Hanford Waste Vitrification Plant Hydrogen Generation Study
Hanford Waste Vitrification Plant Hydrogen Generation Study

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Published: 1996

Total Pages: 20

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Oxalic, glyoxylic, glycolic, malonic, pyruvic, lactic, levulinic, and citric acids as well as glycine have been evaluated as possible substitutes for formic acid in the preparation of feed for the Hanford waste vitrification plant using a non-radioactive feed stimulant UGA-12M1 containing substantial amounts of aluminum and iron oxides as well as nitrate and nitrite at 90C in the presence of hydrated rhodium trichloride. Unlike formic acid none of these carboxylic acids liberate hydrogen under these conditions and only malonic and citric acids form ammonia. Glyoxylic, glycolic, malonic, pyruvic, lactic, levulinic, and citric acids all appear to have significant reducing properties under the reaction conditions of interest as indicated by the observation of appreciable amounts of N2O as a reduction product of, nitrite or, less likely, nitrate at 90C. Glyoxylic, pyruvic, and malonic acids all appear to be unstable towards decarboxylation at 90C in the presence of Al(OH)3. Among the carboxylic acids investigated in this study the [alpha]-hydroxycarboxylic acids glycolic and lactic acids appear to be the most interesting potential substitutes for formic acid in the feed preparation for the vitrification plant because of their failure to produce hydrogen or ammonia or to undergo decarboxylation under the reaction conditions although they exhibit some reducing properties in feed stimulant experiments.

Hanford Waste Vitrification Plant Hydrogen Generation Study
Hanford Waste Vitrification Plant Hydrogen Generation Study

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Published: 1996

Total Pages: 39

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The Hanford Waste Vitrification Plant (HWVP) is being designed for the Departrnent of Energy (DOE) to immobilize pretreated highly radioactive wastes in glass for permanent disposal in the HWVP, formic acid is added to the waste before vitrification to adjust glass redox and melter feed rheology. The operation of the glass melter and durability of the glass are affected by the glass oxidation state. Formation of a conductive metallic sludge in an over-reduced melt can result in a shortened melter lifetime. An over-oxidized melt may lead to foaming and loss of ruthenium as volatile RuO4. Historically, foaming in the joule heated ceramic melter has been attributed to gas generation in the melt which is controlled by instruction of a reductant such as formic acid into the melter feed. Formic acid is also found to decrease the melter feed viscosity thereby facilitating pumping. This technical report discusses the noble metal catalyzed formic acid reduction of nitrite and/or nitrate to ammonia, a problem of considerable concern because of the generation of a potential ammonium nitrate explosion hazard in the plant ventilation system.

Hanford Waste Vitrification Plant Hydrogen Generation
Hanford Waste Vitrification Plant Hydrogen Generation

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Published: 1996

Total Pages: 71

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The most promising method for the disposal of highly radioactive nuclear wastes is a vitrification process in which the wastes are incorporated into borosilicate glass logs, the logs are sealed into welded stainless steel canisters, and the canisters are buried in suitably protected burial sites for disposal. The purpose of the research supported by the Hanford Waste Vitrification Plant (HWVP) project of the Department of Energy through Battelle Pacific Northwest Laboratory (PNL) and summarized in this report was to gain a basic understanding of the hydrogen generation process and to predict the rate and amount of hydrogen generation during the treatment of HWVP feed simulants with formic acid. The objectives of the study were to determine the key feed components and process variables which enhance or inhibit the.production of hydrogen. Information on the kinetics and stoichiometry of relevant formic acid reactions were sought to provide a basis for viable mechanistic proposals. The chemical reactions were characterized through the production and consumption of the key gaseous products such as H2. CO2, N20, NO, and NH3. For this mason this research program relied heavily on analyses of the gases produced and consumed during reactions of the HWVP feed simulants with formic acid under various conditions. Such analyses, used gas chromatographic equipment and expertise at the University of Georgia for the separation and determination of H2, CO, CO2, N2, N2O and NO.

Modeling Hydrogen Generation Rates in the Hanford Waste Treatment and Immobilization Plant
Modeling Hydrogen Generation Rates in the Hanford Waste Treatment and Immobilization Plant

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Published: 2004

Total Pages: 5

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This presentation describes a project in which Hanford Site and Environmental Management Science Program investigators addressed issues concerning hydrogen generation rates in the Hanford waste treatment and immobilization plant. The hydrogen generation rates of radioactive wastes must be estimated to provide for safe operations. While an existing model satisfactorily predicts rates for quiescent wastes in Hanford underground storage tanks, pretreatment operations will alter the conditions and chemical composition of these wastes. Review of the treatment process flowsheet identified specific issues requiring study to ascertain whether the model would provide conservative values for waste streams in the plant. These include effects of adding hydroxide ion, alpha radiolysis, saturation with air (oxygen) from pulse-jet mixing, treatment with potassium permanganate, organic compounds from degraded ion exchange resins and addition of glass-former chemicals. The effects were systematically investigated through literature review, technical analyses and experimental work.

Noble Metal Catalyzed Hydrogen Generation from Formic Acid in Nitrite-containing Simulated Nuclear Waste Media
Noble Metal Catalyzed Hydrogen Generation from Formic Acid in Nitrite-containing Simulated Nuclear Waste Media

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Published: 1994

Total Pages: 37

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Simulants for the Hanford Waste Vitrification Plant (HWVP) feed containing the major non-radioactive components Al, Cd, Fe, Mn, Nd, Ni, Si, Zr, Na, CO32−, NO3-, and NO2- were used as media to evaluate the stability of formic acid towards hydrogen evolution by the reaction HCO2H --> H2 + CO2 catalyzed by the noble metals Ru, Rh, and/or Pd found in significant quantities in uranium fission products. Small scale experiments using 40-50 mL of feed simulant in closed glass reactors (250-550 mL total volume) at 80-100°C were used to study the effect of nitrite and nitrate ion on the catalytic activities of the noble metals for formic acid decomposition. Reactions were monitored using gas chromatography to analyze the CO2, H2, NO, and N2O in the gas phase as a function of time. Rhodium, which was introduced as soluble RhCl3·3H2O, was found to be the most active catalyst for hydrogen generation from formic acid above (almost equal to)80°C in the presence of nitrite ion in accord with earlier observations. The inherent homogeneous nature of the nitrite-promoted Rh-catalyzed formic acid decomposition is suggested by the approximate pseudo first-order dependence of the hydrogen production rate on Rh concentration. Titration of the typical feed simulants containing carbonate and nitrite with formic acid in the presence of rhodium at the reaction temperature ((almost equal to)90°C) indicates that the nitrite-promoted Rh-catalyzed decomposition of formic acid occurs only after formic acid has reacted with all of the carbonate and nitrite present to form CO2 and NO/N2O, respectively. The catalytic activities of Ru and Pd towards hydrogen generation from formic acid are quite different than those of Rh in that they are inhibited rather than promoted by the presence of nitrite ion.