The Complete Buyer's Guide to Small Modular Reactors

Why This Guide Matters

The small modular reactor market is fragmenting into six or more distinct reactor types, each with fundamentally different engineering approaches, coolants, fuels, safety profiles, and deployment timelines. Unlike the conventional nuclear fleet where pressurized water reactors dominate (accounting for ~70% of global capacity), the next generation of nuclear plants will feature genuine technological diversity. For utilities, data center operators, industrial buyers, and investors, understanding these differences is essential for making informed decisions.

The choice of reactor type determines nearly everything: what fuel is needed (standard LEU vs HALEU), how quickly it can be licensed, what applications it serves (grid power vs process heat vs remote deployment), and when it will be available. Each type carries different supply chain risks, regulatory timelines, and cost trajectories.

This guide covers all six major reactor types with technical specifications, key players, advantages, and challenges. For deployment timelines, funding data, and market analysis, see our State of SMR 2026 Annual Report.

Pressurized Water Reactors (PWR)

PWR-based SMRs are the most proven and regulatory-ready reactor type, based on the same fundamental technology that powers ~70% of the world's existing nuclear fleet. They use ordinary (light) water as both coolant and moderator, with the primary cooling loop pressurized to prevent boiling. Modern SMR designs like NuScale's VOYGR incorporate integral designs where the steam generator sits inside the reactor vessel, eliminating large-bore piping and reducing the potential for loss-of-coolant accidents.

The critical advantage of PWR SMRs is fuel supply: they use standard LEU enriched below 5%, the same fuel produced at scale by the global nuclear fuel supply chain. This means no dependency on the constrained HALEU supply chain. PWR designs also benefit from decades of operating experience, established regulatory frameworks, and an existing workforce trained on light-water reactor technology.

Molten Salt Reactors (MSR/FHR)

Molten salt reactors use liquid salts — typically fluoride-based compounds like FLiBe (lithium fluoride-beryllium fluoride) — as the primary coolant, and in some designs, as both coolant and fuel carrier. The Kairos Power KP-FHR is a fluoride salt-cooled high-temperature reactor that uses solid TRISO pebble fuel with molten salt coolant, while Terrestrial Energy's IMSR dissolves the fuel directly in the salt.

MSR designs have inherent safety advantages: the salt operates at atmospheric pressure (eliminating pressurization risks), and a freeze plug at the bottom of the reactor vessel passively drains fuel to a dump tank if temperatures exceed design limits. Kairos Power's Hermes demonstration reactor at Oak Ridge received the first NRC construction permit for an advanced reactor in December 2023.

Sodium-Cooled Fast Reactors (SFR)

Sodium-cooled fast reactors use liquid sodium metal as the primary coolant and operate with a fast neutron spectrum (no moderator). The "fast" designation means neutrons are not slowed down, enabling more efficient use of fuel and the ability to "breed" new fissile material from fertile isotopes. TerraPower's Natrium design adds an innovative molten salt thermal energy storage system, enabling the plant to ramp from 345 MWe baseload to 500 MWe peak output — a load-following capability that makes it particularly attractive for grids with high renewable penetration.

SFR technology has decades of operational precedent: sodium-cooled reactors have operated in the US (EBR-II), France (Phenix, Superphenix), Russia (BN-600, BN-800), Japan (Monju), and India (PFBR). TerraPower's Natrium plant at Kemmerer, Wyoming secured its NRC construction permit and is the furthest-along US advanced reactor project with a 2030 target completion.

Lead-Cooled Fast Reactors (LFR)

Lead-cooled fast reactors use liquid lead (or lead-bismuth eutectic) as the primary coolant. Lead's extremely high boiling point (1,749 C) means the reactor operates at atmospheric pressure with enormous thermal margins — the coolant cannot boil under any credible accident scenario. Lead is also chemically inert with water and air, eliminating the fire risk associated with sodium coolant.

Newcleo is the leading LFR developer, with a distinctive approach: using MOX fuel fabricated from reprocessed spent nuclear fuel, addressing both waste management and fuel supply simultaneously. The company moved its headquarters from the UK to Paris in 2025 and is building a non-nuclear PRECURSOR prototype in Italy. Blykalla's SEALER reactor in Sweden is another promising LFR design.

High Temperature Gas Reactors (HTGR)

HTGRs use helium gas as the coolant and TRISO (Tri-structural Isotropic) fuel particles — tiny uranium kernels coated in multiple layers of ceramic that can withstand temperatures above 1,600 C without releasing fission products. This makes fuel meltdown physically impossible: the fuel itself is the containment. HTGRs achieve the highest outlet temperatures of any reactor type (700-950 C), making them uniquely suitable for industrial process heat applications like hydrogen production, petrochemical refining, and desalination.

China's HTR-PM at Shidaowan became the world's first Gen IV reactor in commercial operation in 2023, providing real-world proof of the HTGR concept. X-energy's Xe-100 design is the leading Western HTGR, backed by Amazon's investment and a DOE ARDP award of up to $1.2 billion. X-energy also operates TRISO-X, the first NRC-licensed commercial TRISO fuel fabrication facility.

Microreactors

Microreactors are the smallest category of nuclear reactors, typically producing 1-20 MWe. They are designed for factory fabrication, truck transportability, rapid deployment, and autonomous operation with minimal on-site staffing. Use cases include remote communities, military bases, mining operations, disaster relief, edge data centers, and industrial facilities. The key value proposition is replacing diesel generators with decades-long, carbon-free power sources.

Radiant Industries is targeting the first US civilian microreactor criticality test on July 4, 2026 at the INL DOME facility, with commercial production planned for 2028 at its R-50 factory in Oak Ridge (50 units/year capacity). Last Energy has taken a different approach with a 20 MWe PWR-based microreactor and 80+ commercial agreements across Europe, with half targeting data center customers.

Head-to-Head Comparison

The following table compares all six reactor types across the key metrics that determine commercial viability: output range, coolant, fuel type, HALEU dependency, regulatory readiness, construction timeline, best application, and passive safety characteristics.

Which Reactor Type Is Best For...

Fuel Supply Implications

The choice of reactor type has direct implications for fuel supply chain risk. Designs requiring HALEU face a significant bottleneck: US production is currently limited to ~900 kg/year from Centrus Energy's demonstration cascade, while planned reactors will need multi-ton annual supplies. Designs using standard LEU avoid this constraint entirely.

Investor Implications

Each reactor modality carries a different risk/reward profile for investors. The fundamental tension is between proven technology (PWR) with lower returns and advanced technology (SFR, HTGR, MSR) with higher upside but greater execution risk.

Frequently Asked Questions