PNNL

Abstract

The U.S. Department of Energy Hanford Site in Washington state stores about 56 million gallons of high level radioactive waste in 155 of the original 177 tanks, with 22 already retrieved. The Hanford Waste Treatment and Immobilization Plant (WTP) will vitrify this waste, separating it into low-activity waste (LAW) and high-level waste (HLW) streams. These will be converted into immobilized low-activity waste (ILAW) and immobilized high-level waste (IHLW) glass products. ILAW will be disposed of in the onsite Integrated Disposal Facility, while IHLW will be stored on site until it is sent to a national deep geological repository. Pacific Northwest National Laboratory used estimated Direct Feed High-Level Waste (DFHLW) compositions, generated by the Hanford tank operations contractor, to define target glass compositions. This process recently determined that one gap in the database of glass properties is the high alkali (specifically Na and K) region. Glasses with high alkali content tend to have lower chemical durability and can be highly corrosive to melter components. Data from LAW glasses are used to inform the DFHLW property models; therefore, expanding the LAW compositional space directly extends the applicable composition envelope for DFHLW glasses. To expand the useable composition envelope for LAW glasses, 20 glass compositions were designed in the high Na2O + K2O composition space. The glass compositions selected were specifically targeting product consistency test (PCT) and vapor hydration test (VHT) responses near and above the contractual limits as this property response range has significantly less data than the range of glasses that easily pass contractual constraints. To more accurately predict the location of the constraint in composition space, data on both sides of the constraint are required. Of the 20 quenched glasses, seven were fully amorphous, and one had a sodium, aluminum silicate crystalline phase > 10 wt%. The remainder of the glasses had a total crystalline fraction of