RU2645737C1 - Method of immobilization of liquid high-salt radioactive waste - Google Patents

Abstract

FIELD: nuclear energy.

SUBSTANCE: invention refers to the field of nuclear power, in particular to the management of liquid radioactive waste (LRW) with the purpose of their subsequent long-term storage and/or disposal. Method of immobilizing LRW in the phosphate compound involves adjusting the pH level of the waste, introduction of the divalent nickel and potassium ferrocyanide ions into the resulting solution successively with continuous stirring and subsequent solidification of the obtained mixture by means of potassium dihydroorthophosphate and magnesium oxide coupling reagents addition. PH level of the waste is adjusted up to the values pH = 1.8–2.2 by means of adding the aqueous solution of sodium hydroxide at the concentration of 550–650 g/dm³. After the introduction of nickel ions and potassium ferrocyanide, boric acid powder is added.

EFFECT: invention allows to immobilize acidic high-salt ammonium and iron-containing LRW of the average activity level, which contain actinides and fission products of nuclear fuel.

10 cl, 2 dwg, 3 ex, 3 tbl

Description

The invention relates to the field of nuclear energy, in particular to the management of liquid radioactive waste (LRW) for the purpose of their subsequent long-term storage and / or disposal.

The development of the nuclear energy industry of the Russian Federation is impossible without solving the problem of handling LRW generated during the functioning of the nuclear fuel cycle, during decommissioning of nuclear and radiation hazardous facilities, as well as accumulated nuclear industry enterprises during defense programs. Various methods have been developed for their conditioning, depending on the type and radiotoxicity of LRW. At the same time, the search continues for effective matrix materials for LRW conditioning, which are optimal from the point of view of the physicochemical stability of the resulting compounds and the possibility of using them for the expanded LRW range. The quality indicators of the compounds for LRW immobilization (primarily water resistance, radiation and mechanical stability) must meet the applicable requirements of NP-019-15 [NP-019-15. Federal rules and regulations in the field of atomic energy use. Collection, processing, storage and conditioning of liquid radioactive waste. Safety requirements].

The most hazardous for humans and the environment are LRW of high and medium activity levels resulting from the reprocessing of spent nuclear fuel containing highly toxic long-lived actinides, as well as radionuclides - fission products of nuclear fuel (cesium, strontium, technetium, etc.). An example of this type of waste is highly acidic high-salt LRW of an average level of activity containing nitric and sulfuric acids, as well as large quantities of ammonium and iron ions. Currently, a concept is underway in Russia that provides for the conditioning of LRW of an average level of activity with the complete exclusion of their discharges into open hydraulic systems. High-temperature (glass, ceramics) and low-temperature materials (cement, low-temperature crystalline matrices) can be considered as matrices for immobilizing such waste.

The high-temperature technology for immobilizing LRW into glass-like compounds (vitrification) is currently the only technology brought to the industrial stage for handling LRW with a high level of activity [Dmitriev S.A., Stefanovsky S.V. Radioactive waste management. M .: Publishing. Center RCTU them. DI. Mendeleev. 2000, 125 p.]. In most countries of the world (France, USA, Great Britain, Germany, Japan, India, South Korea), sodium borosilicate glass is used to immobilize high level activity LRW.

In the known method, it is proposed to carry out vitrification of waste, including radioactive waste, at 1050-1250 ° C, but usually vitrification processes are performed at a temperature of about 1400 ° C [US 6258994, C03C 3/064, 2001.07.10].

The disadvantage of this method is that at high temperatures of about 1000-1200 ° C there is a risk of the radioactive isotopes of volatile elements at high temperatures contained in high salt LRW, for example, cesium and technetium.

Since 1986, FSUE Mayak PA has been using vitrification technology to immobilize LRW in a direct-heating electric bath furnace of the EP-500 type to produce glass on a sodium-aluminum phosphate basis [Phosphate glasses with radioactive waste. Ed. A.A. Vashman and A.S. Polyakova. M.: Central Research Institute of Atominform, 1997. - 172 p.].

A known method of vitrification of LRW involves fluxing them with phosphoric acid, neutralizing the resulting glass-forming solution with ethylene diamine, and supplying the glass-forming solution to the melter. In this case, the neutralization of the glass-forming solution is carried out until the pH reaches from 7 to 9 [RU 2293385, G21F 9/16, 02/10/2007].

The disadvantages of this method are that LRW containing large amounts of corrosive components, primarily sulfate ions and iron, cannot be involved in processing, since the production of melts with components of such LRW can lead to failure of the molybdenum electrodes of the electric furnace, as well as a violation of homogeneity and subsequent devitrification of glass-like compounds.

As an alternative to glass, various high-temperature mineral-like crystalline (ceramic) materials have been proposed for the immobilization of LRW radionuclides, including those based on synthetic analogues of natural phosphate minerals (for example, monazite, apatite) [Radioactive Waste Forms for the Future. Eds. Lutze W. and Ewing R.C. Amsterdam: Elsevier, 1988. - 688 p.].

For example, in the known method for curing LRW of a high level of activity, it is proposed to transfer the waste into a gel state, when zirconium, iron and glycerol are introduced into the waste solutions to their concentration in solutions of at least 0.12, 0.6 and 0.23 mol / l, respectively . The resulting mixture was kept for at least 2.5 hours, followed by the addition of a solution of monosubstituted potassium phosphate in phosphoric acid to a molar ratio of the components Zr: Fe: K: PO4 = 1: 3: 2: 5-8, dried, and calcined the obtained polymer zirconylphosphate gel, respectively, at 70-90 ° C and 300-400 ° C and the obtained granules are melted at 980-1000 ° C [RU 2293385, G21F 9/16, 02/10/2007].

A known method of immobilizing LRW into phosphate ceramics involves concentrating a radioactive solution, mixing it with a phosphate matrix and further heat treatment. Waste concentrated to the level of LRW with a high level of activity, after mixing with amorphous zirconium phosphate, is calcined to obtain a ceramic cake. Speck is encapsulated in glass-crystalline compounds. All stages of the process are carried out in a single reaction vessel at temperatures not exceeding 1000 ° C. EFFECT: invention enables to obtain stable mineral-like phosphate forms (cosnarite [Na, Cs, Sr, Ln) (Zr, An, Fe) 2 (PO ₄ ) ₃ ], monazite [(Ln, An) PO ₄ ]) [RU 2432631, G21F 9 / 16, 10.27.2011].

The ceramic materials proposed in these methods have high physicochemical stability that is superior to that of glass, however, these methods of immobilizing LRW into ceramics have common significant drawbacks consisting in the need to carefully observe the composition of the charge due to possible differences in the multiplicity of concentration of LRW for subsequent curing, as well as the implementation of the methods requires the development and implementation of new technologies that currently do not exist in the industry, primarily calcine LRW and gas treatment plants.

The main disadvantage of the known high-temperature methods for LRW immobilization (vitrification and incorporation into ceramic material) is that the methods require the creation or purchase of special expensive massive melters, the elimination of which after the end of their service life poses a great radioecological problem and is not currently carried out.

To immobilize LRW of medium and low activity levels, low-temperature cementing methods are considered [Kozlov PV, Gorbunova OA Cementation as a method of immobilization of radioactive waste. - Ozersk: RIC VRB FSUE “PO Mayak”, 2011. - 144 p.]. The main binder used in industrial low-activity LRW cementing technology is Portland cement, consisting of tri- and dicalcium silicates, calcium aluminoferrites and tricalcium aluminate [Bazhenov Yu.M. Concrete Technology: A Textbook. M .: DIA Publishing House, 2003. - 500 p.].

For example, in the known method, the conditioning of LRW is carried out by cementing using electromagnetic processing in a vortex layer with ferromagnetic bodies of revolution and subsequent curing of the product. LRW is subsequently subjected to electromagnetic processing in a vortex layer and mixing with Portland cement at a mortar-cement ratio of at least 0.6. According to this method, it is possible to cure LRW with a total salt content of up to 500 g / dm ³ [RU 2516235, G21F 9/16, 05.20.2014].

A disadvantage of cementing technology for the treatment of LRW with an average level of activity is the use of expensive Portland cement as a basis, which is a hydraulic binder with a long set of strength and insufficient physical and chemical stability to ensure the immobilization of long-lived actinides. Moreover, mixing Portland cement is possible LRW solutions with a mineral composition is usually not more than 500-600 g / DM ³ .

It should be specially noted that ammonium-containing LRW cannot be immobilized by cementing due to the fact that the process of cementing LRW occurs in the alkaline region of pH> 11, which leads to the formation and release of toxic ammonia. Moreover, according to paragraph 41 of NP-019-15, “it is forbidden to send LRW containing substances that interact with cement to form toxic substances” to cure LRW by incorporating the radioactive substances contained in them into a cement matrix material to produce a cement compound (cementing) ” .

The effectiveness of immobilizing LRW of complex composition can be achieved by using a low-temperature crystalline magnesium-potassium phosphate (MKF) matrix, a synthetic analogue of the natural phosphate mineral struvite [Vinokurov S.E., Kulyako Yu.M., Myasoedov B.F. Immobilization of radioactive waste in magnesium-potassium phosphate matrices. Russian chemical journal. 2010.T. LIV. Number 3. S. 81-88].

A known method of stabilizing uranium and plutonium-containing materials in an MKF matrix, comprising adjusting the pH of nuclear materials to a pH of at least 5 by adding calcined MgO and aluminum oxide, to the nuclear material thus treated add a binder containing at least 20 MgO and KH ₂ PO ₄ mass %, of which 15 mass. % is magnesium oxide, with the formation of a suspension, and additional introduction of MgO in an amount in excess of stoichiometric - up to 45 mass. % of the amount of nuclear material and a binder depending on the composition of the nuclear material. Sometimes, during the stabilization process, borate or boric acid is added to control the reaction rate and an additional filler — fly ash or tetravalent metal oxide — to give high stability to the waste forms. The mixture is cured within 1-24 hours. The final product is waste in the form of phosphate-bound radioactive materials encapsulated in a MgKPO ₄ ⋅ 6H ₂ O matrix [RF No. 2307411, G21F 9/04, 2007.09.27].

The disadvantage of this method is that the method is unsuitable for stabilization of high salt LRW with a mineralization of at least 600 g / dm ³ containing residues of uranium, plutonium, as well as transplutonium elements, cesium, strontium, technetium and other fission and corrosion products.

In addition, a pH level of at least 5 is not acceptable for the treatment of LRW containing ammonium ions, and can lead to the release of toxic ammonia.

Closest to the claimed method is a method of immobilizing liquid high salt radioactive waste (LRW) in a phosphate compound, including adjusting the pH of the waste, introducing into the resulting solution successively with continuous mixing of divalent nickel ions and potassium ferrocyanide and subsequent curing of the mixture by adding potassium dihydroorthophosphate binders and magnesium oxide [RU No. 2381580, G21F 9/16, 02/10/2010].

The stabilization method is intended for liquid alkaline high-salt HLW with a salinity of up to 750 g / dm ³ .

The method includes adjusting the pH of the waste to pH = 8-9 by adding phosphoric acid, introducing the AB-17 ion exchange resin with the CT form in series, divalent nickel ions and potassium ferrocyanide, the latter in amounts of 0.2-0.4 and 0.3, respectively -0.6 mass. %, and sodium sulfide, the resulting mixture is cured by adding binders - potassium dihydrogen phosphate and prepared by calcining magnesium oxide in a stoichiometric ratio based on the amount of water of the cured mixture with an excess of magnesium oxide 5-10 mass. %, with obtaining MKF compound based on MgKPO ₄ ⋅ 6H ₂ O.

The disadvantage of this method is that the method is not applicable for strongly acid LRW with a high content of ammonium ions. In addition, at pH = 8–9, high iron-containing LRW suspensions contain a precipitate of iron hydroxide with coprecipitated waste elements, which can interfere with high-quality mixing of the mixture and thus lead to insufficient homogenization of the compounds and the uneven composition of the main components and radionuclides.

The objective of the invention is to develop a method of immobilization of acidic high-salt ammonium and iron LRW of medium activity level containing actinides (primarily plutonium and transplutonium elements), as well as nuclear fuel fission products (including cesium and strontium isotopes).

The problem is solved by the method of immobilization of liquid high-salt radioactive waste (LRW) in a phosphate compound, including adjusting the pH level of the waste, introducing divalent nickel and potassium ferrocyanide ions into the resulting solution successively with continuous mixing of the mixture by adding potassium dihydroorthophosphate binder reagents and oxide in which the regulation of the pH of the waste is carried out to pH = 1.8-2.2 by adding an aqueous solution of sodium hydroxide At a concentration of 550-650 g / dm ³ , boron acid powder is added after the introduction of nickel ions and potassium ferrocyanide.

Mostly nickel ions in the amount of 0.3-0.4% by weight of the initial LRW solution are added as part of the nickel nitrate solution, potassium ferrocyanide is added in an amount of 2-3% by weight of the initial LRW solution, and after the introduction of nickel ions and potassium ferrocyanide, powder is added boric acid in an amount of 3-4% by weight of the initial LRW solution.

It is advisable to pre-grind the potassium dihydroorthophosphate powder to a particle size in the range of 0.15-0.25 mm, and pre-prepare magnesium oxide by calcining at 1300-1400 ° C for at least 3 hours.

It is advisable to mix the mixture at all stages with a mechanical stirrer at a speed of 110-130 rpm, and when the temperature of the resulting mixture reaches 48-52 ° C, stop mixing and leave the mixture to cure in the reaction vessel or containers.

It is advisable to obtain strength obtained phosphate compound can withstand at least 12 days, and when carrying out the immobilization of LRW in containers up to 200 l in order to homogenize the mixture to use the lost mixer with the possibility of vertical movement.

In FIG. 1 shows a diffraction pattern of MgO prepared by calcining at 1300 ° C for 3 hours.

In FIG. 2 is a diffraction pattern of a sample of the MKF compound after immobilization of a solution simulating LRW.

The proposed method uses a low-temperature MKF matrix formed according to the exothermic reaction (1) at room temperature in a LRW solution after it is neutralized with a sodium hydroxide solution to a pH = 2.0 ± 0.2

This level of acidity of the resulting LRW solution does not lead to the release of toxic ammonia, and also prevents the precipitation of an iron-containing precipitate due to the prevention of hydrolysis by the iron (III) cation.

The proposed method is as follows.

The initial acid solution of LRW is neutralized to pH = 1.8-2.2 by introducing a solution of sodium hydroxide under a layer of the waste solution with continuous stirring at a speed of up to 120 rpm. Effective neutralization of the acid solution of LRW is achieved using a solution of sodium hydroxide with a concentration of 550-650 g / DM ³ .

The increase in the efficiency of immobilization of cesium as the most mobile component of LRW in the MKF matrix is carried out when the element is converted to a sparingly soluble state in the form of its sparingly soluble mixed ferrocyanides. The capture of small amounts of cesium is due to the lower solubility of the mixed iron-synergy salts of this cation and heavy metal cations, in particular, the sparingly soluble mixed salt of the composition Cs ₂ Ni [Fe (CN) ₆ ].

Nickel ions in the oxidation state of 2+ and potassium ferrocyanide in the amount of 0.3-0.4 and 2-3% of the mass of the initial LRW solution, respectively, followed by stirring the mixture at a speed of 110-132 rpm are added to the resulting neutralized LRW solution; within 30 minutes. It is advisable to introduce nickel ions in the form of soluble salts (nickel nitrate or sulfate), and potassium ferrocyanide in the form of crystalline hydrate K ₄ [Fe (CN) ₆ ] ⋅ 3H ₂ O.

In the prepared LRW solution, the potassium dihydroorthophosphate powder KH ₂ PO ₄ is dissolved in an amount of 98-102 mass. % of the stoichiometric amount of KH ₂ PO ₄ relative to the amount of water in the LRW solution according to reaction (1), with stirring at a speed of about 120 rpm for 30 minutes. Effective dissolution of the binder is achieved by preliminary grinding the powdered reagent to a particle size of 0.15-0.25 mm.

After that, boric acid powder is added and dissolved in the solution to control the reaction rate (1) in an amount of 3-4% by weight of the initial LRW solution (which will be no more than 1.5% by weight of the compound) with stirring for 10 minutes.

Next, in the resulting LRW solution with continuous stirring at a speed of about 120 rpm, powdered magnesium oxide MgO is gradually added in an amount of 105-110 wt.% Of the stoichiometric amount of MgO relative to the amount of water in the LRW solution according to reaction (1) (or 33.4 ± 0.1% of the amount introduced KH ₂ PO ₄ ), and the resulting mixture is stirred for at least 20 minutes. Preliminary preparation of the MgO powder used is carried out by calcining it at 1300-1400 ° C for at least 3 hours.

The prepared mixture is left to cure in a reaction vessel or transferred to containers. The exposure time of the obtained samples for curing is not less than 12 days.

The most effective use of the claimed method can be during the curing of LRW in cylindrical containers with a volume of up to 200 l using a lost mixer with the possibility of vertical movement to homogenize a mixture of binding agents and a solution of LRW.

Example 1

A solution simulating LRW solution of an average level of activity with a volume of 1.0 dm ³ and a density of 1.37 g / cm ³ containing nitrogen (hereinafter in parentheses is the formula, purity and standard of the reagents used to prepare the solution) (HNO ₃ , hch, GOST 4461-77) and sulfuric (H ₂ SO ₄ , hh, GOST 4204-77) acids in the amount of 300 and 150 g / dm ³ , respectively, as well as ammonium nitrate (NH ₄ NO ₃ , hh, GOST 22867-77) , iron nitrate (Fe (NO ₃ ) ₃ ⋅ 9H ₂ O, hch, TU 6-09-02-553-96), cesium nitrate (CsNO ₃ , hch, TU 6-09-437-83) and strontium nitrate ( Sr (NO ₃ ) ₂ , bhd, GOST 2820-73) in amounts of 250, 65, 13 and 10 g / dm ³ , respectively, neutralized to pH = 2.0 when applied under a layer of an aqueous solution of sodium hydroxide (NaOH, chemically pure, GOST 4328-77) with a concentration of 600 g / dm ³ . Mixing the mixture at all stages is carried out with a mechanical stirrer at a speed of 120 rpm.

The preliminary preparation of MgO powder used as a hardener is carried out by calcining it at 1300 ° C for 3 hours in a high-temperature laboratory resistance electric furnace. As a result of calcination, the specific surface of magnesium oxide is reduced by 5 times to a level of 6.6 g / m ² . The obtained x-ray diffraction data (Fig. 1) unambiguously show that the result is crystalline MgO, the structure of which corresponds to periclase.

In the obtained neutralized solution with a density of 1.34 g / cm ³ and mineralization of 980 g / dm ^3, powdered reagents are added with continuous stirring in the quantities and order of administration according to table 1.

When the mixture reaches 50 ° C, it is placed in Teflon molds to set the mixture. Part of the mixture is placed in a sealed container to determine the possible ammonia content in the evolving gas phase during hardening of the compounds. The exposure time of the obtained samples of MKF compounds with an immobilized solution-simulator of LRW is 15 days. LRW solution not included in the compound was absent.

The gas mixture obtained by hardening the compounds is passed through an aqueous solution of 0.01 n sulfuric acid. It was found that the ammonia content in the solution according to GOST 33045-2014 is below the detection limit (less than 0.1 mg / dm ³ ).

Samples of MKF compounds containing salts of a neutralized solution-simulator of LRW in the amount of 20.8 masses were obtained. %, with a density of 1.8 ± 0.1 g / cm ³ and mechanical compressive strength of 15.7 ± 3.7 MPa.

The constancy of the mechanical compressive strength of the obtained MFC compounds was established before and after their irradiation of the compounds with accelerated electrons, the absorbed dose is 1.1 × 10 ⁶ Gy.

It was shown that the compressive strength of the obtained MFC compounds after 30 freezing and thawing cycles (-40 ... + 40 ° C), as well as after 90 days of immersion in water, is more than 5 MPa.

It has been established that the basis of the MFC compounds is the crystalline phosphate phase, the X-ray diffraction data of which correspond to the natural mineral struvite MgNH ₄ PO ₄ ⋅ 6H ₂ O (Fig. 2). The composition also contains the following crystalline phases: Niter KNO ₃ , nitratine NH ₄ NO ₃ , as well as partially unreacted (1) binder KH ₂ PO ₄ and hardener MgO, introduced in excess of up to 10% of reaction stoichiometry (1) .

Thus, the effectiveness of the proposed method for the immobilization of acidic high-salt ammonium and iron-containing LRW was established (by the example of a simulator). The quality indicators of the obtained MKF compound (mechanical strength, radiation resistance, resistance to thermal cycles, water resistance) comply with the requirements of NP-019-15 for the cement compound.

Example 2

According to the claimed method, the immobilization of a solution of a simulator LRW with a volume of 20 cm ³ containing radionuclides Cs-137 and Sr-90. The chemical composition of the solution, the ratio of reagents and immobilization conditions corresponded to those indicated in Example 1.

Data on the specific activity of radionuclides in the obtained MKF compound, as well as on the water resistance of samples of MKF compounds with respect to the leaching of radionuclides, determined according to GOST R 52126-2003, are shown in table 2.

Thus, it was found that the MKF compound has high water resistance to leaching of fission products of nuclear fuel: the integral leach rate on the 28th day of contact of samples of MKF compounds with water is 4.1–10 ^-4 and 4 for Cs-137 and Sr-90, 7⋅10 ^-5 g / (cm ² days), respectively, which is significantly lower than the permissible limit, the leaching rate of these radionuclides according to NP-019-15 for cement compounds is not more than 1⋅10 ^-3 g / (cm ² days) .

Example 3

According to the claimed method, the immobilization of a solution of a simulator of LRW with a volume of 20 cm ³ containing long-lived actinides Pu-239 and Am-241 was carried out. The chemical composition of the solution, the ratio of reagents and immobilization conditions corresponded to those indicated in Example 1.

Data on the specific activity of actinides in the obtained MKF compound, as well as on the water resistance of samples of MKF compounds with respect to leaching of actinides, determined according to GOST R 52126-2003, are shown in table 3.

Thus, it was found that the MFC compound has high water resistance to actinide leaching: the integral leaching rate on the 28th day of contact of the MFC compound samples with water is 8.1 810 ^-6 and 6.3⋅10 ^- for Pu-239 and Am-241 ⁶ g / (cm ² day), respectively, which approaches the requirements of NP-019-15 for glass-like compounds - no more than 1 10 ^-7 g / (cm ² day) for Pu-239.

The inventive method allows you to:

- to immobilize high-salt LRW with a high content of nitric and sulfuric acids (at least up to 300 and 150 g / dm ³ , respectively), ammonium ions (up to 60 g / dm ³ ) and iron (up to 15 g / dm ³ ), which are impractical include in glass-like, ceramic or cement compounds;

- to immobilize high-salt LRW solutions neutralized to pH = 2.0 ± 0.2 with a mineralization of at least 980 g / dm ³ when filling compounds with LRW salts to at least 20.8 mass. %;

- cure LRW in the form of a solution, which guarantees the homogeneity of the obtained compounds and the uniform distribution of the main components and radionuclides in the volume of the compound;

- to avoid precipitation of iron-containing sludge, which can clog the pipeline to transfer the resulting LRW solution to its curing unit and lead to the need for periodic washing of the pipeline from the sediment;

- receive MKF compounds at room temperature without the need to create expensive high-temperature melters, decommissioning of which after the end of their service life poses a radioecological problem;

- immobilize LRW containing both fission products of nuclear fuel, including Cs-137 and Sr-90 with a half-life of about 30 years, and long-lived actinides, including Pu-239 and Am-241;

- immobilize LRW containing volatile radionuclides, including isotopes of cesium, iodine, technetium;

- immobilize LRW into the ICF compound, the main quality indicators of which (water resistance, mechanical strength, radiation resistance, resistance to thermal cycles, water resistance, the volume of those not included in LRW compound) correspond to the quality indicators of the cement compound according to NP-019-15;

- immobilize LRW in the ICF compound based on a crystalline matrix - a synthetic analogue of the natural mineral struvite MgNH ₄ PO ₄ ⋅ 6H ₂ O, which has high physical and chemical stability in the geological environment;

- due to the proximity of methods to immobilize LRW using equipment used in cementing waste;

- use both small containers and large near-surface bulk storage facilities when immobilizing LRW.

Claims (10)

1. A method of immobilizing liquid high-salt radioactive waste (LRW) in a phosphate compound, comprising adjusting the pH of the waste, introducing into the resulting solution sequentially with continuous mixing of divalent nickel ions and potassium ferrocyanide and subsequent curing of the mixture by adding potassium dihydroorthophosphate and magnesium oxide binders, characterized in that the regulation of the pH level of the waste is carried out to pH = 1.8-2.2 by adding an aqueous solution of sodium hydroxide with a concentration 550-650 g / dm ³ , after the introduction of nickel ions and potassium ferrocyanide, boric acid powder is added. 2. The method according to p. 1, characterized in that the nickel ions in the amount of 0.3-0.4% by weight of the initial solution of LRW contribute in the composition of the solution of Nickel nitrate. 3. The method according to p. 1, characterized in that the potassium ferrocyanide is added in an amount of 2-3% by weight of the initial LRW solution. 4. The method according to p. 1, characterized in that after the introduction of nickel ions and potassium ferrocyanide, boric acid powder is added in an amount of 3-4% by weight of the initial LRW solution. 5. The method according to p. 1, characterized in that the potassium dihydroorthophosphate powder is pre-crushed to a particle size in the range of 0.15-0.25 mm. 6. The method according to p. 1, characterized in that the preliminary preparation of magnesium oxide is carried out by calcination at 1300-1400 ° C for at least 3 hours. 7. The method according to p. 1, characterized in that the mixing of the mixture at all stages is carried out with a mechanical stirrer at a speed of 110-130 rpm 8. The method according to p. 1, characterized in that when the temperature of the resulting mixture reaches 48-52 ° C, stirring is stopped and the mixture is left to cure in the reaction vessel or containers. 9. The method according to p. 8, characterized in that the exposure time of the obtained phosphate compound for curing is at least 12 days. 10. The method according to p. 8, characterized in that during the immobilization of LRW in containers up to 200 l in order to homogenize the mixture using a lost mixer with the possibility of vertical movement.

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