Absorbed dose: the energy imparted by ionizing radiation per unit mass of irradiated material. The units of absorbed dose are called the gray (gy).

Absorber: any material that stops ionizing radiation. Lead, concrete, and steel attenuate gamma rays. A thin sheet of paper or metal will stop or absorb alpha particles and most beta particles.

Acceptable level of risk: a level of risk associated with a particular activity at which dangers are acceptable to the evaluator.

Accessible environment: the area surrounding a nuclear waste disposal site.

Accident leakage rate: the primary-to-secondary leakage rate occurring during postulated accidents other than a steam generator tube rupture.

Acid rain: also called acid precipitation or acid deposition, acid rain is precipitation containing harmful amounts of nitric and sulfuric acids formed primarily by nitrogen oxides and sulfur oxides released into the atmosphere when fossil fuels are burned. It can be wet precipitation (rain, snow, or fog) or dry precipitation (absorbed gaseous and particulate matter, aerosol particles or dust). Acid rain has a ph below 5.6. Normal rain has a ph of about 5.6, which is slightly acidic. The term ph is a measure of acidity or alkalinity and ranges from 0 to 14. A ph measurement of 7 is regarded as neutral. Measurements below 7 indicate increased acidity, while those above indicate increased alkalinity.

Actinides: elements with atomic numbers from 89 (actinium) or 90 (thorium) to 103 (lawrencium) inclusive.

Action level: a derived media-specific radionuclide-specific concentration or activity level of radioactivity that triggers a response such as seizure of contaminated foodstuffs following a nuclear accident . The action level is called the investigation level and would trigger the response of further investigation or site cleanup if the release criterion is exceeded.

Activation products: nuclides formed through transformation of stable reactor components into radioactive isotopes after intense bombardment with fission products. Radioactivity is thus induced through neutron bombardment or other types of radiation in reactor vessel components and corrosion products (and also in weapons casings) which were stable before the reactor vessel went on-line. The transuranic nuclides Plutonium, americium, curium, etc., are also neutron activation products, originating from neutron capture in Uranium nuclides rather than from the fission of these nuclides. Other important activation products include carbon-14 and tritium as well as activation products derived from activated stainless steel and carbon steel, activated sludge, corrosion deposits and concrete, and contaminated building products e.g. ⁵⁵fe, ⁵⁴mn, ⁶⁵zn, ⁵⁸co and ⁶⁰co.

Active degradation mechanisms: new indications associated with defect types that have been identified during inservice inspection.

Activity:rate of disintegration, transformation, or decay of radioactive material. The units of activity are the curie (ci) and the becquerel(bq).

Acute dose: an acute dose means a person received a radiation dose over a short period of time.

Acute exposure: large exposure received over a short period of time.

Agency for toxic substances and disease register (atsdr): the atsdr was established as a component of the superfund act of 1980 (cercla) and has the mission of preparing toxicological profiles for hazardous substances most commonly found at facilities on the cercla national priorities list. The atsdr recently issued a draft for public comment of toxicological profile for ionizing radiation and is a well-spring of important information on toxic substances in general.

Agreement state: a state that has entered into an agreement with the U.S. Nuclear Regulatory Commission (as specified by the atomic energy act of 1954) and has authority to regulate the disposal of low-level radioactive waste under such an agreement. This term is used in the low-level radioactive waste policy act (public law 99-240).

Airborne radioactivity area: a room, enclosure, or area in which airborne radioactive materials, composed wholly or partly of licensed material, exist in concentrations that: (1) exceed the derived air concentration limits, or (2) would result in an individual present in the area without respiratory protection exceeding, during the hours the individual is present in the area, 0.6 percent of the annual limit on intake or 12 derived air concentration-hours (see 10 CFR §20.1003 definitions).

ALARA: acronym for "as low as reasonably achievable." make every reasonable effort to maintain exposures to radiation as far below the dose limits as is practical consistent with the purpose for which the activity is undertaken, taking into account the state of technology, the economiCs of improvements in relation to benefits to the public health and safety, and other societal and socioeconomic considerations, and in relation to utilization of ionizing radiation in the public interest.

Alpha decay: radioactive decay in which an alpha particle (⁴He nucleus) is emitted.

Alpha emission: emission of an alpha particle, from an unstable nucleus.

Alpha particle: a particle emitted from the nucleus of an atom, containing two protons and two neutrons, identical to the nucleus (without the electrons) of a helium atom.

Alpha radiation: e.g. Emitted by Plutonium-239: a nucleus of a helium atom; large in mass, unable to penetrate more than a few microns of biological tissue. (e.g. Cannot penetrate a piece of paper)

Ampere: the unit of measurement of electrical current produced in a circuit by 1 volt acting through a resistance of 1 ohm.

Annual limit on intake (ALI): the derived limit for the amount of radioactive material taken into the body of an adult worker by inhalation or ingestion in a year. For a given radionuclide, ali is defined as the smaller of the intakes that would result in a committed effective dose equivalent of 5 rems and a committed dose equivalent of 50 rems to any individual organ or tissue. < p 

Anthracite: a hard, black lustrous coal, often referred to as hard coal, containing a high percentage of fixed carbon and a low percentage of volatile matter. Comprises three groups classified according to the following astm specification d388-84, on a dry mineral-matter-free basis:

As low as reasonably achievable (ALARA): the reduction of exposure to ionizing radiation so as to reduce collective doses as far below regulatory limits as is reasonably possible.

Ash: impurities consisting of silica, iron, alumina, and other noncombustible matter that are contained in coal. Ash increases the weight of coal, adds to the cost of handling, and can affect its burning characteristiCs. Ash content is measured as a percent by weight of coal on an :as received or a "dry" (moisture-free, usually part of a laboratory analysis) basis.

Atmospheric dispersion models: the prediction of concentrations within a plume far downwind and far beyond the point at which a plume becomes invisible. Similar modeling for releases from nuclear facilities can estimate the impacts of releases long past by reconstructing exposure and dose estimates.

Atom: a particle of matter which cannot be broken up by chemical means. Atoms have a nucleus consisting of positively-charged protons and uncharged neutrons of the same mass. The positive charges on the protons are balanced by a number of negatively-charged electrons in motion around the nucleus.

Atomic: of or relating to an atom.

Atomic bomb: an explosive device whose energy comes from the fission of heavy elements such as Uranium or Plutonium.

Atomic number: the number of protons (or number of positive charges) in the nucleus of an atom. The number of protons determines what an atom is chemically, and, hence, identifies it as belonging to a certain chemical element.

Atomic weight: the sum of the protons and neutrons in the nucleus of an atom.

Auxiliary feedwater: backup water supply used during nuclear plant startup and shutdown to supply water to the steam generators during accident conditions for removing decay heat from the reactor.

Available but not needed capability: net capability of main generating units that are operable but not con sidered necessary to carry load, and cannot be connected to load within 30 minutes.

Average revenue per kilowatthour: the average revenue per kilowatthour of electricity sold by sector (residential, commercial, industrial, or other) and geo graphic area (state, census division, and national), is calculated by dividing the total monthly revenue by the corresponding total monthly sales for each sector and geographic area.