Experiments and simulations of large scale hydrogen-nitrogen-air gas explosions for nuclear and hydrogen safety applications

Hydrogen safety is a general concern because of the high reactivity compared to hydrocarbon-based fuels. The strength of knowledge in risk assessments related to the physical phenomena and the ability of models to predict the consequence of accidental releases is a key aspect for the safe implementation of new technologies. Nuclear safety considers the possibility of accidental leakages of hydrogen gas and subsequent explosion events in risk analysis. In many configurations, the considered gaseous streams involve a large fraction of nitrogen gas mixed with hydrogen. This work presents the results of an extensive large scale explosion experimental campaign for hydrogen-nitrogen-air mixtures. The experiments were performed in a 50 m 3 vessel at Gexcon’s test site in Bergen, Norway. Covering a wide nitrogen fraction range from 0 vol.% to 80 vol.%, equivalence ratio range from 0.8-1.3 and exploring 4 distinct congestion levels, this research provides comprehensive insights into the complex interplay of variables influencing explosion behaviours in such mixtures. The experiments are simulated in the FLACS-CFD software to inform about the current level of conservatism of the predictions for engineering application purposes. The study shows the reduced overpressure with nitrogen added to hydrogen mixtures and supports the use of FLACS-CFD-based risk analysis for hydrogen-nitrogen scenarios. • Large-scale hydrogen-nitrogen gas explosions experiments and simulations. • Equivalence ratio, congestion and nitrogen addition to hydrogen effects in gas explosions. • Overpressure-time curves and maximum overpressure with equivalence ratio and nitrogen addition.