Physics / mechanism
SMRs are nuclear fission reactors smaller (50-300 MWe per module vs 1,000-1,600 MWe for traditional plants) and modular (factory-built, shipped as units, assembled on site — “Ford assembly line for nuclear”). Architecture varies widely, and maturity tracks that variance (2024 11 12 Atomic Energy Can Nuclear Power Our):
- Light-Water Reactors (LWR-SMR) — most mature, proven PWR/BWR physics scaled down, ~15-16 MPa, ~315 °C. GE Hitachi BWRX-300 (300 MWe), Rolls-Royce SMR (470 MWe), NuScale VOYGR (250 MWe/module, the only US-design-certified SMR). Challenge is cost, not physics.
- High-Temperature Gas-Cooled (HTGR) — helium-cooled, ~750 °C, TRISO fuel; enables industrial process heat + hydrogen. X-energy Xe-100 (80 MWe), General Atomics EM2, USNC MMR.
- Molten-Salt (MSR) — atmospheric pressure, >600 °C, liquid or salt-cooled solid fuel. Terrestrial Energy IMSR, Moltex SSR, Seaborg CMSR, Copenhagen Atomics, Kairos KP-FHR (fluoride-salt-cooled, TRISO — Google’s 500 MWe partner).
- Sodium-Fast (SFR) — low pressure, ~500 °C, closed fuel cycle. TerraPower Natrium (345 MWe + molten-salt thermal storage to 500 MWe), ARC-100.
- Heat-pipe microreactors — newest, 1-25 MWe, simplest. Westinghouse eVinci, Oklo Aurora, Los Alamos Kilopower lineage.
Key advantage cluster: capacity factor >90% (true baseload, vs 35-45% wind / 15-30% solar), tiny land footprint (15-20 acres vs 1,500-2,000 for solar+storage equivalent), 60-80 year life, fuel ~10% of LCOE (price stability), and high-grade process heat the non-nuclear alternatives cannot supply. See Baseload Power for why those properties matter now.
Market driver — datacentre power is the catalyst
Decarbonisation and energy security are secondary. The catalyst is AI datacentre firm-power demand (2024 11 12 Atomic Energy Can Nuclear Power Our, Ai Power Thermal Binding): Google-Kairos (500 MWe, ~$2B incl. dedicated manufacturing), Amazon-X-energy (4× Xe-100), Microsoft-Constellation (Three Mile Island restart, ~$65/MWh PPA benchmark), Meta (load-following AI-datacentre design). Hyperscalers are becoming the anchor customers next-gen nuclear never had. Global nuclear is ~10% of electricity, ~$350-400B/yr, 440 reactors; IAEA sees capacity potentially doubling by 2050 mostly via SMRs, and datacentres are demand outside those forecasts.