Heat capacity of complex aluminoborosilicate glasses

ABSTRACT For nuclear waste vitrification in the Tank Waste Treatment and Immobilization Plant (WTP) at the Hanford site, waste feed is charged into a continuously fed electric melter and the molten glass is poured into stainless steel containers to solidify. The heat from the molten glass must be removed from the facility within plant operating constraints, making knowledge of thermal properties of the waste glasses critical. The heat capacity of Hanford low‐activity waste glasses with systematic variations in composition were studied using complementary thermal analyses – power‐compensated differential scanning calorimetry (pcDSC) at 50–630°C, heat‐flux differential scanning calorimetry (hfDSC) at 200–800°C, and drop calorimetry at 600–1200°C. Variations of the heat capacity with composition have been observed around the transition temperature ( T _g ) and above, particularly when B ₂ O ₃ and Al ₂ O ₃ is varied. Above T _g , all glasses exhibit decreasing heat capacity with increasing temperature. A correlation was found between this curve and the fraction B ^[4] ₂ O ₃ in glasses, suggesting boron coordination plays a role in this anomalous behavior. These measurements will be used as critical input to validate the heat balance calculations used for facility design and thus the overall operation of the WTP.