Technetium Retention in WTP Law Glass With Recycle Flow-Sheet Dm10 Melter Testing VSL-12r2640-1 Rev 0

Abstract

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...

Reactions during melting of low-activity waste glasses and their effects on the retention of rhenium as a surrogate for technetium-99

“…The highly soluble TcO 4 − does not adsorb well onto the surface of minerals [8][9][10] and, thus, migrates nearly at the same velocity as groundwater [11]. More importantly, the primary concern with processing the 99 Tc-containing waste into a glass is its extreme volatility, which results in low concentrations of Tc retained in the final product relative to target concentrations [12][13][14][15][16]. Recent small-scale melter tests with seven representative Hanford LAW glass feeds (simulated waste plus additives) for the WTP showed that the fraction of technetium retained in glass (referred to as retention) varied from 18% to 66% depending on the feed composition [12][13][14].…”

Iodine solubility in a low-activity waste borosilicate glass at 1000°C

“…Retention of halides in sodium aluminum borosilicate glasses decreases consistently with increasing ionic radius where iodine has the lowest retention of the halides, i.e., F > Cl > Br > I [15,16]. Recent scaled melter tests with various simulated LAW glass feeds spiked with 1000 ppm iodine by mass showed that the retention ratio of iodine in LAW glass is approximately 20%, on average [17].…”

Laboratory Scoping Tests Of Decontamination Of Hanford Waste Treatment Plant Low Activity Waste Off-Gas Condensate Simulant

“…The current WTP baseline assumption is that technetium will not be removed from the aqueous waste in the WTP, and will primarily end up immobilized in the LAW glass waste form after several recycle passes to improve retention [Abramowitz, 2012]. The LAW glass will be disposed in the IDF.…”