Small Modular Reactor Design and Safety Systems

Small modular reactors (SMRs) represent a paradigm shift in nuclear energy, delivering enhanced safety, scalability and economic flexibility compared with large‐scale plants. Typical SMR designs integrate primary components within a single vessel or compact containment, minimising piping and external connections to reduce both the probability and potential severity of accident scenarios. Passive safety systems exploit natural forces—gravity, convection and condensation—to remove decay heat and maintain core cooling without reliance on active components or off‐site power. Modular fabrication in factory environments allows for standardised quality control and shorter on‐site construction schedules. SMRs span a spectrum of coolant technologies, including light water, high‐temperature gas and molten salt, each with distinct neutronic and thermal characteristics. Core designs vary from integral pressurised water reactors with internal steam generators and control rod drive mechanisms to advanced fast and thermal spectrum concepts employing novel fuels and materials. Safety systems encompass decay heat removal loops, safety injection trains, depressurisation valves and containment isolation features, often arranged to function without operator intervention. Regulatory and licensing frameworks are adapting to these innovations, focusing on module standardisation, multi‐unit site zoning and staged deployment. Globally, SMRs are poised to support grid stability, cogeneration of process heat, desalination and remote power applications, with potential contributions to low‐carbon energy transitions and sustainable development goals.

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Small Modular Reactor Design and Safety Systems publication trend

The graph below shows the total number of articles in small modular reactor design and safety systems across all publications each year (not limited to Nature Index journals).

Technical terms

Passive safety system: A configuration that uses natural forces (gravity, convection, conduction) rather than powered equipment to maintain core cooling and limit accident progression.

Integral pressurised water reactor (iPWR): A reactor design in which key components—reactor core, steam generator, pressuriser and control rod mechanisms—are housed within a single pressure vessel to minimise external piping and leak sources.

Decay heat removal: The process of extracting residual thermal power produced by radioactive decay in the reactor core after fission has ceased, crucial for preventing overheating.

Safety injection system: A set of hardware and fluid circuits designed to deliver coolant into the reactor core under accident conditions to maintain adequate cooling.

Containment isolation: A function that seals the reactor containment building to prevent release of radioactive material during abnormal events.

Thermal energy storage (TES): A system that stores heat—often in molten salt or other media—for later use, enabling flexible power output and load following.

References

1. Integral PWR-Type Small Modular Reactor Developmental Status, Design Characteristics and Passive Features: A Review. Energies (2020).
2. Deeds not words: Barriers and remedies for Small Modular nuclear Reactors. Energy (2020).
3. Repowering a Coal Power Unit with Small Modular Reactors and Thermal Energy Storage. Energies (2022).
4. Small Modular and Advanced Nuclear Reactors: A Reality Check. IEEE Access (2021).