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This report describes a method for estimating the ventilation rates of the high-level radioactive waste tank headspaces at the Hanford Site in Southeastern Washington state. The method, using hydrogen concentration data, is applied to all passively ventilated and selected mechanically ventilated tanks equipped with Standard Hydrogen Monitoring Systems (SHMS) and covers the time period from when the SHMS were installed through July 12, 1998. Results of the analyses are tabulated and compared with results from tracer gas studies and similar analyses of SHMS data. The method relies on instances of above-normal hydrogen releases and assumes the rate at which hydrogen is released by the waste is otherwise approximately constant. It also assumes that hydrogen is uniformly distributed in the tank headspace, so that at any given time the concentration of hydrogen in the effluent is approximately equal to the average headspace concentration and that measured by the SHMS. In general, the greatest single source of error in the method is the determination of the baseline hydrogen concentration, which in this study has been estimated by visual inspection of plotted data. Uncertainties in the calculated ventilation rates due to inaccurate baseline measurements are examined by performing a sensitivity analysis with upper and lower bounding values for the baseline concentration (in addition to the best estimate). A table lists the tanks considered in this report and the range of estimated ventilation rates obtained for each tank. When multiple events of above-normal hydrogen releases were observed, the range of estimated ventilation rates is given. Resulting values and their variability are consistent with those determined using tracer gases

Ventilation rates calculated from hydrogen release data in tanks equipped with standard hydrogen monitoring systems (SHMS)