Small Modular Reactors (SMRs)

Small Modular Reactors (SMRs) are advanced nuclear fission reactors with a generating capacity of up to 300 megawatts electric (MWe) per unit, roughly one-third the output of a conventional gigawatt-scale plant. The defining characteristic is not size alone but modularity: major components — the reactor pressure vessel, steam generators, and in some designs the entire nuclear island — are manufactured in a controlled factory setting and transported to the site for assembly, rather than being constructed in place. The International Atomic Energy Agency (IAEA), which maintains the Advanced Reactors Information System (ARIS) database, formalised the 300 MWe threshold and tracks roughly 80-plus designs at varying maturity. The conceptual lineage runs through naval propulsion reactors developed from the 1950s, whose compact, sealed cores demonstrated that small fission plants could operate reliably for long fuelling cycles. The contemporary policy push dates to the 2010s, driven by capital-cost overruns on large reactors such as Vogtle (Georgia) and Flamanville (France) and by demand for dispatchable low-carbon power.

The procedural logic of SMR deployment inverts the traditional build sequence. In a conventional plant, regulators license a bespoke design tied to a single site, and construction proceeds through stick-built fabrication on the ground. With SMRs, a vendor first secures a standardised design certification or design approval from a national regulator — in the United States the Nuclear Regulatory Commission (NRC) issues these under 10 CFR Part 52. The certified design is then replicated across multiple orders, with serial factory production intended to drive learning-curve cost reductions analogous to those in aircraft or shipbuilding. On site, the operator pours a far smaller civil-works footprint, lowers pre-fabricated modules into position, connects balance-of-plant systems, and commissions the unit. Multiple modules can be co-located and added incrementally as demand grows, allowing a phased capital commitment rather than a single multi-billion-dollar outlay.

A second pillar is passive safety. Many SMR designs rely on natural circulation, gravity-fed coolant, and large heat sinks so that the core can be cooled without external power or operator intervention following a shutdown — a direct response to the 2011 Fukushima Daiichi loss of off-site power. Designs span several technology families: light-water reactors (NuScale's VOYGR, GE Hitachi's BWRX-300), high-temperature gas-cooled reactors (X-energy's Xe-100), molten-salt reactors, and sodium-cooled fast reactors (TerraPower's Natrium). A subset, the microreactors, falls below roughly 20 MWe and targets remote communities, mining operations, and military forward bases. Smaller source terms and underground siting also allow regulators to consider reduced emergency planning zones, a contested but consequential licensing advantage.

Named programmes illustrate the global field. In 2020 the NRC issued its first design approval for NuScale Power's module, though the company's flagship Carbon Free Power Project in Idaho was cancelled in November 2023 amid rising costs. Canada selected GE Hitachi's BWRX-300 for Ontario Power Generation's Darlington site, with construction approved in 2025. India's Union Budget 2025-26 announced a Nuclear Energy Mission targeting 100 GW of nuclear capacity by 2047 and committed roughly ₹20,000 crore toward developing at least five indigenously designed SMRs by 2033; the Department of Atomic Energy and Bharatiya Nabhikiya Vidyut Nigam Limited (BHAVINI) are central actors, and amendments to the Atomic Energy Act and the Civil Liability for Nuclear Damage Act, 2010 were proposed to enable private participation. Russia's Akademik Lomonosov, a floating plant with two KLT-40S units commissioned in 2020 at Pevek, remains the only operating commercial SMR in the strict sense.

SMRs must be distinguished from adjacent concepts. They are not the same as microreactors, which are a sub-category an order of magnitude smaller. Nor are they identical to Generation IV reactors, a classification defined by the Generation IV International Forum around fuel-cycle and coolant innovations; some SMRs are Gen-IV designs, but many are scaled-down Generation III+ light-water reactors. They also differ from conventional large reactors chiefly in deployment economics and modularity, not in the underlying fission physics. In the Indian civil-service context, the term overlaps with the indigenous Bharat Small Reactor (BSR) — a 220 MWe pressurised heavy-water design adapted from proven units for captive industrial use.

The principal controversies concern economics, fuel, and proliferation. The promised cost advantage depends on serial production volumes that no vendor has yet achieved, and several analyses note that smaller units sacrifice the economies of scale of large plants; the NuScale cancellation crystallised these doubts. Many advanced designs require High-Assay Low-Enriched Uranium (HALEU), enriched between 5 and 20 percent, for which commercial supply outside Russia remains nascent, raising both supply-security and non-proliferation questions under IAEA safeguards. Critics also flag higher per-megawatt spent-fuel volumes in some designs and the regulatory burden of licensing novel coolants. India's liability regime, which channels supplier liability under Section 17(b) of the 2010 Act, has historically deterred foreign vendors, making the proposed amendments pivotal.

For the working practitioner, SMRs sit at the intersection of energy security, climate policy, industrial strategy, and arms-control diplomacy. A desk officer tracking India's GS3 energy agenda must read the Nuclear Energy Mission alongside net-zero-by-2070 commitments and the geopolitics of HALEU supply. Diplomats negotiate technology transfer, 123-type agreements, and safeguards protocols that determine which designs a state may import. Analysts should treat vendor capacity announcements with caution, anchoring assessments to regulatory milestones — design certification, first concrete, grid connection — rather than to projected fleet figures, because the gap between announced and operational SMRs remains the defining feature of the sector.