The impact of crystalline phase precipitation in glass during canister
cooling on chemical durability of the waste form limits waste loading in
glass, especially for vitrification of certain high-level waste (HLW)
streams rich in Na2O and Al2O3. This study
investigates compositional effects on nepheline precipitation in simulated
Hanford HLW glasses during canister centerline cooling (CCC) heat treatment.
It has been demonstrated that the nepheline primary phase field defined by
the Na2O-Al2O3-SiO2 ternary
system can be used as an indicator for screening HLW glass compositions that
are prone to nepheline formation. Based on the CCC results, the component
effects on increasing nepheline precipitation can be approximately ranked as
Al2O3 > Na2O > Li2O ≈
K2O ≈ Fe2O3 > CaO >
SiC2. The presence of nepheline in glass is usually
detrimental to chemical durability. Using x-ray diffraction data in
conjunction with a mass balance and a second-order mixture model for 7-day
product consistency test (PCT) normalized B release, the effect of glass
crystallization on glass durability can be predicted with an uncertainty
less than 50% if the residual glass composition is within the range of the
PCT model.
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