The kinetics of the conversion of high-level waste (HLW) feed to glass controls the rate of HLW processing. Simulated HLW feed and low silica - high sodium (LSHS) feed with co-precipitated Fe, Ni, Cr, and Mn hydroxides (to simulate the chemical and physical makeup of these components in the melter feed) were heated at constant temperature increase rates (0.4, 4, and 14?C/min), quenched at different stages of conversion, and analyzed with optical microscope, scanning electron microscope, and x-ray diffraction (XRD). Quartz, sodium nitrate, carnegieite (Na8Al4Si4O18), sodalite (Na8(AlSiO4)6(NO2)2), and spinel were identified in the samples. Mass fractions of these phases were determined as functions of the temperature and the heating rate. The fractions of nitrates and quartz decreased with increasing temperature, starting above 550?C and dropping to zero at 850?C. Spinel was present in the feed within the temperature interval from 350?C to 1050?C, peaking between 550 and 700?C. Sodalite (in HLW feed) and carnegieite (in LSHS feed) formed at temperatures above 600?C and then began to dissolve. TGA and DSC were use to determine the mass loss and the conversion heat as functions of temperature and heating rate and were compared with the reaction progress reached in quenched samples.
Revised: September 12, 2002 |
Published: December 1, 2001
Citation
Izak P., P.R. Hrma, and M.J. Schweiger. 2001.Kinetics of Conversion of High-level Waste to Glass. In Nuclear Site Remediation, ACS Symposium Series, edited by Heineman, W.R.; Eller, P.G., 778, 314-328. Washington, District Of Columbia:American Chemical Society.PNNL-SA-32514.