Small modular reactors trace their origins to the 1950s US Navy submarine program, where compact pressurized water reactors powered the USS Nautilus and established the engineering principles that modern SMRs build upon. The commercial SMR movement began in earnest in the 2000s with companies like NuScale Power (founded 2007), TerraPower (founded 2006), and X-energy (founded 2009). By 2026, the industry has reached a commercial inflection point: the BWRX-300 is under construction at Darlington, Canada; TerraPower's Natrium is advancing in Kemmerer, Wyoming; and tech hyperscalers have committed over 9.7 GW of nuclear capacity for AI data centers. This timeline tracks every major milestone from Chicago Pile-1 (1942) through the current SMR construction boom.
| YEAR | EVENT | SIGNIFICANCE |
|---|---|---|
| 1942 | Chicago Pile-1 achieves first controlled nuclear chain reaction | Proves nuclear fission can be controlled, launching the nuclear age |
| 1954 | USS Nautilus launched — first nuclear-powered submarine (STR/S1W, ~10 MWe) | Demonstrates compact reactor technology that becomes the engineering basis for modern SMRs |
| 1957 | Army SM-1 reactor at Fort Belvoir — first small land-based nuclear power plant (2 MWe) | First small modular-style reactor producing electricity for a US military installation |
| 1957 | Shippingport Atomic Power Station begins operation (60 MWe) | First full-scale commercial nuclear power plant in the US |
| 1979 | Three Mile Island Unit 2 partial meltdown | Halts US nuclear construction; drives demand for passive safety systems used in modern SMRs |
| 1986 | Chernobyl disaster | Transforms global nuclear regulation; motivates inherent safety designs central to SMR philosophy |
| 2000 | Generation IV International Forum (GIF) established | Defines six advanced reactor concepts that inspire next-generation SMR designs (SFR, HTGR, MSR, etc.) |
| 2006 | TerraPower founded by Bill Gates and Nathan Myhrvold | Launches sodium-cooled fast reactor (Natrium) development; becomes one of the leading SMR developers |
| 2007 | NuScale Power founded by Jose Reyes and Paul Lorenzini | First company dedicated to a factory-built light-water SMR for commercial electricity |
| 2009 | X-energy founded by Kam Ghaffarian | Begins development of the Xe-100 high-temperature gas-cooled reactor (HTGR) with TRISO fuel |
| 2011 | Fukushima Daiichi disaster | Accelerates global shift toward passive safety; reinforces the case for SMRs with inherent safety features |
| 2012 | DOE SMR Licensing Technical Support Program launched ($452M) | Federal cost-share program catalyzes commercial SMR development; NuScale selected as primary awardee |
| 2013 | Oklo founded to develop compact fast reactors | Pursues Aurora microreactor (1.5 MWe) for remote and distributed power applications |
| 2016 | NuScale submits first-ever SMR Design Certification Application to NRC | Initiates the formal NRC review process that would take 7 years to complete |
| 2020 | NRC issues Final Safety Evaluation Report for NuScale 50 MWe design | First positive safety finding for an SMR by any Western nuclear regulator |
| 2020 | DOE ARDP selects TerraPower Natrium and X-energy Xe-100 for $3.2B demonstration funding | Largest federal investment in advanced reactors since the Manhattan Project era; targets operational demos by 2028–2030 |
| 2022 | Inflation Reduction Act signed — includes nuclear production tax credits | Provides $15/MWh PTC for existing nuclear and up to $25/MWh for new clean energy, improving SMR economics |
| 2023 | NRC issues Design Certification Rule for NuScale 50 MWe module (January) | NuScale becomes the first and only SMR with full NRC Design Certification |
| 2023 | NuScale/UAMPS Carbon Free Power Project cancelled (November) | Cost escalation from $5.3B to $9.3B forces cancellation of the first planned US SMR plant; resets deployment expectations |
| 2024 | TerraPower breaks ground on Natrium demo plant in Kemmerer, Wyoming (June) | First advanced reactor construction start in the US; 345 MWe sodium-cooled fast reactor on former coal plant site |
| 2024 | Microsoft signs $16B 20-year PPA for Three Mile Island Unit 1 restart (September) | Largest corporate nuclear deal in history; signals tech industry commitment to nuclear for AI data centers |
| 2024 | Google signs 500 MW deal with Kairos Power (October) | First corporate commitment to a next-generation SMR fleet specifically for data center power |
| 2024 | Amazon invests $700M in X-energy for up to 12 Xe-100 reactors (October) | Major cloud provider commits to SMR fleet; validates HTGR technology for industrial-scale deployment |
| 2025 | GE Hitachi BWRX-300 receives CNSC Licence to Construct at Darlington, Ontario (April) | First SMR construction licence in North America; regulatory milestone for light-water SMR technology |
| 2025 | BWRX-300 construction begins at OPG Darlington site (May) | First SMR under construction in North America; targeted for operation in 2029 |
| 2025 | NuScale receives NRC Standard Design Approval for 77 MWe US460 module (May) | Uprated design certified; positions NuScale for Romania (RoPower) and Poland deployments |
| 2025 | Rolls-Royce SMR wins UK competition; Wylfa site selected (June) | Largest SMR design (470 MWe) selected for UK's first SMR; GDA Step 3 underway |
| 2025 | Meta announces up to 6.6 GW nuclear commitment across four partners (Q3–Q4) | Largest corporate nuclear commitment ever; includes TerraPower, Oklo, Vistra, and Constellation Energy |
| 2025 | DOE closes $1B loan for Three Mile Island Unit 1 restart (November) | Federal financing de-risks the first nuclear plant restart for a tech company |
| 2026 | TerraPower Natrium construction advancing in Kemmerer; NRC CP expected 2026 | First US advanced reactor nearing Construction Permit; on track for 2030 operation |
| 2026 | 70+ SMR designs in development globally; 9.7+ GW committed by hyperscalers | SMR industry reaches commercial inflection point with multiple designs in construction or late-stage licensing |
From Chicago Pile-1 to the USS Nautilus and Shippingport. Compact military reactors prove small nuclear is viable. Three Mile Island ends the first nuclear era.
Chernobyl reshapes regulation. Generation IV Forum defines advanced designs. TerraPower, NuScale, and X-energy founded. SMR concept takes commercial form.
DOE invests $452M+ in SMR development. NuScale submits first NRC application (2016). Fukushima reinforces passive safety. ARDP funds TerraPower and X-energy demos.
NuScale certified. BWRX-300 under construction. TerraPower building Natrium. Hyperscalers commit 9.7+ GW. SMR industry reaches inflection point.
The history of small modular reactors spans seven decades, from military propulsion to the commercial nuclear renaissance. The critical insight is that SMR development accelerated dramatically after 2020: NuScale achieved the first NRC design certification, TerraPower broke ground on the first US advanced reactor, and the BWRX-300 became the first SMR under construction in North America. Most importantly, the demand side transformed in 2024-2025 when tech hyperscalers committed over 9.7 GW of nuclear capacity for AI data centers. SMRs are no longer a research curiosity or a policy aspiration; they are now an active construction category with committed customers, licensed designs, and a multi-decade order pipeline.