Analysis of Isotopic Effects on Hydrogen Oxidation

Tritium generation presents a significant hazard during operation of nuclear reactors and necessitates safety precautions in the case of a combustion incident. Accurate kinetic models should inform these safety precautions, however, reliable tritium data do not exist to generate such models. This work focuses on laminar flame speed, which is an important component of kinetic models. Current estimates based on established kinetic theories and experimental measurements of the other isotopes of hydrogen predict tritium to have a flame speed approximately 70% that of standard protium over a broad range of stoichiometries at one atmosphere in air. These estimates are based solely on isotopic mass differences and do not account for radioactive decay, which, in the case of tritium, is energetic enough to cause significant radiolysis reactions and potentially alter the radical pool for combustion. Simulations of a protium flame present compelling evidence that hydrogen flames are controlled by preferential radical diffusion from the rigorous flame region towards the unburned gases and not by heat conduction and dissociation of stable molecules. These flames rely on very low radical concentrations at the initiation region of the flame and the chemistry may be altered by a slight increase in radicals due to radioactive decay. This work also presents an experimental method suitable for measuring these radioactivity effects on tritium flame speed utilizing direct measurements of a flame propagating through a transparent tube. Measurements of protium and deuterium flame speeds using this method have proven highly repeatable and consistent with literature values while consuming much less reactant than other potential methods.