An Experimental Comparison of Alternative Solid Forms for Savannah River High-Level Wastes
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AN EXPERIMENTAL COMPARISON OF ALTERNATIVE SOLID FORMS FOR SAVANNAH RIVER HIGH-LEVEL WASTES
JOHN A. STONE E. I. du Pont de Nemours & Co., Aiken, South Carolina, USA
Savannah River Laboratory,
ABSTRACT Samples of borosilicate glass, high-silica glass, tailored ceramic, and SYNROC, incorporating simulated Savannah River high-level defense waste sludges, were leached by the MCC-l procedure for times up to 28 days. Cesium, uranium, and cerium leach rates are reported for waste forms containing a composite sludge, at 40°C in deionized water, and at 90°C in deionized water, silicate water, and brine. The ordering of the waste forms from best to worst differs for each element leached, and none of the forms show a clear advantage for all the key radwaste elements. Some cesium leach rates for forms containing high-aluminum or high-iron sludges also are presented. So far, only small effects of sludge type have been observed, with one exception. This study is one of several inputs for selection of an alternative waste form for Savannah River waste.
INTRODUCTION The Savannah River Laboratory (SRL) Comparative Leach Test Program is designed to provide part of the data base for comparing the most promising waste forms for immobilization of Savannah River high-level defense waste [1]. This program is one of several sources of leaching data on alternative waste forms. Leachability [2] is the dominant property considered in a product performance evaluation, which in turn, is one of several inputs for selecting a waste form [3]. Key results of the SRL studies are reported in this paper. Four waste forms were selected for comparative leach testing at SRL. Wasteform developers prepared the materials incorporating simulated Savannah River high-level waste sludges supplied by SRL. The waste forms and developers are:
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Borosilicate Glass [4], Savannah River Laboratory High-Silica Glass [5], Catholic University of America Tailored Ceramic [6], Rockwell International - Energy Systems SYNROC [7], Lawrence Livermore National Laboratory
Waste forms were tested with the Materials Characterization Center (MCC) Static Leach Test, MCC-l [81. The importance of comparing waste forms by testing in a single laboratory was illustrated by experience with MCC-I which showed that the intra-laboratory variance of the test is considerably less than the variance between laboratories. Thus, comparisons by one experimenter are subject to much less relative uncertainty than comparisons among several different experimenters.
The information contained in this article was developed during the course of work under Contract No. DE-ACO9-76SR00001 with the U.S. Department of Energy.
2 EXPERIMENTAL PROCEDURE The Comparative Leach Test Program was performed by the following steps: Large batches of three different simulated sludges were prepared at SRL. Portions of the simulated sludges were distributed to the developers. The developers then incorporated the sludges into state-of-the-art, laboratory-scale waste forms. 4. The waste form materials
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