The results of a complex of tests of refractories for glass resistance under static and dynamic conditions and the electric resistance during glass melting are presented.The tests of the refractories in a phosphate glass melt at 800-1100°C showed that the most stable material is the fusion-cast chromia-alumina-zirconia refractory ER-2161 with chromium oxide content 26 mass%. The pressed chromia-corundum refractory KhKT-10 possesses adequate glass resistance and is an electric insulator under the glass melting conditions in the ÉP-500 melter. On the basis of the results of comparative tests of chromia-containing refractories and Bakor-33, the refractories ER-2161 and KhKT-10 are recommended for the masonry of future furnaces as a material for the bridgewall and the electric-insulation layer in a two-layer threshold.Three ÉP-500 ceramic melters for vitrifying high-level liquid radioactive wastes have operated successfully for 20 years in the radiochemical plant RT-1 at the Mayak Industrial Association. Wastes with different composition and activitỹ 450 MCi are converted into phosphate glass by a single-stage method in these melters [1]. The main internal masonry of the ÉP-500 furnaces consists of bricks made of the baddeleyite-corundum refractory Bakor-33, which showed good glass resistance. However, elevated erosion of the refractory was observed in individual, most strongly attacked, sites of the masonrythe bridgewall and the threshold. The life span of these structures can be increased either by introducing water or air cooling or by using refractories with a higher glass resistance.The French company SEPR has obtained positive results by using fusion-cast chromia-alumina-zirconia refractories as the material for the bridgewall in glass-melting furnaces. Over the last 30 years, refractories such as ER-2161 (European analog) and Monofrax K-3 (American) have been widely used for the masonry in furnaces which are used for melting corrosive and high-temperature glasses. The operation of DWPF melters for vitrifying high-level liquid radioactive wastes from the nuclear weapons complex in Savannah River (USA) has shown that the life span of single-course masonry made of the refractory Monofrax K-3 in a borosilicate glass melt is 7-8 yr.In our country, an experimental batch of bricks consisting of fusion-cast KhATs-30 chromia-alumina-zirconia refractory, which was used for the masonry in the experimental ÉPBS-100 furnace at Mayak, was developed and fabricated. A comparative assessment of the KhATs-30 and Bakor-33 refractories after operation for 2 yr in a furnace confirmed that both refractories have a high-resistance to phosphate glass melt. However, because the KhATs-30 refractory is no longer produced,
Phosphate glasses are used as matrices, including and fixing radionuclides, in the technology for solidification of radioactive liquid wastes. To optimize the conditions of this technology, it is necessary to have data not only on the physicalchemical and mechanical properties of the glass with the main composition, but also about the structural and valence state of impurity components in the glass, specifically iron, which is always present in an appreciable quantity in the solutions being solidified.Our aim in the present paper is to study the structural and valence state of iron ions in sodium-aluminum-phosphate (SAP) glass by means of electron paramagnetic resonance (EPR), M6ssbauer spectroscopy (MS), and nuclear magnetic resonance (NMR). Our results enabled us to determine the characteristics of the occupancy and distribution of iron ions over tetra-and octahedral positions as a function of the ratio of the concentration of iron and aluminum oxides, to determine the concentration of Fe 3+ and Fe 2+ ions and the number of phosphorus and aluminum atoms in the nearest-neighbor environment of the impurity iron ions, as well as to estimate the effect of the concentration of aluminum oxide on the average distance between the phosphorus atoms in the SAP glass.Experimental Conditions. To synthesize the SAP glasses, we prepared a charge consisting of powders of the pure reagents NaPO3, AI203, and NaNO 3. The charge was held at 1100~ in an alundum crucible for 4 h in air to obtain frits of three-component glass, corresponding to the following oxide composition (mass %): 25 Na20-(10-21)AIxO3-(53-63)P205. The frit was mixed with Fe203 powder and held at 1050~ for 6 h, after which the melt was allowed to cool in air to room temperature within 3 h. The samples of SAP glass contained from 0.4 to 6 mass % Fe203.The EPR, M6ssbauer, and NMR spectra were recorded using glass powders with grain size not exceeding 120/zm; all measurements were performed at room temperature.The EPR spectra of the Fe 3 + ions were recorded on a RI~-1301 radio spectrometer, the 57Fe M6ssbauer spectra were recorded on a YAGRS-4 spectrometer with a 57Co ,,/-ray source in chromium with the signals recorded in a NTA-1024 multichannel analyzer, followed by least-squares analysis of the two doublets on a IBM PC/AT computer. The 27AI and 31p spectra were recorded on a Brucker (Germany) SKHR-90 pulsed Fourier spectrometer, using a "solid-echo" sequence in the high-power regime with external stabilization of the magnetic field. The chemical shifts in the 3tp NMR spectra were read from the signal from an 85 % solution of H3PO 4 used as an external standard.EPR Spectra of Fe 3+ Ions. Figure 1 displays the EPR spectrum of Fe 3 + ions in SAP glass, containing 6 mass % Fe203. For [Fe203] < 4 mass% the EPR spectrum consists of two lines with g-factors of 4.3 and 2, which are determined by the isolated Fe 3+ ions occupying, respectively, tetra-(FeO4) and octahedral positions (FeO6) in the glass structure [1]. The third (wider) line in the region g = 2 (dashed line...
There are indisputable advantages to using microwave radiation in technological processes for reprocessing liquid wastes, and they have been partially or completely realized in the apparatus developed. Testing of the apparatus has confirmed that it holds great promise for liquifying radioactive wastes with a complicated composition in a large range of the salt concentration in the initial solution.Microwave melting is a promising method for reprocessing almost all types of wastes except metallic wastes. The fundamental difference between microwave melting and other types of melting is that the microwave source can be placed in a safe service zone. Only individual parts of the melter structure, which are made of corrosion-resistant materials, are in contact with the material being processed. These parts are made so as to allow for decontamination and, as necessary, disassembly. During microwave heating, a one-time-use metal crucible-container which is used to store the wastes to be reprocessed can be used.The main advantage of microwave heating combined with a crucible-container is that only the stationary cover and crucible-container are placed in a hot chamber or canyon. This method will permit doing the following:• simplify the reprocessing of radioactive wastes, since all stages of the process from water evaporation to the formation of the glass mass can be performed in the same crucible-container, which is then buried; • eliminate from the technological process the stage of repouring of the fused glass mass; • choosing efficiently the scheme and regimes for feeding the wastes into the crucible-container; and • improve the ecological conditions. A different composition of the glass matrix can be used at the vitrification stage. Depending on the nature of the physicochemical state of the materials being processed, the process can be conducted in a wide temperature range. The final product can be obtained in the form of a glass block with the required chemical stability. Preliminary work [1, 2] on the vitrification of some forms of liquid and pulp wastes from radiochemical operations on a microwave setup with a 5-kW generator at 2375 MHz has confirmed that such wastes can in principle be processed in an approximately 20-liter metal crucible-container.The purpose of the present work is to check the solidification of liquid radioactive wastes with complicated chemical composition and different concentration in a single-stage technological process in replaceable one-time-use crucible-con-
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