DWPF Recycle Evaporator Shielded Cells Testing

Abstract

Testing was performed to determine the feasibility and processing characteristics of evaporation of actual Defense Waste Processing Facility (DWPF) recycle material. Samples of the Off Gas Condensate Tank (OGCT) and Slurry Mix Evaporator Condensate Tank (SMECT) were transferred from DWPF to the Savannah River National Lab (SRNL) Shielded Cells and blended with De-Ionized (DI) water and a small amount of Slurry Mix Evaporator (SME) product. A total of 3000 mL of this feed was concentrated to approximately 90 mL during a semi-batch evaporation test of approximately 17 hours. One interruption occurred during the run when the feed tube developed a split and was replaced. Samples of the resulting condensate and concentrate were collected and analyzed. The resulting analysis of the condensate was compared to the Waste Acceptance Criteria (WAC) limits for the F/H Effluent Treatment Plant (ETP). Results from the test were compared to previous testing using simulants and OLI modeling. Conclusions from this work included the following: (1) The evaporation of DWPF recycle to achieve a 30X concentration factor was successfully demonstrated. The feed blend of OGCT and SMECT material was concentrated from 3000 mL to approximately 90 mL during testing, a concentration of approximately 33X. (2) Foaming wasmore » observed during the run. Dow Corning 2210 antifoam was added seven times throughout the run at 100 parts per million (ppm) per addition. The addition of this antifoam was very effective in reducing the foam level, but the impact diminished over time and additional antifoam was required every 2 to 3 hours during the run. (3) No scale or solids formed on the evaporator vessel, but splatter was observed in the headspace of the evaporator vessel. No scaling formed on the stainless steel thermocouple. (4) The majority of the analytes met the F/H ETP WAC. However, the detection limits for selected species (Sr-90, Pu-238, Pu-240, Am-243, and Cm-244) exceeded the ETP WAC limits. (5) I-129 was calculated to have exceeded the ETP WAC limits based on an assumed Decontamination Factor (DF) of 1 during evaporation. (6) The DF for most species was limited by the detection limits of the sample analysis. Based on iron, manganese, total alpha, total beta, and other species, very low entrainment was noted and evaporator DF was >10,000 for non-volatile species. (7) Very low DF's were obtained for selected species, especially mercury and formate. These species are present as volatile compounds and will exceed ETP WAC limits if sufficient concentrations are in the evaporator feed. (8) The evaporator DF's for the radioactive test were in good agreement with simulant test results. Differences noted in the DF of selected species, such as Hg, were more likely attributed to analytical issues than differences in the performance of the two evaporators. (9) The simulant appeared to be conservative in terms of foaming and scaling characteristics of the evaporator. The initial spike in foaming that occurred during all simulant runs did not occur during the Shielded Cells run and overall foaminess after the start of the test was controlled by antifoam additions. The splatter that was deposited during the radioactive test was less than the simulant runs and was more easily removed. (10) The OLI model results were overly conservative due to the manner that entrainment of solids was incorporated into the model.« less