Evaluation of Ceramic Materials to Immobilize ICPP Calcines
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BASIS
Stephen V. Topp,
FOR NUCLEAR WASTE
Inc.
MANAGEMENT
37
editor
EVALUATION OF CERAMIC MATERIALS TO IMMOBILIZE B. A. STAPLES, H. S. COLE, AND J. Exxon Nuclear Idaho Company, Inc, 83401
ICPP CALCINES
C. MITTL P. 0. Box 2800,
Idaho Falls,
Idaho
ABSTRACT Various ceramic materials as well as Formula 127 glass have been developed to immobilize ICPP zirconia calcine. Tailored, titanate and matrix encapsulated ceramics were prepared by cold pressing and sintering reactants, while glass-ceramics were prepared by melting in a manner similar to that of preparing the glass. X-ray diffraction techniques were used to determine the presence of radionuclide and calcine matrix element host phases in each ceramic material. The aqueous leachability, practical loading capacity and the incorporation of waste elements into host phases was investigated and compared to those of Formula 127 glass through application of the Soxhlet and MCC-I static leach tests. Potential process requirements for each material were evaluated based on the number of steps needed for laboratory-scale preparation. INTRODUCTION Aqueous wastes from the reprocessing of nuclear fuels at the Idaho Chemical Processing Plant (ICPP) are solidified in the Waste Calcination Facility. The calcined wastes are then stored in stainless steel bins contained in concrete vaults. This operation has been performed routinely since 1963 resulting in about 2000 m3 of calcined wastes presently being stored at ICPP. Many of the storage bins contain different calcines and various bed start-up materials, each with a unique chemical composition[l]. In the future, new tvyes of calcines such as that made from reprocessing wastes from Fluorinel fuels will fill bin sets presently under c 9 nstruction. It is projezted that by the year 2000 about 8000 m of calcines will be stored at ICPP [2]. It has been determined that radionuclides of cesium and strontium leach readily on contact with aqueous solutions from the particulate calcines [3,4]. Regulatory criteria may require that calcined radioactive wastes stored at ICPP be retrieved, immobilizated by conversion to a more stable solid form, and transferred to a federa repository for final disposal. MATERIALS INVESTIGATED Candidate materials to immobilize ICPP zirconia calcines for final disposal include titanate ceramics[5], tailored ceramics[6], glass-ceramics[7], and matrix encapsulant ceramics[8]. These materials are composed of individual synthetic mineral phases into which radionuclides and calcine matrix elements can be chemically
38 incorporated. The glass-ceramic also includes a glassy phase which The physically entraps radionuclides and calcine matrix elements. synthetic phases in each material investigated contain cations that Thus, in the successfully are constitutents of zirconia calcine. prepared products of these candidates, radionuclides and calcine matrix elements would be immobilized mainly by chemical combination by forming discreet phases or as members of solid state substituAll these materials, when properly t
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