HIGH LEVEL WASTE (HLW) SLUDGE BATCH 4 (SB4): SELECTING GLASSES FOR A VARIABILITY STUDY

A critical step in the Sludge Batch 4 (SB4) qualification process is to demonstrate the applicability of the durability models, which are used as part of the Defense Waste Processing Facility's (DWPF's) process control strategy, to the frit / SB4 glass system via a variability study. A variability study is an experimentally-driven assessment of the predictability and acceptability of the vitrified waste product quality that is anticipated from the processing of a sludge batch. The quality of the waste form is a measure of its durability as determined by the Product Consistency Test (PCT). At the DWPF, the durability of the vitrified waste product is not directly measured by this test during normal operation. Instead, the durability is predicted using a set of models that relate the PCT response of a glass to the chemical composition of that glass. The main objective of a variability study is to demonstrate that these models are applicable to the glass composition region anticipated during the processing of the sludge batch. The success of this demonstration allows the DWPF to confidently rely on the predictions of the durability/composition models as they are used in the control of the DWPF process. The glass region for the SB4 variability study was determined using the most recent projections of the compositions of this sludge batch. Variation was introduced into the composition of the sludge to account for the uncertainty present in these projections as well as for process variation that may be experienced at the DWPF during its normal operations. The primary focus will be on the use of Frit 503, as this frit was recommended for SB4 processing. However, the frit recommendation memorandum also stated that Frit 418 is a viable option, especially for DWPF processing during the transition from SB3 to SB4 (i.e., an acceptable product can be produced with both SB3 and SB4 when Frit 418 is used).a As a result, there is interest in selecting some glasses from the SB4 / Frit 418 system. In this report, glasses are selected for the variability study using a nominal SB4 composition combined with Frits 418 or 503, covering a range of waste loadings (WLs) that are likely to be processed at DWPF. In addition, three sets of corner points or extreme vertices (EVs) for regions representing different levels of variation in the SB4 composition are combined with Frit 503 to identify glasses that will allow for an evaluation of the effect of sludge variation on the durability of the vitrified waste product. These glasses also cover a range of WLs that are likely to be processed at DWPF. A thorough statistical analysis is used to allow for a wide range of sludge compositions to be examined while minimizing the number of glasses that must be made in the laboratory. A total of 35 glasses are selected for the SB4 variability study. These glasses will be batched and melted following standard SRNL procedures, and testing will be completed to measure the chemical durability of each glass composition. A subsequent report will document the results of the experimental portion of the SB4 variability study