What are small modular reactors (SMRs)?

A small modular reactor (SMR) is a reactor of less than 300 MW output whose main components are built in a central factory and assembled on site. SMRs bring factory economics to nuclear power, in principle cutting construction from ten years to three and turning the risk profile from a mega-project into a mass-produced product. Many designs are inherently safe: even in a total blackout the core shuts down safely on gravity and natural convection alone.

The core promise of SMRs is modularity. A conventional nuclear plant is a large-scale bespoke civil-engineering project — every unit is a one-off construction site, which is precisely why cost and schedule are so hard to control. SMRs instead build components under strict factory quality control and assemble them on site. In theory this compresses construction from ten years to three and lets buyers purchase capacity in smaller increments rather than committing to a single gigawatt-scale unit in one go. The shift is from a mega-project risk profile to that of a manufactured product.

The second feature is inherent safety. Many SMR designs cannot melt down even in a complete station blackout: gravity and natural convection alone bring the core to a safe shutdown with no human intervention. This continues the passive-safety logic of Generation III+ designs such as Westinghouse's AP1000 and China's Hualong One, moving safety from 'dependence on active systems' to 'the laws of physics performing the safety function'. The practical consequence is a smaller regulatory exclusion zone, which in principle allows reactors to sit much closer to cities or industrial areas — the decisive feature for land-constrained countries.

For a city-state like Singapore this is the whole question. The 2012 Pre-Feasibility Study on Nuclear Energy concluded that under the safety standards of the time, the exclusion zone for a 1,000 MW reactor would span the entire 730 km2 island: there was simply no point on the map where a conventional reactor could sit without endangering the whole population. An SMR's exclusion radius might be only a few hundred metres, which could permit deployment on Jurong Island or even on an offshore floating platform. Japan's 2023 Green Transformation (GX) policy likewise commits to next-generation advanced reactors including SMRs and high-temperature gas-cooled reactors (HTGRs).

One of the most compelling SMR applications is not electricity but high-temperature process heat. Steelmaking, chemicals and hydrogen production need temperatures above 500°C and today depend almost entirely on fossil fuels; high-temperature SMRs can supply that heat directly, reaching hard-to-abate sectors that solar and wind struggle to serve. The obstacles are real, however: the 2023 collapse of NuScale's flagship US project showed that even 'small' nuclear faces very large challenges, and the supply chain for the high-assay low-enriched uranium (HALEU) that next-generation SMRs need is still being built — even with domestically mined uranium, the United States still relies on Russia's Tenex for close to 20% of its enriched fuel.

SMRs shift nuclear's risk profile from a mega-project to a mass-producible product.

This question is covered in depth in The Full Spectrum Every Energy Source Explained — A Singapore Perspective，第六章 6.8