FY 1999 Saltcake Dissolution Workshop

Abstract

During 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.