Understanding of cyclic venting phenomena in Hanford Site high-level waste tanks: The evaluation of Tank 241-SY-101

Tank 241-SY-101 is a double-shell, high-level waste tank located in the 200 West Area on the Hanford Site. This tank contains about one million gallons of concentrated neutralized waste. Shortly after the waste was put in the tank, the waste began to expand because of gas generation. In 1990 this tank was declared to have an unreviewed safety question because of the generation of flammable mixtures of hydrogen and nitrous oxide gas that was periodically released to the tank dome space and ventilation system. A safety program was established to characterize the waste and released gases and to determine an effective means to prevent the accumulation of those gases in the tank dome space and ventilation system. Results of the expanded characterization conducted in fiscal year 1991 are presented. Instrumentation placed in the tank helped to provide more detailed information on tank temperatures, gas pressure, gas flow rates, and gas composition. An extensive laboratory study involving the Westinghouse Hanford Company, Pacific Northwest Laboratory, Argonne National Laboratory, and the Georgia Institute of Technology was initiated to determine the mechanisms responsible for the generation and retention of various gases. These studies evaluate both radiolytic and thermochemical processes. Results of the first series of experiments are described. (author)