Minor component study for simulated high-level nuclear waste glasses (Draft)

Abstract

. Impact of sulfate on glass durability appears to be strongly glass composition dependent. For CCW glasses, two distinct types of glass dissolution were obsemed, om by network dissolution, and another by preferential leaching of NaOS-0 and Ii-0-SO groups. 'Ihe preferential leaching, however, is not associated w i t h crystah of Na2S04 and Ii2S04 in glass, suggesting that clusters of Na-Os-0 and IiQS-0 exist in glass. Mi-hannels of these cIusters are suspected to cause high-Ieaching rates of these species frmn the glass matrix. Chemical durability of HLW glasses is affected by phosphate in h w aspects, which are associated w i t h crystal formation in glass through the change of residual glass conpsition. For a glass w i t h a d l fraction of phosphate crystals, Na3po,0r Li3p04 or both, glass &rabidity was either unchanged or improved slightIy. ?his can be explained by the remvaI of aIkali oxides from the glass matrix, which in tum strengthens the residual glass xtwork, Howver, crystallization decreases gIass dmbility when large amunts of allcali-phosphate crystals V precipitate in the glass. For: @ass containing high P205, crystallizaGon of &Po, and W S i 0 4 occurs in slowly cooled glass samples (using the canister centerline cooling treatment). The crystallization is detrir~ntal to glass durability, resulting in a sharp increase (up to a factor of IO) in sodium release tested using the 74ay PcTproCedure. The deteriorationof glass durabirity in this case can be attributed to wakening of the glass network by remvd of Al or Si from the glass matrix through crystalIization. In HLW glasses spiked w i t h Cr2Q (up to 0.8 wt%) a d X Q (up to 5 wt%), no impact on glass durability was found.vi

Glass Formulation Development for INEEL Sodium-Bearing Waste

“…to 60 mass YO was added to avoid nepheline precipitation in the glass.b Tfiically, a constraint on S03 concentration' would be used to avoid sulfate accumulation in the melter (Li et al 1995;Lambert et al 1996). However, the tests planned to demonstrate SBW processability include the use ofa melter with a salt drain that will tolerate salt separation.d Therefore, no constraint on salt separation from glass was used for SBW glass foirnulation (i.e., salt formation will not limit waste loading).…”

“…The primary difference appears to be in the SOSconcentration. This will impact the formation of a secondary salt phase since the volubility of SOS is expected to be roughly 1 mass 'Yo (Li et al 1995, andLambert et al 1996). q at 1150°C (using the 3rdand 4* columns of Table 2.2) 6.0 (P&S) 5.9 (Pas) r~, (using the 5* column of Table 2.2) 0.9 (g/m*) 0.8 (g/m*) r~(using 6* column of Table 2.2) 1.0 (g/m2) 1.0 (g/m*)…”

Retention of Halogens in Waste Glass

“…Therefore, from nineteen nineties onwards crucible studies were performed and melter tests were evaluated with respect to the halogen retention in LAW glasses. Li et al (1995) melted borosilicate LAW glasses at temperature 1300°C to 1450°C. The excess of F above the solubility limit formed CaF 2 and NaF crystals and the excess Cl formed spherical NaCl inclusions (crystallized NaCl droplets).…”

“…In a similar study, Li (1995) added NaF and NaCl to Glass L6-5412 and measured both the mass loss due to volatilization and the maximum concentrations of F and Cl that remained dissolved in the glass without residual microscopic inclusions. For each melt, the batch mass was 130 g, and the melt surfaceto-volume ratio was 0.2 mm -1 .…”

“…In-depth studies of F, Cl, and I solubilities and volatilization were performed by Crichton et al (1995a and1995b). They used the same Glass L6-5412 as Li (1995). Unlike Li, who used XRF, they measured halogen concentrations in glass with scanning electron microscopy (SEM) energy-dispersive spectroscopy (EDS) analysis.…”