Mechanistic Studies Related to the Thermal Chemistry of Simulated Nuclear Wastes That Mimic the Contents of a Hanford Site Double-Shell Tank

Ashby, E. C.; Barefield, E. Kent; Liotta, Charles L.; Neumann, H. M.; Doctorovich, Fabio; Konda, Atsuo; Zhang, K.; Hurley, J.D.; Boatright, David; Annis, Allen; Pansino, Gary; Dawson, Myra; Juliao, Milene

doi:10.1021/bk-1994-0554.ch016

Cited by 12 publications

(39 citation statements)

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“…From studies using simulated wastes, the kinetics of formation and the stoichiometry of these gaseous products have been shown to be sensitive to the composition of the waste mixture (Delegard 1980; Jansky and Meissner, in Reynolds et al 1991;Ashby et al 1992Ashby et al , 1993Ashby et al , -1994aMeisel et al 1991Meisel et al , 1992Meisel et al , 1993Bryan et al , 1993Bryan and Pederson 1994). Nitrite, hydroxide, and aluminate ion concentrations are critical factors affecting gas generation behavior; other important factors include the identity and concentration of organic waste components, temperature, the presence and concentration of transition metal salts and chloride ions, and radiation dose/dose rate.…”

Section: I Gas Reactions Under Thermal and Combined Thermal And Radimentioning

confidence: 99%

Thermal and combined thermal and radiolytic reactions involving nitrous oxide, hydrogen, and nitrogen in the gas phase; comparison of gas generation rates in supernate and solid fractions of Tank 241-SY-101 simulated waste

Bryan¹,

Pederson²

1995

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DISCLAIMERPortions of this document may be illegible in electronic image products. lrnages are produced from the best available original document. Executive Summary. This report summarizes progress made in evaluating mechanisms by which flammable gases are generated in Hanford double-shell tank wastes, based on the results of laboratory tests using simulated waste mixtures. Work described in this report was conducted at Pacific Northwest Laboratory (PNL)Ca) for the Flammable Gas Safety Project, the purpose of which is to develop information needed to support Westinghouse Hanford Company (WHC) in their efforts to ensure the safe interim storage of wastes at the Hanford Site. This work is related to gas generation studies being performed at Georgia Institute of Technology (GIT), under subcontract to PNL, using simulated wastes, and to studies being performed at WHC using actual wastes.Described in this report are 1) the results of tests to evaluate the rates of thermal and combined thermal and radiolytic reactions involving flammable gases, and 2) the results of experiments intended to compare gas generation rates in a homogeneous liquid with those in a heterogeneous slurry. Flammable gases generated by the radiolysis of water and by the the&al and radiolytic decomposition of organic waste constituents may themselves participate in further reactions. Examples include the decomposition of nitrous oxide to yield nitrogen and oxygen, the reaction of nitrous oxide and hydrogen to produce nitrogen and water, and the reaction of nitrogen and hydrogen to produce ammonia. The composition of the gases trapped in bubbles in the wastes therefore may change continuously as a function of the time that the gas bubbles are retained. It has often been assumed, although not demonstrated, that the rates of flammable gas generation in the convecting liquid layer and nonconvecting settled solids layer in W o r d double-shell waste tanks are approximately equal. Factors that could lead to different gas generation rates in the two layers include different water content, different concentrations of organic waste components, and catalysis by solid phases. Gas Reactions under T h e m l and Combined T h e m 1 and Radiolytic Conditions:The decomposition of nitrous oxide, reactions between nitrous oxide, and reactions between nitrogen and hydrogen under thermal and combined thermal and radiolytic conditions were investigated in the temperature range of 60 to 150°C. Radiation doses ranged from 0 to more than 100 Mrad (60Co), while reaction times extended to 500 hours. Reactions were performed in stainless steel vessels that allowed continuous monitoring of gas pressures. Gas compositions were evaluated using mass spectrometry and infrared spectrometry. Simulated waste mixtures were excluded from these tests.The primary radiolytic/thermal products of nitrous oxide decomposition were nitrogen, oxygen, and nitrogen dioxide. Under thermal-only conditions, the extent of nitrous oxide decomposition was too small to be observable. Under combined the...

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Section: I Gas Reactions Under Thermal and Combined Thermal And Radimentioning

confidence: 99%

Thermal and combined thermal and radiolytic reactions involving nitrous oxide, hydrogen, and nitrogen in the gas phase; comparison of gas generation rates in supernate and solid fractions of Tank 241-SY-101 simulated waste

Bryan¹,

Pederson²

1995

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“…In all known studies of gas generation from simulated or actual Hanford waste mixtures by thermal and radiolytic processes, the product gases consist of a mixture of hydrogen, nitrous oxide, and nitrogen (Ashby et al 1992Barefield et al 1995Barefield et al , 1996Bryan et al 1992Bryan et al , 1994 Delegard 1980;Meisel et a]. 1991 Meisel et a].…”

Section: Mechanisms Of Gas Generationmentioning

confidence: 99%

“…Because of the complexity of the organic fraction of the wastes stored at Hanford (see, for example, Campbell et al 1994Campbell et al , 1995Campbell et al , 1996, it would be very difficult to prepare a simulant that behaves identically to an actual waste mixture. Past studies have established that gas generation rates are sensitive to a number of parameters, including the identity of organic solutes and the concentrations of nitrite, hydroxide, aluminate, and various minor and trace components (Ashby et al 1992Babad et al 1991;Barefield et al 1995Barefield et al , 1996Bryan et al 1992Bryan et al , 1994 Delegard 1980; Meisel et al. 199 1, 1993;Person 1996).…”

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confidence: 99%

Status and integration of studies of gas generation in Hanford wastes

Pederson¹,

Bryan²

1996

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DISCLAIMERThis report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, make any warranty, express or impiied, or assumes any legal liability or rrsponsibility for the accuracy, completeness, or usefulness of any infonnation, apparatus, product, or procxss disdosed, or represents that its use w w l d not infringe privately owned rights. Refemtee herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. DECLAIMERPortions of this document may be illegible in electronic image products. Images are produced from the best available original document. Executive SummaryThe purpose of this report is to review recent progress made in determining the chemical mechanisms, kinetics, and stoichiometry of gas generation in Hanford waste tanks. Information has been gathered from the results of laboratory studies with simulated wastes, laboratory studies with actual waste core samples (Tanks SY-10 1 and SY-103), studies of thermal and radiolytic reactions in the gas phase, and gas solubility evaluations. In-tank gas composition data are also briefly reviewed. Laboratory Studies Using Simulated WastesStudies at the Georgia Institute of Technology (GIT), which were aimed at developing a mechanistic understanding of the formation of flammable gases via the thermal decomposition of complexants, have been completed and a summary report issued . Conducted under subcontract to Pacific Northwest National Laboratory (PNNL)?) these studies also established thermal fragmentation pathways for chelators in simulated Hanford double-shell tank wastes. Barefield et al. (1995Barefield et al. ( , 1996 studied the long-term thermal decomposition of HEDTA under thermal conditions. They have determined changes in the concentration of HEDTA and decomposition fiagments as a function of time to approximately 7000 hours. Breakdown products of HEDTA include ethylenediaminetriacetic acid (ED3A), glycine, unsymmetric ethylenediaminediacetic acid (u-EDDA), symmetric ethylenediaminediacetic acid (s-EDDA), ethylenediaminemonoacetic acid (EDMA), imidodiacetic acid (IDA), formaldehyde, formate, and acetate, all of which have been identified in Hanford double-shell tank wastes.Hydrogen is one of the byproducts of chelator fragmentation by thermal processes Barefield et al. 1995Barefield et al. , 1996. The aluminate and nitrite ions are believed to play an important role in initiating the decomposition reaction, through the formation of a coordination complex involving those two ions. The coordinated nitrito ligand is expected to be much more electrophilic than the fiee nitrite ion and more reac...

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“…Physicochemical mechanisms leading to the buildup and periodic release of large volumes of flammable gases, u p until now, have not been understood (Allemam, 1992a(Allemam, , 1992bAshby et al, 1994;Babad et al, 1992aBabad et al, , 1992bBabad et al, , 1992cBabad et al, , 1991Burke et al, 1993;Strachan et al, 1993). As a consequence, approaches for the long-term, passive mitigation of flammable gas release have not been successfully implemented.…”

Section: Pmsicochemical Mechanismsmentioning

confidence: 99%

Physicochemical mechanisms controlling the periodic release of flammable gases from hanford tanks

Alexander¹,

Soundararajan

Morcos³

1995

Remediation Journal

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Mechanistic Studies Related to the Thermal Chemistry of Simulated Nuclear Wastes That Mimic the Contents of a Hanford Site Double-Shell Tank

Cited by 12 publications

References 0 publications

Thermal and combined thermal and radiolytic reactions involving nitrous oxide, hydrogen, and nitrogen in the gas phase; comparison of gas generation rates in supernate and solid fractions of Tank 241-SY-101 simulated waste

Thermal and combined thermal and radiolytic reactions involving nitrous oxide, hydrogen, and nitrogen in the gas phase; comparison of gas generation rates in supernate and solid fractions of Tank 241-SY-101 simulated waste

Status and integration of studies of gas generation in Hanford wastes

Physicochemical mechanisms controlling the periodic release of flammable gases from hanford tanks

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