Uranium-233 ( or U-233) is a

fissile In nuclear engineering, fissile material is material that can undergo nuclear fission when struck by a neutron of low energy. A self-sustaining thermal Nuclear chain reaction#Fission chain reaction, chain reaction can only be achieved with fissil ...

isotope of uranium Uranium (U) is a naturally occurring radioactive element (radioelement) with no stable isotopes. It has two primordial isotopes, uranium-238 and uranium-235, that have long half-lives and are found in appreciable quantity in Earth's crust. The dec ...

that is bred from

thorium-232 Thorium-232 () is the main naturally occurring isotope of thorium, with a relative abundance of 99.98%. It has a half life of 14.05 billion years, which makes it the longest-lived isotope of thorium. It decays by alpha decay to radium-228; its de ...

as part of the

thorium fuel cycle The thorium fuel cycle is a nuclear fuel cycle that uses an isotope of thorium, , as the fertile material. In the reactor, is transmuted into the fissile artificial uranium isotope which is the nuclear fuel. Unlike natural uranium, natural ...

. Uranium-233 was investigated for use in

nuclear weapon A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission or atomic bomb) or a combination of fission and fusion reactions (thermonuclear weapon), producing a nuclear exp ...

s and as a reactor fuel. It has been used successfully in experimental

nuclear reactor A nuclear reactor is a device used to initiate and control a Nuclear fission, fission nuclear chain reaction. They are used for Nuclear power, commercial electricity, nuclear marine propulsion, marine propulsion, Weapons-grade plutonium, weapons ...

s and has been proposed for much wider use as a

nuclear fuel Nuclear fuel refers to any substance, typically fissile material, which is used by nuclear power stations or other atomic nucleus, nuclear devices to generate energy. Oxide fuel For fission reactors, the fuel (typically based on uranium) is ...

. It has a

half-life Half-life is a mathematical and scientific description of exponential or gradual decay. Half-life, half life or halflife may also refer to: Film * Half-Life (film), ''Half-Life'' (film), a 2008 independent film by Jennifer Phang * ''Half Life: ...

of 160,000 years. Uranium-233 is produced by the

neutron The neutron is a subatomic particle, symbol or , that has no electric charge, and a mass slightly greater than that of a proton. The Discovery of the neutron, neutron was discovered by James Chadwick in 1932, leading to the discovery of nucle ...

irradiation Irradiation is the process by which an object is exposed to radiation. An irradiator is a device used to expose an object to radiation, most often gamma radiation, for a variety of purposes. Irradiators may be used for sterilizing medical and p ...

of thorium-232. When thorium-232 absorbs a neutron, it becomes thorium-233, which has a half-life of only 22 minutes. Thorium-233 decays into

protactinium Protactinium is a chemical element; it has symbol Pa and atomic number 91. It is a dense, radioactive, silvery-gray actinide metal which readily reacts with oxygen, water vapor, and inorganic acids. It forms various chemical compounds, in which p ...

-233 through

beta decay In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which an atomic nucleus emits a beta particle (fast energetic electron or positron), transforming into an isobar of that nuclide. For example, beta decay of a neutron ...

. Protactinium-233 has a half-life of 27 days and beta decays into uranium-233; some proposed

molten salt reactor A molten-salt reactor (MSR) is a class of nuclear fission reactor in which the primary nuclear reactor coolant and/or the fuel is a mixture of molten salt with a fissile material. Two research MSRs operated in the United States in the mid-20th ...

designs attempt to physically isolate the protactinium from further neutron capture before beta decay can occur, to maintain the

neutron economy Neutron economy is defined as the ratio of excess neutron production divided by the rate of fission. The numbers are a weighted average based primarily on the energies of the neutrons. Nuclear fission is a process in which the nuclei of atoms a ...

(if it misses the ²³³U window, the next fissile target is ²³⁵U, meaning a total of 4 neutrons needed to trigger fission). ²³³U usually fissions on

neutron absorption Neutron capture is a nuclear reaction in which an atomic nucleus and one or more neutrons collide and merge to form a heavier nucleus. Since neutrons have no electric charge, they can enter a nucleus more easily than positively charged protons, wh ...

, but sometimes retains the neutron, becoming

uranium-234 Uranium-234 ( or U-234) is an isotope of uranium. In natural uranium and in uranium ore, 234U occurs as an indirect decay product of uranium-238, but it makes up only 0.0055% (55 parts per million, or 1/18,000) of the raw uranium because its half ...

. For both thermal neutrons and fast neutrons, the capture-to-fission ratio of uranium-233 is smaller than those of the other two major fissile fuels,

uranium-235 Uranium-235 ( or U-235) is an isotope of uranium making up about 0.72% of natural uranium. Unlike the predominant isotope uranium-238, it is fissile, i.e., it can sustain a nuclear chain reaction. It is the only fissile isotope that exists in nat ...

and

plutonium-239 Plutonium-239 ( or Pu-239) is an isotope of plutonium. Plutonium-239 is the primary fissile isotope used for the production of nuclear weapons, although uranium-235 is also used for that purpose. Plutonium-239 is also one of the three main iso ...

Fissile material

In 1946, the public first became informed of uranium-233 bred from thorium as "a third available source of nuclear energy and atom bombs" (in addition to

and

), following a

United Nations The United Nations (UN) is the Earth, global intergovernmental organization established by the signing of the Charter of the United Nations, UN Charter on 26 June 1945 with the stated purpose of maintaining international peace and internationa ...

report and a speech by

Glenn T. Seaborg Glenn Theodore Seaborg ( ; April 19, 1912February 25, 1999) was an American chemist whose involvement in the synthesis, discovery and investigation of ten transuranium elements earned him a share of the 1951 Nobel Prize in Chemistry. His work i ...

. The United States produced, over the course of the

Cold War The Cold War was a period of global Geopolitics, geopolitical rivalry between the United States (US) and the Soviet Union (USSR) and their respective allies, the capitalist Western Bloc and communist Eastern Bloc, which lasted from 1947 unt ...

, approximately 2 metric tons of uranium-233, in varying levels of chemical and isotopic purity. These were produced at the

Hanford Site The Hanford Site is a decommissioned nuclear production complex operated by the United States federal government on the Columbia River in Benton County in the U.S. state of Washington. It has also been known as SiteW and the Hanford Nuclear R ...

and

Savannah River Site The Savannah River Site (SRS), formerly the Savannah River Plant, is a U.S. Department of Energy (DOE) reservation in the United States, located in the state of South Carolina on land in Aiken, Allendale and Barnwell counties adjacent to the ...

in reactors that were designed for the production of plutonium-239.

Nuclear fuel

Uranium-233 has been used as a fuel in several different reactor types, and is proposed as a fuel for several new designs ( see thorium fuel cycle), all of which breed it from thorium. Uranium-233 can be bred in either

fast reactor A fast-neutron reactor (FNR) or fast-spectrum reactor or simply a fast reactor is a category of nuclear reactor in which the fission chain reaction is sustained by fast neutrons (carrying energies above 1 MeV, on average), as opposed to slow t ...

s or

thermal reactor A thermal-neutron reactor is a nuclear reactor that uses slow or thermal neutrons. ("Thermal" does not mean hot in an absolute sense, but means in thermal equilibrium with the medium it is interacting with, the reactor's fuel, moderator and stru ...

s, unlike the

uranium-238 Uranium-238 ( or U-238) is the most common isotope of uranium found in nature, with a relative abundance of 99%. Unlike uranium-235, it is non-fissile, which means it cannot sustain a chain reaction in a thermal-neutron reactor. However, it i ...

-based fuel cycles which require the superior

of a

in order to breed plutonium, that is, to produce more fissile material than is consumed. The long-term strategy of the nuclear power program of India, which has substantial thorium reserves, is to move to a nuclear program breeding uranium-233 from thorium feedstock.

Energy released

The fission of one atom of uranium-233 generates 197.9

MeV In physics, an electronvolt (symbol eV), also written electron-volt and electron volt, is the measure of an amount of kinetic energy gained by a single electron accelerating through an electric potential difference of one volt in vacuum. When us ...

= 3.171·10⁻¹¹ J (i.e. 19.09 TJ/ mol = 81.95 TJ/kg = 22764 MWh/kg that is 1.8 million times more than the same mass of diesel).

Weapon material

As a potential weapon material, pure uranium-233 is more similar to plutonium-239 than uranium-235 in terms of source (bred vs natural), half-life and

critical mass In nuclear engineering, critical mass is the minimum mass of the fissile material needed for a sustained nuclear chain reaction in a particular setup. The critical mass of a fissionable material depends upon its nuclear properties (specific ...

(both 4–5 kg in beryllium-reflected sphere). Unlike reactor-bred plutonium, it has a very low

spontaneous fission Spontaneous fission (SF) is a form of radioactive decay in which a heavy atomic nucleus splits into two or more lighter nuclei. In contrast to induced fission, there is no inciting particle to trigger the decay; it is a purely probabilistic proc ...

rate, which combined with its low critical mass made it initially attractive for compact gun-type weapons, such as small-diameter

artillery shells A shell, in a modern military context, is a projectile whose payload contains an explosive, incendiary, or other chemical filling. Originally it was called a bombshell, but "shell" has come to be unambiguous in a military context. A shell c ...

. A declassified 1966 memo from the US nuclear program stated that uranium-233 has been shown to be highly satisfactory as a weapons material, though it was only superior to plutonium in rare circumstances. It was claimed that if the existing weapons were based on uranium-233 instead of plutonium-239, Livermore would not be interested in switching to plutonium. The co-presence of

uranium-232 Uranium-232 () is an isotope of uranium. It has a half-life of around 69 years and is a side product in the thorium cycle. It has been cited as an obstacle to nuclear proliferation using 233U as the fissile material, because the intense gamma ...

"The US tested a few uranium-233 bombs, but the presence of uranium-232 in the uranium-233 was a problem; the uranium-232 is a copious alpha emitter and tended to 'poison' the uranium-233 bomb by knocking stray neutrons from impurities in the bomb material, leading to possible pre-detonation. Separation of the uranium-232 from the uranium-233 proved to be very difficult and not practical. The uranium-233 bomb was never deployed since plutonium-239 was becoming plentiful." can complicate the manufacture and use of uranium-233, though the Livermore memo indicates a likelihood that this complication can be worked around. While it is thus possible to use uranium-233 as the fissile material of a

, speculation aside, there is scant publicly available information on this isotope actually having been weaponized: * The United States detonated an experimental device in the 1955

Operation Teapot Operation Teapot was a series of 14 nuclear test explosions conducted at the Nevada Test Site in the first half of 1955. It was preceded by ''Operation Castle'', and followed by ''Operation Wigwam''. ''Wigwam'' was, administratively, a part of ...

"MET" test which used a plutonium/²³³U composite pit; its design was based on the plutonium/²³⁵U pit from the TX-7E, a prototype

Mark 7 nuclear bomb Mark 7 "Thor" (or Mk-7) was the first tactical fission bomb adopted by US armed forces. It was also the first weapon to be delivered via toss bombing with the help of the low-altitude bombing system (LABS). The weapon was tested in Operation Bust ...

design used in the 1951

Operation Buster-Jangle Operation or Operations may refer to: Arts, entertainment and media * ''Operation'' (game), a battery-operated board game that challenges dexterity * Operation (music), a term used in musical set theory * ''Operations'' (magazine), Multi-Man ...

"Easy" test. Although not an outright fizzle, MET's actual yield of 22

kiloton TNT equivalent is a convention for expressing energy, typically used to describe the energy released in an explosion. A ton of TNT equivalent is a unit of energy defined by convention to be (). It is the approximate energy released in the det ...

s was sufficiently below the predicted 33 kt that the information gathered was of limited value. * The

Soviet Union The Union of Soviet Socialist Republics. (USSR), commonly known as the Soviet Union, was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 until Dissolution of the Soviet ...

detonated its first

hydrogen bomb A thermonuclear weapon, fusion weapon or hydrogen bomb (H-bomb) is a second-generation nuclear weapon design. Its greater sophistication affords it vastly greater destructive power than first-generation nuclear bombs, a more compact size, a lo ...

the same year, the

RDS-37 RDS-37 () was the Soviet Union's first two-stage hydrogen bomb, first tested on 22 November 1955. The weapon had a nominal yield of approximately 3 megatons. It was scaled down to 1.6 megatons for the live test. Leading to the RDS-37 The R ...

, which contained a fissile core of ²³⁵U and ²³³U. * In 1998, as part of its

Pokhran-II Pokhran-II (''Operation Shakti'') was a series of five nuclear weapon tests conducted by India in May 1998. The bombs were detonated at the Indian Army's Pokhran Test Range in Rajasthan. It was the second instance of nuclear testing conducted ...

tests, India detonated an experimental ²³³U device of low-yield (0.2 kt) called Shakti V. The

B Reactor The B Reactor at the Hanford Site, near Richland, Washington, was the first large-scale nuclear reactor ever built, at 250 MW. It achieved criticality on September 26, 1944. The project was a key part of the Manhattan Project, the United States ...

and others at the

optimized for the production of

weapons-grade Weapons-grade nuclear material is any fissionable nuclear material that is pure enough to make a nuclear weapon and has properties that make it particularly suitable for nuclear weapons use. Plutonium and uranium in grades normally used in nuc ...

material have been used to manufacture ²³³U. Overall the United States is thought to have produced two tons of ²³³U, of various levels of purity, some with ²³²U impurity content as low as 6 ppm.

²³²U impurity

Production of ²³³U (through the irradiation of

) invariably produces small amounts of

as an impurity, because of parasitic (n,2n) reactions on uranium-233 itself, or on

protactinium-233 Protactinium (91Pa) has no stable isotopes. The four naturally occurring isotopes allow a standard atomic weight to be given. Thirty radioisotopes of protactinium have been characterized, ranging from 210Pa to 239Pa. The most stable isotope is 2 ...

, or on thorium-232: :²³²Th (n,γ) → ²³³Th (β⁻) → ²³³Pa (β⁻) → ²³³U (n,2n) → ²³²U :²³²Th (n,γ) → ²³³Th (β⁻) → ²³³Pa (n,2n) → ²³²Pa (β⁻)→ ²³²U :²³²Th (n,2n) → ²³¹Th (β⁻) → ²³¹Pa (n,γ) → ²³²Pa (β⁻) → ²³²U Another channel involves neutron capture reaction on small amounts of

thorium-230 Thorium (90Th) has seven naturally occurring isotopes but none are stable. One isotope, 232Th, is ''relatively'' stable, with a half-life of 1.405×1010 years, considerably longer than the age of the Earth, and even slightly longer than the gen ...

, which is a tiny fraction of natural thorium present due to the decay of

: :²³⁰Th (n,γ) → ²³¹Th (β⁻) → ²³¹Pa (n,γ) → ²³²Pa (β⁻) → ²³²U The

decay chain In nuclear science a decay chain refers to the predictable series of radioactive disintegrations undergone by the nuclei of certain unstable chemical elements. Radioactive isotopes do not usually decay directly to stable isotopes, but rather ...

of ²³²U quickly yields strong

gamma radiation A gamma ray, also known as gamma radiation (symbol ), is a penetrating form of electromagnetic radiation arising from high energy interactions like the radioactive decay of atomic nuclei or astronomical events like solar flares. It consists o ...

emitters. Thallium-208 is the strongest of these, at 2.6 MeV: : ²³²U (α, 68.9 y) : ²²⁸Th (α, 1.9 y) : ²²⁴Ra (α, 5.44 MeV, 3.6 d, with a γ of 0.24 MeV) : ²²⁰Rn (α, 6.29 MeV, 56 s, with a γ of 0.54 MeV) : ²¹⁶Po (α, 0.15 s) : ²¹²Pb (β⁻, 10.64 h) : ²¹²Bi (α, 61 min, 0.78 MeV) : ²⁰⁸Tl (β⁻, 1.8 MeV, 3 min, with a γ of 2.6 MeV) : ²⁰⁸Pb (stable) This makes manual handling in a

glove box A glovebox (or glove box) is a sealed container that is designed to allow one to manipulate objects where a separate atmosphere is desired. Built into the sides of the glovebox are gloves arranged in such a way that the user can place their hand ...

with only light shielding (as commonly done with

plutonium Plutonium is a chemical element; it has symbol Pu and atomic number 94. It is a silvery-gray actinide metal that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhibits six allotropes and four ...

) too hazardous, (except possibly in a short period immediately following chemical separation of the uranium from its decay products) and instead requiring complex remote manipulation for fuel fabrication. The hazards are significant even at 5

parts per million In science and engineering, the parts-per notation is a set of pseudo-units to describe the small values of miscellaneous dimensionless quantity, dimensionless quantities, e.g. mole fraction or mass fraction (chemistry), mass fraction. Since t ...

. Implosion nuclear weapons require ²³²U levels below 50 ppm (above which the ²³³U is considered "low grade";

cf. The abbreviation cf. (short for either Latin or , both meaning 'compare') is generally used in writing to refer the reader to other material to make a comparison with the topic being discussed. However some sources offer differing or even contr ...

"Standard weapon grade plutonium requires a ²⁴⁰Pu content of no more than 6.5%." which is 65,000 ppm, and the analogous ²³⁸Pu was produced in levels of 0.5% (5,000 ppm) or less).

Gun-type fission weapon Gun-type fission weapons are fission-based nuclear weapons whose design assembles their fissile material into a supercritical mass by the use of the "gun" method: shooting one piece of sub-critical material into another. Although this is someti ...

s additionally need low levels (1 ppm range) of light impurities, to keep the neutron generation low. The production of "clean" ²³³U, low in ²³²U, requires a few factors: 1) obtaining a relatively pure ²³²Th source, low in ²³⁰Th (which also transmutes to ²³²U), 2) moderating the incident neutrons to have an energy not higher that 6 MeV (too-high energy neutrons cause the ²³²Th (n,2n) → ²³¹Th reaction) and 3) removing the thorium sample from neutron flux before the ²³³U concentration builds up to a too high level, in order to avoid fissioning the ²³³U itself (which would produce energetic neutrons). The

Molten-Salt Reactor Experiment The Molten-Salt Reactor Experiment (MSRE) was an experimental molten-salt reactor research reactor at the Oak Ridge National Laboratory (ORNL) in Oak Ridge, Tennessee. This technology was researched through the 1960s, the reactor was constructed ...

(MSRE) used ²³³U, bred in

light water reactor The light-water reactor (LWR) is a type of thermal-neutron reactor that uses normal water, as opposed to heavy water, as both its coolant and neutron moderator; furthermore a solid form of fissile elements is used as fuel. Thermal-neutron react ...

s such as

Indian Point Energy Center Indian Point Energy Center (I.P.E.C.) is a now defunct three-unit nuclear power station located in Buchanan, just south of Peekskill, in Westchester County, New York. It sits on the east bank of the Hudson River, about north of Midtown Manh ...

, that was about 220 ppm ²³²U.

Further information

Thorium, from which ²³³U is bred, is roughly three to four times more abundant in the Earth's crust than uranium. The decay chain of ²³³U itself is part of the

neptunium series In nuclear science a decay chain refers to the predictable series of radioactive decay, radioactive disintegrations undergone by the nuclei of certain unstable chemical elements. Radionuclide, Radioactive isotopes do not usually decay directly ...

, the decay chain of its grandparent ²³⁷Np. Uses for uranium-233 include the production of the medical isotopes

actinium-225 Actinium-225 (225Ac, Ac-225) is an isotope of actinium. It undergoes alpha decay to francium-221 with a half-life of 10 days, and is an intermediate decay product in the neptunium series (the decay chain starting at neptunium-237, 237Np). Exc ...

and

bismuth-213 Bismuth (83Bi) has 41 known isotopes, ranging from 184Bi to 224Bi. Bismuth has no stable isotopes, but does have one very long-lived isotope; thus, the standard atomic weight can be given as . Although bismuth-209 is now known to be radioactive, i ...

which are among its daughters, low-mass nuclear reactors for space travel applications, use as an

isotopic tracer Isotopic labeling (or isotopic labelling) is a technique used to track the passage of an isotope (an atom with a detectable variation in neutron count) through chemical reaction, metabolic pathway, or a Cell (biology), biological cell. The reactant ...

, nuclear weapons research, and reactor fuel research including the

. The

radioisotope A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess numbers of either neutrons or protons, giving it excess nuclear energy, and making it unstable. This excess energy can be used in one of three ...

bismuth Bismuth is a chemical element; it has symbol Bi and atomic number 83. It is a post-transition metal and one of the pnictogens, with chemical properties resembling its lighter group 15 siblings arsenic and antimony. Elemental bismuth occurs nat ...

-213 is a decay product of uranium-233; it has promise for the treatment of certain types of

cancer Cancer is a group of diseases involving Cell growth#Disorders, abnormal cell growth with the potential to Invasion (cancer), invade or Metastasis, spread to other parts of the body. These contrast with benign tumors, which do not spread. Po ...

, including

acute myeloid leukemia Acute myeloid leukemia (AML) is a cancer of the myeloid line of blood cells, characterized by the rapid growth of abnormal cells that build up in the bone marrow and blood and interfere with haematopoiesis, normal blood cell production. Sympt ...

and cancers of the

pancreas The pancreas (plural pancreases, or pancreata) is an Organ (anatomy), organ of the Digestion, digestive system and endocrine system of vertebrates. In humans, it is located in the abdominal cavity, abdomen behind the stomach and functions as a ...

kidney In humans, the kidneys are two reddish-brown bean-shaped blood-filtering organ (anatomy), organs that are a multilobar, multipapillary form of mammalian kidneys, usually without signs of external lobulation. They are located on the left and rig ...

s and other

organs In a multicellular organism, an organ is a collection of tissues joined in a structural unit to serve a common function. In the hierarchy of life, an organ lies between tissue and an organ system. Tissues are formed from same type cells to a ...

Notes

{{Isotopes of uranium Actinides Isotopes of uranium Fissile materials Special nuclear materials