spray to mobilize transition line deposits into the SBS to make them available for recycle. The resulting system provided a robust and reliable platform to address the test objectives.Seven different LAW waste compositions were processed in nine nominally 72-hour tests. All feeds were spiked with a solution containing 99mTc in the pertechnetate form; the feeds used in these tests also contained measureable amounts of nonradioactive iodine and rhenium. In each test, a mass balance for technetium and other feed constituents of concern was measured across the glass pool, discharge glasses, throughout the off-gas system, evaporator overheads, and WESP exhaust. The nominal melter operating conditions employed for the majority of the tests were: an llSO°C glass pool temperature, sugar as an organic reductant at a stoichiometric sugar ratio of 0.5, and air bubbled through the glass pool at a rate to achieve a constant target glass production rate of 2,250 kglm 2 /day. Throughout the tests, enhancements were made to the feed system, WESP, evaporators, and operational procedures in order to optimize unit performance and minimize test interruptions. In addition to the mass balance for key constituents (Tc, Re, S, I, Cl, F), data collected from these tests were used to calculate retention factors across the melter and each of the various off-gas system components. These results were used as input into process models ofthe system which were used to calculate the predicted concentrations in the glass product for comparison to the measured values. The data were also used to quantify the amount oftechnetium that escapes the recycle loop through the WESP exhaust and the evaporator overheads.In the WTP system, technetium can exit the recycle loop via two routes: In the off-gas stream exiting the WESP and in the liquid condensate from the vacuum evaporator. Constituents in the offgas stream from the WESP are further removed in the PBS. The PBS effiuent and evaporator condensate secondary waste from the WTP are directed ultimately to non-glass waste forms. Consequently, the fraction of technetium exiting the recycle loop via these routes is a significant factor in the Performance Assessment for the Hanford Integrated Disposal Facility. There have been no previous measurements of this fraction.These tests have produced the first ever data on:• Technetium retention factors for key WTP unit operations (SBS, WESP, vacuum evaporator).• The effect of recycle on the incorporation oftechnetium and other key species in LAW glass.• The distribution and fate oftechnetium throughout the vitrification system and recycle loop, and the extent of partitioning to secondary waste streams.Key findings from this work include:• With recycle, retentions of technetium and rhenium in the glass product are increased by factors of at least 2 to 3 over the corresponding single-pass values for almost all glass compositions. The average technetium and rhenium retentions in glass across all compositions tested were 68% and 79%, respectively. All but two compos...

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