Natrium
About
The Natrium is a modular SFR that operates at 345 MWe, with a molten salt-based energy storage system capable of 500 MWe. It is well suited for utility-scale deployment, and it could be adapted for medium-range process heat applications, such as desalination and district heating.
| Developer | Terrapower |
|---|---|
| Country of Origin | United States |
| Size | Medium |
| Type | Sodium-Cooled Fast Reactor (SFR) |
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Analysis
3
Deployment Timescale
Score Justification
The U.S. NRC has approved the environmental impact statement and final safety review for the Natrium. The NRC also issued a construction permit for the Natrium’s first plant in the United States. There is a history of several sodium-cooled fast reactors operating around the world, mostly at pilot scale. Once licensed, the Natrium’s modular design and specialized components result in a medium timeframe for deployment.
By indicator
- 2/4 Regulatory Engagement
To what extent has the reactor developer engaged with a recognized nuclear regulatory authority in the licensing process? (30% of total score) - 3/6 Technology Precedent
Has the reactor design, or a sufficiently similar design, been certified anywhere in the world? (10% of total score) - 2/3 Modularity
What share of total reactor systems can be manufactured off-site in controlled factory environments rather than constructed on-site? (15% of total score) - 3/4 Specialization
To what extent do construction activities and components require lengthy qualification processes? (15% of total score) - 2/5 Supply Chain
How mature and available are suppliers for key reactor components and fuel services? (30% of total score)
3
Overnight Cost
Score Justification
The Natrium does not require robust containment structures that can drive up overnight costs; however, the complexity of the design and the separate energy island increase costs.
By indicator
- 2/4 Component Cost
What is the expected cost of the reactor’s major components? (40% of total score) - 4/6 Construction Cost
To what extent does the design reduce construction cost and risk through modular fabrication and limited nuclear-grade specialization? (60% of total score)
3
Operational Cost
Score Justification
The Natrium’s operational costs are driven by expensive metallic HALEU fuel and maintenance and decommissioning costs related to its sodium coolant. It has a smaller footprint than traditional GW-scale reactors, which lessens the overall operational cost.
By indicator
- 1/3 Fuel Cost
What is the estimated cost of nuclear fuel per unit of electricity generated, including enrichment, fabrication, and back-end costs? (15% of total score) - 3/4 Maintenance Cost
What is the expected annual maintenance cost for the reactor and balance of plant systems, including consumables? (25% of total score) - 4/5 Staffing Level
How many full-time personnel are required to safely operate and maintain the reactor unit? (40% of total score) - 2/5 Spent Fuel & Radioactive Waste Management Cost
What are the expected operational costs associated with managing spent fuel, including interim storage, transport, disposal, or recycling? (10% of total score) - 2/5 Decommissioning Cost
What are the total lifetime contributions required for decommissioning, regardless of funding mechanism? (10% of total score)
2
Cost Predictability
Score Justification
The Natrium’s cost estimates are difficult to predict because it will be first-of-a-kind, though construction of a demonstration reactor is underway. The reactor’s modularity will help reduce the likelihood of cost overruns once a proven cost baseline has been established.
By indicator
- 0/5 Prototype
To what extent has the reactor design been built, demonstrated, or commercially deployed in practice? (75% of total score) - 2/3 Modularity
What share of total reactor systems can be manufactured off-site in controlled factory environments rather than constructed on-site? (25% of total score)
4
Security
Score Justification
TerraPower has integrated security by design into the Natrium, including cybersecurity. As a fast reactor, the Natrium could produce large amounts of plutonium, but it does not have a fertile blanket in its core to optimize this production.
By indicator
- 2/3 Fuel
What is the enrichment level and composition of the reactor fuel? (40% of total score) - 3/4 Nuclear Material Production
What is the potential for the reactor to produce weapons-usable nuclear material? (40% of total score) - 1/1 Security by Design
Has the reactor developer built in security by design? (20% of total score)
3
Safety
Score Justification
The Natrium’s natural circulation cooling enables indefinite heat removal. The reactor operates at ambient pressure, reducing the need for redundant high-pressure containment structures, but the sodium coolant that enables this ambient pressure poses a chemical reactivity hazard. The NRC completed its final safety evaluation of the first Natrium plant in December 2025.
By indicator
- 1/2 Safety Case
How mature and publicly established is the reactor’s safety case with the regulator? (40% of total score) - 1/2 Shutdown Mechanism
How diverse, independent, and passive are the reactor’s shutdown systems? (20% of total score) - 1/1 Fuel With Safety Characteristics
Does the reactor use fuel with accident tolerance or inherent safety characteristics? (10% of total score) - 2/4 Pressure & Containment
How well does the reactor’s containment strategy protect from the release of radioactive material? (10% of total score) - 3/3 Passive Heat Removal
How long can the reactor remove core heat without operator intervention? (10% of total score) - 1/4 Coolant Reactivity
How chemically reactive is the reactor coolant? (10% of total score)
2
Spent Fuel & Radioactive Waste Management
Score Justification
The Natrium produces relatively low levels of spent fuel per unit of electricity generated, due to the high burn-up levels that the reactor can achieve. However, there is no regulatory disposal precedent for the metallic HALEU spent fuel form. The Natrium’s sodium coolant creates an additional waste stream to manage.
By indicator
- 0/1 Spent Fuel Licensing Precedent
Has the spent fuel form been previously licensed for disposal? (20% of total score) - 2/4 Waste Streams
How many distinct waste streams require separate conditioning or handling pathways? (20% of total score) - 2/3 On-Site Storage
How much on-site area is required for interim spent fuel storage? (10% of total score) - 3/3 Spent Fuel Volume
What volume of spent fuel is produced per unit of electricity generated? (15% of total score) - 1/2 Decay Heat
What is the decay heat output of spent fuel at the 50-year interim storage milestone? (20% of total score) - 1/2 Time to Interim Storage
What is the average time until spent fuel can be transferred to interim storage? (15% of total score)
2
Supply Chain
Score Justification
TerraPower has developed partnerships aimed at securing enrichment services as well as deconversion, metallization, and fabrication for the Natrium’s HALEU metallic fuel. This supply chain remains at a pilot or low-volume scale.
By indicator
- 1/2 Key Component Availability
To what extent are commercial or pilot-scale suppliers available for the reactor’s major components? (60% of total score) - 2/4 Fuel Availability
Are suppliers available for both fuel fabrication and enrichment required by the reactor design? (40% of total score)