Half life
The time in which one half of the atoms of a particular radioactive substance disintegrates into another nuclear form. Each radioactive isotope has a characteristic half life, e.g. U235 = 0.7038 x 109 years; U238 = 4.468 x 109 years.
Half value layer
The thickness of any given absorber that will reduce the intensity of a beam of radiation to one half of its initial value.
Hazardous waste
Nonradioactive waste containing concentrations of either toxic, corrosive, flammable, or reactive chemicals above maximum permissible levels.
Health physics
That science devoted to recognition, evaluation, and control of all health hazards from ionizing radiation.,
Heat exchanger
A unit in which the heat from one fluid (liquid or gas) is transferred to another. It usually takes the form of a bank of tubes carrying one (the primary) fluid flows. In the case of steam generators used in a PWR, both fluids are water, with the primary fluid circulating round the reactor and the secondary fluid circulating as steam through the turbine.
Heavy Bomber
a heavy bomber is one plane with a range greater than 8,000 kilometers and/or equipped with long range nuclear air launched cruise missiles.
Heavy ICBM
The START I Treaty defines a "heavy" ICBM as "an intercontinental ballistic missile of a type, any one of which has a launch weight greater than 106,000 kilograms or a throw weight greater than 4,350 kilograms." The Soviet SS 18 missile is an example of a heavy ICBM.
Heavy Water Reactor
A reactor that uses heavy water as its moderator and natural uranium as fuel.
High level waste
There are two levels of high level waste (HLW): the liquid waste from reprocessing which contains the fission products; and the entire unreprocessed used fuel (if direct disposal is planned). HLW is highly radioactive and contains long lived activity; it generates a considerable amount of heat and requires constant cooling for many years.
Highly enriched uranium (HEU)
Uranium that is enriched from its naturally occurring 0.7 percent to above 20 percent of the U-235 isotope.Weapons-grade material is usually enriched to 90 percent of the U-235 or greater.
High Radiation Area
Any area with dose rates greater than 100 mrem in one hour 30 cm from the source or from any surface through which the radiation penetrates. These areas must be posted as "high radiation areas" and access into these areas is maintained under strict control.
Horizontal proliferation
The acquisition of nuclear weapons by countries other than the five recognised weapons states.
Hot
Colloquial term meaning highly radioactive
Hot Cells
Any type of shielded room with remote handling equipment, such as robotic arms, for handling and processing radioactive materials. Hot cells may also be used in reprocessing spent reactor fuel.
"Hot Line" Agreement
An agreement between the United States and the Soviet Union, signed in June 1963 and twice updated, that establishes a communications link between Washington and Moscow for use by heads of government during crises.
Hot Spot
The region in a radiation/contamination area in which the level of radiation/contamination is noticeably greater than in neighboring regions in the area.
Hydrofracture
A process formerly used for permanent disposal of low level liquid waste at the Oak Ridge National Laboratory. The process involved mixing the waste with a blend of cement and other additives with the resulting grout being injected into shale at a depth of 200 to 300 m. The injected grout hardened into thin, horizontal sheets several hundred meters wide.
Hydrogen Bomb
Also known as a thermonuclear weapon, the source of energy for this type of nuclear weapon is largely from fusion.
ICBM
Intercontinental ballistic missile
IFF
Identification, friend or foe
IFR Integral Fast Reactor
A type of reactor based on a closed fuel cycle at the site. The key to this design is that the plutonium fission product never occurs in a pure form. This feature is considered proliferation resistant.
Institutional waste
Commercial low level waste resulting from bioresearch, medical, and certain nonbioresearch sources. Bioresearch wastes include wastes from animal studies at universities. Medical wastes include those generated from diagnostic and therapeutic procedures on humans at hospitals. Nonbioresearch wastes include research reactor wastes; small volume, sealed radiation sources; and accelerator targets.
Intercontinental Ballistic Missile (ICBM)
A land based ballistic missile generally comprised of a rocket booster, one or more reentry vehicles, penetration aids, and, in the case of MIRVed missiles, a post boost vehicle, or "bus," to deploy the reentry vehicles with a range of more than 5,500 kilometers.
Internal Radiation
Nuclear radiation resulting from radioactive substances in the body. Some examples are iodine 131 (found in the thyroid gland) and strontium 90 and plutonium 239 (found in bone).
Ion
An atom that has too many or too few electrons, causing it to have an electrical charge, and therefore, be chemically active.
Ionization Chamber
An instrument that detects and measures ionizing radiation by measuring the electrical current that flows when radiation ionizes gas in a chamber, making the gas a conductor of electricity.
Ionization
The process of adding one or more electrons to, or removing one or more electrons from, atoms or molecules, thereby creating ions. High temperatures, electrical discharges, or nuclear radiations can cause ionization.
Ionizing Radiation
Any radiation capable of displacing electrons from atoms or molecules, thereby producing ions. Some examples are alpha, beta, gamma, X-rays, neutrons. High doses of ionizing radiation may produce severe skin or tissue damage.
Irradiate
To expose to some form of radiation.
Isomer
One of several nuclides with the same number of neutrons and protons capable of existing for a measurable time in different nuclear energy states.
Isometric transition
The capture by an atom's nucleus of an orbital electron from the first K-shell surrounding the nucleus.
Isotope
Isotopes of a given element have the same atomic number (same number of protons in their nuclei) but different atomic weights (different number of neutrons in their nuclei). Uranium 238 and uranium 235 are isotopes of uranium.
Joint Consultative Group (JCG)
Established under the CFE Treaty, this group is responsible for overseeing implementation of and compliance with the treaty.
K
K capture
The capture by an atom's nucleus of an orbital electron from the first K-shell surrounding the nucleus.
Kilowatt/hour (kWh)
Dissipation of 1000 watts of power for one hour. One unit on a domestic electricity meter represents I kWh.
Leaching
The process of removal or separation of soluble components from a solid by percolating water or other liquids through the solid.
Lethal Dose
The dose of radiation expected to cause death within 30 days to 50% of those exposed. Generally accepted to range from 400 to 450 rem received over a short period of time.
Light Water Moderated Nuclear Reactor (LWR)
The most common type of nuclear reactor, in which ordinary water is used as the moderator and coolant and enriched uranium as fuel. Two LWRs (which produce less plutonium during the fuel cycle than the existing North Korean graphite moderated reactors) were part of the 1994 Agreed Framework settlement with North Korea (see Agreed Framework).
Light water
Term used to distinguish ordinary water from heavy water. A light water reactor is cooled by ordinary water. Heavy water, on the other hand, is water that is rich in the heavy isotopes of hydrogen. It is an efficient moderator used in some other types of reactors
Load factor
The percentage of power stations potential output which is actually produced in the course of a year. Sometimes also referred to as capacity factor, it is a widely used measure of power station performance.
Longer Range Intermediate Nuclear Force (LRINF) Missiles
As defined by the INF Treaty, such missiles have ranges between 1,000 and 5,500 kilometers.
Loss of coolant accident (LOCA)
In the case of a PWR this is an accident in which some of the coolant water leaks out of the primary circuit. The PWR is provided with emergency core cooling systems to make good any loss of coolant.
Low enriched uranium(LEU)
Any form of uranium having a U 235 isotope concentration greater than 0.711% but below 20%. Typical concentrations used in light water reactors range from 3% to 5%.
Low level waste
As specified in the Low Level Radioactive Waste Policy Amendments Act of 1985 (Public Law 99?240), radioactive waste not classified as high level waste, spent nuclear fuel, or by product material specified as uranium or thorium tailings and waste. Most are generally short lived and have low radioacitivity.
Magnox
Alloy of magnesium used for the tubing (can) of fuel elements in some gas cooled reactors. Used in the first commercial power reactors in the UK which are consequently called Magnox reactors.
Mass number
The total number of protons and neutrons in the nucleus of an atom.
Medical physicist
A medical physicist has training and experience in the application of radiation to the human body for purposes of diagnosis or therapy. The individual works closely with doctors to make sure that the dose prescribed for a treatment or diagnostic image is delivered.
Mega-
Prefix for one million, e.g. megawatt (MWe) = 1,000,000 watts. Commercial nuclear reactors today have power outputs in the range 600 to 1300 MWe.
Megacurie
One million curies.
MeV
One million electron volts.
Micro-
Prefix that divides a basic unit into one million parts.
Microcurie
One millionth of a curie.
Milk
To elute a cow.
Mill tailings, uranium
Earthen residues that remain after the extraction of uranium from ores. Tailings may also contain other minerals or metals not extracted in the process.
Milli-
Prefix that divides a basic unit by 1,000
Milling
Process by which uranium is extracted from its ore, usually at the mine site or close by.
Millirem
One thousandth of a rem.
Millirontgen
One thousandth of a rontgen.
Mixed low level waste
Waste that satisfies the definition of low level radioactive waste (LLW) in the Low Level Radioactive Waste Policy Amendments Act of 1985 and that contains hazardous waste that has at least one of the following characteristics: (1) is listed as a hazardous waste in Subpart D of 40 CFR Part 261, (2) exhibits any of the hazardous waste characteristics identified in Subpart C of 40 CFR Part 261, or (3) contains PCB?containing wastes subject to regulation under the Toxic Substances Control Act and 40 CFR Parts 702 799.
Mixed oxide fuel (MOX)
A fuel containing a mixture of plutonium oxide and depleted or natural uranium oxide which can be used in standard LWRs.
Mixed waste
Waste that includes concentrations of both radionuclides and hazardous chemicals.
Mobile Missile
Any ballistic or cruise missile mounted on and/or fired from a movable platform, such as a truck, train, ship, or aircraft.
Moderator
A substance in which neutrons tend to bounce from atom to atom instead of being captured by nuclei. Moderators are therefore used to slow down ("moderate") the neutrons emitted by fissioning uranium atoms, and increase their chance of being captured by another uranium atom. Deuterium, graphite and light water are frequently used moderators.
Molecule
A group of atoms held together by chemical forces. A molecule is the smallest unit of a compound that can exist by itself and retain all of its chemical properties.
Monitoring
Periodic or continuous determination of the amount of ionizing radiation or radioactive contamination present in an occupied region, as a safety measure, for the purpose of health protection.
MOX
Mixed Oxide Fuel
Nano
A prefix that divides a basic unit by one billion.
Nanocurie
One billionth of a curie.
Natural uranium
Uranium with the isotopic concentrations found in nature, i.e. 99.3% uranium238 and 0.7% uranium235.
Naturally occurring and accelerator produced radioactive material
Any radioactive material that can be considered naturally occurring and is not source, special nuclear, or byproduct material or that is produced in a charged particle accelerator.
Neutrino
An electrically neutral particle with negligible mass. It is produced in many nuclear reactions such as in beta decay.
Neutron activation
The process of irradiating a material with neutrons so that the material itself is transformed into a radioactive nuclide.
Neutron
One of the particles found in the nucleus of an atom, so called because of its neutral electric charge. Free neutrons, released by fissioning or radioactive disintegration of atoms, are very penetrating. When they do collide with the nuclei of other atoms they are likely to cause a wide variety of changes, or transmutations, in the physical characteristics of the atoms they strike.
Nonfuel components
Nuclear reactor core parts and hardware, excluding the nuclear fuel itself. Such components include shrouds, control rods, fuel channels, in core chambers, support tubes, and dummy fuel rods.
NORM
Naturally Occurring Radioactive Material
North Atlantic Treaty Organization (NATO)
Created in 1949 to counter the rising threat of the Soviet Union, this security alliance comprises the United States, Canada, and 14 European nations.
Nuclear Energy
The energy liberated by a nuclear reaction (fission or fusion) or by radioactive decay.
Nuclear Non Proliferation Treaty (NPT)
A multilateral treaty opened for signature July 1, 1968, and entered into force on March 5, 1970, designed to prevent the spread of nuclear weapons to non nuclear nations. The NPT was extended indefinitely and unconditionally in May 1995.
Nuclear Proliferation
The spread of nuclear weapons related components or technology to countries that are not currently nuclear capable.
Nuclear Reactor
A device in which a controlled, self sustained nuclear chain reaction can be maintained and generated heat removed. Types include power reactors, research and test reactors, and fissile material production reactors (for fissile material).
Nuclear Weapon
A device that releases nuclear energy in an explosive manner as the result of nuclear chain reactions involving the fission or fusion, or both, of atomic nuclei.
Nucleon
A constituent of the nucleus; that is, a proton or a neutron
Nucleonics
The science, technology, and application of nuclear energy.
Nucleus; nuclei
The small, central positively charged region of an atom that carries essentially all the mass. Except for the nucleus of ordinary (light) hydrogen, which has a single proton, all atomic nuclei contain both protons and neutrons. The number of protons determines the total positive charge, or atomic number. This is the same for all the atomic nuclei of a given chemical element. The total number of neutrons and protons is called the mass number.
Nuclide
Any species of atom that exists for a measurable length of time. A nuclide can be distinguished by its atomic weight, atomic number, and energy
On Site Inspections
Visits by teams of specialists to allow parties to a treaty to verify each others compliance with the treaty provisions. Inspections generally take place throughout the implementation of a treaty and may include review of force deployments or inspection of treaty,specific equipment and support structures. The INF Treaty provides for five types of inspections: baseline, elimination, close out, short notice, and portal monitoring.
Outage
A planned shut down of a reactor, for refuelling and general maintenance.
Parent
A radionuclide that upon radioactive decay or disintegration yields a specific nuclide (the daughter).
Peakload
Maximum power which must be provided by an electricity supply network during a given time period.
Periodic Table
An arrangement of chemical elements in order of increasing atomic number. Elements of similar properties are placed one under the other, yielding groups or families of elements. Within each group, there is a variation of chemical and physical properties, but in general, there is a similarity of chemical behavior within
Personnel Monitoring
The use of survey meters to determine the amount of radioactive contamination on an individual, or the use of dosimetry to determine an individual's radiation dose.
Pico
A prefix that divides a basic unit by one trillion.
Picocurie
One trillionth of a curie.
Pig
A container (usually lead) used to ship or store radioactive materials. The thick walls protect the person handling the container from radiation.
Pitchblende
A common mineral containing uranium.
Planned Special Exposure
An infrequent exposure to radiation, separate from and in addition to the annual dose limits
Plutonium
A metallic by product of nuclear fission of uranium. It is formed by the capture of a neutron by atoms of uranium 238. Plutonium also fissions and hence can be recycled as fuel either in the same type of reactor as it was produced or in future fast breeder reactors. The most important isotope is Plutonium 239, which is the primary isotope used in nuclear weapons. Plutonium can also be used for reactor fuel. The PVTR produces plutonium more slowly than the Magnox reactor.
Pocket Dosimeter
A small ionization detection instrument that indicates radiation exposure directly. An auxiliary charging device is usually necessary.
Pressure vessel
A large vessel of steel or pre-stressed concrete containing the whole of the reactor core. Such a vessel is used to pressurize the coolant in gas-cooled and light water cooled reactors.
Pressurized water reactor (PWR)
A reactor type which uses ordinary (light) water at high pressure both as coolant and moderator. It is the most widely used type of reactor for producing electricity.
Proton
Elementary particle with positive electrical charge which forms part of the nucleus of every atom. The number of protons determines what element the atom is.
PURIEX process
A solvent extraction process that may be employed in the reprocessing of uranium/plutonium based nuclear fuels.