Sodium Combustion Phenomena in Fast Reactor Safety

Fast reactors cooled by liquid sodium offer significant advantages in breeding capability and thermal efficiency, but they introduce unique safety challenges associated with sodium’s high chemical reactivity. When liquid sodium escapes containment through a leak or breach, it can form a spray that contacts air or moisture, triggering a vigorous exothermic reaction known as a sodium spray fire. This combustion process produces aerosols—fine solid or liquid particles—that disperse throughout the reactor containment building. The characteristics of these aerosols, including their initial size distribution, hygroscopic growth, coagulation dynamics and deposition behaviour, critically influence heat transfer, radiological source terms and filtration requirements. Understanding sodium fire ignition thresholds, droplet evaporation and flame propagation is essential for accurate accident scenario modelling. Moreover, advanced diagnostic methods and computational tools are required to predict aerosol evolution in real time, assess containment integrity and guide design of passive and active mitigation systems. Global efforts focus on refining experimental protocols, improving semi‐empirical and mechanistic models of droplet size distributions, and integrating aerosol dynamics into probabilistic risk assessments. This body of work underpins the development of next‐generation sodium‐cooled fast reactors by ensuring that fire suppression strategies, emergency response measures and containment filtration systems are robust against rapid aerosol generation and subsequent radiological hazards.

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Sodium Combustion Phenomena in Fast Reactor Safety publication trend

The graph below shows the total number of articles in sodium combustion phenomena in fast reactor safety across all publications each year (not limited to Nature Index journals).

Technical terms

Sodium aerosol: Fine particles formed by the combustion or vaporisation of metallic sodium, suspended in a gas medium.

Sodium spray fire: A vigorous exothermic reaction that occurs when liquid sodium is dispersed as droplets into air or moisture, leading to rapid combustion and aerosol generation.

Mass median diameter (MMD): The particle diameter at which half of the aerosol mass is in particles smaller and half in particles larger, used to characterise size distributions.

Aerodynamic particle size distribution (APSD): A measurement of aerosol particles sorted by their aerodynamic diameter, reflecting both size and density effects on motion.

Brownian coagulation: The process by which aerosol particles collide and merge due to random thermal motion, leading to size growth over time.

References

1. Real-time measurements and modeling of sodium combustion aerosol dynamics in test chamber to improve the evaluation of SFR containment aerosol behaviour. Nuclear Engineering and Technology (2024).
2. Theoretical simulation on evolution of suspended sodium combustion aerosols characteristics in a closed chamber. Nuclear Engineering and Technology (2022).
3. Semi-Empirical Model of Droplet Size Distribution From the Maximum Entropy Principle in Sodium Spray. Frontiers in Energy Research (2022).