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Savannah River National Laboratory's frit development effort for SB4 is being driven by the most current CBU option for this sludge, referred to as Case 15C Blend 1. Candidate frits have been identified for this option via a paper study approach developed by Peeler and Edwards with the intent of down-selecting to a set of key frits whose operating windows (i.e., WL intervals that meet PCCS MAR criteria) are robust to and/or selectively optimal for this sludge option. The primary frits that appear attractive on paper (i.e., down-selected via the paper study) are now being incorporated into this experimental study. The potential for the formation of a nepheline primary crystalline phase is an important factor in frit development for SB4, due to the high Al{sub 2}O{sub 3} content of this sludge. Based upon earlier work by Li et al., glasses that do not satisfy the constraint: (SiO{sub 2}/SiO{sub 2} + Na{sub 2}O + Al{sub 2}O{sub 3}) &gt; 0.62 where the oxides are expressed as mass fractions in the glass, will precipitate nepheline as their primary crystalline phase, hindering the durability of the glass. Based on the most recent compositional projection from the CBU for SB4 (Case 15C Blend 1), 16 glasses have been selected to complement the earlier work by continuing the investigation into the ability of the above constraint to predict the occurrence of a nepheline primary crystalline phase for SB4 glasses and into the impact of such phases on the durability of the SB4 glasses. Glasses were selected to cover WLs which tightly bound the nepheline discriminator value of 0.62, with the intent of refining this value to a level of confidence where it can be incorporated into offline administrative controls and/or the PCCS to support SME acceptability decisions. In addition, glass specimens at WLs of 35 and 40% will be prepared and analyzed to contribute needed data to the ComPro{trademark} database in anticipation of a variability study for SB4. The glasses in Table 4-3 are to batched and fabricated using standard procedures. Visual observations and other analytical techniques are to be used, as needed, to assess the presence of crystals with specific interest in the nepheline primary phase. The durability of these glasses (for both quenched and centerline canister cooled versions) is to be measured using the ASTM PCT Method A. The results from these efforts are to be documented in a subsequent report. The results of this study will provide valuable input for the frit development efforts and subsequent feedback to the CBU regarding the relative viability of the current SB4 option under consideration. The refined nepheline discriminator value will provide a guideline for the avoidance of nepheline crystallization in SB4 glasses and aid in down-selection of frit compositions. These data will be combined with the results of melt rate studies and a paper study of the frits robustness with regard to variability in the sludge composition to provide an optimized frit recommendation to DWPF for immobilization of SB4

NEPHELINE FORMATION POTENTIAL IN SLUDGE BATCH 4 AND ITS IMPACT ON DURABILITY: SELECTING GLASSES FOR A PHASE 3 STUDY