Waste tank hazard assessments using a plume burn model

Flammable gases are generated in the presence of radioactive waste in some of the Hanford waste storage tanks. In worst-case accident scenarios, ignition is postulated for the flammable gases, primarily hydrogen, nitrous oxide, and ammonia. Studies for the double-shell tanks show they remain intact when burning the maximum postulated gas inventory. However, a concern remains about the potential for burning gas to ignite a floating surface crust found in some tanks. The crust consists of organic carbon compounds mixed with the oxidants, sodium nitrate/sodium nitrite. This mixture suggests the potential for exothermic reactions that could self-propagate until the entire crust is aerosolized. This paper presents results for a waste tank, showing that if crust ignition occurs, the reaction will self-terminate and that aerosol generation is small.