What follows is a glossary of terms that will be useful in understanding the information on the Inyo County Yucca Mountain website and other websites that discuss the proposed use of Yucca  Mountain as a nuclear waste repository.

  • Yucca Mountain Project

A proposal by the U.S. Department of Energy to construct and operate an underground nuclear waste repository in Nye County, Nevada, at a site approximately 17 miles from Inyo County.

  • Nuclear Waste Policy Act of 1987

The Congressional Act authorizing the U.S. Department of Energy to study the Yucca Mountain site for suitability as an underground nuclear waste repository and (if found suitable by DOE, Congress and the President), pursue licenses from the Nuclear Regulatory Commission to construct and operate the repository.

  • Nuclear Waste Policy Act Section 116[c]

That section of the Act providing a mechanism by which jurisdictions impacted by Yucca Mountain shipments can request funding to mitigate impacts.

Nuclear Waste Policy Act Section 180[c] That section of the Act providing a funding mechanism to augment emergency response planning and capabilities on transportation corridors hosting Yucca Mountain shipments.

  • Alternate Route

U.S. Department of Transportation rules for the routing of Yucca Mountain shipments require that such shipments travel on Interstates unless an impacted State designates an "Alternate Route" (a route to be used in lieu of an Interstate). Sections of California State Routes 127, 178 and/or 190 could feasibly be designated by the State of California as part of an Alternate Route.

  • High-Level Nuclear Waste

Primarily nuclear waste originating from the development and manufacturing of nuclear weapons. Most High-Level Nuclear Waste slated for Yucca Mountain will be in the form of radioactive glass logs encased in metal cylinders.

  • Spent Fuel

Used fuel rods discharged from commercial nuclear power reactors.

  • Transuranic Nuclear Waste

Radioactive waste produced at federal facilities during research and production of nuclear weapons. These wastes include protective clothing, laboratory tools and equipment, debris, rags, glass, and soils that are contaminated with small amounts of radioactive materials, such as plutonium and americium. They also may contain small amounts of hazardous chemicals.

  • Low-Level Nuclear Waste

Any radioactive waste that is not spent nuclear fuel, high-level waste, transuranic waste, mixed-waste or uranium-mill tailings. It is produced by virtually every process involving radioactive materials. Low-level waste spans a wide range of characteristics, but most of it contains small amounts of radioactivity in large volumes of material.

  • Advanced Burner Reactor

A new type of nuclear reactor that accepts recycled nuclear fuel and consumes more transuranic elements than it creates, while generating electricity.  It typically belongs to the class of nuclear power plants called "fast reactors."  "Burn" does not mean incinerate or combust, it means to transmute or convert transuranics into shorter-lived isotopes.

  • Advanced Fuel Cycle Facility

A multi-purpose research and development laboratory to serve fuel cycle testing needs for the next 50 years or more.

  • Advanced Fuel Cycle Initiative

The mission of the current Advanced Fuel Cycle Initiative (AFCI) is to develop proliferation-resistant spent nuclear fuel treatment and transmutation technologies to enable a transition from the current once-through nuclear fuel cycle to a future sustainable, closed nuclear fuel cycle where valuable material is separated from waste and recycled, whereby extracting energy and reducing waste.

  • Advanced Simulation Laboratory

A laboratory to support robust research, computer simulation and visualization, reducing the cost of future experiments by state-of-the-art computer simulation of relevant chemical and physical processes.

  • Atom

At atom is the basic component of matter; all matter is divided into one hundred different chemical element having all the chemical properties of the element.

  • Closed Fuel Cycle

An approach to handling used nuclear fuel in which useful parts of used nuclear fuel are recycled; also called "recycle" fuel cycle, in contrast with the "throw away" or "open" fuel cycle.


  • Energy Security

A reliable supply of affordable energy.

  • Enrichment

The physical process of increasing the proportion of isotope uramium-235 to uranium-238 to make the mixture more usable as nuclear fuel.

  • Enriched Uranium

Uranium in which the proportion of uranium-235 (to uranium-238) has been increased above the natural 0.7 percent uranium-235.  Reactor-grade uranium is usually enriched to three to five percent uranium-235.  Uranium can be fabricated into nuclear fuel and fissioned in nuclear reactor to produce energy.

  • Engineering Scale Demonstration

Demonstration of the steps of a technology on a scale sufficient to obtain cost and performance data required to support potential subsequent commercialization of the technology.

  • Fast Reactor (fast spectrum reactor)

A nuclear reactor that can extract energy via fission from all types of uranium, including depleted uranium, which is otherwise waste from enrichment, and all isotopes of the transuranic elements.  Neutrons are kept at higher average energy in a fast reactor than in a thermal reactor; these higher energy neutrons are able to fission more isotopes.  contrast with "thermal reactor."

  • Fission

The splitting of an atom into at least two other atoms and the release of a relatively large amount of energy.  Two or three neutrons are usually released during this type of transformation.

  • Fission Product

The atoms (fission fragments) formed by the fission of heavy elements such as uranium.

  • Open Fuel Cycle

Nuclear fuel is used once in a nuclear power plant and then thrown away; also called "throw away" or "once-through" fuel cycle.  Contrast with "recycle or closed fuel cycle."

  • Plutonium

An artificial radioactive isotope that can be fabricated into nuclear fuel and fissioned in a reactor to produce energy.  Some plutonium isotopes also can be used in nuclear weapons..  Others can't.

  • Proliferation

The spread of nuclear weapon materials and/or technologies.

  • PUREX (Plutonium Uranium Extraction)

An older technology for separating used nuclear fuel into components that produce both pure plutonium and uranium, all else is waste.  The separation uses a water-based acid dissolution of the used nuclear fuel.  Contrast with UREX+.

  • Pyroprocessing

A technology for separating used nuclear fuel into components that separates uranium, but keeps all the transuranic elements together.  The separation uses a molten chloride salt to dissolve the used nuclear fuel, rather that water-based acid as is used in PUREX and UREX+.

  • Radioisotope

An unstable isotope of an element that decays or disintegrates spontaneously, emitting radiation.  Approximately 5,000 natural and artificial radioisotopes have been identified.

  • Reactor

A device in which nuclear fission may be sustained and controlled in a self-supporting nuclear reaction. The varieties are many, but all incorporate certain features, including fissionable material or fuel, a moderating material (unless the reactor is operated on fast neutrons), a reflector to conserve escaping neutrons, provisions of removal of heat, measuring and controlling instruments, and protective devices.  The reactor is the heart of nuclear power plant.

  • Recycling

A process that separates used fuel into: uranium; waster (fission products); and transuranics (a mixture of plutonium, americium, neptunium and curium)  for reuse in reactors.  The transuranic elements are incorporated into fuel for fast reactors and then destroyed while the reactor generates electricity.  Recycling would be done with UREX+ or pyroprocessing depending on the type of fuel to be recycled.  Contrast with "throw away" fuel cycle.

  • Spent Nuclear Fuel (used nuclear fuel)

Nuclear fuel that is used in a reactor for a number of years before losing its ability to efficiently create energy.  As a typical nuclear reactor operates, the fission process creates energy to generate electricity.  During this process, the uranium is being used up and fission products accumulate and interfere with efficiency until the fuel can no longer effectively produce energy.  At this point, the used fuel is said to be "spent" and is replaced.  If directly disposed, spent nuclear fuel can only be disposed in a geologic repository where the waste is to be isolated essentially permanently from the biosphere.  Contrast with "low-level waste".

  • Thermal Reactor (thermal pectrum reactor)

A nuclear power plant that can use only certain isotopes of uranium and the transuranic elements.  Neutrons producing fission are slowed down, or moderate to relatively low energies before creating new fission reactions.  Contrast with "fast reactor".

  • Throw Away Fuel Cycle

A process in which nuclear fuel is used once in a nuclear power plant and then thrown away; also called "open" or "once-through".  Contrast with "recycle" or "closed" fuel cycle.

  • Tonnes (metric ton)

1,000 kilograms; 2,200 pounds.