SU1036257A3 - Method for solidifying radioactive wastes by fixing them in a mass of substance resistant to leaching - Google Patents

Description

The invention relates to the processing of radioactive wastes with a high level of radioactivity, in particular to their conversion into a cured state by fixing a substance resistant to water leaching in the mags, allowing reliable fixation of radioactive particles in solid matter and preventing contamination by them. environment. A known method of encapsulating solid radioactive waste for storage involves mixing radioactive waste with a polymer material, encapsulating the mixture in a glassy capsule, heating the capsule in a vacuum or inert medium to 600–1000 ° C at a rate of 6 ° per hour . a period of time sufficient to carbonize the cured polymeric material to a glassy state. In this case, the radioactive waste is encapsulated in a capsule suitable for storing Cl. However, the pressure and temperature at which the method is carried out do not ensure reliable fixation of the radioactive particles in the solid. The closest to the invention to the technical essence and the achieved result is the method of turning off radioactive waste by fixing it in the mass of a substance resistant to water leaching, including mixing radioactive waste with substances resistant to leaching, loading the mixture into a capsule made of solid material with a high melting point, heg letization of the capsule and processing by isostatic pressing at high pressure, while isostatic pressing is carried out at a temperature of 70Q ° C and pressure SRI 2 to 10 MPa. A disadvantage of the known method is that the temperature and pressure at which it is carried out do not ensure reliable fixation of the radioactive particles in the solid. The purpose of the invention is to secure the fixation of radioactive particles in a solid. The goal is achieved by the method of opening radioactive waste by fixing it in a mass of substance that is resistant to leaching with water, including mixing radioactive waste with substances resistant to leaching loading the mixture into a capsule made of solid material with a high melting point. / sealing the capsule and processing by isostatic pressing at high pressure, the capsule is filled with a mixture containing 2.5-40% of radioactive waste and 60-97 5% curing of the chemicals selected from groups 502,6,0, FAOgO, Ti 02, 2Г202,. A isostatic pressing is carried out at a temperature of 700-1350 ° C and a pressure of 50-300 MPa. The invention provides for the introduction of high: radioactive waste into a matrix, which provides for extremely effective controlled treatment of radioactive waste in the process of incorporating it into the mass of a matrix substance, as well as efficient retention of these wastes in a chemically resistant mass. After much radioactive waste is removed from the solution, it is possible, for example, to be carried out. By conventional evaporation and subsequent calcination, they are kept in a sealed capsule during the intrusion process, with the result that neither gaseous nor liquid products can go beyond the walls of the capsule. This process is carried out by isostatic pressing the capsule at a high temperature after pre-sealing the hole in it. The isostatic pressure prevents the formation of volatile substances inside the capsule, which can be released from the material in the capsule when heated. In addition, the isostatic pressure is needed to transform the material inside the kössula into a coherent dense mass, as well as to compress this material. The process of filling the material capsule capsules can be performed at room temperature as well, la. The proposed method provides a great deal of freedom in choosing resistant materials into which they are then introduced with highly radioactive substances. According to the invention, part 1 of a radioactive substance is mixed with particles of a material resistant to water elimination, resulting in a mass mixture. The resulting mass is placed in an e-capsule and subjected to isostatic pressing at pressures and temperatures sufficient to form a solid solid mass. A material resistant to leaching with water may consist of oxides, which are usually included in the composition of various types of glass and rocks, such as SiOj, BjO, / iBj - alkaline oxides, alkaline rocks, 2g202, FftjO,, FpjO m CrjOa In addition, this material can consist of natural stable minerals, for example, silicates, aluminates, chromates and titanates. It is preferable to use minerals that can hold a few times, as well as zolites, which can selectively extract strontium and cesium from a solution. Borosilicate and phosphate glass can also be used. Of the natural minerals, alumina, titanium oxide and other compounds are most suitable for use as a matrix.

The particle sizes of the radioactive material and the leach resistant matrix material should be such that they can be sifted through a 125 mesh / cm screen (or 325 cells / inch. The weight of the radioactive material should be 2.5-40% by weight of the mixture, and matrix material - 60-97,5% by weight of the mixture.

According to the proposed method mass. A water containing mat, resistant to leaching, containing particles of radioactive substances (or material containing radioactive substances, acquiring resistance to water leaching after heating) can be placed in a capsule, which is then subjected to isostatic pressing at a pressure and temperature corresponding to conditions for the formation of a bound dense mades. .

 Water resistant to leaching, in which radioactive substances are found, consists of non-soluble salts or other insoluble compounds of radioactive substances, such as titanates, aluminates, phosphates, silicates and oxides. Salts or other compounds can be recovered from solutions containing radioactive substances by adding appropriate soluble salts, resulting in these compounds precipitating. Particles of material that is resistant and extruded should have sizes less than 1.

Material containing lactic agents, which becomes stable to leaching with water after heat treatment, may consist of ion exchangers that absorb radioactive substances from the solution during its exchange. The process of ion exchange occurs when the ion exchangers come into contact with a solution containing radioactive substances. Particles of this material should be sized on the order of 0.1-1 mm. Zeolites and compounds of the MfMJfO type can be used as ion exchangers to extract radioactive substances from a solution. where M is. cationite with charge n, and as M you can take TI, Ne, Zr or Ta, for example NoiTijO H .. Ionites, which take up radioactive substances from solution 1, when heated, form

multi-phase polycrystalline or ceramic structure resistant to water release. For example, when in contact with a solution containing radioactive strontium, the compound NaT ZODN forms, which decomposes into Ci-TiO, and TiO2 when heated.

In accordance with this method of carrying out the invention, the matrix may include one or several types of materials resistant to water leaching, containing Pschioactive agents, or materials that acquire resistance after preliminary heat treatment. As such materials, it is possible to use oxides that are part of various rocks, namely, B20, AK20j, alkaline oxides, alkaline rocks TiO iZrOj, Fe2Oz I, and other natural stable pamnj rocks, for example, rocks consisting of silicates, aluminates, phosphates and titanates. It is advisable to use aluminum oxide, titanium, quartz and other minerals. Resistant materials can be added to substances that are matrices for radioactive substances and are in contact with these radioactive substances, and therefore can be mixed with ion exchangers before they come into contact with radioactive substances, which contributes to increased safety during operation. with radioactive substances. The amount of resistant material introduced into the mass of the matrix can be 60-97.5% of the total weight of the mass of the substance of the matrix and the material embedded in it. Particles of resistant material introduced into the matrix should have dimensions not exceeding mm.

The capsule can be made from sheets of tantalum, titanium, zirconium, from alloys of these metals, for example, zircallo, from steel, cast iron, nickel and also from quartz or borosilicate glasses. The material for the capsule, depending on the type of resistant material, must be sufficiently high. What is the melting point at which the capsule can perform ovo functions? In addition, the volume expansion coefficient of the material of the capsule must be close to or equal to the coefficient of volume expansion of a resistant material, which is necessary in the case when the capsule is intended to act as a containment | Leucorium as a resistant material is used quartz or titanium oxide, keshsulu should be made of quartz glass. If borosilicate glass is used as a resistant material, the capsules should be made of the same material. In some cases, it is convenient to use metal capsules, the inner surface of which is covered with a layer of quartz or borosilicate glass. An intermediate layer of resistant material should be introduced between the walls of the capsule and the mass of the substance in it, which can be used as an intermediate material. It is preferable to use a material whose chemical composition is identical to the chemical composition of the mass inside the capsule, but it should not have a radio ivnye isotopes. The particle size of the material of the intermediate layer should not exceed 1 mm, preferably 0.2 mm. The intermediate layer adjacent to the inner wall of the capsule may be on the order of a few millimeters or centimeters. The pressure developed in the process of isostatic pressing should be 50-300 MPa. The sintering temperature of the mass. Inside the capsule, determined by the type of materials that make up the mixture, the minimum limit corresponds to 1200 ° C. The temperature most suitable for sintering the mass containing titanates, quartz or titanium oxylate is 1200-1300s, while long Sintering a mass containing aluminates and alumina requires temperatures on the order of 1250-1350 ° C. Max. Sintering temperature 1350. Figure 1 shows a solid containing a mixture of highly radioactive waste and a material resistant to water leaching; 2 shows a high pressure furnace. The capsule (FIG.) Comprises a housing 1 with an opening and a recess 3 and is filled with a mixture 4. The high pressure furnace (Fig. 2) contains a movable press stand 5, which is mounted on wheels b, rolling along rails 7 fixed to the floor. The press stand consists of the upper part 8 of the frame, the lower part of the 9 frame and a pair of spacer elements 10 held together by means of a pre-stressed tape sheath 11. The press stand can be moved from the position shown in figure 2 to the position where the chambers are high pressure goes inside the walls yes. The high pressure chamber 12 is fixed on the column 13. It consists of a high pressure cylinder including an inner tube 14 surrounded by a prestressed tape shell 15 and end rings 16, holding the turns of the belt together, forming the shell with which the chamber the high pressure is attached to the column 13 .. In the chamber there is a bottom end cap 17, which is inside the pipe 14 of the high pressure cylinder. In the end cap there is a gap in which a ring 18 is inserted into the seal, as well as a channel 19 through which a gaseous medium is introduced into the chamber, creating a necessary pressure inside the chamber, such as argon or neon. In addition, in the plug there is a channel 20 in which there are cables supplying heating elements 21, heating the internal volume of the furnace. The heating elements 21 are wound on a cylinder 22 mounted on an insulating base 23 inserted into an insulating cylinder 24. The upper end cap includes an annular part 25 with a sealing ring 26 providing a seal on the inner surface of the pipe 14, the cylinder 24 is tightly attached to the bottom surface of the part 25 , and the place of contact of these parts is impermeable to gas. A Tube plug includes 27 covering the hole in the part 25, which is usually firmly connected to the high pressure cylinder. The cap has a sealing ring 28 that seals on the inner surface of the part 25, as well as an insulating plate 29, which in the fully assembled high-pressure chamber enters inside the cylinder 24 and forms part of the insulating sheath surrounding the internal volume 30 of the furnace. The lid 27 is attached to the crown of theine 31, which, thanks to the rod 32, can turn around the axis of the rod and also move up and down. The upper 8 and lower 9 parts of the PM take on themselves the compressive forces acting on the end plug 17 and the cover 27 in the case when high pressure is created in the internal space of the furnace. Example 1. 25 weight.h. strongly radioactive nuclear fuel processing wastes, converted to oxides in an appropriate way and having a particle size of less than 0.18 mm, are mixed with 75 weight parts. quartz powder with part size; less than 0.15 mm The quartz powder is pretreated under vacuum to remove dissolved gases from it. The prepared mixture 4 is placed in a capsule made of Vicor glass (Vytoi-), which is 96% quartz and corresponds to quartz glass, when the capsule is filled with a mixture of its wall, it should not bend. Filled) the capsule is degassed at room temperature and the pressure is about

0.1 pa using a vacuum pump connected to port 2. After degassing, the capsule is sealed at the same pressure by fusing web 3,

After the capsule has been installed in the internal volume 30, the cover 27 is raised first and the cover 27 is lowered, closing the opening in the furnace. The pressure - and the temperature in the furnace gradually increase to values of the order of 200 MPa and, respectively. Such pressures and temperatures are maintained for about two hours until the weight in the capsule reaches a predetermined degree of density and sintering. At the end of this process, the capsule with the contents is cooled, after which the pressure is reduced to atmospheric and the capsule is removed from the oven. The mass thus treated is not removed from the capsule, and the capsule plays the role of a protective sheath. Capsules should, if possible, be placed in steel containers, after which they can be transported to an R storage site.

Example 2. A solution of radioactive waste, obtained from a plant for the processing of highly radioactive waste generated in a nuclear reactor, consists of a solution of nitric acid with a concentration of 2 mol, containing as radioactive substances, g / L Zr 7.0; MO, Uoc, 2.5 Nd 8.0 / Ru 4, 5 OS 5, 4; Ce 4, 0, Pe. 3, 8; Pd3, 1, - VAZ, 3; C5 1.5; Pr 2, 3 Am 2, 3; “12.12, 6 j 23.8Cd, and a host of other radioactive substances in smaller quantities. The pH of the solution is adjusted to 1 by the addition of ammonia. This solution is passed through a cylindrical column made of titanium, containing ion exchangers in the form of particles NctTi with a size of 0.1-1.0 mm. Ionite is mixed with the same weighed amount of tiOj in the form of particles in a size of 0.1-0.5 mm. After that, the solution is passed through a vortex cylindrical titanium column containing IONIT in the form of a zeolite with the formula NOg L Eg SLVO Ojg. This IONITE is also cocTojf v from particles of 0.1–1 mm in size.

Water is removed from both columns by heating them to 900 ° C. under vacuum. The ion exchangers under such treatment partially decompose. This leads to the formation in the first column of titanite containing radioactive substances and titanium dioxide.

Each column, together with its contents, is placed in a cylindrical capsule of mild steel, provided with a bottom. The space between the rtena capsules and columns, including the space below the bottom of the column and above

In addition, this volume also contains titanium dioxide and fills the entire volume inside the column. Each capsule is then closed with a tight-fitting lid with an opening for pumping out. After each capsule is pumped out, the pressure is approx. 0.1 Pa and its sealing last, together with the contents, will be placed in a high pressure furnace (Fig. 2). The oven with a cassette is closed with a lid. The pressure and temperature inside the furnace rise to about 100 MPa and 1300 ° C, respectively. pod It lasts for about two hours until the contents of the capsule turn into a sintered mass with a given density. At the end of the heat treatment, the capsule with the contents cools / after which the pressure decreases to atmospheric pressure and the capsule: la is removed from the oven. The finished product is removed from the capsule, and the capsule itself plays the role of additional litters of the contents.

Example 3. A solution of nitric acid with a concentration of 0.9 mol contains, in the form of radioactive substances, g / l: lNHj (, Mo202.4-4I20 1.17) NdtNO Jy b HZP 3.75; C # - mOz 0.59; ce (NOj b6H201.23;

FelNOjf - ENGO 2.80; Н02Т Oz) e6, 5 and F (Oz) 0, b3. The pH of the solution is adjusted to 1.3 by adding NctOHL and the solution is passed through a cylindrical column containing ionite in the form of NotTljOjH particles, 0.1-1 mm in size. The ion exchanger is mixed with the same amount of mixture T1025402I in the form of particles with a size of 0.05-0.5 mm. The ion-exchange capacity of an ion exchanger corresponds to about 2.5% of the absorbed waste, calculated as the amount of oxides attributable to a certain amount of dried ion exchanger. The ion exchanger is then heated in an air atmosphere before and ground into a fine powder. The mixture of powders is poured into a cast-iron capsule, fitted with a tight-fitting KRYETZ with a pumping hole. After a 24-hour pumping out at a pressure of about 0.1 Pa and heating the mixture at a rio temperature of about 750 ° C, the capule connected to the pump is sealed off. The sealed capsule is dipped into a high pressure furnace (Fig. 2). The furnace is closed with a lid. The furnace pressure and temperature rise to 150 MPa and 1300 ° C, respectively. These conditions are maintained for two hours. At the end of the heat treatment, the capsule with the contents is cooled, after which the pressure is reduced to atmospheric and the capsule is removed from the oven. The contents of the capsule are a dense mass without pores and voids, containing various crystalline phases, such as Tt02, Nc4TiOj HA9., Which are fixed as radioactive substances in the matrix, being in a water-insoluble state. Example 4. A waste solution from the processing of highly radioactive products formed; in a nuclear reactor, consists of a solution of anothic acid with a concentration of 2 mol, containing in fory radioactive substances, g / H: Nd 60,, 9; CS 10.6; Mo11.5; 5g 10.5; Zr 10.1; Fe 5.1, - and # 0. In this solution, 7.2 g / l Ca and 2.2 g / l M in the form of nitrates are added, as well as 65 g finely ground Si0 in the form of grains. 100 A. This solution is evaporated and the precipitate is calcined in an air atmosphere for one hour at 500 s. After this, 60 parts by weight of the cinder are mixed with 40 parts by weight. in a ball mill. The mixture thus prepared is kept in an air atmosphere for two hours, as a result of which the remaining nitrates and water are removed. The mixture is poured into a cast-iron capsule, fitted with a tight-fitting lid with an opening for pumping. The capsule is pumped off for 24 hours at a pressure of about 0.1 Pa at the pump and at temperatures up to 750 ° C, after which the capsule is sealed under vacuum. After that, the capsule is placed in a high-pressure furnace (Fig.2, the internal volume of which is covered with a lid. The pressure and temperature in the furnace rises to 150 Pa, respectively. These conditions are maintained for seven hours. At the end of the heat treatment, the capral is cooled, the pressure decreases to atmospheric and Kancyj is taken out of the oven. The contents of the capsule are a dense mass without pores and voids with a density of about 4.82 g / cm, containing corundum-type crystalline phases (luorite (yy, Co |, gi) (; polyluxite (csAeSijOft ), eelite (tr, Cq) Mo04 and apatite (Co () „(, Р04.) 02 in which the cystans of radioactive substances are embedded. The structural analysis performed using a scanning electron microscope (SEM analysis) showed that the elements of the bend are very evenly distributed throughout the mass the mixture obtained by pressing the powder, Example 5. The solution with radioactive waste, described in example 4, is treated with formic acid at 90 ° C, resulting in decomposition of nitrates in accordance with the formula 2XO3 + 4HCDOH-N20 + 4C02 + 201H, and hydroxide metals precipitate. After drying, the precipitated substance is mixed with At20, the mixture is placed in a capsule and subjected to isostatic pressing in accordance with the method described in the previous example. The proposed method can be used not only for the treatment of highly radioactive nuclear fuel processing waste. It can also be used to treat highly radioactive waste, the formation of dichs from the production of plutonium, as well as to treat other radioactive materials in order to introduce them into the matrix of a substance that is resistant to leaching with water.

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Claims (1)

METHOD FOR CURING RADIOACTIVE WASTE BY FIXING THEM IN A MASS OF SUBSTANCE RESISTANT TO WATER LEACHING, including mixing radioactive waste with substances resistant to leaching, loading the mixture into a capsule is done. a solid material with a high melting point, sealing the capsule and processing by isostatic pressing at high pressure, characterized in that, in order to increase the reliability of the fixation of radioactive particles in a solid, the capsule is filled with a mixture containing 2.5-40% of radioactive waste and 60 -97.5% of curing agents. Selected from the group Pe ₃ _0 ₄ and Cr ₂ 0 _{3 (} and isostatic pressing is carried out; at a temperature of 700-1350 ° C and a pressure of 50-300 MPa. Fig a