Flame structures and ignition thresholds of hydrogen jets containing sodium mist under various gas concentrations

ABSTRACT

Non-premixed combustion of hydrogen jets containing sodium vapor and mist reduces threats to reactor containment integrity in sodium-cooled fast reactors (SFRs) because it gradually consumes hydrogen gas generated mainly by a reaction between sodium and concrete. Previous studies have been limited to experimentally determining ignition thresholds on the jet temperature and the sodium concentration under specific gas concentrations. In this study, ignition experiments on hydrogen jets containing sodium mist were carried out at a specific jet temperature and sodium concentration under various gas concentration conditions (1–15 vol% hydrogen and 3–21 vol% oxygen). As a result, a stable sodium flame was observed in the jet and then formed a lifted hydrogen flame from a fuel nozzle outlet. An attached hydrogen flame on the outlet was also formed under high hydrogen concentration conditions. These flame structures seemed to be attributed to hydrogen flame propagation, which depends on the hydrogen concentration, jet temperature, and jet velocity. Additionally, the experimental results revealed ignition thresholds on the gas concentration and indicated a flammable region where the hydrogen-sodium jet combustion was more advantageous than an explosive premixed hydrogen combustion. Our study will enable the advancement of safety assessment technology in SRFs.

KEYWORDS:

• sodium-cooled fast reactor
• severe accident
• hydrogen
• sodium
• ignition
• combustion
• experiment
• flame structure
• PRA

Acknowledgments

We thank Professor M. Konomura and Professor T. Watanabe of the University of Fukui for years of collaboration and advice. We would also like to take this opportunity to thank the collaborators on this experiment in Japan Atomic Energy Agency and offer special thanks to Mr T. Watanabe for the operation of the Sodium Engineering Research Facility. This study is part of the results of ‘Development of Estimation Technology for Availability of Measure for Failure of Containment Vessel in Sodium Cooled Fast Reactor’ and supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT).

Disclosure statement

No potential conflict of interest was reported by the author(s).