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Experimental Synthesis of Crystalline Matrices Based on Ce, Ba, Sr Zirconates for Immobilization of High-Level Radioactive Actinides

by E. B. Anderson, Radium Inst, St. Petersburg, Russia,
B. E. Burakov, Radium Inst, St. Petersburg, Russia,
V. G. Vasiliev, Radium Inst, St. Petersburg, Russia,
V. A. Starchenko, Radium Inst, St. Petersburg, Russia,



Document Type: Proceeding Paper

Part of: High Level Radioactive Waste Management 1993

Abstract:

Experimental investigations are carried out at the Radium Institute to create different by their properties crystalline matrices, alternative to SYNROC, for incorporation of partitioned high-level wastes. It seems promising to produce such matrices on the basis of rare-earth garnets, zircons, oxides of Zr, Ce, some types of zirconates, etc.. This paper considers the results of laboratory experiments on the synthesis of crystalline matrices based on Ce, Ba, Sr and Ca zirconates. Zirconates are salts of metazirconic (H₂ZrO₃) and orthozirconic (H₄ZrO₄) acids used in industry for obtaining high-temperature ceramics and refractory materials. They are high-melting crystalline compounds (the melting temperature: CaZrO₃-2550?C, BaZrO₃-2480?C, SrZrO₃- 2700?C, etc.), insoluble in water and alkalies. Note, that zirconates may be potentially used for immobilization of cesium and strontium. It seems, however, that most promising is their application for fixing transplutonium and rare-earth elements. Matrices were produced by the method of solid-phase synthesis from a mixture of starting oxides (blend). The blend was prepared by plasmochemical denitration of nitrate solutions, of corresponding salts. A nitric solution containing 2-3 mol/l of nitric acid and 10-15 g/l of calcium, barium, strontium, cerium nitrates or zirconyl nitrate, or their mixture, was fed into a plasmochemical reactor with a flow rate 30 l/h. The plasmochemical reactor was connected with an induction plasmotron in which air is the plasma-forming gas. The plasmochemical installation contained also a high-frequency induction generator with a power 60 kW and frequency 1.76 MHz, a system of oxide powder separation from the air flow and air purification. The obtained mixture of oxides underwent gas-static pressing under a pressure of 300-350 MPa and at a temperature about 1000?C, or axial pressure in graphite matrices under a pressure of 30 MPa and a temperature 1200?C. In both the cases the pressing was done in argon atmosphere.

Subject Headings: Matrix (mathematics) | Radioactive wastes | Temperature effects | Waste disposal | Nitrates | Mixtures | Air flow

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