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WHC-SD-WM-TI-7 18Revision 0This page intentionally left blank... 11 WHC-SD-WM-TI-718Revision 0 This document presents the results of a preliminary investigation into options for preliminary flowsheets for 9 Y T~ removal from Hanford Site tank waste. A model is created to show the path of 99Tc through pretreatment to disposal. The Tank Waste Remediation System (TWRS) flowsheet (Ormr -395) is used as a baseline. Ranges of important inputs to the model are developed. such as 'Yc inventory in the tanks and important splits through the TWRS flowsheet. Several technetium removal options are discussed along with sensitivities of the removal schemes to important model parameters. LIST OF FIGURES SUMnlARYThe results of the low-level waste (LLW) performance assessment have the greatest impact on techixtium remo\:al. One preliminary performance assessment (Rawlins et al.4 mremiyr, without any engineering improvement to the disposal systcr~. IU:'. 95.3 percent and 97.8 percent of the soluble 9 Y T~ must be removed (o\.eriiil decontziifiaiion factor [DF] of 21-46). The performance assessment (Rawlir:: et al. 1991) also indicates that even after technetium removal other radionuclides may be present in large enough quantities that the 4 mremiyr specification will still not be met without their removal as well. The performance assessment (Rawlins et al. 1994) is currently being revised, but the results of this revision were not yet available for incorporation into this report. Another preliminary performance assessment (Kincaid and White 1995) indicate that only about 80 percent of the soluble technetium may require removal (overall DF of 5) to meet the 4 mrem/yr drinking water dose rate specification. 1994) indicates that to meet the recommended drinking water dose rate specific.. glass performance, larger glass particles, vault water barriers, a sulfur E:.,' ::!.. Even if ' YTc is extensively removed, doses due to other radionuclides such as "'I, ljYPu, selenium. or uranium. may prevent meeting the required drinking water dose rate of 4 mrem/yr. These other radionuclides also may require removal. or an engineering improvement to the waste form may he needed to provide the further drop in dose rate. A combination of some technetium removal with some engineering improvement to the waste form may be the optimum of low cost and low technical risk. Assessments are needed of the overall costs and ~echnolo~ical risks versus the benefits of technetium removal options andRevision 0 also those of LLW form engineering options.High 'Tc removal requirements due to the performance assessment will not permit a selective removal strategy, Le., removal of 9 T c from only some tanks. An estimation of 9'Tc inventory distribution among the different waste types is not highly reliable at this point due to a lack of data. Preliminary indications, however, indicate technetium is distributed throughout the tank waste types to the extent that a selective removal scheme (i.e., removal from only certain tanks or waste types) would probably not be p...
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