Mathematical analysis of hydrogen mixing and diffusion in the vapor space of a high-level nuclear waste tank

This paper presents mathematical analyses of the possible accumulation of radiolytically produced hydrogen in the vapor space in a tank storing liquid high-level radioactive waste. Under normal operating conditions, these tanks are continuously ventilated with air to ensure that the concentration of hydrogen never reaches its lower flammability limit (4%). These scenarios are considered in which it is postulated that hydrogen may accumulate and present a flammability hazard. These scenarios are stratification due to gravity, slow mixing when the ventilation system is operating, and slow mixing when the ventilation system is not operating. In all three cases, the analyses indicate that the accumulation of hydrogen is not likely and thus does not present a flammability problem so long as controls are in place to dilute its concentration to less than 4%.