FRIT DEVELOPMENT FOR SLUDGE BATCH 6

Abstract

The Savannah River National Laboratory (SRNL) evaluated a large number of Sludge Batch 6 (SB6) composition projections to support frit optimization for SB6 vitrification at the Defense Waste Processing Facility (DWPF). The evaluations discussed in this report occurred over a period of about 4 months, and included about 40 composition projections, developed by both Savannah River Remediation (SRR) and SRNL. Paper study assessments were used to evaluate the sludge composition projections with arrays of potential frit compositions using the predictive models in the DWPF Product Composition Control System (PCCS). Both nominal sludge compositions and sludge compositions with anticipated compositional variation were considered. The model predictions were used to identify candidate frit compositions for each SB6 projection and to provide some guidance to SRR on washing and blending strategies for SB6 preparation. This report presents a chronological review of this process and summarizes the findings at each stage. Following initial feedback from this work, the number of washes in Tank 51 was reduced to increase the projected sodium concentration in SB6. Analyses of predicted frit performance before and after a potential decant of Tank 40 showed that the post-decant SB6 composition would be difficult to process with any frit composition and that this scenario should be avoided. Based on the most recent SB6 projections (February 2010 SB6 composition projections developed at SRNL using the measured SB6 qualification sample composition and the revised Tank Farm washing plan), Frit 418 appears to be viable for SB6 processing at a target waste loading of 36%. A Nominal Stage PCCS Measurement Acceptability Region (MAR) assessment gave projected operating windows of 25-41% waste loading, limited by predictions of nepheline crystallization. The projected operating window is reduced to 25-38% waste loading when anticipated compositional variation is considered, again limited by predictions of nepheline crystallization. Blend points between 62 and 40 inches of Sludge Batch 5 (SB5) heel in Tank 40 had no practical impact on the projected performance of Frit 418. This assessment is made from a paper study approach only and assumes that no decant of Tank 40 will occur during SB6 processing. A decant of Tank 40 would reduce the Na2O concentration in Tank 40 to a point where it would be very difficult to target a waste loading of 36% for SB6 with Frit 418. The performance of Frit 418 with SB6 is limited by predictions of nepheline crystallization, which is a durability limiting constraint. Alternatives to Frit 418 are available that can provide equivalent projected operating windows and are limited by process related constraints (i.e., liquidus temperature predictions) rather than durability limiting constraints. A separate memorandum has recently been issued that discusses the use of Frit 418 for SB6 vitrification.1 potential differences in melt rate among these alternative frits will be discussed in a forthcoming technical report.