Special nuclear material
Encyclopedia
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.
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.
s by irradiating uranium-238
with neutron
s, 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 mass
es. 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
.
Nuclear Regulatory Commission
The Nuclear Regulatory Commission is an independent agency of the United States government that was established by the Energy Reorganization Act of 1974 from the United States Atomic Energy Commission, and was first opened January 19, 1975...
of the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
to classify fissile
Fissile
In nuclear engineering, a fissile material is one that is capable of sustaining a chain reaction of nuclear fission. By definition, fissile materials can sustain a chain reaction with neutrons of any energy. The predominant neutron energy may be typified by either slow neutrons or fast neutrons...
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
Nuclear weapon
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion. Both reactions release vast quantities of energy from relatively small amounts of matter. The first fission bomb test released the same amount...
or for its use in the production of nuclear material
Nuclear material
Nuclear material refers to the metals uranium, plutonium, and thorium, in any form, according to the IAEA. This is differentiated further into "source material", consisting of natural and depleted uranium, and "special fissionable material", consisting of enriched uranium , uranium-233, and...
for use in a nuclear weapon.
- Strategic SNM (SSNM)
- SNM of moderate strategic significance
- SNM of low strategic significance
Category I
| 235U | 5 kg |
| 233U | 2 kg |
| 239Pu | 2 kg |
| .4×235U+233U+239Pu | 2 kg |
Category I is strategic special nuclear material.
- Uranium-235Uranium-235- References :* .* DOE Fundamentals handbook: Nuclear Physics and Reactor theory , .* A piece of U-235 the size of a grain of rice can produce energy equal to that contained in three tons of coal or fourteen barrels of oil. -External links:* * * one of the earliest articles on U-235 for the...
(contained in highly enriched uranium: >20% or more 235U), - Uranium-233Uranium-233Uranium-233 is a fissile isotope of uranium, bred from Thorium as part of the thorium fuel cycle. It has been used in a few nuclear reactors and has been proposed for much wider use as a nuclear fuel. It has a half-life of 160,000 years....
, or - Plutonium-239Plutonium-239Plutonium-239 is an isotope of plutonium. Plutonium-239 is the primary fissile isotope used for the production of nuclear weapons, although uranium-235 has also been used and is currently the secondary isotope. Plutonium-239 is also one of the three main isotopes demonstrated usable as fuel in...
.
Category I, SSNM means SSNM in any combination in a quantity of
- 2 kilograms(4.4 pounds) or more of Pu-239; or
- 5 kilograms or more of U-235(11 pounds) (contained in uranium enriched to 20 percent or more in the U-235 isotope); or
- 2 kilograms(4.4 pounds) or more of U-233; or
- 5 kilograms(11 pounds) or more in any combination computed by the equation grams = (grams contained U-235) + 2.5 (grams U-233 + grams Pu-239).
This is often referred to as a formula quantity.
Category II
Category II is special nuclear material of moderate strategic significance.- Less than a formula quantity of strategic special nuclear material but more than 1,000 grams of uranium-235 (contained in uranium enriched to 20 percent or more in the U-235 isotope) or more than 500 grams of uranium-233 or plutonium-239, or in a combined quantity of more than 1,000 grams(2.2 pounds) when computed by the equation grams = (grams contained U-235) + 2 (grams U-233 + grams Pu-239); or
- 10,000 grams(22 pounds) or more of uranium-235 (contained in uranium enriched to 10 percent or more but less than 20 percent in the U-235 isotope).
Category III
Category III is special nuclear material of low strategic significance.- Less than an amount of special nuclear material of moderate strategic significance (see category II above) but more than 15 grams(0.5 oz.) of uranium-235 (contained in uranium enriched to 20 percent or more in U-235 isotope) or 15 grams of uranium-233 or 15 grams of plutonium-239 or the combination of 15 grams when computed by the equation grams = (grams contained U-235) + (grams Pu-239) + (grams U-233); or
- Less than 10,000 grams but more than 1,000 grams of uranium-235 (contained in uranium enriched to 10 percent or more but less than 20 percent in the U-235 isotope); or
- 10,000 grams or more of uranium-235 (contained in uranium enriched above natural but less than 10 percent in the U-235 isotope).
Uranium-235
Uranium-235 has different rules because it often is not in a pure form. Plutonium-239 is made in nuclear reactorNuclear reactor
A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...
s by irradiating uranium-238
Uranium-238
Uranium-238 is the most common isotope of uranium found in nature. It is not fissile, but is a fertile material: it can capture a slow neutron and after two beta decays become fissile plutonium-239...
with neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
s, and uranium-233 is made the same way using thorium-232. Since they are different elements
Chemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...
than the source material, they can be separated relatively easily through chemical differences. However, uranium-235 is produced from uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
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 mass
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...
es. 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
Nuclear weapon
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion. Both reactions release vast quantities of energy from relatively small amounts of matter. The first fission bomb test released the same amount...
.