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A Collection of Nuclear Reactor Terms...
absorber rod
A synonym for control rod.

access hatch
An airtight door system that preserves the pressure integrity of a reactor containment while allowing access to personnel and equipment.

active fuel length
The length of fuel within a fuel element.

Acronym: AFL.

AF
An acronym for auxiliary feedwater.

AFL
An acronym for active fuel length.

after heat
Heat produced by the decay of radioactive materials in a reactor that has been shut down.

Related to decay heat.

AFW
An acronym for auxiliary feedwater.

atomic pile
A synonym for pile.

atomic power
A synonym for nuclear power.

auxiliary building
A building at a nuclear power plant, typically adjacent to the reactor containment structure, that houses the reactor auxiliary and safety systems, such as the radioactive waste system, the chemical and volume control systems, and the emergency cooling system.

auxiliary feedwater
A backup water supply for a nuclear power plant. It is used to supply water to steam generators during reactor startup and shutdown, and during accident conditions to remove decay heat from the reactor.

Acronym: AF.
Acronym: AFW.
Synonym: emergency feedwater


biological shield
A radiation shield placed around a reactor or other radiation-producing device to reduce dose rates to safe levels.

boiling-water reactor
A reactor design in which the coolant water flows to the core where it is heated and is allowed to boil. Steam that is produced is passed through a heat exchanger where it is condenses to water and returned to the reactor.

Acronym: BWR.
Related to pressurized water reactor.


breed
To form fissile nuclei, usually as a result of neutron capture, possibly followed by radioactive decay.

breeder
A synonym for breeder reactor.

breeder reactor
A nuclear reactor designed to produce more fuel (fissile material) than it consumes. Such reactors surround the fuel with a fertile (non-fissile) material that, when irradiated, produces fissile material. Also known as a converter reactor because it converts fertile material into fissile material.

Acronym: BR.
Synonym: breeder.
Synonym: nuclear breeder.
Related to converter reactor.


burnable fission poison
A strong neutron absorber added to reactor fuel or coolant water to control reactivity. The poison initially reduces the reactivity of new fuel. Neutron production by the fuel decreases over time, occurring as the concentration of the poison decreases due to neutron capture. This burning of the poison compensates for the loss of reactivity of the fuel, helping maintain the overall reactivity of the reactor.

Synonym: burnable poison.

burnable poison
Synonym for burnable fission poison.

burnup
A measure of nuclear reactor fuel consumption defined as the ratio of the fissile material consumed to that originally present.

Synonym: depletion.

BWR
An acronym for boiling-water reactor.

CANDU
Acronym for Canadian Deuterium Uranium Reactor.

capacity factor
A ratio of the average power output of a power plant to its rated capacity.

Synonym: load factor.
Synonym: plant capacity factor.
Synonym: plant factor.


cent
A unit of reactivity in a reactor defined as one hundredth of a dollar.

Related to dollar.
Related to effective multiplication factor.
Related to inhour.
Related to reactivity.


cladding
A synonym for fuel cladding.

cleanup system
A continuous water filtration and demineralization system for reactor coolant systems. It serves to reduce contamination levels in the water and to reduce corrosion.

condensate
Water formed by cooling steam in a condenser.

confinement
A synonym for containment.

confinement systems
Those systems, including ventilation, that act as barriers between areas containing radioactive substances and the environment.

Reference: 10CFR72.

containment
(1) (general) The process of confining radioactive nuclides within a vessel.

(2) (nuclear reactors) The process of confining radioactive nuclides to a reactor vessel. It also applies to the reactor building which is designed to confine fission products in the event of a major accident.

(3) (waste disposal) Confinement of radioactive waste within a designated boundary.

(4) (fusion research) The process of confining a plasma.

Synonym: confinement.

containment vessel
Acronym: CV.
A synonym for reactor vessel.


control absorber
A synonym for control rod.

controlled area
(1) It is the area outside of a restricted area but within the area whose access is limited by the operator (licensee). Generally, it is the non-restricted area within the site boundary.

(2) A surface location, to be marked by suitable monuments, extending horizontally no more than 10 kilometers in any direction from the outer boundary of the underground facility, and the underlying subsurface, which area has been committed to use as a geologic repository and from which incompatible activities would be restricted following permanent closure.

(3) It is the area immediately surrounding the storage installation for which the licensee exercises authority over its use and within which spent fuel storage operations are performed.

References: 10CFR20, 10CFR60, 10CFR72.

control rod
A component of a reactor that contains strong neutron absorbers and which is used to control reactor reactivity. General control rods have a reactivity worth of a little more than a dollar and are used to control and regulate the reactor power. Regulator rods are used for fine adjustments, shim rods are used for large changes to the reactivity, and safety rods are used to rapidly decrease the reactivity in the event of accidents.

Acronym: CR.
Synonym: absorber rod.
Synonym: control absorber.
Synonym: power rod.
Related to reactivity worth.
Related to reactivity.
Related to regulator rod.
Related to safety rod.
Related to shim rod.


converter
A synonym for converter reactor.

converter reactor
A reactor that converts fertile material into fissile material. The term converter often is used to classify reactors that produce fissile material that is different than the reactor fuel. An example is a reactor fueled with 235U that converts 238U into 239Pu (neutron capture followed by beta decay). When the reactor produces a fissile material that is used as the fuel, it is known as a breeder reactor.

Synonym: converter.
Related to breeder reactor.


coolant
A liquid or gas circulated through a reactor to remove heat. Coolants can also act as neutron moderators.

cooldown
Cooling of the fuel rods following reactor shutdown by circulation of coolant through the reactor core.

Acronym: C/D.

critical assembly
Sufficient fissionable material arranged in a geometry that supports a chain reaction. The critical assembly can include a moderator.

Acronym: CCA.

criticality
Of or pertaining to a system that supports a sustained fission chain reaction.

criticality factor
A synonym for effective multiplication factor.

critical mass
That minimum mass of fissionable material that supports a sustained fission chain reaction.

Synonym: critical size.
Synonym: critical volume.


critical size
A synonym for critical mass.

critical volume
A synonym for critical mass.

CSD
An acronym for cold shutdown.

CV
An acronym for containment vessel.

decommission
The process of dismantling a reactor or accelerator. It involves removing fuel, contaminated water, and decontaminating removable devices, preparing the remaining structure for long-term, safe storage or isolation.

dollar
A unit of reactor reactivity defined as $1.00 = keff/b, where keff is the effective multiplication factor and b is the total fraction of delayed neutrons.

Symbol: $.
Related to cent.
Related to effective multiplication factor.
Related to inhour.
Related to reactivity.


effective multiplication factor
The measure of criticality in a given system. Effective multiplication factor is an indication of whether the number of neutrons produced by a fissionable mass is increasing or decreasing. When the effective multiplication factor is less than 1.0, the system is sub-critical; when the effective multiplication factor exceeds 1.0, the system is super-critical; and when the effective multiplication factor is exactly 1.0, the system is critical.

Symbol: Keff.
Synonym: criticality factor.
Related to cent.
Related to dollar.
Related to inhour.
Related to reactivity.


EFW
An acronym for emergency feedwater.

emergency feedwater
Acronym: EFW.
A synonym for auxiliary feedwater.


exclusion area
The area surrounding a reactor in which the reactor operator (licensee) has the authority to determine all activities. This includes limiting or excluding access to the area by personnel or property.

excursion
A rapid increase in reactor power. Excursions may be accidental or they may be deliberate. A safety system test is an example of a deliberate excursion.

fast reactor
A nuclear reactor in which the fission chain reaction is sustained primarily by fast neutrons.

FC
An acronym for fuel cycle.

FDW
An acronym for feedwater.

feedwater
Water used to remove heat from a reactor and produce steam to drive the turbine generators. This water is supplied directly to the reactor pressure vessel in a boiling water reactor. It is supplied to the steam generator in a pressurized water reactor.

Acronym: FW.
Acronym: FDW.


fission poison
Materials with ultra-high neutron capture cross sections that significantly reduce neutron fields in a reactor, reducing reactivity, thereby creating a barrier to reactor operations. The nuclides 149Sm and 135Xe are two poisons that are produced as fission products with a high yield and which have an impact on reactor operations.

Synonym: neutron poison.
Synonym: poison.


fuel assembly
A synonym for fuel element.

Acronym: F/A.
Acronym: FFA.


fuel cladding
Material used to construct reactor components and designed to maintain a separation between their contents and the coolant. An example is the cladding of a fuel pin that separates the fuel pellets from the coolant. Zirconium and zirconium alloys (e.g., Zircaloy) are common cladding materials.

Synonym: cladding.

fuel cycle
All steps in the use of fissile material as fuel for a reactor, including mining, purification, isotopic enrichment, fuel fabrication, irradiation, storage of irradiated fuel, reprocessing and disposal.

Acronym: FC.

fuel element
A cluster of fuel pins mounted into a single assembly.

Synonym: fuel assembly.
Synonym: fuel rod.
Related to fuel pellet.
Related to fuel pin.


fuel pellet
A small cylinder of enriched uranium, typically as UO2. Several fuel pellets are assembled into a fuel pin which forms a component of a fuel element.

Synonym: pellet.
Related to fuel element.
Related to fuel pin.


fuel pin
A long slender tube made of a zirconium alloy and containing fuel pellets. Several fuel pins are bundled together to form a fuel element.

Related to fuel element.
Related to fuel pellet.


fuel reprocessing
A synonym for reprocessing.

fuel rod
A synonym for fuel element.

gap
The space between a fuel pellet and the cladding in a fuel rod.

Related to fuel element.
Related to fuel pellet.


gas-cooled reactor
A nuclear reactor design which uses gas as a coolant.

Acronym: GCR.
Synonym: high temperature gas-cooled reactor.


GCR
An acronym for gas-cooled reactor.

heavy-water-moderated reactor
A reactor that uses heavy water as its moderator.

high temperature gas-cooled reactor
A synonym for gas-cooled reactor.

Ih
A symbol for inhour.

inhour
A unit of reactor reactivity. It is that reactivity which will make the stable reactor period equal to 1 hour.

Symbol: Ih.
Related to cent.
Related to dollar.
Related to effective multiplication factor.
Related to reactivity.


keff
A symbol for effective multiplication factor.

light-water reactor
A reactor that uses ordinary water as a moderator and a coolant.

Acronym: LWR.

LOCA
An acronym for loss-of-coolant accident.

LOOP
An acronym for loss of offsite power.

loss-of-coolant accident
Inadvertent escape of water from the primary coolant system.

Acronym: LOCA.

low population zone
The area immediately surrounding a reactor in which the population density is kept low for safety concerns.

Acronym: LPZ.

LPZ
A symbol for low population zone.

LWR
Acronym for light-water reactor.

moderator
A synonym for neutron moderator.

mixed-oxide fuel
Nuclear fuel that contains plutonium oxide mixed with natural or depleted uranium oxide.

Acronym: MOX.
Acronym: MOXF.


MOX
An acronym for mixed-oxide fuel.

MOXF
An acronym for mixed-oxide fuel.

neutron leakage
Neutrons that escape the moderator of a reactor or a neutron source without undergoing capture by the fissile material or other material in the system.

neutron moderator
A substance used to reduce the energy of neutrons through inelastic scattering. Good moderators have a large scattering cross section and a small absorption cross section. Graphite, water, and heavy water are examples of good neutron moderators.

Synonym: moderator.
Related to capture cross section.
Related to cross section.
Related to scattering cross section.


neutron poison
A synonym for fission poison.

neutron reflector
(1) Material containing elements with a high neutron scattering cross section that is used to reflect neutrons back into a neutron source, thereby increasing the neutron flux inside the source. Beryllium is a common element in reflectors because it has an ultra-high scattering cross section and a very low capture cross section.

(2) A device containing elements with a high neutron scattering cross section that is used to reflect neutrons back into the reactor core, thereby increasing the reactor reactivity and thus the energy output of the reactor.

Synonym: tamper.
Related to neutron capture cross section.
Related to scattering cross section.
Related to reactivity.


nuclear breeder
A synonym for breeder reactor.

nuclear fuel
Fissile material used in a reactor.

Synonym: fuel.

nuclear power
Electric power generated using nuclear reactors.

Acronym: NP.
Synonym: atomic power.


nuclear power plant
Any device that converts nuclear energy into electrical power. Many nuclear power plants use the energy from fission to produce steam (directly or indirectly) to drive a turboelectric generator thereby generating electricity.

Acronym: NPP.
Related to nuclear reactor.


nuclear reactor
(1) A device that produces a sustained, controlled fission chain reaction.

(2) A device in which a sustained fission reaction can be maintained. The core is made of a fissile material such as uranium enriched in the isotope 235U. It is usually surrounded by water which moderates neutrons and removes heat from the core.

Synonym: reactor.
Related to nuclear power plant.
Related to research reactor.


pile
A nuclear reactor constructed by stacking graphite blocks and uranium.

Synonym: atomic pile.

pool reactor
A synonym for swimming pool reactor.

power coefficient
The change in reactor reactivity with an increase in power.

Related to reactivity.

power reactor
A reactor designed to produce electricity.

power rod
A synonym for control rod.

pressure vessel
Acronym: PV.
A synonym for reactor vessel.


pressurized water reactor
A reactor design in which water flows through the core at very high pressures. The water is not allowed to boil in the core but flows to a steam generator.

Acronym: PWR.
Related to boiling water reactor.


PWR
A synonym for pressurized water reactor.

PZR
An acronym for pressurizer.

r
A symbol for reactivity.

RCS
An acronym for reactor coolant system.

reactivity
A measure of the departure of a reactor from criticality. It is defined as r = keff - 1, where keff is the effective multiplication factor. Reactivity is expressed in units of cent, dollar, and inhour.

Symbol: r.
Synonym: reactor reactivity.
Related to cent.
Related to control rod.
Related to dollar.
Related to effective multiplication factor.
Related to inhour.
Related to power coefficient.


reactivity worth
The effect that a parameter or component has on the reactivity of a reactor.

Synonym: worth.
Related to control rod.


reactor
A synonym for nuclear reactor.

reactor core
The region of a nuclear reactor containing the fissionable material.

Synonym: core.

reactor period
The time required for the neutron flux to increase by a factor of e.

Symbol: pile period.

reactor reactivity
A synonym for reactivity.

reactor trip
Acronym: RT.
A synonym for scram.


reactor vessel
A large steel container that houses the reactor core, control rods, moderator and coolant, and other control systems to maintain safe operation of the reactor.

Acronym: RV.
Synonym: containment vessel.
Synonym: pressure vessel.


reactor vessel head
The top section of a reactor pressure vessel. It is bolted in place during reactor operation and is removed to provide access to the core during maintenance and refueling.

reflector
A synonym for neutron reflector.

regulator rod
A control rod that has a small reactivity equivalent and is used to make fine adjustments to the reactor reactivity. It usually moves more quickly than a shim rod and has a reactivity worth of less than a dollar.

Related to control rod.
Related to safety rod.
Related to shim rod.


research reactor
A nuclear reactor designed for radionuclide production, materials testing, and training.

RT
An acronym for reactor trip.

RV
An acronym for reactor vessel.

safety injection
The rapid insertion of a soluble neutron poison into the reactor coolant system to ensure reactor shutdown.

Acronym: SI.

safety rod
A control rod used to decrease the reactor reactivity in the case of emergencies. Safety rods have a large reactivity and their motion is very fast.

Acronym: SR.
Synonym: scram rod.
Related to control rod.
Related to regulator rod.
Related to shim rod.


scram
The sudden shutting down of a reactor, typically by the rapid insertion of control rods. It may occur either automatically or manually by the reactor operator. It originally stood for safety control rod axe man, a title given to personnel who were assigned to insert the emergency rod at the original Chicago pile.

Synonym: reactor trip.
Synonym: trip.


scram rod
A synonym for safety rod.

SD
An acronym for shutdown.

S/D
An acronym for shutdown.

SDM
An acronym for shutdown margin.

SF
An acronym for spent fuel.

SG
An acronym for steam generator.

shim rod
A control rod or group of control rods that has a large reactivity equivalent (several dollars) that is used for course control of the reactor power. It is used to bring the reactor approximately up to the desired power level and to make periodic adjustments to the power level to compensate for fuel depletion or poisoning. The shim rod moves slowly to prevent unsafe changes in the power level.

Related to control rod.
Related to regulator rod.
Related to safety rod.


spent fuel
A synonym for spent nuclear fuel.

Acronym: SF.


spent nuclear fuel
(1) Fuel that has been withdrawn from a nuclear reactor following irradiation, has undergone at least one year's decay since being used as a source of energy in a power reactor, and has not been chemically separated into its constituent elements by reprocessing. Spent nuclear fuel includes the special nuclear material, by-product material, source material, and other radioactive materials associated with fuel assemblies.

(2) Fuel that has been permanently withdrawn from a nuclear reactor following irradiation, but has not been processed to remove its constituent elements. (Does not include material categorized as waste that has been removed from the DOE accountability system in accordance with DOE 5633.3A, 5633.4 and 5633.5.)

Synonym: depleted fuel.
Synonym: spent fuel.


SR
An acronym for safety rod.

S/U
An acronym for startup.

subcritical
The state of having insufficient neutrons to sustain a fission chain reaction. A system whose effective multiplication factor is less than 1.0.

Related to criticality.
Related to effective multiplication factor.
Related to supercritical.


subcriticality
Of or pertaining to a system that has insufficient neutrons to sustain a fission chain reaction.

subcritical mass
An amount of fissile material that by its mass or geometry is incapable of sustaining a fission chain reaction. The multiplication factor of the mass is less than 1.0.

supercritical
The state of a system whose effective multiplication factor is greater than 1.0.

Related to criticality.
Related to effective multiplication factor.
Related to subcritical.


supercriticality
Of or pertaining to a system whose effective multiplication factor is greater than 1.0.

supercritical reactor
A reactor in which the effective multiplication ractor is greater than 1.0 and therefore whose power is increasing.

swimming pool reactor
A research reactor in which the core is immersed in a large tank of liquid. The top of the tank is open, allowing access to the core and radiation positions, thus giving the appearance of a swimming pool. Life boats and life savers are often located around the facility to rescue personnel that may fall into the pool, adding further to the appearance of a pool-like environment.

Synonym: pool reactor.
Related to tank reactor.


tank reactor
A reactor design that places the reactor core in a large enclosed tank. Compare with pool reactor.

Related to swimming pool reactor.

TG
An acronym for turbine generator.

T/G
An acronym for turbine generator.

thermal breeder reactor
A breeder reactor that uses thermal neutrons to sustain the fission reaction.

thermal reactor
A reactor in which the fission reaction is sustained primarily by thermal neutrons.

thermal shield
A layer of high-density material placed between the reactor vessel and the biological shield. The thermal shield reduces radiation heating that could damage the biological shield.

zircaloy
An alloy of zirconium used for cladding and structural materials in water-cooled reactors. Properties include high mechanical strength, low neutron absorption cross section, and resistance to corrosion. Zircaloy contains primarily zirconium with small amounts of tin, iron, and nickel.

$
A symbol for dollar.
 
 
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