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Executive SummaryTo prove the technical and economic feasibility of the dispositioning of excess weapons usable materials by vitrification, it is necessary to demonstrate that PuO2 feedstock can be dissolved in glass in sufficient quantity and in less than 8 h. The objective of this study is to demonstrate a high Pu02 solubility in glass and to identify the rough time scale required for Pu02 dissolution in a candidate immobilization glass. The results of this study confirm that the Pu solubility can be as high as 10 wt% in glass (1 1.4 wt% P u 0 2 ) and the time required for dissolution of Pu@ in glass was less than 4 h in every case and as low as 1 to 2 k This time requirement is based on a single glass composition and two P u 0 2 source materials with similar particle size distributions (PSD); one high-fired and one low-fmd. Temperature, glass composition, and PSD of PuO2 are suspected being the major factors in PuO2 dissolution rates in glass. Additional tests are required to examine the effects of temperature, PSD, and glass composition on Pu02 dissolution kinetics.

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. 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