Radioactive Waste Sludge Washing and Demonstration of the Nitric-Glycolic Acid Flowsheet for Sludge Batch 10 Qualification

Abstract

For each sludge batch that is processed in the Defense Waste Processing Facility (DWPF), the Savannah River National Laboratory (SRNL) performs qualification testing to demonstrate that the sludge batch (SB) is processible. During processing of SB9, DWPF will be transitioning from the Nitric-Formic Acid (NFA) flowsheet to the Nitric-Glycolic Acid (NGA) flowsheet. Thus, the qualification of SB10 was requested to only be performed using the NGA flowsheet.In order to qualify the batch for the NGA flowsheet, Sludge Receipt and Adjustment Tank (SRAT) and Slurry Mix Evaporator (SME) cycles, designated SC-19, were performed using SB10 Tank 51 sample material. SRNL received Tank 51 material in the midst of Tank Farm washing. SRNL continued the washing in the SRNL Shielded Cells. The SRNL process included the addition of Sodium Reactor Experiment (SRE) material from H Canyon, simulating the transfer of SRE from H Canyon to Tank 51 during Tank Farm washing. The washed SB10 Tank 51 material, with SRE, was characterized prior to flowsheet qualification testing.The Chemical Process Cell demonstration with the NGA flowsheet utilized an acid stoichiometry of 107% Koopman Minimum Acid basis (102% Hsu basis). The qualification was performed on the "batch", which is representative of the Tank 51 material that will be transferred to Tank 40, rather than the "blend", which is representative of the Tank 40 material that will be fed to DWPF. Thus, specifics for the DWPF processing of the Tank 40 blend may differ in varying degrees from this qualification test. Additionally, the qualification did not include Salt Waste Processing Facility (SWPF) feeds (Monosodium Titanate (MST)/Sludge Solids and Strip Effluent), which would contribute soluble salts and the MST solids, which could influence the acid addition and the product rheology, respectively. For these reasons, the results of this qualification testing demonstration are used in conjunction with simulant testing to inform the processing of the Tank 40 blend with inclusion of SWPF feeds.Highlights of the testing results are summarized in the paragraphs below.Prior to the addition of antifoam, foaming was encountered in the SRAT cycle during the addition of nitric acid to the extent that sludge foamed over into the off-gas system. Based on observations from simulant testing, during which foaming was not noted during nitric acid addition, the plan involved addition of Momentive TM Y-17112 antifoam after the completion of nitric acid addition and prior to glycolic acid addition. The foaming during nitric acid addition was likely due to the release of carbon dioxide from the acid reacting with carbonate. After a time out (3 weeks), the SRAT cycle was resumed with an antifoam addition prior to resumption of nitric acid addition. Foaming was successfully mitigated during the remainder of the SRAT and SME cycles.Total dried solids measurements of the SRAT and SME Products were 20.1 and 48.1 weight percent (wt%), respectively. Calcined solids measured 11.3 wt% in the SRAT Receipt and SRAT Pr...

Technical Evaluation of Accelerated Basin De-Inventory Material Addition to Sludge Batch 11 (Rev. 1)

“…It is unknown whether other interactions may occur with antifoam components, but any such interactions with Gd or other metals in the system had not been observed to impact the effectiveness of antifoam during SB10 qualification testing. 34 Due to the lack of a study specifically designed to elucidate gadolinium interactions, it has not been determined whether there is a glycolic acid and gadolinium interaction beyond what is expected from the lowering of the pH. Studies have shown that the gadolinium goes from partitioning completely in the solid phase in the basic SRAT Receipt to partitioning almost fully (≥80%) into the liquid phase in the acidic DWPF CPC products that have received excess acid addition.…”

“…Increases in metal solubilities after moderate to high acid addition (approximately ≥100% Koopman minimum acid (KMA)) in the NGA flowsheet can lead to higher supernate densities and soluble solids in the SRAT and SME Products. 34,[37][38] This dissolution of metals is part of the NGA flowsheet and does not have significant adverse chemical or physical impacts on the remainder of the DWPF process. 39 If there is a foamover that introduces SRAT or Slurry Mix Evaporator (SME) material containing glycolate into the SME condensate tank, the glycolate (and glycolate complexes) will be destroyed in the RCT by sodium permanganate added to the RCT prior to transfer to Tank 22.…”

“…Additionally, DWPF has implemented an NGA flowsheet that renders the catalytic production of hydrogen from formic acid much less of a concern. Radioactive qualification testing for several SBs, including SB9 46 and SB10 34 with the NGA flowsheet, included gadolinium in the sludge feed at very minor but measurable levels (Gd of SRNL-STI-2022-00502 Revision 1 approximately 0.08 and 0.05 wt% of TS in SB9 and SB10 testing SRAT Receipt, respectively). Although gadolinium will increase to approximately 0.4 wt% of TS in the SRAT Receipt sample due to ABD additions, the amount of gadolinium will still remain a minor component of the slurry.…”

SRNL Sludge Batch 10 Qualification SRAT and SME Off-Gas Results

“…Savannah River National Laboratory (SRNL) completed a small-scale demonstration of the Defense Waste Processing Facility (DWPF) Chemical Process Cell (CPC) utilizing the nitric-glycolic acid (NGA) flowsheet to support Sludge Batch 10 (SB10) qualification. [1][2][3][4][5] The demonstration utilized a Tank 51 slurry sample washed by SRNL 6,7 . During washing, material from H-Canyon Tanks 16.3 and 16.4 was also added.…”