A series of chemical elements with atomic numbers from 89 to 109.
Uranium having a higher abundance of fissile isotopes than natural uranium.
Enriched uranium is considered a special fissionable material.
Enrichment plant (or isotope separation plant)
An installation for
the separation of isotopes of uranium to increase the abundance of U-235. The main
isotope separation processes used in enrichment plants are gas centrifuge or gaseous
diffusion processes operating with uranium hexafluoride (UF6) (which is also the
feed material for aerodynamic and molecular laser processes). Other isotope separation
processes include electromagnetic, chemical exchange, ion exchange, and atomic
vapor laser and plasma processes.
Fast reactor (fast neutron spectrum reactor)
A reactor that, unlike
thermal reactors, operates mainly with fast neutrons (neutrons in the energy range
above 0.1 MeV) and does not need a moderator. Fast reactors are generally designed
to use plutonium fuels and can be designed to burn actinides.
In general, an isotope or a mixture of isotopes capable of nuclear fission.
Isotopes U-233, U-235, Pu-239, and Pu-241 are referred to as both fissionable and fissile,
while U-238 and Pu-240 are fissionable but not fissile.
Fuel element (fuel assembly, fuel bundle)
A grouping of fuel rods,
pins, plates, or other fuel components held together by spacer grids and other structural
components to form a complete fuel unit that is maintained intact during fuel transfer
and irradiation operations in a reactor.
Fuel fabrication plant
An installation for manufacturing fuel elements.
Underground installation for the disposal of nuclear material, such as used
fuel and/or high-level and transuranic nuclear waste.
High enriched uranium (HEU)
Uranium containing 19.8 percent or more of the isotope U-235.
High-level radioactive waste (HLW)
Highly radioactive materials produced as a byproduct of the reactions that
occur inside nuclear reactors. HLW takes one of two forms: used reactor fuel when
it is accepted for disposal; or second cycle aqueous rafinnate or other radioactive
materials remaining after used fuel is reprocessed.
One of two or more atoms of the same element that has the same number of
protons in its nucleus but different numbers of neutrons. Isotopes have the same
atomic number but different mass numbers.
A series of chemical elements with atomic numbers from 57 to 71.
Light water reactor (LWR)
A power reactor that is both moderated and cooled by ordinary (light) water.
LWR fuel assemblies usually consist of clad fuel rods containing uranium oxide pellets
of low enrichment, generally less than 5 percent U235, or MOX having low plutonium
content, generally less than 5 percent. There are two types of LWR: boiling water
reactors (BWRs) and pressurized water reactors (PWRs).
Low enriched uranium (LEU)
Enriched uranium containing less than 19.8 percent of the isotope U-235.
Mixed oxide (MOX)
A mixture of the oxides of uranium and plutonium used as reactor fuel for
the recycling of plutonium in thermal nuclear reactors (thermal recycling) and for
Uranium as it occurs in nature, having an atomic weight of approximately
238 and containing minute quantities of U-234, about 0.7 percent U-235, and 99.3 percent
U-238. Natural uranium is usually supplied in raw form by uranium mines and concentration
(ore processing) plants as uranium ore concentrate, most commonly the concentrated
crude oxide U3O8, often called yellow cake.
Nuclear fuel cycle
The nuclear fuel cycle is a system of nuclear installations and activities
interconnected by streams of nuclear material. The characteristics of the fuel cycle
may vary widely from state to state, from a single reactor supplied from abroad
with fuel to a fully developed system. Such a system may consist of uranium mines
and concentration (ore processing) plants, thorium concentration plants, conversion
plants, enrichment (isotope separation) plants, fuel fabrication plants, reactors,
used fuel conventional reprocessing or more advanced chemical partitioning plants,
and associated storage installations. The fuel cycle can be “open” by
direct disposal of used nuclear fuel or “closed” in various ways: for
example, by the recycling of enriched uranium and plutonium through thermal reactors
(thermal recycle), by the reenrichment of the uranium recovered as a result of used
fuel dissolution and partitioning, or by the burning of actinides in fast reactors.
A radioactive element that occurs only in trace amounts in nature, with
atomic number 94 and symbol Pu.
Any device in which a controlled, self-sustaining fission chain reaction can
be maintained. Depending on their power level and purpose, reactors are subdivided
into power reactors, research reactors, and critical assemblies.
An installation for the chemical partition of nuclear material from fission
products following dissolution of used fuel. The installation may also include the
associated storage, head-end (cutting and dissolution) operations, conversion and
analytical sections, a waste treatment facility, and liquid and solid waste storage.
Conventional reprocessing involves the following steps: fuel receipt and storage;
fuel decladding and dissolution; partition of uranium, plutonium, and possibly other
actinides (for example, americium and neptunium) from fission products; partition
of uranium from plutonium; and purification of uranium and plutonium. Once purified,
uranium nitrate and plutonium nitrate may be converted, respectively, to UO2
and PuO2 powder at an adjoining plant. Depending
on the economics, these powders may be either indefinitely stored or recycled as
MOX fuel into an LWR or advanced burner or breeder reactor. More advanced chemical
partitioning involves separation of the actinides and some fission products that
could simultaneously provide a fuel stream that is burnable in advanced reactors
and is proliferation-resistant.
A radioactive element with atomic number 90.
The conversion of one nuclide into another through one or more nuclear reactions,
and more specifically, the conversion of an isotope of one element into an isotope
of another element through one or more nuclear reactions.
Transuranic elements are the chemical elements with atomic numbers greater
A naturally occurring radioactive element with atomic number 92.
Used nuclear fuel
Fuel from a reactor that is no longer efficient in power production because
its fission process has slowed.