Characterization of Slag Product from Plasma Furnace for Unsorted Solid Radioactive waste Treatment
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CHARACTERIZATION OF SLAG PRODUCT FROM PLASMA FURNACE FOR UNSORTED SOLID RADIOACTIVE WASTE TREATMENT SERGEY.A.DMITRIYEV, SERGEY.V.STEFANOVSKY, IGOR.A.KNYAZEV, FYODOR.A.LIFANOV State Corp.,RADON,, 7 Rostovskii per., 2/14, 119121 Moscow, Russia ABSTRACT The shaft furnace equipped with plasma-fuel burners for high temperature slagging treatment has been developed in State Corp.,*RADON-. A slag is considered as final wasteform. From this point of view a slag formation mechanism, radionuclides immobilization and basic slag properties have been studied. A chemical and phase compositions of institutional and nuclear power station waste slags were determined. Some details of slags structure were investigated by infra-red spectroscopy. A study of radionuclides distribution has shown that caesium and strontium are concentrated in the silicate slag constituent while iron and cobalt enter the metal fraction. INTRODUCTION In the high-temperature treatment of solid radioactive waste (SRW), the main bulk of organic constituents destructs and transforms to gaseous phase as a result of oxidizing and decomposition processes. Inorganic SRW constituents are subjected to intimate structural transformation (redox processes, solid phase mineral formation reactions) and yield a slag are able to be melted and maintained in liquid flowable state at high temperatures. Such process occurs in FLK furnace [1] and ,RADON, plasma shaft furnace as well [2-5]. As slag is to be considered as final wasteform for long-term storage or ultimate disposal it has to satisfy overall demands for solidified intermediate level waste as follows: - radionuclide retention degree in slag has to be as high as possible (radionuclide loss has not to exceed of 1-2 %);
- leach rate of the most easily removable radionuclides of caesium by IAEA technique [6] has not to exceed by order of magnitude 10-4 and 10-1 g/(cm 2 day) in the first 7 days and after 2835 days of contact with distilled water respectively; - slag must be a long-term stable; - slag density must be as high as possible with the aim of increasing of waste volume reduction coefficient; - good radiation stability - the radiation absorbed dose accumulated by slag for all storage period can not result in slag properties alteration more than allowed limits from ecological point of view; - good mechanical strength - solidified slag block has not to be broken at the falling from 2 m of height. Moreover a set of process demands (melting point, fluidity, viscosity etc.) must be ensured. a slag from FLK furnace partially satisfies to above-mentioned demands. However, the process temperature rising by means of application of plasma-fuel heating sources has to create a conditions for more complete slag formation, consolidation, homogenization and gas removal. It must resultin an improvement of itsphisical, chemical and mechanical properties and the rising in safety and relability of radionuclides isolation from biosphere. In the present work a question on sutability for ultimate disposal of solidified slag product, pr
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