Activation
Radioactivity induced in structural materials by neutron exposure; a key materials and maintenance issue for D-T fusion systems.
Phase 4 + Phase 5 • Technical Education & Public Trust Authority
Reactor & Fusion Technical Glossary
A controlled public-learning vocabulary for the Reactor Programs branch. Definitions explain engineering meaning and system relationships without becoming design instructions, operating procedures, licensing determinations, or protected implementation detail.
Use rule: technical definitions explain public engineering concepts; licensing, environmental, security, safeguards, emergency, and waste terms remain project- and jurisdiction-specific.
A
Active safety
A safety function that depends on powered equipment, actuators, controls, or operator-supported systems.
Advanced materials
Materials engineered or selected to tolerate demanding combinations of temperature, stress, corrosion, neutron damage, and radiation exposure.
Airworthiness
The demonstrated ability of an aircraft or aviation system to meet applicable safety and flightworthiness requirements.
ALARA
As Low As Reasonably Achievable. A radiation-protection principle requiring exposures to be kept as far below regulatory limits as reasonably achievable, considering technology, economics, and societal factors.
Availability
The fraction of time a plant is capable of performing its intended function, accounting for maintenance, component replacement, outages, and faults.
B
Balance of plant
All supporting systems outside the fusion core or plasma device, including heat transport, power conversion, electrical systems, cooling, buildings, maintenance, and controls.
Beyond-design-basis event
An event or condition more severe than those explicitly used as the design basis. It is analyzed to understand plant robustness, severe-event response, and risk.
Black start
The capability to begin restoring electrical service without depending on the normal external grid. Whether a reactor plant can perform this is design-specific.
Blanket
Structures surrounding a fusion plasma that absorb neutron energy, protect equipment, and in future power plants may breed tritium and transfer heat.
Bootstrap current
A self-generated plasma current arising from pressure gradients and particle orbits in toroidal confinement systems.
Brayton cycle
A thermodynamic power-conversion cycle based on compression, heating, expansion through a turbine, and heat rejection; often discussed for advanced and space power systems.
Breeding blanket
A blanket containing lithium-bearing material intended to produce tritium when struck by fusion neutrons.
Burning plasma
A plasma in which fusion-produced alpha particles provide a substantial fraction of the heating needed to maintain fusion conditions.
Burnup
A measure of energy extracted from nuclear fuel relative to the amount of fuel material.
Byproduct material
A legal/regulatory category of radioactive material. In U.S. law, the ADVANCE Act added radioactive material produced by fusion machines to the definition relevant to fusion regulation.
C
Capacity factor
Actual electricity produced over a period divided by what the plant could have produced if it operated at full rated output continuously.
Central solenoid
A transformer-like magnet used in many tokamaks to induce plasma current and assist plasma startup and control.
Chain reaction
A sequence in which neutrons from one fission event cause additional fissions. Reactor systems control this process rather than allowing it to grow unchecked.
Commercial fleet
A population of operating reactors providing electricity or other commercial services, distinct from prototypes, research reactors, and one-off demonstrations.
Compact toroid
A toroidal plasma configuration without the large central magnet structure typical of a conventional tokamak.
Compression
Rapid increase of plasma or target density through mechanical, electromagnetic, plasma, or inertial forces.
Condenser
A heat exchanger that turns turbine exhaust steam back into liquid water so the working fluid can be reused.
Containment
A robust physical barrier surrounding key reactor systems to limit release of radioactive material during abnormal events.
Coolant
Fluid that carries heat away from the reactor core to a heat exchanger or power-conversion system.
Coolant freezing
Solidification of a coolant if temperature falls below its melting point, an engineering concern for some liquid-metal or salt systems.
Coolant salt
Molten salt used only to carry heat, while the nuclear fuel remains in a separate solid form.
Core power density
Thermal power produced per unit volume or mass of the reactor core; higher values can reduce size but intensify heat-removal and materials demands.
Corrosion allowance
A materials-engineering margin or design strategy that accounts for expected interaction between coolant chemistry and structural materials.
Critical point of water
The thermodynamic point near 374 °C and 22.1 MPa above which water becomes a supercritical fluid rather than distinct liquid and steam phases.
Criticality
The condition in which, on average, one neutron from each fission generation causes another fission, keeping reactor power steady.
Cryogenics
Technology for producing and maintaining very low temperatures, used in superconducting magnet systems and some fusion fuel or diagnostic systems.
D
D-T reaction
The deuterium-tritium fusion reaction, which produces a helium nucleus and a high-energy neutron.
Decay heat
Heat that continues after the fission chain reaction stops because radioactive fission products continue to decay.
Decommissioning
The controlled process of removing a nuclear or radioactive-material facility from service, dismantling or decontaminating as required, managing wastes, and achieving the approved end state.
Decommissioning funding assurance
Financial arrangements required to provide reasonable assurance that funds will be available to decommission a regulated facility when needed.
Defense-in-depth
Use of multiple independent and complementary layers of prevention, protection, mitigation, and emergency response so safety does not depend on one barrier or action.
DEMO
A generic name used internationally for demonstration fusion power plants intended to follow major experimental devices and demonstrate integrated power-plant capability.
Design basis
The defined set of conditions, events, assumptions, and performance requirements used to establish how safety-significant structures, systems, and components are designed and evaluated.
Deuterium
A stable isotope of hydrogen containing one proton and one neutron; commonly used as fusion fuel.
Diagnostics
Instrumentation used to measure physical conditions, performance, radiation, temperatures, flows, or other variables during research and operation.
Direct cycle
A power-cycle arrangement in which reactor-heated working fluid reaches the turbine without an intervening secondary steam generator.
Direct energy conversion
Conversion of charged-particle or electromagnetic energy into electricity without first converting all energy to bulk heat; specific implementations remain technology-dependent.
Direct steam cycle
A power cycle in which steam produced in the reactor system is sent directly to the turbine.
Disruption
A rapid loss of tokamak plasma confinement and current. Avoiding and mitigating disruptions is a major engineering and control challenge.
Divertor
A plasma-facing system in many magnetic-confinement devices that exhausts heat, helium ash, and impurities from the edge of the plasma.
Driver
The laser, pulsed-power, particle-beam, or mechanical system that supplies the energy used to compress or heat an inertial-fusion target.
Driver efficiency
The fraction of input electrical energy converted into the laser, pulsed-power, mechanical, or other driver energy delivered to a fusion target.
E
Emergency planning zone
A geographic area used for planning protective actions for certain radiological emergencies. Its size and basis are regulatory and design/site specific; it is not determined by reactor marketing category alone.
Emergency preparedness
The organized capability to classify emergencies, communicate, protect workers and the public, coordinate response, conduct drills and exercises, and maintain readiness for credible events.
End loss
Loss of plasma particles along open magnetic field lines, a central challenge for linear magnetic-mirror systems.
Endurance
The length of time a platform can remain operational before refueling, resupply, major maintenance, or other limiting events.
Enrichment
The fraction of a fissile isotope, typically uranium-235, in uranium fuel. Exact fuel specifications are design- and licensing-specific.
Environmental impact statement
A detailed environmental review document prepared under applicable law for actions expected to have significant environmental effects; exact requirements depend on jurisdiction and project.
Environmental review
Formal evaluation of environmental impacts, alternatives, mitigation, and permits associated with siting, construction, operation, transport, and decommissioning.
F
Factory fabrication
Manufacturing major plant modules in a controlled factory environment before transport and site installation.
Fast neutron
A higher-energy neutron that has not been strongly slowed by a moderator.
Fast spectrum
A neutron-energy environment dominated by fast neutrons rather than strongly moderated thermal neutrons.
Feedwater
Condensed, treated water returned to a reactor vessel or steam generator to continue the steam cycle.
Field-reversed configuration
A compact-toroid plasma in which the internal magnetic field reverses direction relative to the externally applied field.
First wall
The material surface closest to the fusion plasma and directly exposed to heat and particle loads.
Fission
The splitting of a heavy atomic nucleus into lighter nuclei, releasing energy and additional neutrons.
Fission surface power
A compact reactor-based electrical system intended to provide long-duration power on a planetary surface such as the Moon or Mars.
FOAK
First-of-a-kind: the first implementation of a new design or major design configuration, typically carrying higher execution and learning risk.
Fuel assembly
An engineered grouping of nuclear fuel elements arranged to support cooling, structural integrity, neutron control, and refueling.
Fuel cladding
Protective material surrounding nuclear fuel that helps retain fission products and separates fuel from coolant.
Fuel cycle
The sequence of activities involving nuclear fuel resources, enrichment or fabrication where applicable, reactor use, storage, recycling options, and waste management.
Fuel salt
Molten salt that contains dissolved fissile and fertile fuel material.
Fusion
The joining of light atomic nuclei into heavier nuclei, releasing energy when the final state has lower mass-energy than the starting nuclei.
Fusion diagnostics
Instruments that measure plasma temperature, density, magnetic fields, radiation, impurities, instabilities, and other conditions needed for control and research.
Fusion gain Q
A ratio comparing fusion power produced to external heating power delivered to the plasma or target. Definitions must state the system boundary.
Fusion pilot plant
A proposed intermediate facility intended to demonstrate integrated electricity production and plant technologies beyond standalone plasma-physics experiments.
Fusion target
The small fuel assembly or plasma volume compressed or heated in an inertial or magneto-inertial fusion experiment.
G
Graphite moderator
Graphite used to slow neutrons while tolerating high temperatures; common in several gas-cooled and pebble-bed concepts.
Ground test
A test performed at a terrestrial facility rather than in flight or operational service.
H
HALEU
High-assay low-enriched uranium, enriched above 5% and below 20% uranium-235. Many—but not all—advanced reactor concepts may require it.
Heat exchanger
Equipment that transfers heat between fluid systems without mixing the fluids.
Heat pipe
A sealed passive heat-transfer device using evaporation and condensation of an internal working fluid to move heat with no mechanical pump.
Heat rejection
Transfer of unusable or excess heat from a system to an external heat sink such as air, water, or space radiators.
Heat sink
The environment or engineered system that ultimately receives waste heat, such as cooling water, air, or a radiator.
Helium coolant
Inert gas used as a reactor coolant in many high-temperature gas-cooled concepts because it remains single phase and does not become radioactive through ordinary chemical activation pathways as readily as many alternatives.
High-temperature gas-cooled reactor
A graphite-moderated reactor family using gas coolant, commonly helium, and fuel capable of high-temperature operation.
High-temperature superconductor
A superconducting material that can operate at higher cryogenic temperatures or magnetic fields than conventional low-temperature superconductors; still requires cryogenic cooling.
Hohlraum
A cavity used in indirect-drive inertial confinement to convert laser energy into x-rays that symmetrically compress a fusion capsule.
I
Ignition
A fusion condition in which self-heating from fusion products becomes strong enough to sustain or amplify burn within the target or plasma under the defined experimental boundary.
Implosion
Rapid inward acceleration and compression of a fusion target to raise density and temperature.
Indirect cycle
A power-cycle arrangement in which reactor heat crosses a heat exchanger before a separate working fluid reaches the turbine or engine.
Indirect steam cycle
A power cycle in which reactor heat is transferred across a heat exchanger to a separate steam system before reaching the turbine.
Inertial confinement
Fusion approach in which a small fuel target is rapidly compressed and heated so fusion occurs before the target can expand apart.
Integral reactor
A reactor architecture that places major primary-system components such as steam generators or pressurizers inside or very close to the reactor vessel to reduce large external primary piping.
Intermediate loop
A heat-transfer circuit inserted between a reactor primary coolant and a power-conversion system to isolate fluids or reduce chemical/radiological interactions.
Irradiation
Exposure of a material, component, or sample to neutron or other radiation fields for research, testing, isotope production, or qualification.
K
Kilowatt electric
A unit of electrical output equal to one thousand watts; often used for small space-power systems.
L
Lawson criterion
A relationship among plasma density, temperature, and energy-confinement time that indicates the conditions required for net fusion-relevant performance.
Lead coolant
Liquid lead used as a dense, high-boiling-point coolant in some fast-reactor concepts.
Lead-bismuth eutectic
A lead-bismuth alloy that melts at a lower temperature than pure lead and has historical use in specialized reactor programs.
License renewal
Regulatory process for extending the authorized operating period of a licensed facility after review of applicable aging-management, safety, and other requirements; it is not automatic.
Liner
A moving material shell or layer used in some pulsed fusion concepts to compress a magnetized plasma.
Liquid metal coolant
A liquid metal used to carry reactor heat. Sodium, lead, and lead-bismuth are examples used in fast-reactor concepts.
Loop-type reactor
A reactor layout in which primary coolant circulates through external piping loops connecting the reactor vessel to heat exchangers.
M
Magnetic confinement
Use of magnetic fields to restrict the motion of charged plasma particles and keep hot plasma away from material walls.
Magnetic helicity
A measure related to the linkage and twist of magnetic-field lines, important in the formation and relaxation of some compact-toroid plasmas.
Magnetic mirror
A linear magnetic-confinement concept that uses stronger magnetic fields at the ends of a plasma chamber to reflect many charged particles back toward the center.
Magnetized target
A fusion target or plasma that is magnetized before compression to reduce thermal losses and alter confinement behavior.
Magneto-inertial fusion
A family of approaches combining magnetic pre-confinement with rapid mechanical, electromagnetic, or plasma compression.
Mass fraction
The proportion of total system mass assigned to a subsystem such as shielding, structure, propulsion, coolant, or power conversion.
Materials control and accounting
Administrative and technical measures used to track, control, and account for regulated nuclear material so losses, diversion, or unauthorized movement can be detected and addressed.
Materials qualification
Testing and evidence used to demonstrate that materials can perform under the temperature, pressure, radiation, chemistry, and lifetime conditions required by a design.
MHD instability
An instability described by magnetohydrodynamics that can distort, move, or disrupt a conducting plasma.
Microgrid
A localized electrical network that can coordinate generation, storage, and loads and may operate connected to or isolated from a larger grid.
Microreactor
A very small reactor class intended for compact, often transportable deployment. Exact power range and architecture vary by program and regulator.
Minimum-B field
A magnetic configuration in which field strength rises in every direction away from a central minimum, used to improve plasma stability in some mirror concepts.
Mirror ratio
The ratio of magnetic-field strength at a mirror throat to that in the central region; one parameter used to characterize magnetic-mirror confinement.
Moderator
Material used to slow neutrons. Light water and graphite are common examples; fast reactors generally avoid strong moderation.
Modular coils
Separately manufactured three-dimensional magnet coils used to generate the complex magnetic field of many stellarators.
Module
A standardized reactor or plant section intended to be manufactured, transported, installed, or replicated as a defined unit.
Molten salt
A salt mixture operated as a high-temperature liquid. Depending on reactor design, it can act as coolant, fuel carrier, or both.
Multi-module plant
A site containing multiple reactor modules that may share selected balance-of-plant or infrastructure systems.
MWe
Megawatts electric: the electrical power output delivered by a generating system.
MWth
Megawatts thermal: the rate of heat production before conversion to electricity or useful process heat.
N
Natural circulation
Fluid motion driven by density differences rather than by a mechanical pump.
Naval nuclear propulsion
Use of reactor-generated heat to produce ship propulsion and onboard power. Detailed military designs are not public engineering baselines.
Neoclassical transport
Particle and energy transport arising from collisions and particle orbits in nonuniform magnetic fields, beyond simple classical diffusion.
Neutral beam injection
A plasma-heating and current-drive technique that injects high-energy neutral atoms which become ionized inside the plasma.
Neutron activation
Production of radioactive isotopes when stable nuclei absorb neutrons.
Neutron flux
The rate at which neutrons pass through a unit area; an important quantity in irradiation and reactor-physics work.
Neutron spectrum
The distribution of neutron energies in a reactor. Thermal-spectrum and fast-spectrum systems use very different neutron-energy ranges.
Neutron wall load
The intensity of fusion-neutron energy deposited on structures surrounding the plasma; important for materials lifetime and blanket design.
NOAK
Nth-of-a-kind: later deployments expected to benefit from standardization, experience, and repeated manufacturing or construction.
Non-power reactor
A reactor licensed or operated primarily for research, training, testing, or isotope production rather than commercial electricity generation.
NPDES
National Pollutant Discharge Elimination System. A U.S. Clean Water Act permitting program for point-source discharges, relevant to some industrial and power-plant water discharges.
Nuclear electric propulsion
A space-propulsion architecture in which a reactor generates electricity that powers an electric thruster.
Nuclear thermal propulsion
A propulsion concept in which a reactor directly heats propellant before expansion through a rocket nozzle; distinct from a space power reactor.
O
Once-through cycle
A power-conversion arrangement in which the working fluid passes through the heating section and turbine without steam separation and recirculation as in a conventional boiling cycle.
Online refueling
A design feature in some pebble-bed systems that permits fuel circulation or replacement without a long refueling outage; implementation is design-specific.
P
Part 53
A U.S. NRC risk-informed, performance-based, technology-inclusive regulatory framework that became available in 2026 as an alternative licensing pathway for eligible class 103 commercial nuclear plants.
Part 57 (proposed)
A proposed U.S. NRC licensing framework for high-volume microreactors and reactors with comparable risk profiles. As of October 2026 it is proposed, not an available licensing pathway.
Passive safety
A safety function that relies strongly on physical effects such as gravity, stored energy, natural circulation, or thermal expansion rather than continuous powered actuation.
Pebble fuel
Spherical graphite fuel elements containing many coated fuel particles, used in pebble-bed reactor concepts.
Physical protection
Security measures used to protect nuclear facilities and materials against theft, diversion, sabotage, and other malicious acts using a graded approach appropriate to the material and facility.
Pinch effect
Magnetic compression of a current-carrying plasma produced by the interaction between the current and its magnetic field.
Plasma
An ionized gas containing free electrons and ions. Fusion experiments must heat, shape, and confine plasma under extreme conditions.
Plasma current
Electric current flowing through a plasma. In tokamaks it helps create the poloidal field and contributes to equilibrium and heating.
Plasma-facing material
Material directly exposed to the plasma or energetic particles, requiring high heat-flux and radiation tolerance.
Poloidal field
Magnetic field directed around the short way of the plasma cross-section, contributing to plasma shaping and equilibrium.
Pool-type reactor
A liquid-metal fast-reactor layout placing much of the primary system inside a large reactor vessel or pool.
Pressure boundary
The set of vessels, piping, and connected components that retain pressurized reactor coolant or working fluid.
Pressurizer
A PWR component that controls primary-system pressure so bulk boiling does not occur in the reactor core.
Primary loop
The heat-transport circuit that directly removes heat from the reactor core.
Probabilistic risk assessment
A structured method for estimating the likelihood and consequences of accident sequences, identifying dominant contributors to risk, and supporting risk-informed decisions.
Process heat
Useful thermal energy supplied directly to industrial processes rather than first being converted to electricity.
Propulsion train
The machinery that transfers energy from a power source to a ship propeller, electric motor, or other propulsion device.
Public dose
Radiation exposure received by members of the public, evaluated against regulatory limits and protection standards.
Pulse reactor
A research reactor designed to produce short, controlled increases in neutron output for experiments, testing, or training.
Pulsed power
Technology that stores energy and releases it over very short times to create extremely high electrical power for experiments such as Z-pinches or magnetized-target compression.
R
Radiation shielding
Material and geometry used to reduce radiation exposure to workers, equipment, passengers, spacecraft, or the public.
Radiator panel
A surface engineered to reject heat by thermal radiation, crucial in vacuum where there is no atmospheric convective cooling.
Radio-frequency heating
Use of electromagnetic waves at selected frequencies to transfer energy to plasma particles and, in some systems, help drive plasma current.
Radioactive waste
Material containing radionuclides for which no further use is intended and that requires controlled characterization, handling, storage, treatment, transport, or disposal under the applicable regulatory framework.
Radioisotope power system
A device that converts heat from natural radioactive decay into electricity. It is not a nuclear reactor because it does not sustain a fission chain reaction.
Reactivity
A measure of how far a reactor is from the exact critical state. Control systems manage reactivity to change or stabilize power.
Reactor coolant pump
A pump that circulates primary coolant through the reactor core and connected heat exchangers in designs that use forced circulation.
Reactor pressure vessel
The heavy engineered vessel that contains the reactor core and, in many reactor families, the primary coolant under operating pressure.
Reactor test
A controlled experiment or test campaign involving a reactor or reactor-related hardware under a licensed or authorized test program.
Refueling interval
Time between scheduled fuel-replacement activities. Naval values are generally program-specific and not public design assumptions.
Remote handling
Robotic or remotely operated maintenance used where radiation, activation, vacuum boundaries, or geometry make direct human access impractical.
Repetition rate
How often a pulsed fusion system can repeat its fusion cycle. Practical power plants require high rate, reliability, target or load handling, and thermal recovery.
Research reactor
A reactor used primarily for research, education, testing, or isotope production rather than commercial electricity generation.
Rotational transform
The twist of magnetic field lines around a torus that helps confine particles; produced differently in tokamaks and stellarators.
S
Safeguards Information
A special U.S. category of sensitive unclassified information concerning physical protection of certain nuclear facilities and materials. It is protected from unauthorized disclosure.
Salt chemistry control
Management of salt composition and chemical state to limit corrosion, maintain heat-transfer properties, and support materials compatibility.
Sample environment
The controlled physical location and conditions in which a material or component is irradiated or tested.
Secondary loop
A separate heat-transport or steam circuit that receives heat through a heat exchanger without directly circulating through the core.
Security plan
A regulator-approved or otherwise authorized plan describing how a facility or activity will meet applicable physical-protection and security requirements. Details can be sensitive and are not appropriate for public design pages.
Shadow shield
A directional radiation shield placed so sensitive equipment or crew lie in a protected region rather than surrounding a reactor uniformly with heavy shielding.
Ship service power
Electrical power used by onboard systems other than direct propulsion, including sensors, habitability, communications, and auxiliaries.
Site preparation
Civil, electrical, security, environmental, and utility work needed before installing a transportable or modular energy system.
Site restoration
Actions taken during decommissioning or demobilization to achieve the regulator-approved or contractually required end state for land, structures, contamination, utilities, and environmental conditions.
SMR
Small modular reactor: generally an advanced reactor designed for modular fabrication and an electrical output up to roughly 300 MWe per module in IAEA usage.
Sodium coolant
Liquid sodium used as a high-temperature, low-pressure coolant in sodium-cooled fast reactors. Its strong chemical reactivity requires dedicated plant design controls.
Source term
The amount, type, physical form, and release characteristics of radioactive material that could be available for release in an accident analysis.
Specific power
Power output relative to mass or volume. It is especially important in aircraft, mobile, and space applications where mass is highly constrained.
Spent fuel
Fuel removed from a reactor after use. It remains radioactive and produces decay heat, requiring controlled handling and storage.
Spent nuclear fuel
Irradiated reactor fuel that has been removed from the core and remains highly radioactive, requiring shielding, cooling or secure storage, and an approved long-term disposition pathway.
Spheromak
A compact toroidal plasma configuration containing linked toroidal and poloidal magnetic fields, with much of the confining field carried by currents in the plasma itself.
Steady state
Operation intended to continue without relying on short inductive pulses as the fundamental time limit. Actual plant availability still depends on maintenance and supporting systems.
Steam dryer
Equipment that removes additional moisture from separated steam before it enters the main steam line.
Steam generator
A heat exchanger that uses reactor-system heat to produce steam in a separate water circuit.
Steam separator
Equipment that removes liquid water from a steam-water mixture before steam is sent onward.
Stellarator
A toroidal magnetic-confinement device that uses externally shaped three-dimensional magnetic fields and does not require a large transformer-driven plasma current for basic confinement.
Stirling conversion
Power conversion using a closed-cycle reciprocating engine driven by a temperature difference; used in some space power studies.
Superconducting magnet
A magnet using superconducting conductors to produce strong magnetic fields with low electrical resistance at cryogenic temperature.
Supercritical fluid
A fluid above its thermodynamic critical point, where liquid and vapor are no longer distinct phases.
Suppression pool
A large water inventory used in certain BWR containment designs to condense steam and support pressure suppression.
T
Target gain
For inertial confinement, the ratio of fusion energy released from a target to driver energy delivered to that target; it is not the same as whole-facility electrical gain.
Tertiary cooling loop
The external heat-rejection circuit associated with a condenser or heat sink, often using water or air.
Test article
A material, component, instrument, or assembly intentionally exposed to experimental conditions for measurement and qualification.
Thermal discharge
Release of heat to the environment, commonly through water or air heat-rejection systems. Environmental permits can limit temperature, flow, location, and ecological effects.
Thermal efficiency
The fraction of reactor heat converted into useful electrical or mechanical output.
Thermal neutron
A comparatively low-energy neutron that has been slowed by repeated interactions with a moderator.
Tokamak
A toroidal magnetic-confinement configuration that uses external magnets plus a large plasma current to shape and confine the plasma.
Toroidal field
Magnetic field directed around the long way of a torus, produced by toroidal-field coils in tokamaks and related devices.
Transient
A temporary change in reactor or plant conditions over time. Research reactors may intentionally create bounded transients for experimental purposes.
Transportable reactor
A reactor system designed so major modules can be moved between sites. Transportability does not imply operation while in transit.
Triple product
The product of plasma density, temperature, and energy-confinement time, widely used to compare fusion performance.
TRISO fuel
Tristructural-isotropic coated-particle fuel. Each tiny fuel kernel is surrounded by multiple ceramic and carbon layers designed to retain fission products.
Tritium
A radioactive hydrogen isotope containing one proton and two neutrons; one of the fuels considered for deuterium-tritium fusion.
Tritium fuel cycle
The systems that store, process, account for, recover, and return tritium for fusion use.
V
Vacuum vessel
The sealed chamber that provides the low-pressure environment required for a fusion plasma and supports many internal components.
Void fraction
The fraction of a coolant volume occupied by vapor rather than liquid. It is an important thermal-hydraulic variable in boiling systems.
W
Wall-plug efficiency
The fraction of electrical input power converted into useful driver or heating energy; important when moving from physics experiments toward practical fusion power plants.
Waste acceptance criteria
Technical and administrative requirements that waste must meet before a storage, treatment, transport, or disposal facility will accept it.
Water chemistry
Control of dissolved species and impurities in reactor water to manage corrosion, radiation fields, deposition, and materials performance.
Z
Z-pinch
A pulsed plasma configuration in which axial electric current generates an azimuthal magnetic field that compresses the plasma inward.
Phase 5 • Safety + Lifecycle Vocabulary
Learn the language behind credible nuclear claims
Phase 5 adds the vocabulary needed to understand why “safe,” “licensed,” “clean,” “low-waste,” and “small emergency zone” are not single engineering facts. Look for terms such as ALARA, defense-in-depth, source term, emergency planning zone, Part 53, proposed Part 57, safeguards information, probabilistic risk assessment, spent nuclear fuel, thermal discharge, waste acceptance criteria, and decommissioning funding assurance.
Open Phase 5 authority →Primary Learning References
Authoritative starting points
Phase 7 • Release Certification & Production Integration
Release certification
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Production boundary: this certification covers the Reactor Programs branch package. Parent-site shared CSS, navigation, search, logo, and global assets remain controlled by the Aurora website root and must already exist in production. Live deployment is not implied until the package is uploaded and the production URLs are rechecked.