Mechanisms of gas retention and release: Experimental results for Hanford single-shell waste tanks 241-A-101, 241-S-106, and 241-U-103

Abstract

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...

Strong-Sludge Gas Retention and Release Mechanisms in Clay Simulants

“…The average void fraction peaks at about 7% and then decreases to about 5%, which are the average gas void fractions reported by . This is strikingly low gas retention in comparison with smaller-scale tests of bubble retention reported by Van Kesteren (see Figure 11.5 of Winterwerp and Van Kesteren 2004), Van Kessel (1998), and similar studies focused on bubble retention in actual waste and simulants for Hanford waste (Gauglitz et al 1996;Rassat et al 1998). …”

“…These previous tests were typically analyzed to determine the maximum, or peak, retained-gas fraction and results were compared based on the shear strength of the material. Figure 1.7 reproduces a summary of many of these tests provided by Rassat et al (1998). In comparison with the large-scale test discussed above, the maximum gas fraction is substantially higher in small-scale tests.…”

“…The small-scale studies on the mechanisms of gas retention and bubble behavior in tank waste have been the subject of a number of studies (see for example, Gauglitz et al 1994Gauglitz et al , 1995Gauglitz et al , 1996Gauglitz et al , 2001Gauglitz et al , 2009Stewart et al 1996;Rassat et al 1997Rassat et al , 1998Rassat et al , 1999Bredt et al 1995;Bredt and Tingey 1996;and Walker et al 1994). Gauglitz et al (2009) have recently summarized these studies.…”

“…While gas retention decreases with increasing shear strength beyond a peak value at about 50 Pa, the gas fraction is still about 25% for a shear strength of a few thousand Pa, which is roughly the shear strength measured in the largescale Ketelmeer sludge test. Rassat et al 1998) Understanding the mechanisms causing the low retained-gas fraction in the large Ketelmeer sludge experiment and reproducing this behavior is the overall objective of the current study. In general, the large-scale test discussed above differs from the previous small-scale tests in six significant aspects:…”

Dynamics of Crust Dissolution and Gas Release in Tank 241-SY-101

“…Mechanisms of gas retention and release from simulated and actual wastes were described by Gauglitz et al (1994Gauglitz et al ( , 1995 and further refined in later work (Bredt et al 1995;Bredt and Tingey 1996;Gauglitz et al 1996;Stewart et al 1996;Rassat et al 1997Rassat et al , 1998. These studies focused on naturally occurring retention and release from the nonconnective.…”