Uranium-233 (²³³U or U-233) is a

fissile In nuclear engineering, fissile material is material capable of sustaining a nuclear fission chain reaction. By definition, fissile material can sustain a chain reaction with neutrons of thermal energy. The predominant neutron energy may be typ ...

isotope of uranium 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 billion years, which makes it the longest-lived isotope of thorium. It decays by alpha decay to radium-228; its decay ...

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 tho ...

. 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 bomb) or a combination of fission and fusion reactions ( thermonuclear bomb), producing a nuclear explosion. Both bom ...

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 fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat from nu ...

s and has been proposed for much wider use as a

nuclear fuel Nuclear fuel is material used in nuclear power stations to produce heat to power turbines. Heat is created when nuclear fuel undergoes nuclear fission. Most nuclear fuels contain heavy fissile actinide elements that are capable of undergoing ...

. It has a

half-life Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ato ...

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

neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons beh ...

irradiation Irradiation is the process by which an object is exposed to radiation. The exposure can originate from various sources, including natural sources. Most frequently the term refers to ionizing radiation, and to a level of radiation that will serve ...

of thorium-232. When thorium-232 absorbs a neutron, it becomes

thorium-233 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 has a half-life of only 22 minutes. Thorium-233 decays into

protactinium Protactinium (formerly protoactinium) is a chemical element with the symbol Pa and atomic number 91. It is a dense, silvery-gray actinide metal which readily reacts with oxygen, water vapor and inorganic acids. It forms various chemical compounds ...

-233 through

beta decay In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which a beta particle (fast energetic electron or positron) is emitted from an atomic nucleus, transforming the original nuclide to an isobar of that nuclide. For ...

. 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 molten salt mixture. Only two MSRs have ever operated, both research reactors in the United States. The 1950's Ai ...

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 an adjoint weighted average of the excess neutron production divided by an adjoint weighted average of the fission production. The distribution of neutron energies in a nuclear reactor differs from the f ...

(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, ...

, but sometimes retains the neutron, becoming

uranium-234 Uranium-234 (234U 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) of the raw uranium because its half-life ...

. The capture-to-fission ratio of uranium-233 is smaller than those of the other two major fissile fuels,

uranium-235 Uranium-235 (235U 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 exis ...

and

plutonium-239 Plutonium-239 (239Pu 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 ...

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 an intergovernmental organization whose stated purposes are to maintain international peace and international security, security, develop friendly relations among nations, achieve international cooperation, and be ...

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 is a term commonly used to refer to a period of geopolitical tension between the United States and the Soviet Union and their respective allies, the Western Bloc and the Eastern Bloc. The term '' cold war'' is used because the ...

, 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. The site has been known by many names, including SiteW a ...

and

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

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 or greater, on average), as opposed 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 struct ...

s, unlike the

uranium-238 Uranium-238 (238U 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 ...

-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 from rest through an electric potential difference of one volt in vacu ...

= 3.171·10⁻¹¹ J (i.e. 19.09 TJ/ mol = 81.95 TJ/kg).

Weapon material

Operation Teapot - MET (Military Effects Test)

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, a critical mass is the smallest amount of fissile material needed for a sustained nuclear chain reaction. The critical mass of a fissionable material depends upon its nuclear properties (specifically, its nuclear fissi ...

(both 4–5 kg in beryllium-reflected sphere). In 1994, the US government declassified a 1966 memo that states that uranium-233 has been shown to be highly satisfactory as a weapons material, though it is 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 gamm ...

"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 using the toss method with the help of the low-altitude bombing system (LABS). The weapon was tested in Operation ...

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. The is a unit of energy defined by that convention to be , which is the approximate energy released in the detonation of a t ...

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

Soviet Union The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen national ...

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 lowe ...

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 RDS-3 ...

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

Pokhran-II The Pokhran-II tests were a series of five nuclear bomb test explosions conducted by India at the Indian Army's Pokhran Test Range in May 1998. It was the second instance of nuclear testing conducted by India; the first test, code-named ''Smil ...

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. The project was a key part of the Manhattan Project, the United States nuclear weapons development program during World War II. I ...

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 or has properties that make it particularly suitable for nuclear weapons use. Plutonium and uranium in grades normally used in nucle ...

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 three naturally occurring isotopes allow a standard atomic weight to be given. Thirty radioisotopes of protactinium have been characterized, with the most stable being 231Pa with a half-life of 32, ...

, 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 gene ...

, 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, the decay chain refers to a series of radioactive decays of different radioactive decay products as a sequential series of transformations. It is also known as a "radioactive cascade". Most radioisotopes do not decay direct ...

of ²³²U quickly yields strong

gamma radiation A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically s ...

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 radioactive chemical element with the symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhibi ...

) 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 A remote manipulator, also known as a telefactor, telemanipulator, or waldo (after the 1942 short story "Waldo" by Robert A. Heinlein which features a man who invents and uses such devices), is a device which, through electronic, hydraulic, or mec ...

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 small values of miscellaneous dimensionless quantities, e.g. mole fraction or mass fraction. Since these fractions are quantity-per-quantity measures, they ...

Implosion nuclear weapon Nuclear weapon designs are physical, chemical, and engineering arrangements that cause the physics package of a nuclear weapon to detonate. There are three existing basic design types: * pure fission weapons, the simplest and least technically ...

s require ²³²U levels below 50 ppm (above which the ²³³U is considered "low grade";

cf. The abbreviation ''cf.'' (short for the la, confer/conferatur, both meaning "compare") is used in writing to refer the reader to other material to make a comparison with the topic being discussed. Style guides recommend that ''cf.'' be used onl ...

"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 sometim ...

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). This technology was researched through the 1960s, the reactor was constructed by 1964, it went critica ...

(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 reacto ...

s such as

Indian Point Energy Center Indian Point Energy Center (I.P.E.C.) is a three-unit nuclear power plant 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 Manhattan. Th ...

, 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, the decay chain refers to a series of radioactive decays of different radioactive decay products as a sequential series of transformations. It is also known as a "radioactive cascade". Most radioisotopes do not 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 237Np). Except for minus ...

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 unstable, it h ...

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 a reaction, metabolic pathway, or Cell (biology), cell. The reactant is 'labeled' by rep ...

, 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 nuclear energy, making it unstable. This excess energy can be used in one of three ways: emitted from the nucleus as gamma radiation; transferr ...

bismuth Bismuth is a chemical element with the Symbol (chemistry), 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 ...

-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 abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...

, 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 normal blood cell production. Symptoms may includ ...

and cancers of the

pancreas The pancreas is an organ of the digestive system and endocrine system of vertebrates. In humans, it is located in the abdomen behind the stomach and functions as a gland. The pancreas is a mixed or heterocrine gland, i.e. it has both an end ...

kidney The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; blood ...

s and other

organs In biology, 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 act together in a f ...

Notes

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