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Due to a lapse in appropriations, the NRC has ceased normal operations. However, excepted and exempted activities necessary to maintain critical health and safety functions—as well as essential progress on designated critical activities, including those specified in Executive Order 14300—will continue, consistent with the OMB-Approved NRC Lapse Plan.

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Fast fission

Fast fission … Fission of a "heavy" atom (such as uranium-238 ) when it absorbs a fast (high energy) neutron . All fissionable materials can fission with fast neutrons. However, some (such as uranium-235 and Plutonium-239 ) fission more readily with slow …

Transuranic waste

Transuranic waste … Material contaminated with transuranic elements —artificially made, radioactive elements , such as neptunium, plutonium , americium, and others—that have atomic numbers higher than uranium in the periodic table of elements . …

Beta particle

Beta particle … A charged particle (with a mass equal to 1/1837 that of a proton ) that is emitted from the nucleus of a radioactive element during radioactive decay (or disintegration) of an unstable atom . A negatively charged beta particle is identical …

Becquerel (Bq)

Becquerel (Bq) … One of three units used to measure radioactivity , which refers to the amount of ionizing radiation released when an element (such as uranium ) spontaneously emits energy as a result of the radioactive decay (or disintegration) of an …

Poison, neutron

Poison, neutron … In reactor physics, a substance (other than fissionable material ) that has a large capacity for absorbing neutrons in the vicinity of the reactor core . This effect may be undesirable in some reactor applications because it may prevent …

Deuteron

Deuteron … The nucleus of deuterium . It contains one proton and one neutron . See also Heavy water (D2O) . … Deuteron …

Atom

Atom … The smallest particle of an element that cannot be divided or broken up by chemical means. It consists of a central core (or nucleus ), containing protons and neutrons , with electrons revolving in orbits in the region surrounding the nucleus. … …

Breeder

Breeder … A reactor that produces more nuclear fuel than it consumes. A fertile material , such as uranium-238, when bombarded by neutrons , is transformed into a fissile material , such as plutonium-239, which can be used as fuel. … …

Zirconium

Zirconium … A chemical element used (in the form of "Zircaloy" metals) in cladding for nuclear fuel rods . The thin zirconium tubes contain pellets of nuclear fuel and are bundled together into assemblies for use in a reactor . … …

Fissionable material

Fissionable material … A nuclide that is capable of undergoing fission after capturing either high-energy (fast) neutrons or low-energy thermal (slow) neutrons . Although formerly used as a synonym for fissile material , fissionable materials also include …