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Executive SummaryThe 177 underground waste storage tanks at the Hadord Site contain millions of gallons of radioactive waste resulting fiom the purification of nuclear materials and related processes.Through various mechanisms, flammable gas mixtures of hydrogen, ammonia, methane, and nitrous oxide are generated and retained in significant quantities within the waste in many (-25) of these tanks. The potential for large releases of retained gas from these wastes creates a flammability hazard. It is a critical component of the effort to understand the flammability hazard and a primary goal of this laboratory investigation to establish an understanding of the mechanisms of gas retention and release in these wastes. The results of bubble retention experimental studies using waste samples from several waste tanks and a variety of waste types support resolution of the Flammable Gas Safety Issue. Gas bubble retention information gained in the pursuit of safe storage will, in turn, benefit future waste operations including salt-well pumping, waste transfers, and sluicinghetrieval. Waste SamplesPrevious laboratory studies on simulated and actual wastes established a framework within which to classify gas bubble retention mechanisms. The behavior observed in earlier gas retention experiments on four Hanford double-shell tank ( D S T ) wastes (24 1 -AN-1 03 , 24 1 -AW-10 1, 24 1 -SY-101, and 241-SY-103) and one single-shell tank (SST) waste (241-S-102) is captured within this general framework. Considering the relatively large number (19) of SSTs on the Hanford Flammable Gas Watch List, the experimental study of SST waste gas retention and release is limited. To answer this, the current gas retention experiments were conducted on four samples fiom three Hanford SSTs (one each fiom 241-A-101 and 241-S-106 and two fiom 241-U-103).These SSTs were selected using several criteria, including diversity of waste classification (type), behavior indicating that the waste retains, or has the potential of retaining, significant quantities of gas, status of supporting flammable gas data (e.g., retained gas sampler [RGS] results), and sample availability.Tank 241-A-101 (A-101) is of interest because RGS results indicate that the waste exists in an unexpected configuration, with the nonconvective (solids-containing) layer on top of the convective (liquid) layer. Tank A-101 contains double-shell slurry feed waste type, and it is reported to consist primarily of saltcake. The sample tested (Core 154, segment 5) was previously used (spent) in RGS testing.Tank 241-S-106 (S-106) contains noncomplexed waste type and is characterized as predominantly saltcake waste. This tank was of interest because barometric pressure evaluation (dL/dP) showed high gas retention (1519%) while the majority of RGS measurements showed a maximum of 10%. The S-106 gas retention sample was fiom the upper half of Core 183, segment 8.Tank 241-U-103 (U-103) also contains noncomplexed waste type but is reported to have a Two U-103 composite significant fraction of salt...

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