Calculation of reaction energies and adiabatic temperatures for waste tank reactions

Abstract

SummaryContinual concern has been expressed over potentially hazardous exothermic reactions that might occur in Hanford Site underground waste storage tanks. These tanks contain many different oxidizable compounds covering a wide range of concentrations. Several compounds may be in concentrations and quantities great enough to be considered a hazard in that they could undergo rapid and energetic chemical reactions with nitrate and nitrite salts that are present it heated to the initiating or critical temperature. The chemical hazards are a function of several interrelated factors, including the amount of energy (heat) produced, how fast it is produced, and the thermal absorption and heat transfer properties of the system. The reaction path(s) will determine the amount of energy produced and kinetics will determine the rate that it is produced. The tanks also contain many inorganic compounds inert to oxidation. These compounds act as diluents and can inhibit exothermic reactions because of their heat capacity and thus, in contrast to the oxidizable compounds, provide mitigation of hazardous reactions.In this report the energy that may be released when various organic and inorganic compounds react is computed as a function of the reaction-mix composition and the temperature. The enthalpy, or integrated heat capacity, of these compounds and various reaction products is presented as a function of temperature; the enthalpy of a given mixture can then be equated to the energy release from various reactions to predict the maximum temperature which may be reached. This is estimated for several different compositions. Alternatively, the amounts of various diluents required to prevent the temperature from reaching a critical value can be estimated. Reactions W i g different paths, forming different products such as N20 in place of N2 are also considered, as are reactions where an excess of caustic is present. Oxidants other than nitrate and nitrite are considered briefly.The relative available energy per unit mass of the various oxidizable compounds, or "fuels," that may be present ranges from 1 to about 25. Stoichiometric mixes with oxidant, e.g., fuel plus the required amount of sodium nitrate (NaNO,) for a complete reaction, compared on a mass basis, also show large differences. This "energy density" covers a range of 1 to about 5.A consequence of different stoichiometries for different fuels is that an excess of sodium nitrate or nitrite for one reactant may be a deficiency for another. This is significant since excess nitrate or nitrite is an excellent heat sink, especially at elevated temperatures.The efficiency of various compounds as heat sinks, i.e., their enthalpies, vary greatly. In the wastes water is the most significant material at temperatures up to slightly above 100°C. From 100°C to about 300°C the greatest effect is probably from hydrated salts, with some contribution from concentrated caustic solutions. The loss of water from these materials requires a large energy input, some 50% to 100% greater than f...

Thermal reactivity of mixtures of VDDT lubricant and simulated Hanford Tank 241-SY-101 waste

“…The major inorganics in the simulated waste were sodium nitrate, sodium nitrite, sodium aluminate, sodium phosphate, and sodium hydroxide. Although recent analyses by Campbell et al (I 994) and studies by Delegard (1 987) and Camaioni et al (1 994;1995) indicate that HEDTA originally present in 101 SY waste has degraded to a wide variety of organic species, we chose HEDTA to represent the organic waste constituents since it was originally present in the waste and to provide consistency with our earlier studies to assess the chemical compatibility of pump oil and 101 SY waste. We dried our simulant at 50°C using the building vacuum of about 120 torr for 2 to 3 weeks and ground it using a mortar and pestle to provide a high-surface-area material to enhance reactivity.…”

Use of organic functional group concentrations as a means of screening for energetics

“…1995;Campbell et al 1994 b, c) or in waste simulants that have been subjected to accelerated aging via gamma radiolysis (Meisel et al 1993;Camaioni et al 1995) or thermolysis (Ashby et al 1994;Delegard 1987). Table 2.1 also lists nitrate reaction energies (Burger 1995) and information relevant to the subsequent discussion. Clearly, there is great uncertainty in assuming the wastes are equivalent to sodium acetate in energy content.…”

“…To illustrate, we calculated the reaction energies for tank waste organic compounds mixed with amounts of nitrate that yield stoichiometric, 4.5% TOC, and 1% TOC mixtures. (Burger 1995).…”

“…Table 4.2 presents the DSC-and DTA-measured exothermic reaction enthalpies for the tested 6 mass percent organic carbon mixtures of selected organics and sodium nitrite. In addition, the predicted maximum theoretical reaction enthalpies as calculated by Burger (1995) are included for comparison. Similar results were obtained for DSC and DTA measurements of the sodium nitrite mixtures as for the sodium nitrate mixtures.…”

“…The DSC and DTA measured reaction enthalpies at 6 mass percent organic carbon in sodium nitrate solution for the organics studied are compared to maximum theoretical reaction enthalpies predicted (Burger 1995) in Table 4.1. It is shown that the amount of heat produced or o6served by the two instruments is a fraction of the maximum theoretical enthalpy.…”