RU2168226C1 - Method for vitrifying radioactive wastes in cooled metal induction melter - Google Patents

Abstract

FIELD: recovery of radioactive wastes by converting them into vitreous state. SUBSTANCE: method involves producing starting radioactive vitreous melt in cooled metal induction melter, feeding radioactive charge onto it, dipping electrodes into radioactive vitreous melt produced in the process, applying commercial-frequency current, filling working space of melter with radioactive vitreous melt, and discharging the latter through drain unit. EFFECT: enhanced capacity, reduced amount of volatile nuclides separated to gas phase, reduced power requirement.

Description

 The inventive method relates to the field of environmental protection, and more specifically to the field of processing of radioactive waste (RAW). The most effectively claimed method can be used for vitrification of solid radioactive waste with subsequent cooling of the melt to obtain a monolithic final product suitable for long-term storage.

 A known method of vitrification of radioactive waste in a direct heating ceramic electric furnace (1), including supplying a cullet of direct heating to a ceramic electric furnace, turning on starting heaters, heating the furnace to a temperature at which the glass melt begins to pass electric current, applying voltage to the electrodes, heating the glass to its working temperature, dismantling of starting heaters, supply of radioactive waste together with glass-forming agents to the surface of the molten glass before filling the working volume of the electric furnace, draining of images the resulting radioactive molten glass into a container and its cooling to the formation of a final product suitable for long-term storage.

The disadvantages of this method are:
- its increased duration associated with the increased duration of the operation of preheating the electric furnace with starting heaters to a temperature at which the glass melt begins to pass electric current;
- increased total content of volatile forms of radionuclides in the exhaust gases.

 A known method of vitrification of radioactive waste in an uncooled metal induction melter (2), comprising supplying a high-frequency current to an inductor, heating the metal induction melter to operating temperature, subsequent supply of RAW into it together with glass former, their melting, filling of the working volume of the metal induction metal with the resulting radioactive molten glass melter, exposure of the radioactive glass melt to its homogenization, draining of the radioactive glass melt into a container and its o cooling to form a final product suitable for long-term storage.

The disadvantages of this method are:
- its increased specific energy costs associated with increased heat loss to the environment;
- increased total content of volatile forms of radionuclides in the exhaust gases.

 The closest in technical essence to the claimed method is a method of vitrification of radioactive waste in a cooled metal induction melter (3), which includes applying a high frequency current to the inductor of the cooled metal induction melter, loading a portion of the radioactive charge (a mixture of glass-forming materials with radioactive waste) into the cooled metal induction melter with the addition of electrically conductive material (graphite, metal chips, magnetite paste or metal short-circuited circuit a) its melting to form a radioactive starting glass melt (4), feeding a radioactive charge to a radioactive starting glass melt at a rate ensuring its full melting, filling the working volume (3/4 of the total volume) of the cooled metal induction melter with the resulting radioactive glass melt and draining the radioactive glass melt through the drain assembly.

The disadvantages of this method are:
- reduced specific productivity associated with increased process time due to the need to heat the central zone of the radioactive glass melt (homogenization of the radioactive glass melt), which has a lower temperature compared to the temperature in the wall zones of the cooled metal induction melter, which is working (component of the order of 1400-1500 ^o C ):
- increased total amount of volatile forms of radionuclides released into the gas phase;
- increased specific energy consumption due to the cooling of the metal induction melter and the increased duration of the process.

 The advantages of the proposed method are a simultaneous increase in its specific productivity, as well as a decrease in the total amount of volatile forms of radionuclides released into the gas phase and specific energy consumption for the process.

 These advantages are provided due to the fact that the inventive method of vitrification of radioactive waste in a cooled metal induction melter includes applying a high frequency current to the inductor of the cooled metal induction melter, loading a portion of the radioactive charge (a mixture of glass-forming materials with radioactive waste) into the cooled metal induction melter with the addition of an electrically conductive material ( graphite, metal shavings, magnetite paste or metal short-circuited circuit), its melted prior to the formation of a radioactive starting glass melt, supplying a radioactive charge to a radioactive starting glass melt at a speed that ensures its complete melting, immersion in a radioactive glass melt resulting from the supply of a radioactive charge, electrodes to a radioactive starting glass melt at a distance H from the walls of a metal induction melter equal to not less than 1/3 L, where L is the depth of penetration of the electromagnetic field of the inductor into the volume of the cooled metal induction melts pouring, feeding to the electrodes of alternating current of industrial frequency, filling the working volume (3/4 of the total volume) of the cooled metal induction melter with the resulting radioactive glass melt and draining the radioactive glass melt through the drainage unit.

Distinctive features of the proposed method are
- immersion in a radioactive glass melt formed during the supply of a radioactive charge and electrodes to a radioactive starting glass melt at a distance H from the walls of a metal induction melter equal to at least 1/3 L, where L is the penetration depth of the electromagnetic field of the inductor into the volume of the cooled metal induction melter and supply to electrodes of alternating current of industrial frequency.

 The method is implemented as follows.

 First, coolant is supplied to the housing of the cooled metal induction melter consisting of tubes, after which a high frequency current (1.76 MHz) is supplied to the inductor of the cooled metal induction melter. Then, a portion of the radioactive charge with the addition of electrically conductive material (for example, graphite) is loaded into the cooled metal induction melter, it is melted using the electromagnetic field of the inductor until the formation of the radioactive starting glass melt (occupying about 10% of the internal volume of the cooled metal induction melter). After that, a radioactive charge is fed to the radioactive starting glass melt at a rate that ensures its complete melting (25 kg / h of charge in case of a melt surface area in a cooled metal induction melter equal to 0.15 square meters), and to the radioactive glass melt formed in the process supply to the radioactive starting glass melt of the radioactive charge, immerse the electrodes at a distance H from the walls of the metal induction melter equal to 1/3 L (the most stringent conditions), where L is the penetrating depth I inductor electromagnetic field in the volume of the cooled metal induction melter, fed to the electrodes an alternating current of industrial frequency formed and filled with radioactive steklorasplavom working volume (3/4 of total volume) of a cooled metal induction melting unit, after which the radioactive steklorasplav drained through the drain assembly.

 When applied to the electrodes of alternating current of industrial frequency, they are short-circuited through a radioactive glass melt, which is electrically conductive, with the release of an additional amount of heat that provides accelerated heating of the central zone of the radioactive glass melt, which initially has a lower temperature compared to the temperature in the wall zones of a cooled metal induction melter. At the same time, due to a very significant reduction in the process implementation time, a simultaneous increase in the specific productivity of the method is provided, as well as a decrease in the total amount of volatile forms of radionuclides released in the gas phase and specific energy consumption, moreover, if the electrodes are lowered into the molten glass at a distance H less than 1 from the walls of the metal induction melter / 3 L It will be impossible to obtain all the above technical effects at the same time.

 Tests have shown that, in comparison with the closest analogue method, the specific productivity of the proposed method increases by 30-40%, the total amount of volatile forms of radionuclides released into the gas phase is reduced by 5-10%, and specific energy consumption is reduced by 30%.

LITERATURE
1. Davydov V.I., Burdinsky V.P., Dobrygin P.G., Luchnikov N.V., Kostin V.V., Filippov S.N., Kolupaeva T.I., Rakov N.A., "EQUIPMENT FOR A GLASS INSTALLATION FOR NPP WASTE IN CERAMIC FURNACE DIRECT HEATING", Atomic energy, v. 80, no. 3, 1996, p. 219-221.

 2. A.S. Nikiforov, V.V. Kulichenko, M.I. Zhikharev, "DISPOSAL OF LIQUID RADIOACTIVE WASTE". Moscow, Energoatomizdat, 1985, pp. 92-94.

 3. Sobolev I.A., Lifanov F.A., Stefanovsky S.V., Kobelev A.P., Kornev V.N., Knyazev O.A., Dmitriev S.A., O.N. Tsveshko, " Glazing of Radioactive Wastes by the Method of Induction Melting in the Cold Crucible "," Physics and Chemistry of Materials Processing ", Nauka, N 4-5, 1994, pp. 161 - 170.

 4. RF patent N 2065214 C1, IPC G 21 F 9/16, op. 08/10/96, Bull. N 22.

Claims (1)

 A method for vitrification of radioactive waste in a cooled metal induction melter, comprising supplying a high frequency current to an inductor of a cooled metal induction melter, loading a portion of a radioactive charge with an electrically conductive material into a cooled metal induction melter, melting it to form a radioactive starting glass melt, supplying a radioactive starting glass melt to a radioactive charge at a speed ensuring its complete melting, until filled forming the working volume of the cooled metal induction melter by the formed radioactive glass melt and draining the radioactive glass melt through a drainage unit, characterized in that the electrodes are immersed in the radioactive glass melt formed during the supply of the radioactive charge to the radioactive starting glass melt, which is not equal to the walls of the metal induction melter less than 1/3 L, where L is the depth of penetration of the electromagnetic field of the inductor into the volume of the cooled metal induction a melter and fed to an alternating current of industrial frequency electrodes.