RU205723U1 - Device for vitrification of radioactive waste - Google Patents

Abstract

The invention relates to the field of localization of liquid radioactive waste, in particular, to installations for solidification of liquid radioactive solutions and pulps by vitrification. The design of the refractory masonry, in addition to the main row of blocks made of material that is corrosion-resistant to the glass melt, has an additional guarding layer of refractory backfill, which is sealed in the gap between the blocks and the inner metal shell. The utility model makes it possible to improve the manufacturability of the manufacture of refractory masonry. 3 C.p. f-ly, 1 dwg.

Description

The utility model relates to the localization of liquid radioactive waste (RW), and can be used in nuclear power and radiochemical industries for solidification of liquid radioactive solutions (LRW), pulps and solid bulk RW.

For the solidification of liquid radioactive waste in world practice, various matrix materials are used - bitumen, cement, glass, ceramics [Dmitriev SA, Barinov AS, Batyukhnova OG. et al. Technological foundations of the radioactive waste management system - M .: GUP Moe NPO Radon, 2007. 376 p.]. Glass-like materials are recognized as the most effective both in terms of quality indicators and manufacturability in the Russian Federation and abroad [IA Sobolev, MI Ozhovan, TD Shcherbatova, OG Batyukhnova. Glass for radioactive waste - M .: Energoatomizdat, 1999. 240 p.].

To carry out vitrification of radioactive waste on an industrial scale, in the world practice, installations of three main types are used: direct electric heating furnaces and induction melters with medium and high frequency generators (the so-called "hot" and "cold" crucibles).

The most advanced in technical terms are direct electric heating furnaces. Such installations are also characterized by high productivity and stability of performance indicators with fluctuations in the composition of waste sent for vitrification.

In the USSR, and then in Russia for the industrial implementation of the process of solidification of liquid HLW into aluminophosphate glass since 1987, direct electric heating furnaces of the EP-500 type have been used [Glagolenko Yu.V. Nuclear fuel reprocessing and high-level waste management / Nature protection of the South Urals: regional environmental almanac. - Chelyabinsk, 2008. - S. 36-41.], Which can be considered as an analogue of the claimed utility model [RF Patent No. 1309504, IPC С03В 5/027]. Such installations represent a rectangular pool lined with bacor blocks. The pool is divided into three zones: cooking, overflow and storage. In the lower part of the partition there is an overflow channel through which the welded glass from the working area enters the overflow and further into the accumulating one. The overflow zone is separated from the storage threshold, which serves to maintain a constant level of glass melt in the cooking zone. Drainage devices are installed in the end part of the storage area. In the end part of the cooking zone there is a water-cooled gas duct designed to remove the resulting vapor-gas phase and connecting the oven with a bubbler-refrigerator. The dosage into the cooking zone of the initial solution containing LRW and fluxing components is carried out through water-cooled feeders installed in the roof of the electric furnace. To supply electricity in the hearth of the electric furnace, there are massive water-cooled current leads made of corrosion-resistant steel (alloy), on which molybdenum electrodes made in the form of cylindrical rods are installed in rows. When an electric current passes through the glass melt, heat energy is released between the rows of electrodes, which is necessary for the glass melting process. In the last modification of the EP-500 type furnace, a two-zone layout is used (there is no cross-flow zone and a threshold) [Remizov MB, Kozlov PV, Logunov MV. etc. Conceptual and technical solutions for the creation of vitrification installations for current and accumulated liquid HLW at PA Mayak / Issues of radiation safety. -2014. -No. 3. - S. 17-25.].

A similar type of installation was used to solidify LRW into borosilicate glass in the United States at Savana River as part of the Defense Waste Processing Facility (DWPF) [Plodinec M.J., Kitchen B.C. Establishing the Acceptability of Savannah River Site Waste Glass, Proceeding Spectrum-90, Nuclear and Hazardous Waste Management, Internal. Topic Meeting, sept-oct. 1990, pp. 302] and in Germany (Pamela plant) [Weisenburger S., Roth G. Status and plants for high-level liquid waste vitrification in Federal Republic in Germany / ANS Int. topic meeting on fuel reprocessing and waste management, Avg. 26-29, 1984, Jacks Hole, WY, USA]. These installations have a difference associated with the placement of the drain device in the bottom of the cooking zone. Thus, the design of the furnace is single-zone, with the movement of the molten glass not in the horizontal, but in the vertical direction.

These melters have a number of common disadvantages. Firstly, these are large dimensions, which do not allow the removal of the furnace from the canyon for subsequent installation of a new melter in the vacant place. Such furnaces are being decommissioned along with a large amount of associated infrastructure, which significantly increases the operating costs of maintaining the decommissioned facility and the capital costs of creating a new furnace.

Secondly, these analogs are characterized by the use of a flat hearth. In this case, both during the implementation of the side drainage of glass (with horizontal movement of the melt) and when using the bottom drain (with the vertical movement of the melt), the accumulation of refractory sediments in the bottom part, including the electrically conductive phase (noble metals, nickel sulfide, etc.) is observed. etc.), which leads to a short circuit between the electrodes, overcooling of the bulk of the melt and premature decommissioning of the melter.

To eliminate such problems at the Karlsruhe Institute for Nuclear Technology (KIT), a special design of a small-sized melter (VEK) with an original drain device has been developed that allows the precipitation of precious metal compounds to pass through without delaying them in the bottom of the melter, which can be considered as a prototype of the claimed inventions [Roth G., Weisenburger S. Vitrification of high-level liquid waste: glass chemistry, process chemistry and process technology. Nuclear Engineering and Design, 202, 2000, 197-207]. This melter is a vertical apparatus, the glass-melting basin of which is made of chromium oxide-containing ceramics. Electricity is supplied through one pair of main electrodes made of chromium-nickel alloy. A solution of radioactive waste and dry glass frite is dosed into the upper part of the melter, the melt of borosilicate glass is drained through a bottom drain device with induction heating of a die made of a heat-resistant chromium-nickel alloy. Its special design allows precipitation of precious metals to be discharged together with the glass, avoiding their accumulation in the bottom of the melter.

The disadvantage of this invention is the complex multi-element design of the refractory masonry (about 150 elements forming a multilayer structure, of 12 different brands of refractory and heat-insulating materials), which increases the labor intensity and cost of manufacturing an electric furnace, as well as the low productivity of the furnace in the flow of processed LRW and glass (10, 0 l / h and 7.0 kg / h, respectively).

The technical objective of the invention is to improve the manufacturability of the manufacture of refractory masonry, increase the productivity of the electric furnace up to 20 l / h for liquid radioactive waste and 15 kg / h for glass, lengthen the operating life of the furnace by installing an additional guarding layer of refractory backfill, which protects against melt leakage.

This problem is solved by the fact that the refractory masonry is assembled from a smaller number of elements made of two or three basic types of refractories (not counting electrical insulating inserts and other small elements).

1. Refractory blocks in direct contact with the melt are made of melt-resistant material (bacor, fused-cast chromium oxide-containing refractory, sintered chromium oxide-containing refractory, etc.). Structurally similar to the prototype, several rows in the vertical direction (from 6 to 8), each row is divided into sectors (from 4 to 12).

2. A layer of refractory backfill.

3. Metal shell.

Further, the proposed design, like the prototype, has a layer of thermal insulation. Next is the outer metal case.

If it is necessary to increase the resistance of the masonry to the corrosive action of the glass melt and, accordingly, the service life of the melter, a layer of refractory blocks is additionally placed between 1 and 2 layers of refractory with overlapping seams between the blocks of layer 1.

The increase in productivity is achieved by increasing the volume of the furnace bath (height and diameter). At the same time, to ensure the required current density throughout the bath volume, one or two additional pairs of main electrodes are installed along the vertical axis.

Thus, as a result of the implementation of the proposed invention, an improvement in the declared characteristics relative to the prototype is provided: productivity increases 1.5-2.0 times, the number of refractory masonry elements decreases 1.6 times, an additional guarding layer of refractory backfill protects against melt leakage and lengthens the period oven service. A schematic of the melter is shown in Fig.

The small-sized removable melter is a glass-making furnace of direct electric heating in a vertical cylindrical design with refractory masonry (14) placed in a metal shell (13) with filling the space between the shell and the masonry with chamotte-quartz powder (12). Refractory masonry consists of eight sequentially established levels, each of which is assembled from 12 sectors - fireclay blocks of various shapes (14). Five levels include electrodes (15), which are installed during assembly of the corresponding level. A silica cloth is placed between the crucible blocks and the electrodes.

The shell is closed with a fibrous refractory thermal insulator (glass fiber) (8, 10) and an outer metal casing (9). The glass melting process takes place in a refractory pool made of fused-cast or ceramic blocks.

The electrodes (15) are metal products of complex shape made of a heat-resistant alloy. The electrodes (15) are placed in pairs along the height of the melting bath. Paired electrodes (15) have the same design and are located on the same axis relative to each other. All electrodes (15) are air cooled through the internal cavities.

The crucible cover is formed of three fireclay plates (11) assembled on a single suspension (suspension plate) (11). Top - metal cover (6). There are six main penetrations in the ceiling and the cover - three for filling glass frit (4), a penetration for dosing the solution (1), installation of thermocouples (3) and placement of a gas duct (7) and technological penetrations (5). During the start-up period, there are six additional penetrations in the crucible roof to accommodate starting heaters (SiC) (2).

The bottom drain unit is designed for batch or complete drainage of the molten glass.

The bottom drain unit consists of the following main parts:

- bottom electrode with a die (18);

- inductor (20);

- induction heating system.

Between the fourth pair of electrodes (15) and the fifth pair of electrodes (15) there is a fireclay spacer (16). Also, a refractory block spacer (19) is located between the fifth pair of electrodes and the inductor (19).

The base of the melter (17) is located on a metal support frame. A layer of heat-insulating cardboard (hereinafter - cardboard) (21) and a metal bottom of the furnace are laid on top of the base.

The body is mounted in the base of the electric furnace. In the central part of the body there is a drain die, around which there is a water-cooled copper inductor, securely fixed in the body, connected to the induction heating system and the water cooling system. There is a hole in the end of the body, which allows visual observation of the pouring of the molten glass. A drain die is located in the lower part of the body.

Install a mixer feeder in the ceiling of the electric furnace for mixing and supplying the initial solution with ethylene glycol.

Heating of the melt and glass melting occurs by supplying an alternating electric current of industrial frequency to the melt through three pairs of electrodes. Further, after warming up the bottom of the melter, the fourth pair of electrodes is connected. The inductor is switched on for draining. The molten glass is drained through a die. The drain is closed by "freezing" the glass in the die channel, opening by melting the glass plug when the inductor is turned on using the induction heating system.

Claims (4)

1. A device for vitrification of radioactive waste, which is a direct electric heating furnace with a bottom drain device, including an induction heating system for the drain die, metal air-cooled electrodes, refractory masonry, characterized in that the structure of the refractory masonry, in addition to the main row of blocks made of corrosion-resistant to the melt glass material, has an additional guarding layer of refractory backfill, sealed in the gap between the blocks and the inner metal shell, and a removable fibrous heat-insulating layer, closed by a detachable outer metal casing. 2. The device according to claim 1, characterized in that it has two pairs of main electrodes, which ensures greater reliability of the melter operation and leads to a more uniform heating of the melt bath and an increase in the productivity of the processed LRW and the produced glass melt. 3. The device according to claim 1, characterized in that it has three pairs of main electrodes, which ensures greater reliability of the melter operation and leads to a more uniform heating of the melt bath and an increase in the productivity of the processed LRW and the produced glass melt. 4. The device according to claim. 1, characterized in that the refractory masonry of the melter is supplemented with a layer of refractory blocks with overlapping seams between the blocks of the main row to increase the resistance of the masonry to the corrosive action of glass melt.

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