Development and Testing of a New Porous Crystalline Matrix (Gubka) for Stabilizing Actinide Solutions
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(DNFSB) Recommendation 94-1. These solutions include isotopes of americium and curium (Am/Cm) at SRS and plutonium nitrate solutions at Hanford. The "Gubka" ("sponge" in Russian) material, was developed by the Institute of Chemistry and Chemical Technology (Siberian Branch of the Russian Academy of Sciences) from coal power plant fly ash and consists of sintered glass-ceramic microspheres, or cenospheres, of mainly calcia-silica-alumina compositions. The Gubka material was previously tested for high-temperature catalysis applications [1]. Preliminary studies have shown the feasibility of using Gubka matrices to stabilize such rare earth elements as well as long-lived radionuclides technetium-99, zirconium95, neptunium and plutonium. The process consists of repeated saturation-drying cycles at below boiling temperatures. The final waste form is a stable material, suitable for safe, longterm storage or transportation. The trapped isotopes can be recovered by dissolution in acid or immobilized further, such as by vitrification or hot pressing. Inorganic materials were previously studied as a primary matrix for radioactive waste immobilization in porous glasses (P. Macedo, Catholic University, U.S.) [2, 3]; in silica gel (A. Nardova, Institute of Chemical Technology, Russia) [4, 5]; in foam corundum (V. Zakharov, Institute of Physical Chemistry, Russia) [6, 7, 8, 9] and in porous fireclay (chamotte) and diatomite, which were studied by scientists at V. G. Khlopin Radium Institute over many years (1975-1985). However, unlike the new Gubka material described in this paper, the drying process with the previous materials required boiling the solution. 637 Mat. Res. Soc. Symp. Proc. Vol. 608 © 2000 Materials Research Society
This paper describes tests with Gubka samples to stabilize surrogate SRS Am/Cm solutions. The purpose of the tests is to demonstrate technical feasibility of the Gubka technology to stabilize a DNFSB 94-1 problematic actinide solution composition. Future tests are also planned to demonstrate the feasibility of using Gubka to stabilize other problematic solution compositions. EXPERIMENT Gubka Properties Preparation of the Gubka material involves recovery and separation of hollow glass crystal microspheres (cenospheres) of desired composition from Kuznetskii coal fly ash produced by the Tom-Usinskaya and Novosibirskaya power plants. The cenospheres consist of calcia-alumina-silica microspheres with and without ferric phases. The cenospheres are then consolidated with a binder to form a porous crystalline matrix in blocks of different sizes and configurations. Representative characteristics of the Gubka samples used in this study are shown in Table I. The Gubka samples typically sorb water in 30 seconds to about 60 % of the equilibrium value at room temperature. The drying time to constant mass after such water sorption was determined to be 1.5 - 3 hours at 60 - 40 TC, respectively, and one hour at 100 'C. Table I. Representative Gubka sample characteristics. Mass, 9 1.4
Water Volume, Bulk Density, Abso
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