Synthetic Melted Rock-Type Wasteforms
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SYNTHETIC MELTED ROCK-TYPE WASTEFORMS IGOR A. SOBOLEV, SERGEY V. STEFANOVSKY AND FYODOR A. LIFANOV
SIA "RADON", 7 Rostovskii per., 2/14, 119121 Moscow, Russia ABSTRACT
Glass-ceramic materials based on sphene, pyroxenes, apatite as well as various SYNROC formulations have been produced through melting in a laboratory electrically-heated furnace and inductive-heated melter ("cold crucible"). Materials prepared were investigated by X-ray diffraction analysis, electron-probe microanalysis, infra-red and EPR spectroscopies. Basic properties such as leach rates of radionuclides, density and compressive strength have been determined. Melted SYNROC-B and C phase compositions produced by induction melting are similar to hot-pressed SYNROC. INTRODUCTION
Vitrification of radioactive wastes is a convenient method for waste radionuclides immobilization [1]. Borosilicate glass is considered as a candidate material suitable for long-term storage of nuclear waste. A disordered continuous glass network is able to accomodate various radionuclides as well as numerous non-radioactive elements [1]. However, glass is thermodinamically unstable and subjected to devitrification. It can result in the decrease of its chemical durability and the escape of radionuclides in environment. Investigations of vitrified high-level waste (HLW) have shown that self-irradiation, radiogenic heat and nucleators (noble metals, transition metal oxides, spinels, etc.) and high temperature solutions cause alterations in glass matrix resulting in radionuclide delocalization [1]. Crystalline materials are thermodinamically stable and HLW immobilized in both single- and polyphase crystalline materials has remained unaltered for geological periods, e.g. in radiation fields, caused by external or internal sources (uranium and thorium isotopes) [2], which can
guarantee a safe isolation of HLW from the biosphere. In that case, the radionuclides enter the crystal lattice of minerals (fixation on atomic level). Numerous minerals and mineral assemblages such as pollucite [3], sphene [4], apatite, pyrochlore [5], betafite [6], polyphase ceramics [7], clay-based ceramics [8], various SYNROC formulations [9-13], basalt [14], NZP-ceramics [15], etc.were studied as possible wasteforms. Some of thease materials were produced by ceramic technology or hot-pressing, for example, SYNROC [10,11], but some materials wereproduced by melting as well [9,12,13]. In work [13] it was reported that melted materials corresponding to chemical compositions of akmite, andradite, arfvedsonite, sphene, pollucite and SYNROC have been produced. X-ray diffraction (XRD) was not conducted. Respectively, a formation of assumed crystalline phases has not been proved and correspondence between the melted and hot-pressed materials has not been established. In the present work the process of rock-type materials production is studied in more details and comparison of materials melted in laboratory resistive furnace and cold crucible is carried out. Properties of melted and hot-pressed SYNROC are com
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