PNNL

Abstract

Hanford Site nuclear waste is to be vitrified at the Waste Treatment and Immobilization Plant (WTP), which is a part of the safe and efficient retrieval, treatment, and disposal mission of the U.S. Department of Energy Office of River Protection. Hanford tank 241-AP-105 (referred to herein as AP-105) is one of the initial Hanford radioactive tank wastes planned to be processed and vitrified. A portion of AP-105 waste was retrieved by Washington River Protection Solutions, LLC (WRPS) and transferred to Pacific Northwest National Laboratory (PNNL). The waste went through dilution by Columbia River water to reach a target sodium (Na) concentration of 7 M, solids filtration, and cesium removal by ion exchange. A glass composition was calculated from the Kim et al. glass models to satisfy the WTP baseline requirements based on the as-received sample and the target dilution to 7 M, from which a simulant was calculated and glass forming chemical (GFC) additions were determined to form a liquid/solids mixture called melter feed. To prepare for the processing of the 7 M Na AP-105 waste melter feed and learn about the production expectations, the melter feed simulant of 7 M Na AP-105 waste was processed in a non-radioactive, continuous laboratory-scale melter (CLSM) system. The 7 M Na AP-105 simulant melter feed was charged into the CLSM for 7.50 h of processing, which produced 6.13 kg of glass, for an average glass production rate of 1735 kg m¬2 d 1. Since there were no processing issues with the 7 M Na AP-105 simulant melter feed, the actual 7 M Na AP-105 waste melter feed was then processed in a CLSM system built into a contamination area in a radioactive environment. The melting behavior characteristics appeared similar for both the simulant and waste melter feeds. The 7 M Na AP-105 waste melter feed was charged into the CLSM for 6.71 h of processing, which produced 6.58 kg of glass, for an average glass production rate of 2079 kg m¬2 d 1. Samples of the 7 M Na AP-105 simulant and melter feeds as well as selected glass and offgas liquid samples were analyzed to determine the concentration of certain chemical constituents. Based on this analysis, most of the primary components in the glass produced from the conversion of the 7 M Na AP-105 melter feeds were within 10 % of their target values, as has routinely been the case with glasses produced through vitrification in the CLSM system. However, the ZrO2 content in the 7 M Na AP-105 simulant CLSM run was less than its target, due to an under batching of zircon in the melter feed. A constituent of interest present in low quantities in the 7 M Na AP-105 waste is 99Tc or its non-radioactive surrogate, Re, added to the 7 M Na AP-105 simulant. Analysis for the quantities of 99Tc and Re in the 7 M NA AP-105 glass product resulted in an average single-pass retention from the melter feed during relative chemical steady state of 49 ± 2 % for 99Tc and 38 ± 1 % for Re. Compared to the processing of other melter feeds, the retention of 99Tc in the 7 M Na AP-105 glass was greater than in lower Na molarity AP-105 glasses, while the retention of Re in the 7 M Na AP-105 was equivalent to lower Na molarity AP-105 glass. Both the 7 M Na AP-105 waste and 7 M Na AP-105 simulant were processed at greater average glass production rates than their lower Na molarity AP-105 counterparts processed in the CLSM. The 7 M Na AP-105 waste processed faster than the 7 M Na AP-105 simulant likely due to the lower concentration than expected of primary components in the waste compared to the values used to calculate the simulant. A spike of iodine was added into the 7 M Na AP-105 simulant melter feed that could be detected above the analysis detection limits and was measured in all subsequent glass pours after melter feed charging had begun. Iodine appeared in greater quantities in the glass pours immediately preceding or following the burn off of the cold cap. It is recommended to continue to perform future tests wi