Liquid sodium in primary systems, often with an intermediate sodium or other isolated heat-transport circuit.
Fission System • Liquid-Metal Fast Reactor
Sodium Fast Reactor
A sodium-cooled fast reactor uses liquid sodium to move heat from a fast-spectrum core. Pool-type and loop-type arrangements have both been developed, and many plants use an intermediate heat-transport circuit to isolate primary sodium from the power-conversion system.
Liquid Sodium CoolantFast SpectrumOperating + Demonstration HeritageAdvanced Development
Phase 4 • Page-Specific Technical Summary
What this reactor category means
System definition
A fast-neutron reactor family using liquid sodium as the primary heat-transport medium.
A fast-neutron reactor family using liquid sodium as the primary heat-transport medium.
Intended applications
Electricity, fast-reactor fuel and materials research, actinide-management studies, and high-temperature energy-system development.
Electricity, fast-reactor fuel and materials research, actinide-management studies, and high-temperature energy-system development.
Public boundary
Technology classification, system relationships, maturity, and engineering challenges only. No design parameters, calculations, control logic, procedures, procurement data, or build instructions.
Technology classification, system relationships, maturity, and engineering challenges only. No design parameters, calculations, control logic, procedures, procurement data, or build instructions.
Phase 2 • Public-Level System Architecture
Core System Elements
The full-width rendering above provides the visual system map. The callouts below identify the principal public-level functions without repeating the same reactor graphic a second time.
- Primary pool or loop and core region
- Primary sodium circulation
- Intermediate heat exchangers
- Intermediate heat-transport system
- Steam generator or alternative conversion interface
- Power conversion and heat rejection
System roles are family-level and intentionally qualitative. Exact geometry, operating conditions, safety classification, equipment boundaries, and licensing basis remain design-specific.
Phase 4 • Concise Comparison
Engineering comparison
Fast-neutron spectrum without a conventional moderator.
Substantial experimental and demonstration heritage, limited operating deployment, and continued advanced development.
Fast-spectrum electricity and fuel-cycle missions, with high-temperature heat transfer at low coolant pressure.
Sodium-air and sodium-water chemical reactivity, leak detection, opaque-coolant inspection, materials compatibility, steam-generator or conversion-interface design, fuel-cycle policy, licensing, cost, and maintainability.
Phase 4 • Technical Education + Terminology + Accuracy
Learn the System
This learning layer explains the system in public engineering language. Definitions are intentionally conceptual: they teach terminology and relationships without providing operating procedures, design set-points, construction dimensions, or protected implementation details.
Maturity checkpoint: Fast-reactor technology has historical operating experience; in March 2026 the NRC issued a construction permit for TerraPower’s Kemmerer Unit 1 sodium fast reactor project.
System walkthrough
How it works — at a safe public level
- A compact core sustains fission primarily with fast neutrons.
- Liquid sodium removes heat from the core at relatively low pressure.
- Many architectures pass heat through an intermediate sodium loop before the steam or power-conversion system.
- The power cycle produces electricity while keeping water separated from the primary sodium system.
- Fuel-cycle strategy, sodium chemistry, inspection, leak detection, and passive decay-heat removal are major design concerns.
Key distinction: Fast spectrum describes neutron physics; sodium coolant describes heat transport. The combination enables high-temperature, low-pressure operation but introduces sodium chemical-reactivity challenges.
Technical vocabulary
Terms worth knowing
Fast spectrum
A neutron-energy environment dominated by fast neutrons rather than strongly moderated thermal neutrons.
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.
Liquid metal coolant
A liquid metal used to carry reactor heat. Sodium, lead, and lead-bismuth are examples used in fast-reactor concepts.
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.
Pool-type reactor
A liquid-metal fast-reactor layout placing much of the primary system inside a large reactor vessel or pool.
Loop-type reactor
A reactor layout in which primary coolant circulates through external piping loops connecting the reactor vessel to heat exchangers.
Natural circulation
Fluid motion driven by density differences rather than by a mechanical pump.
Decay heat
Heat that continues after the fission chain reaction stops because radioactive fission products continue to decay.
Fuel cycle
The sequence of activities involving nuclear fuel resources, enrichment or fabrication where applicable, reactor use, storage, recycling options, and waste management.
Burnup
A measure of energy extracted from nuclear fuel relative to the amount of fuel material.
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.
Authoritative learning referencesU.S. NRC — Advanced Reactor Highlights ↗Generation IV International Forum ↗
Application Context
Where the family fits
Fast-Reactor Electricity
Grid-power demonstrations and development programs built around sodium’s heat-transfer characteristics.
Fuel & Materials Research
Fast-neutron environments for fuels, structural materials, and reactor-physics validation.
Actinide-Management Studies
Selected closed-fuel-cycle concepts examine resource utilization and long-lived actinide management under national policy controls.
10-Phase Reactor Program • Phase 2
Standardized fission technical specification
Standardized public-safe fields support comparison across every fission and fusion family. Values are intentionally qualitative; licensing data, dimensions, operating windows, calculations, control logic, and build instructions remain offline.
Liquid sodium, usually with an isolated intermediate circuit
Fast spectrum
Metallic or oxide fuel depending program and fuel-cycle mission
Demonstration and limited-deployment fast-reactor plant
Intermediate heat transport to steam or alternative conversion
Substantial experimental and demonstration heritage
Fast-spectrum recycling can improve uranium use and transmute selected actinides, but it does not consume every radionuclide or remove fission-product waste and repository needs.
Specification boundary: Family-level technology classification and lifecycle context—not a vendor datasheet, safety analysis, procurement specification, or construction package.
Ten-Phase Reactor Program · Phase 5
Safety, licensing, lifecycle & public trust
Phase 5 treats safety as a full lifecycle obligation: site and license basis, fuel/material supply, operation, environmental controls, safeguards, emergency preparedness, waste, decommissioning, and disciplined public claims.
Sodium chemical reactivity and fire, decay-heat removal, opaque-coolant inspection, leak detection, fuel and core feedbacks, intermediate heat transport, maintenance, and severe-event mitigation.
In the United States, Parts 50 and 52 remain available, and Part 53 became available in 2026 as a risk-informed, performance-based, technology-inclusive pathway for eligible class 103 commercial plants. For microreactors, the NRC has also proposed Part 57; it is not yet an available licensing route. Exact applicability depends on design, mission, fuel, and site.
Account for sodium's chemical reactivity, fire protection, leak management, intermediate heat transport where used, water/air interfaces, site heat rejection, construction, transmission, and cleanup of sodium-contaminated equipment. Environmental benefit claims must include the actual balance of plant.
Fuel form and enrichment are design-specific. Many advanced-reactor concepts depend on fuels or supply chains that differ from today's light-water fleet, including some designs that require HALEU. Fuel qualification, fabrication capacity, transport packages, and secure material availability can be deployment gates.
Lifecycle planning includes used fuel, activated structures, sodium-contaminated equipment and cleanup media, coolant disposition, maintenance waste, decommissioning, and final disposal or recycling pathways where legally and technically established.
Apply graded material control and accounting, physical protection, cybersecurity, transport controls, insider-risk controls, and international safeguards as applicable to the material, facility, mission, and jurisdiction. Public pages must not reproduce Safeguards Information, sensitive security layouts, response tactics, or adversary-useful detail.
Eligible SMRs, non-light-water reactors, and non-power facilities may use the performance-based 10 CFR 50.160 emergency-preparedness framework. EP scope and any plume-exposure planning zone are consequence- and site-informed; neither reactor size nor passive features automatically reduce the requirement to zero.
State the maturity actually achieved, name the applicable authority, separate family-level evidence from project approval, and distinguish demonstrated performance from projections or marketing.
May describe a design family as research, demonstration, early deployment, or commercially operating only where the cited design actually supports that maturity. May say U.S. licensing pathways exist without claiming that a particular design is licensed.
Do not convert passive features into 'walk-away safe,' fuel robustness into 'meltdown-proof,' smaller size into 'no emergency planning,' or advanced fuel into 'waste-free' or 'proliferation-proof.' Do not treat concept maturity as project approval.
Phase 5 evidence:NRC — Advanced Reactor Licensing ↗NRC — Part 53 / Advanced Reactor Rulemaking ↗NRC — Performance-Based Emergency Preparedness ↗DOE — HALEU Availability Program ↗
Public classification only: This is not a safety finding, licensing opinion, environmental permit, emergency plan, security plan, safeguards determination, waste-acceptance decision, or legal advice. Exact obligations belong to the applicable regulator and project authority.
Phase 7 • Release Certification & Production Integration
Release certification
This page has passed the Reactor Programs Phase 7 branch-level release review for internal routing, asset references, canonical metadata, maturity and terminology controls, source-authority links, accessibility essentials, responsive markup, and release traceability.
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.