Natural uranium (NU or U
nat) refers to
uranium
Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...
with the same
isotopic ratio
In physics, natural abundance (NA) refers to the abundance of isotopes of a chemical element as naturally found on a planet. The relative atomic mass (a weighted average, weighted by mole-fraction abundance figures) of these isotopes is the at ...
as found in nature. It contains 0.711%
uranium-235, 99.284%
uranium-238, and a trace of
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 ...
by weight (0.0055%). Approximately 2.2% of its
radioactivity comes from uranium-235, 48.6% from uranium-238, and 49.2% from uranium-234.
Natural uranium can be used to fuel both low- and high-power
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 fr ...
s. Historically,
graphite-moderated reactors and
heavy water-moderated reactors have been fueled with natural uranium in the pure metal (U) or
uranium dioxide (UO
2)
ceramic
A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelain, ...
forms. However, experimental fuelings with
uranium trioxide (UO
3) and
triuranium octaoxide (U
3O
8) have shown promise.
The 0.72% uranium-235 is not sufficient to produce a self-sustaining critical
chain reaction in
light water reactors or
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 bomb ...
s; these applications must use
enriched uranium. Nuclear weapons take a concentration of 90% uranium-235, and light water reactors require a concentration of roughly 3% uranium-235.
Unenriched natural uranium is appropriate fuel for a
heavy-water reactor
A pressurized heavy-water reactor (PHWR) is a nuclear reactor that uses heavy water ( deuterium oxide D2O) as its coolant and neutron moderator. PHWRs frequently use natural uranium as fuel, but sometimes also use very low enriched uranium. ...
, like a
CANDU reactor.
On rare occasions, earlier in geologic history when uranium-235 was more abundant, uranium ore was found to have naturally engaged in fission, forming
natural nuclear fission reactor
A natural nuclear fission reactor is a uranium deposit where self-sustaining nuclear chain reactions occur. The conditions under which a natural nuclear reactor could exist had been predicted in 1956 by Japanese American chemist Paul Kuroda. ...
s. Uranium-235 decays at a faster rate (
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 ...
of 700 million years) compared to uranium-238, which decays extremely slowly (half-life of 4.5 billion years). Therefore, a billion years ago, there was more than double the uranium-235 compared to now.
During the
Manhattan Project
The Manhattan Project was a research and development undertaking during World War II that produced the first nuclear weapons. It was led by the United States with the support of the United Kingdom and Canada. From 1942 to 1946, the project w ...
, the name ''Tuballoy'' was used to refer to natural uranium in the refined condition; this term is still in occasional use. Uranium was also codenamed "X-Metal" during World War II. Similarly, enriched uranium was referred to as ''Oralloy'' (
Oak Ridge alloy), and
depleted uranium was referred to as ''Depletalloy'' (depleted alloy).
See also
*
List of uranium mines
*
Nuclear engineering
*
Nuclear fuel cycle
*
Nuclear physics
Nuclear physics is the field of physics that studies atomic nuclei and their constituents and interactions, in addition to the study of other forms of nuclear matter.
Nuclear physics should not be confused with atomic physics, which studies t ...
*
Nuclear chemistry
Nuclear chemistry is the sub-field of chemistry dealing with radioactivity, nuclear processes, and transformations in the nuclei of atoms, such as nuclear transmutation and nuclear properties.
It is the chemistry of radioactive elements such as ...
References
*Design Parameters for a Natural Uranium Fueled Nuclear Reactor, C. M. Hopper ''et al.'', ORNL/TM-2002/240, November 2002.
{{reflist
External links
The evolution of CANDU fuel cycles
Uranium
Nuclear fuels
Nuclear materials