactors by irradiating uranium-238 with neutrons, and uranium-233 is made the same way using thorium-232. Since they are different elements than the source material, they can be separated relatively easily through chemical differences. However, uranium-235 is produced from uranium ore, which contains 0.7% uranium-235 with most of the rest consisting of uranium-238. Since they are the same element, they behave in similar ways and must be separated by their slightly different masses. This is far more difficult than chemical separation, so varying levels of uranium-238 may remain after the first enrichment. If uranium is highly enriched, it can be used to make a nuclear weapon.

See also

Sources

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