5 Matching Results

Search Results

Advanced search parameters have been applied.

Radiolytic and Thermal Generation of Gases from Hanford Grout Samples : Interim Report

Description: Gamma irradiation of WHC-supplied samples of grouted Tank 102-AP simulated nonradioactive waste has been carried out at three dose rates, 0.25, 0.63, and 130 krad/hr. The low dose rate corresponds to that in the actual grout vaults; with the high dose rate, doses equivalent to more than 40 years in the grout vault were achieved. An average G(H2) = 0.047 molecules/100 eV was found, independent of dose rate. The rate of H2 production decreases above 80 Mrad. For other gases, G(N2) = 0.12, G(O2) = 0.026, G(N2O) = 0.011 and G(CO) = 0.0042 at 130 krad/hr were determined. At lower dose rates, N2 and O2 could not be measured because of interference by trapped air. The value of G(H2) is higher than expected, suggesting segregation of water from nitrate and nitrite salts in the grout. The total pressure generated by the radiolysis at 130 krad/h has been independently measured, and total amounts of gases generated were calculated from this measurement. Good agreement between this measurement and the sum of all the gases that were independently determined was obtained. Therefore, the individual gas measurements account for most of the major components that are generated by the radiolysis. At 90 C, H2, N2, and N2O were generated at a rate that could be described by exponential formation of each of the gases. Gases measured at the lower temperatures were probably residual trapped gases. An as yet unknown product interfered with oxygen determinations at temperatures above ambient. The thermal results do not affect the radiolytic findings.
Date: October 1993
Creator: Meisel, Dan; Jonah, Charles D.; Kapoor, S.; Matheson, Max S. & Mulac, W. A.
Partner: UNT Libraries Government Documents Department

Radiolytic and Radiolytically Induced Generation of Gases from Synthetic Wastes : Final Report

Description: To better understand the processes leading to the generation and release of gases from waste tanks, the authors studied the radiolytic and thermal generation of H2, N2O, N2, O2, and NH3 in nonradioactive waste simulant solutions and slurries. The radiolytic sources for H2 are e(sub aq)⁻ and its predecessors and H atoms. Radiolysis of the water generates some H2 and an additional amount comes from the hydrogen abstraction reaction H + RH(yields) H2+R(center_dot). Nitrate scavenges e(sub aq)(sup (minus) and its predecessors whereas nitrite is the major H-atom scavenger. Computer modeling shows that if [NO3⁻] is above 0.5 M, and [NO2⁻] is above 2M, the addition of other scavengers will have little effect on the yield of H2. In the presence of organic molecules O2 is efficiently destroyed. Small yields of ammonia were measured and the yields increase linearly with dose. The nitrogen in NH3 comes from organic chelators. The yields of gases in solution depend only weakly on temperature. The rate of thermal generation of gases increases upon preirradiation, reaches a maximum, and then declines. The known radiolytic degradation products of chelators, NTA, IDA, glycolate, glyoxylate, formaldehyde, formate, oxalate, and hydroxylainine were examined for their roles in the thermal generation of H2 and N2O at 60 C. In solution or slurry only radiolytically produced Pd intermediate strongly retains H2. Radiolytic yields of N2O are strongly reduced by Cr(III). In irradiated slurry, loose and tight gas were found. The loose gas could be removed by bubbling from the slurry, but the tight gas could be released only by dissolution of the slurry.
Date: October 1993
Creator: Meisel, Dan; Jonah, Charles D.; Kapoor, S.; Matheson, Max S. & Sauer, M. C.
Partner: UNT Libraries Government Documents Department

Gas Generation from Hanford Grout Samples : Final Report

Description: The radiolytic yields of hydrogen nitrogen, oxygen, nitrous oxide, and carbon monoxide from two batches of WHC-supplied samples of grouted simulated waste have been (gamma) irradiated at several dose rates (0.025, 0.63 and 130 krad/h for hydrogen and 130 krad/h for all other gases). In one batch, the liquid waste simulant that was added to the grout included the original components that were added to Tank 102-AP (labeled "virgin" waste.) The second batch included a similar liquid waste simulant that was preirradiated to 35 Mrad prior to incorporation into the grout. It is believed that the preirradiated samples more closely represent radioactive waste that was stored in the tank for several years. The lowest dose rate corresponds approximately to that expected in the grout; with the high dose rate, doses equivalent to about 85 years storage in grout vaults were achieved. Most of the results on the batch of virgin samples have been reported recently (Report ANL 93/42). Here we report the results from the batch of preirradiated grout samples and compare the results from the two batches. The radiolytic yields of hydrogen and nitrogen are lower in the preirradiated than in the virgin grout. On the other hand G(oxygen) is higher in the preirradiated samples: 0.078 vs. 0.026. The yield of nitrous oxide is essentially the same, G(nitrous oxide) = 0.010, in both. The yields measured from both batches are significantly higher than previously reported values. At 90 C similar amounts of hydrogen were generated thermally from both batches of grout, whereas the total amounts of nitrogen and nitrous oxide were larger for the preirradiated than for the virgin grout samples. At lower temperatures the rate of generation was hardly measurable. Mass spectrometric analysis suggests that NO is thermally (but not radiolytically) released from the grout samples.
Date: March 1994
Creator: Jonah, Charles D.; Kapoor, S.; Matheson, Max S.; Mulac, W. A. & Meisel, Dan
Partner: UNT Libraries Government Documents Department

Radiation Chemistry of Synthetic Waste

Description: The yield of hydrogen from radiolysis of aqueous solutions is substantially reduced by the presence of nitrate and nitrite in the waste solutions. Nitrate is more efficient in scavenging the precursors to hydrogen than is nitrite, therefore, the latter should be maintained at higher levels if minimization of radiolytic gas production is required. Nitrate is the major scavenger for e(sub aq)(sup (minus)) and nitrite is the major scavenger for H atoms. At the concentration levels of the waste solutions some fraction of the radiation energy will be absorbed directly by the solutes, primarily the nitrate/nitrite components. Organic additive will increase the generation of hydrogen and mechanistic information is available to allow predictive modeling of trends in the rate of the generation. Physical parameters such as temperature, viscosity, and pressure will not significantly affect the gas generation relative to its generation under normal conditions. Radiolytic generation of N2O is very inefficient in the absence of organic solutes. No mechanistic information is available on its generation in the presence of organic additives. At the concentration levels of the inorganic salts in the waste solutions, it will be very difficult to find a chemical additive that could efficiently reduce the yield of the generated hydrogen, except, perhaps, increasing the concentration of the nitrite/nitrate components.
Date: November 1991
Creator: Meisel, Dan; Diamond, H.; Horwitz, E. P.; Jonah, Charles D.; Matheson, Max S.; Sauer, M. C. et al.
Partner: UNT Libraries Government Documents Department

Radiolytic Generation of Gases from Synthetic Waste, Annual Report: 1991

Description: Annual report of an Argonne National Laboratory Chemistry Division program on radiolytic generation of gases from synthetic waste. This report includes results of studies on simulated waste solutions to measure the presence and absence of organic chelators and their products.
Date: December 1991
Creator: Meisel, Dan; Diamond, H.; Horwitz, E. P.; Jonah, Charles D.; Matheson, Max S.; Sauer, M. C., Jr. et al.
Partner: UNT Libraries Government Documents Department