Fissile

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Fissile

In nuclear engineering

Nuclear engineering

Nuclear engineering is the application of the breakdown of atomic nucleus and/or other sub-atomic physics, based on the principles of nuclear physics....
, a fissile material is one that is capable of sustaining a chain reaction

Chain reaction

A chain reaction is a sequence of reactions where a reactive product or by-product causes additional reactions to take place. In a chain reaction, positive feedback leads to a self-amplifying chain of events....
of nuclear fission

Nuclear fission

In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the atomic nucleus of an atom splits into smaller parts, often producing free neutrons and lighter atomic nucleus, which may eventually produce photons ....
.

All known fissile materials are capable of sustaining a chain reaction in which either thermal or slow neutrons or fast neutrons predominate. That is, they can all be used to fuel:

sile" is distinguished from "fissionable". "Fissionable" are any materials with atoms that can undergo nuclear fission.

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Encyclopedia

In nuclear engineering

Nuclear engineering

Chain reaction

Nuclear fission

A thermal reactor
Thermal reactor

A thermal reactor uses slow or thermal neutrons. Most power reactors are of this type. These type of reactors use a neutron moderator to slow neutrons until they approach the average kinetic energy of the surrounding particles, that is, to reduce the speed of the neutrons to low velocity thermal neutrons....
, with a neutron moderator
Neutron moderator

In nuclear engineering, a neutron moderator is a medium which reduces the speed of fast neutrons, thereby turning them into thermal neutrons capable of sustaining a nuclear chain reaction involving uranium-235....
A fast reactor, with no moderator
A nuclear explosive
Nuclear explosive

A nuclear explosive is an explosive device that derives its energy from nuclear reactions. Almost all nuclear explosive devices that have been designed and produced are nuclear weapons intended for warfare....

Fissile vs fissionable

"Fissile" is distinguished from "fissionable". "Fissionable" are any materials with atoms that can undergo nuclear fission. "Fissile" is defined to be materials that are fissionable by neutron

Neutron

The neutron is a subatomic particle with no net electric charge and a mass slightly larger than that of a proton.Neutrons are usually found in atomic nucleus....
s with low kinetic energy

Kinetic energy

The kinetic energy of an object is the extra energy which it possesses due to its motion. It is defined as the mechanical work needed to accelerate a body of a given mass from rest to its current velocity....
. "Fissile" thus, is more restrictive than "fissionable" — although all fissile materials are fissionable, not all fissionable materials are fissile. A few writers even restrict the term fissionable to include only fissile materials.

Notably, uranium-238

Uranium-238

Uranium-238 , is the most common Isotopes of uranium of uranium found in nature. When hit by a neutron, it becomes uranium-239 , an unstable isotope which radioactive decay into neptunium-239 , which then itself decays, with a half-life of 2.355 days, into plutonium-239 ....
is fissionable but not fissile. Neutrons produced by fission of e.g. U-235 have an energy of around 1 MeV (100 TJ/kg, i.e. a speed of 14,000 km/s) and usually do not cause fission of U-238, but neutrons produced by the deuterium

Deuterium

Deuterium, also called heavy hydrogen, is a stable isotope of hydrogen with a natural abundance in the oceans of Earth of approximately one atom in 6500 of hydrogen ....
-tritium

Tritium

Tritium is a radioactive isotope of hydrogen. The atomic nucleus of tritium contains one proton and two neutrons, whereas the nucleus of Hydrogen atom contains one proton and no neutrons....
fusion

Nuclear fusion

In nuclear physics and nuclear chemistry, nuclear fusion is the process by which multiple like-charged atomic nuclei join together to form a heavier nucleus....
reaction have an energy of 14.1 MeV (1400 TJ/kg, i.e. a speed of 52,000 km/s), and they can easily fission U-238 and other non-fissile actinides. The neutrons produced by this fission are again not fast enough to produce new fissions, so U-238 does not sustain a chain reaction

Nuclear chain reaction

A nuclear chain reaction occurs when one nuclear reaction causes an average of one or more nuclear reactions, thus leading to a self-propagating number of these reactions....
.

Fast fission

Fast fission

Fast fission is nuclear fission that occurs when a heavy atom absorbs a high-energy neutron, called a fast neutron, and splits. Most fissionable materials need thermal neutrons, which move slower....
of U-238 in the secondary stage of a nuclear weapon contributes greatly to yield

Nuclear weapon yield

The explosive yield of a nuclear weapon is the amount of energy, called the yield, discharged when a nuclear weapon is detonated, expressed usually in the equivalent mass of trinitrotoluene , either in kilotons or megatons , but sometimes also in terajoules ....
and to fallout

Nuclear fallout

Fallout is the residual radiation hazard from a nuclear explosion, so named because it "falls out" of the atmosphere into which it is spread during the explosion....
. The fast fission of U-238 also makes a significant contribution to the power output of some fast neutron reactor

Fast neutron reactor

A fast neutron reactor or simply a fast reactor is a category of nuclear reactor in which the fission chain reaction is sustained by fast neutrons....
s.

Fissile nuclides

Fissile nuclide

Nuclide

A nuclide is a species of atom characterized by the constitution of its Atomic nucleus and hence by the number of protons, the number of neutrons, and the energy content of the nucleus....
s in nuclear fuel

Nuclear fuel

Nuclear fuel is any material that can be consumed to derive nuclear energy, by analogy to chemical fuel that is Combustioned to derive energy....
s include:

Uranium-235
Uranium-235

Uranium-235 is an Isotopes of uranium that differs from the element's other common isotope, uranium-238, by its ability to cause a rapidly expanding nuclear fission chain reaction, i.e., it is fissile....
which occurs in natural uranium
Natural uranium

Natural uranium refers to refined uranium with the same isotopic ratio as found in nature. It contains 0.7 % uranium-235, 99.3 % uranium-238, and a trace of uranium-234 by weight....
and enriched uranium
Enriched uranium

Enriched uranium is a kind of uranium in which the percent composition of uranium-235 has been increased through the process of isotope separation....
Plutonium-239
Plutonium-239

Plutonium-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....
bred from uranium-238
Uranium-238

Uranium-238 , is the most common Isotopes of uranium of uranium found in nature. When hit by a neutron, it becomes uranium-239 , an unstable isotope which radioactive decay into neptunium-239 , which then itself decays, with a half-life of 2.355 days, into plutonium-239 ....
by neutron capture
Neutron capture

Neutron capture is a kind of nuclear reaction in which an atomic nucleus collides with one or more neutrons and they merge to form a heavier nucleus....
Plutonium-241
Plutonium-241

Plutonium-241 is an isotope of plutonium formed when plutonium-240 captures a neutron. Unlike 240Pu, 241Pu is fissionable, with a neutron absorption cross section about 1/3 greater than Pu-239, and a similar chance of fissioning on neutron absorption, around 73%....
bred from plutonium-240
Plutonium-240

Plutonium-240 is an isotope of the metal plutonium formed when plutonium-239 captures a neutron. About 62% to 73% of the time when Pu-239 captures a neutron it undergoes nuclear fission; the rest of the time it forms Pu-240....
by neutron capture. The Pu-240 comes from Pu-239 by the same process.
Uranium-233
Uranium-233

Uranium-233 is a fissile artificial Isotopes of uranium , which has been used in a few nuclear reactors and has been proposed for much wider use as a nuclear fuel....
bred from thorium-232
Thorium-232

Thorium-232 is the primary abundant nuclide of thorium. It is a slightly unstable radionuclide that is found in the earth's crust. It is a fertile material able to absorb a neutron and undergo Nuclear transmutation into a nuclide that is able to support nuclear fission ....
by neutron capture

In general, most actinide

Actinide

According to IUPAC nomenclature, the actinoid series encompasses the 15 chemical elements that lie between actinium and lawrencium included on the periodic table, with atomic numbers 89 - 103....
isotopes with an odd number of neutrons are fissile. Most nuclear fuels have an odd atomic mass number (N = the total number of protons and neutrons), and an even atomic number

Atomic number

In chemistry and physics, the atomic number is the number of protons found in the atomic nucleus of an atom. It is conventionally represented by the symbol Z....
(Z = the number of protons). This implies an odd number of neutrons.

More generally, elements with an even number of protons and an even number of neutrons, and located near a well-known curve in nuclear physics of atomic number vs. atomic mass number are more stable than others - and hence, less likely to undergo fission. They are more likely to "ignore" the neutron and let it go on its way, or else just to absorb the neutron. They are also less likely to undergo spontaneous fission, and have long half-lives for alpha or beta decay. Examples of these elements are U-238

U-238

U238 or U-238 may be:* German submarine U-238, a German World War II U-Boat * Uranium-238, the most common isotope of uranium...
and thorium-232

Thorium-232

Thorium-232 is the primary abundant nuclide of thorium. It is a slightly unstable radionuclide that is found in the earth's crust. It is a fertile material able to absorb a neutron and undergo Nuclear transmutation into a nuclide that is able to support nuclear fission ....
. On the other hand, isotopes with an odd number of neutrons and odd number of protons (odd Z, even N) are short-lived because they readily decay by beta-particle emission

Beta decay

In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted. In the case of electron emission, it is referred to as beta minus , while in the case of a positron emission as beta plus ....
to an isotope with an even number of neutrons and an even number of protons - (even Z, even N) - becoming much more stable.

Fissile nuclides do not have a 100% chance of fissioning on absorption of a neutron. The chance is dependent on the nuclide as well as neutron energy. For low and medium-energy neutrons, the neutron capture

Neutron capture

Neutron capture is a kind of nuclear reaction in which an atomic nucleus collides with one or more neutrons and they merge to form a heavier nucleus....
cross section

Cross section

Cross section can refer to:* Cross section , a three-piece rock band from the Mornington Peninsula, Australia* Cross section , the intersection of a 3-dimensional body with a plane...
s for fission, the cross section for neutron capture

Neutron capture

Neutron capture is a kind of nuclear reaction in which an atomic nucleus collides with one or more neutrons and they merge to form a heavier nucleus....
with emission of a gamma ray

Gamma ray

Gamma rays are a form of electromagnetic radiation produced by atom particle interactions, such as electron-positron annihilation or radioactive decay....
, and the percentage of non-fissions are:

Thermal neutrons				Epithermal neutrons
s_F	s_?	%		s_F	s_?	%
585	99	14.5%	²³⁵U	275	140	34%
750	271	26.5%	²³⁹Pu	300	200	40%
1010	361	26.3%	²⁴¹Pu	570	160	22%
531	46	8.0%	²³³U	760	140	16%

Nuclear fuel

To be a useful fuel for nuclear fission chain reactions, the material must:

Be in the region of the binding energy
Binding energy

Binding energy is the mechanical energy required to disassemble a whole into separate parts. A bound system has a lower potential energy than its constituent parts; this is what keeps the system together....
curve where a fission chain reaction is possible (i.e. above radium
Radium

Radium is a radioactive chemical element which has the symbol Ra and atomic number 88. Its appearance is almost pure white, but it readily oxidizes on exposure to air, turning black....
)
Have a high probability of fission on neutron capture
Neutron capture

Neutron capture is a kind of nuclear reaction in which an atomic nucleus collides with one or more neutrons and they merge to form a heavier nucleus....
Release two or more neutrons on average per neutron capture (which means a higher average number of them on each fission, to compensate for nonfissions, and absorptions in the moderator)
Have a reasonably long half life
Be available in suitable quantities

Legal controls

The International Atomic Energy Agency

International Atomic Energy Agency

The International Atomic Energy Agency is an international organization that seeks to promote the peaceful use of nuclear technology and to inhibit its use for nuclear weapon....
used to categorize fissile materials according to their security requirements for transportation:

Fissile Class I: no controls
Fissile Class II: limits on amount of materials shipped
Fissile Class III: special shipping arrangements are needed

but these classes were replaced in the mid 1990s.

Fissile

Fissile vs fissionable

Fissile nuclides

Nuclear fuel

Legal controls

See also