1,198 research outputs found
Afropean Journeys: A Conversation with E.C. Osondu
Get PDFNigeria-born and US resident author E.C. Osondu debuted with the short story collection Voice of America (2010), followed by the novel This House is Not for Sale (2015) and Alien Stories (2020). His latest novel, When the Sky is Ready the Stars Will Appear, the compelling tale of an African boy’s journey towards Rome in search of a better life, was first published in translation in Italy with the title Quando il cielo vuole spuntano le stelle (2020). Only one year later, the original version of the novel was published in Nigeria. This piece, based on a conversation with the author within the context of the “Afropean Bridges” 2021 Series, introduces E.C. Osondu and his works to the Italian audience
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FY 1999 Saltcake Dissolution Workshop
Get PDFDuring the FY 1998 Saltcake Dissolution Workshop, participants identified nine tasks to be performed prior to the FY 1999 workshop. Discussions during the workshop indicated that significant progress was made in each area. The workshop focused on the strengths and weaknesses of the Environmental Simulation Program (ESP). In addition, the ESP predictions for the Tank SY-101 remediation and the ESP validation efforts were evaluated. Finally, the need for a broader user base was identified. At the request of the Tank Waste Remediation System (TWRS), the ESP model was successfully utilized to predict the effects of Hanford tank farm operations such as waste transfers and water dilutions. The ESP model was originally developed to predict the compositions of solutions from off gas scrubbers. Therefore, the original database for the ESP model was designed for use with solutions with low ionic strengths. However, the Hanford tanks contain waste with very high ionic strengths. TWRS and Tank Focus Area (TFA) staff members have measured the solubilities of key components at high ionic strengths. The results from these studies were used to develop the Hanford database for the ESP model so the model could more accurately predict the compositions of Hanford waste streams with high ionic streams. The OLI Corporation, which developed the ESP model, has now incorporated most of the Hanford database into its standard ESP database. Another deficiency of the ESP model involves the lack of detailed documentation. Most new users of the ESP model normally encounter several obstacles. Therefore, TWRS management has proposed the development of an ESP user guide based on the experiences of TWRS and TFA researchers. The objective of the user guide is to make the ESP model more user friendly for the Hanford process engineers. The saltcake dissolution experiments at Hanford and the SOLGAS calculations at Oak Ridge are critically in the validation of the ESP model. Due to the high costs associated with the experiments with actual waste, the TWRS would prefer to use the ESP model to predict the effects of most tank farm operations. A comparison of the SOLGAS and ESP calculations indicated that the models were not in good agreement at most of the hydroxide concentration. The SOLGAS model uses the Gibbs free energy of formation to determine the solubilities of the chemical constituents while the ESP uses the KFIT subroutine. The agreement between the ESP and SOLGAS predictions improved when the ESP calculations were based on thermodynamic functions. TPA researchers will contact OLI Corporation to determine the experimental results needed to improve the fit. In addition, a high ionic strength model, which was developed by Moonis Ally of Oak Ridge National Laboratory, will be used to validate the ESP model. One of the new points of emphasis involves the need for the TPA researchers to work with a wider range of users at the Hanford site. Most of the previous TFA and users interactions involved the engineering group, which is responsible for the initial remediation of Tank SY-101. A list of other potential users in the areas of process engineering, tank farm operations, and retrieval was developed. Meetings between the TFA researchers and these potential customers will be held over the next several months
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Comparative Calculations of Solubility Equilibria
Get PDFThe uncertainties in calculated solubilities in the Na-F-PO{sub 4}-HPO{sub 4}-OH system. at 25 C for NaOH concentrations up to 5 mol/kg were assessed. These uncertainties were based on an evaluation of the range of values for the Gibbs energies of the solids. Comparative calculations using the Environmental Simulation Program (ESP) and SOLGASMIX indicated that the variation in activity coefficients with NaOH concentration is much greater in the ESP code than in SOLGASMIX. This resulted in ESP calculating a higher solubility in water and a lower solubility in NaOH concentrations above 1 mol/kg: There was a marked discrepancy in the solubilities of the pure components sodium fluoride and trisodium phosphate predicted by ESP and SOLGASMIX. In addition, different solubilities for these components were obtained using different options in ESP. Because of these observations, a Best Practices Guide for ESP will be assembled
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Sludge washing and dissolution of Melton Valley Storage Tank waste
Get PDFFocus is on experimental and modeling R&D for comprehensive sludge/supernatant processing flowsheet being done for the Underground Storage Tank Integration Demonstration; emphasis is on Hanford tank waste disposal involving dissolution of the sluge before pretreatment. Combination of tests on actual Melton Valley Storage Tank (MVST) sludge, tests on sludge simulants, and modeling of sludge chemistry provides a broad evaluation of sludge and supernate processing. The information is useful for both MVST and Hanford tank wastes
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Iodine Volatility and pH Control in the AP-600 Reactor
Get PDFTwo design-basis accidents for the AP-600 reactor are formulated and evaluate~ in which significant bypass of the principal pH control system occurs. Some iodine released from the reactor primary system is retained in the Incontainment Refaeling Water Storage Tank (IRWST) water, never entering the containment where trisodium phosphate produces a high pH. Some of this iodine is volatilized and is transported into the reactor containment airspace. in the worst case, a small fraction is released to the environment at design-basis leak rate, yielding a total cumulative iodine release at 30 days of 0.0352 mol (0.023% of core iodine inventory) due to the iodine volatilization bypassing the pH control system. No fission product removal in the containment atmosphere (i.e., natural deposition sprays) is considered
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Iodine volatility. [PWR; BWR]
No full textThe ultimate aim of this program is to couple experimental aqueous iodine volatilities to a fission product release model. Iodine partition coefficients, for inorganic iodine, have been measured during hydrolysis and radiolysis. The hydrolysis experiments have illustrated the importance of reaction time on iodine volatility. However, radiolysis effects can override hydrolysis in determining iodine volatility. In addition, silver metal in radiolysis samples can react to form silver iodide accompanied by a decrease in iodine volatility. Experimental data are now being coupled to an iodine transport and release model that was developed in the Federal Republic of Germany
Iodine Volatility and pH Control in the AP-600 Reactor
No full textTwo design-basis accidents for the AP-600 reactor are formulated and evaluate~ in which significant bypass of the principal pH control system occurs. Some iodine released from the reactor primary system is retained in the Incontainment Refaeling Water Storage Tank (IRWST) water, never entering the containment where trisodium phosphate produces a high pH. Some of this iodine is volatilized and is transported into the reactor containment airspace. in the worst case, a small fraction is released to the environment at design-basis leak rate, yielding a total cumulative iodine release at 30 days of 0.0352 mol (0.023% of core iodine inventory) due to the iodine volatilization bypassing the pH control system. No fission product removal in the containment atmosphere (i.e., natural deposition sprays) is considered
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Iodine Revolatilization in a Grand Gulf Loca
Get PDFThe TRENDS models are applied at each time step to each control volume. Significant amounts of water occur only in the wetwell and drywell sump (the refueling pool is not a factor, as discussed earlier). In Fig. 2, we show the radiolytic acid production feeding into each of these pools. Since the water is initially neutral and no chemical additives are present, the acid additions are the major factors affecting pH. In Fig. 3, we see the downward trend of pH resulting from these acid additions. The conversion of iodide (I{sup {minus}}) to molecular iodine (I{sub 2}) is most noticeable in the wetwell, since this is the repository of most iodide and HCl. Gradually, during the transient small amounts of more volatile iodine are formed. While iodide remains the dominant form, noticeable amounts of I{sub 2} and intermediate species are created. Once produced in water, some I{sub 2} is free to evaporate into airspace. Fig. 4 indicates the increase in all airborne iodine throughout the transient. This is compared to the MELCOR result for CsI aerosol, which decreases dramatically due to containment sprays. The I{sub 2} in the airspace can be vented to the enclosure building or the environment. In the present accident sequence, the only path to the environment was through the SGTS, which was assumed to operate as in MELCOR. However, both are dwarfed by the MELCOR gaseous release during the first 12 h because MELCOR does not model spray washout of gaseous iodine. Steadily increasing throughout the transient, the revolatilization release is eventually more than an order-or-magnitude higher than the MELCOR aerosol release. Also, 99% of iodine flowing directly through the SGTS was retained in filters. The remaining 1% was released to the environment. In addition, a small flow bypassing the SGTS filters vented directly into the environment. The total released from these two paths is shown in Fig. 5
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