IMSR400
About
The IMSR400 (Integral Molten Salt Reactor) is an MSR that operates at 390 MWe and about 700 degrees Celsius. The IMSR400 can be used for electricity production or process heat applications. Its high outlet temperature makes it well-suited for hydrogen production and industrial refining, in addition to lower heat applications like desalination and district heating.
| Developer | Terrestrial Energy |
|---|---|
| Country of Origin | United States |
| Size | Medium |
| Type | Molten Salt Reactor (MSR) |
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Analysis
2
Deployment Timescale
Score Justification
The IMSR400 incorporates a modular design and relies on fewer nuclear-grade components than traditional LWRs, an approach intended to support shorter construction timelines once the reactor is licensed. The design remains in the pre-application phase of regulatory engagement in the United States and Canada.
By indicator
- 1/4 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) - 3/3 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)
4
Overnight Cost
Score Justification
The IMSR400 does not require expensive containment domes or cooling towers. However, its specialized molten salt systems drive up the cost of components. Its moderate footprint and modularity help to limit on-site construction costs.
By indicator
- 3/4 Component Cost
What is the expected cost of the reactor’s major components? (40% of total score) - 5/6 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
Waste management and fuel costs for the IMSR400 are driven by the higher price and disposition uncertainty of molten-salt relative to traditional ceramic fuel. The reactor’s maintenance costs are less than most LWRs of the same size because MSRs do not have high pressure systems. Decommissioning costs are moderated by the reactor’s modular core unit and reduced reliance on large, pressure-retaining components.
By indicator
- 2/3 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) - 2/4 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) - 3/5 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) - 4/5 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 IMSR400’s construction approach avoids some of the cost and schedule drivers associated with large site-built reactors, supporting a moderate level of cost predictability. The absence of a built prototype limits the availability of a validated cost baseline.
By indicator
- 0/5 Prototype
To what extent has the reactor design been built, demonstrated, or commercially deployed in practice? (75% of total score) - 3/3 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)
5
Security
Score Justification
The IMSR400 uses standard-assay LEU fuel. Its thermal spectrum is not optimized to produce weapons-usable nuclear material. Terrestrial Energy implemented security by design as early as possible into the design development of the IMSR.
By indicator
- 3/3 Fuel
What is the enrichment level and composition of the reactor fuel? (40% of total score) - 4/4 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
While no formal safety case for the IMSR400 has been approved by a nuclear regulator, the design incorporates multiple fully passive shutdown mechanisms, including inherent negative reactivity feedback and a passive temperature-activated freeze-plug system. The IMSR400 uses fuel with inherent safety characteristics associated with molten salt operation and operates at low pressure with functional containment. Passive core heat removal is designed to function without operator action for over 72 hours. The molten salt coolant is chemically reactive relative to water or gas coolants, but less reactive than liquid sodium.
By indicator
- 0/2 Safety Case
How mature and publicly established is the reactor’s safety case with the regulator? (40% of total score) - 2/2 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) - 2/4 Coolant Reactivity
How chemically reactive is the reactor coolant? (10% of total score)
3
Spent Fuel & Radioactive Waste Management
Score Justification
The IMSR400 requires a very small on–site spent fuel storage footprint because the fuel is embedded in the liquid salt, which empties into drain tanks once the reactor is shut down for refueling after about seven years. After seven years, the entire fuel salt container is removed and replaced, simplifying spent fuel management. There is no licensing precedent for a molten salt spent fuel form.
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) - 3/3 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) - 2/2 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
The molten salt supply chain exists but needs more development to support deployment of the IMSR400 at 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)