A Comparison of Rheology Data for Radioactive and Stimulant Savannah River Site Waste

Abstract

The purpose of this study was to review historical rheology data for radioactive Savannah River Site (SRS) wastes from storage tanks through to the melter feeds in the Defense Waste Processing (DWPF) facility. SRS wastes were generated from either the Purex (high iron) or HM (high aluminum) processes. The available rheological data for SRS wastes were then compared to any historical simulant data for equivalent SRS wastes. The comparisons were accomplished by initially obtaining all available radioactive rheology data for sludge, Sludge Receipt and Adjustment Tank (SRAT) product, and Slurry Mix Evaporator (SME) tank product (equivalent to DWPF melter feed). These data were grouped as sludges, SRAT products, or SME products. The data within each group were then subdivided to reflect individual waste tanks or DWPF sludge batches, e.g. Tank 8 sludge or Sludge Batch 1B SRAT product. The comparability of a simulant and a radioactive waste was assessed primarily by the value of the Bingham Plastic model yield stress at equivalent weight % insoluble solids content. Values within 20-30% were considered to be giving "good agreement". Values different by a factor of two or more were considered to be giving "poor agreement". Intermediate cases were rated as "fair agreement". Rheological data for Purex sludges indicated good to fair agreement between real and simulant waste. The presence of HM sludge mixed with Purex sludge gave fair to poor agreement. Similar results were seen for SME products. There is insufficient SRAT product data to make a comparable conclusion. The differences between Tank 8 and Tank 40 sludges used to prepare Sludge Batch 2 also manifested as rheological differences. Similarly, Tank 40 simulant had an order-of-magnitude higher yield stress than Tank 8 simulant. Tank 8 simulant had good agreement with Tank 8 waste rheology. The Tank 8/40 blend that became sludge batch 2 (SB2), however, did not have good agreement in rheology. The implication is that real Tank 40 waste was more viscous than simulant Tank 40 waste, even though simulant Tank 40 waste had ten times the yield stress of both real and simulated Tank 8 waste. Large differences in yield stress in real waste tanks were seen in the work of B.A. Hamm. The main difference there was driven by waste type, Purex vs. HM. HM gave the higher yield stresses. Tank 8 was Purex, while Tank 40 contained a blend.

Sludge Batch 4 Without Tank 4 Simulant Flowsheet Studies: Phase I SRAT Results

“…For the SB4-20 product (see Figure A -1), the up and down flow curves overlaid, but the model was also fitted to the down curve. The SB4-19 product yield stress is within the nominal DWPF operating window and is similar to the yield stress measured for other SRAT products, but the consistency was slightly higher (Koopman 2004). For the SB4-20 product, the yield stress is below the nominal DWPF operating range but is consistent with some of the SRAT products tested during SB3 qualification, while the consistency was within the nominal range (Koopman 2004).…”

Sludge Batch 3 Qualification in the SRTC Shielded Cells

“…An upper limit for its beta activity was estimated from the total beta activity measured in the sample corrected for the beta activities measured for the beta emitting radionuclides that could be measured. The upper limits for 14 C and 129 I are projections from their concentrations in Sludge Batch 2 (SB2) 11 Am presented in Table 3-2 are recommended for use by the DWPF. The concentration of H-3 was measured in three samples of the supernate of the Tank 51 SB3 Qual.…”

Impact of Simulant Production Methods on the Physical Properties of DWPF Sludge Batch 3 Simulant.

“…Previous simulants were not necessarily conservative based upon rheology. 14 The results of the current sludge preparation study indicate that there are many methods of modifying the physical properties of a DWPF sludge simulant. Additional studies are recommended to improve our understanding of the important properties (chemical and physical) of DWPF sludges.…”