Overview of Liquid Sodium Fires: A Case of Sodium–Cooled Fast Reactors

Abstract of the technical paper presented at:
The 25th International Conference on Structural Mechanics in Reactor Technology (SMiRT 25) – 16th International Post Conference Seminar on Fire Safety in Nuclear Power Plants and Installations
October 27 to 30, 2019
Ottawa, Ontario

Prepared by:
J. Eduful, A. Bounagui and H. Shalabi
Canadian Nuclear Safety Commission

Abstract

Six reactor technologies were selected and believed to represent the future shape of nuclear energy in the Generation IV program. These are: Gas-cooled fast reactor (GFR), Lead-cooled fast reactor (LFR), Molten salt reactor (MSR), Sodium-cooled fast reactor (SFR), Supercritical water-cooled reactor (SCWR), and Very high-temperature gas reactor (VHTR). SFR have the largest experience based among the six reactor technologies selected by the Generation IV International Forum (GIF). That is approximately 400 reactor-years experienced over five decades and in over eight countries. The SFR has been the main technology of interest in GIF.

The SFR uses liquid sodium as the reactor coolant, allowing high power density with low coolant volume, at low pressure close to atmospheric and a good safety margin to coolant boiling point. As a result, coolant leaks or pipe breaks does not result in the same loss-of-coolant accident effect such as the possible depressurization, coolant boiling and loss of cooling capability often postulated with light water or heavy water reactors. However, sodium has a high reactivity with air and water. Specifically, sodium leak in air could lead to the production of toxic sodium-oxide aerosols caused by sodium fires. In addition, sodium's fast and exothermic reaction with water produces sodium hydroxide and hydrogen that could cause hydrogen explosions. To meet fire protection regulatory objectives, adequate evaluation and verification is required to be performed. This ensures that fires and explosions that may be associated with sodium’s reactivity are prevented or adequately controlled not to compromise nuclear safety, damage safety related structures, systems and components and put personnel at risk.

This paper presents an overview and discussion of liquid sodium fires associated with SFRs. It further discusses potential fire protection challenges and concerns that require careful evaluation to ensure fire safety of the next generation of nuclear reactors. A better understanding of fire and explosion hazards associated with liquid sodium handling is key to developing appropriates fire protection measures for future SFR design and enhancing regulatory requirements for SFRs.

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