Impacts of Antifoam Additions and Argon Bubbling on Defense Waste Processing Facility (DWPF) REDuction/OXidation (REDOX)

Technical Report · Fri Jun 01 00:00:00 EDT 2012

DOI:https://doi.org/10.2172/1045616· OSTI ID:1045616

Jantzen, Carol M. ^[1]; Johnson, Fabienne C. ^[1]

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1. Savannah River National Laboratory (SRNL), Aiken, SC (United States)

Control of the REDuction/OXidation (REDOX) state of glass in High Level Waste (HLW) melters, such as the Defense Waste Processing Facility (DWPF), is critical in order to eliminate the formation of metallic species from overly reduced melts while minimizing foaming from overly oxidized melts. The REDOX control is normally a balance of the oxidants and reductants from the feed and from processing additives. However, after reflux in the Sludge Receipt and Adjustment Tank (SRAT) and the Slurry Mix Evaporator (SME), the balance between the oxidizing salts vs. reducing salts can be altered once the mixture is fed to the melter if the melt pool is bubbled with gaseous species that either oxidize or sparge the melt of oxygen. Hence, for a bubbled melt pool, the REDOX of the melt pool must be targeted based on the balance of the oxidizing and reducing salts from the feed and from the processing additives, as well as, accounting for the effects of any gas being bubbled through the melt to improve convection and mixing while also increasing melt rate. For example, one would not set a REDOX target of Fe²⁺/ΣFe of 0.20 based on chemical balancing and then bubble pure air through the melter as pure air would oxidize the melt pool to an Fe²⁺/ΣFe ~0. Some gases, such as argon, are inert but act as chemical sparging agents or “degassing” agents that can sparge out oxygen from the melt and cause the glass to become more reducing. This study examines DWPF flowsheets at various concentrations of antifoam (a reducing processing additive) in the absence of melt pool bubbling (crucible and production data) and in the presence of melt pool bubbling with argon (crucible and production data), a known sparging/degassing agent. In order to de-convolute the impacts of antifoam on the melt pool REDOX from the impacts of melt pool bubbling, crucible studies were performed with (1) varying antifoam concentrations without bubbling, and (2) minimal antifoam with Ar bubbling. This allowed an antifoam term to be added to the REDOX model and suggested that (1) more oxidizing Fe²⁺/ΣFe ratios could be targeted which would create more oxidizing species in the cold cap to offset the effects of Ar-sparging or (2) Ar-air gas mixtures could be blended with a mixing valve to control the melt pool REDOX at the same Fe²⁺/ΣFe ratios (same –log fO₂) as chosen for the chemical REDOX balancing. The 2006 EE REDOX model is an electron equivalents (EE) model that balances the electrons lost during oxidation of a reductant against the electrons gained during the reduction of an oxidant. The EE terms for the formates, nitrates, and oxalates in the REDOX model are based on the formatted salts like NaCOOH, the nitrated salts like NaNO₃, and the oxalated salts like Na₂C₂O₄ that have higher decomposition temperatures than their acidic counterparts which flash off. Thus it is the higher decomposition salts that participate in the establishing the melt REDOX during their interactions in the melter cold cap.

• Research Organization: Savannah River Site (SRS), Aiken, SC (United States); Savannah River National Laboratory (SRNL), Aiken, SC (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC09-08SR22470
• OSTI ID: 1045616
• Report Number(s): SRNL--STI-2011-00652
• Country of Publication: United States
• Language: English

Related Subjects

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
ARGON
BUBBLES
EVAPORATORS
GLASS
HLF
MELTING
OXIDATION
OXIDIZERS
PROCESS CONTROL
PRODUCTION
QUALITY CONTROL
SLUDGES
TANKS
TARGETS
VITRIFICATION
WASTE PROCESSING
WASTES
antifoam
oxidation
reduction
vitrification