Ignition of flammable hydrogen/air mixtures by high mass mechanical impact of Magnox contaminated surfaces

Magnox and its corrosion products are a major constituent of some legacy nuclear waste storage silos which generate hydrogen. An experimental study investigates the likelihood of ignition of hydrogen/air when large mass projectiles impact rusty surfaces with Magnox contamination. Ignition is observed with 50kg projectiles impacting a 45º Magnox-smeared rusty anvil plate with KE as low as 40J. Theoretical calculations relating to the angled impacts reveal that they involve substantial tangential energy losses associated with frictional heating of the impact surfaces. It is shown that these energy losses are particularly dependent on the shape of the projectile since projectile geometry determines the radius of gyration and the relationship of centre of gravity to the impact point. In conclusion, the projectile shape is likely to be of greater importance than the mass (i.e. for a given impact energy) because of its direct bearing on the magnitude of the tangential energy loss.