Processing of large-Scale Radwaste-Containing Blocks using Exothermic Metallic Mixtures
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M.1. OJOVAN*, G.A. PETROV*, S.V. STEFANOVSKY*, B.S. NIKONOV** *SIA "Radon", 7th Rostovskii per., 2/14, Moscow 119121 Russia; Institute of Geology of Ore Deposits RAS, Staromonetnii per., 35, Moscow 109017 Russia.
ABSTRACT
The parameters of processing of large-scale (50-100 kg) radwaste-containing blocks were studied. Batches consisted of exothermic mixture, oxidizer, mineral additive, and radwaste surrogate. Such mixtures provide process temperature up to -2400 K. In the present work exothermic mixtures composed of Ca-Fe silicide, zirconium, silicon, and boron were intermixed with oxidizer (mixture of KMnO 4 and V2 05), natural zircon concentrate as mineral additive, and cerium oxide (actinide surrogate). Tests were carried out in a bench-scale plant. Burning of the reaction mixture was remotely initiated from electric supply unit. Melt formation started in the nearbottom area sustained upwards frontally, The melt temperature ranged between 1600 and 1900 K. The melt formation rate during the tests ranged between 0.7 and 2.5 kg/s. Melt cooling after reaction completion was kept for about 15-18 hours. Volatile aerosols were essentially retained in the bulk. The initial volume of the mixture was reduced after reaction by factors of 2 to 3. The densities of the blocks were ranged between 3.2 and 3.9 kg/dm3 . Samples of the materials obtained were examined by optical microscopy, X-ray diffraction, and scanning electron microscopy. The product consisted of glass-like body with metallic spheres (-0.5-1.5 mm) distributed within. The base was composed of glass (-60-80 vol.% of total) and crystalline phases (mainly zirconia). Monoclinic baddeleyite was found to be the major crystalline phase. The minor phase was tetragonal zirconia. Cerium (actinide surrogate) was partitioned among the glass and zirconia. The Ce 203 concentration in glass ranged between -0.4 wt.% and -0.8 wt.% whereas its content in zirconia was found to be lower (up to -0.3 wt %). The metallic constituent consisted Fe70.2V19.3Mn1. Si9 .4.
of vanadium and
Fe-V-Si alloy whose
average composition
was
INTRODUCTION
Among radioactive waste treatment technologies, vitrification and ceramization (incorporation in Synroc) are considered as the most promising [1,2]. Crystalline waste forms are preferable due to their higher long-term stability. Both melting and ceramic routes are being developed to produce vitreous, glass-ceramic and ceramic materials [1-5]. One of the technologies to produce waste forms through melting involves batch heating and melting using energy produced by burning of exothermic metallic mixtures [6,7]. The advantages of this technology over other vitrification technologies are simplicity, efficiency and low process cost. The process does not require a special melter and may be considered as a modification of in-situ vitrification [8]. Therefore, this process can be applied to vitrify both waste streams and contaminated soils. In the present work waste treatment process parameters were studied and the solidified product was characterized
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