Non-linear effects of alumina concentration on Product Consistency Test response of waste glasses

The effect of alumina mole fraction on the 7-day Product Consistency Test (PCT) responses, In[NL alpha], of simulated nuclear waste glasses was examined. It was found that the effect is highly non-linear. At low mole fractions of Al2O3 (x(Al2O3) <= 0.035) the effect of Al2O3 additions is highly negative (d ln NL alpha/dx(Al2O3) = -72). At intermediate concentrations (0.035 < x(Al2O3), <= 0.19) the effect of Al2O3 additions is moderately negative ( d ln NL alpha/dx(Al2O3) = -11). At high concentrations (0.19 < x(Al2O3) ) the effect of Al2O3 additions is highly positive (d ln NL alpha/dx(Al2O3) = +21). This variable impact of Al2O3 on In[NL alpha] is speculated to be caused by the rates at which the glass corrosion process changes through various reaction regimes in static conditions at 90 degrees C. A model for prediction of In[NL alpha] as a function of glass composition is presented. This model represents the data from 2669 glass compositions spanning a broad nuclear waste glass composition region and it is useful up to much higher Al2O3 concentrations than previous models (from similar to 10 to 25 mol% Al2O3 ). The model was validated using data subset validation methods and shown to predict validation data in the same composition region with roughly equal certainty as the model fit data. The potential causes for nonlinear effects of Al2O3 on In[NL alpha] were discussed in context of the progression of glass corrosion rates. Time resolved static corrosion data is needed to better understand these non-linear effects. (C) 2018 Elsevier B.V. All rights reserved.