PL229092B1 - Method for obtaining of spherical grains of uranium-neodymium dioxide - Google Patents

Abstract

The subject of the invention is a method of obtaining spherical neodymium uranium dioxide grains for the production of fuel for reactors in the recycling process by the method of two-stage extraction from highly active waste. The method is that uranyl ascorbic sol is obtained by dissolving the solid organic acid, preferably ASC ascorbic acid, in a solution of uranyl nitrate UO2 (NO3) 2 · 6H2O with vigorous stirring, and then adding an americium surrogate, preferably neodymium, in the form of neodymium nitrate Nd (NO3) 3-6H2O. The resulting sol is made alkaline under intensive stirring by adding ammonia and subjected to extraction, preferably in two stages, with 2-ethyl-1-hexanol with an emulsifier and an aliphatic amine. The obtained spherical gel grains are subjected to thermal conversion by calcination, preferably in two stages, at about 250 ° C with a heating rate of 2 ° C / min and at about 600 ° C with a heating rate of 5 ° C / min, to obtain powders with spherical grains U3O8 subsidized neodymium oxide. The reduction to spherical grained neodymium dioxide is carried out under anaerobic conditions using preferably a mixture of protective and process gases, 95% N2 or 95% Ar with the addition of 5% H2.

Description

C01G 43/025 (2006.01) G21C 3/42 (2006.01)

Patent Office of the Republic of Poland (22) Date of application: 09/05/2013 (54) Method for obtaining uranium-neodymium dioxide with spherical grains (73) The holder of the patent:

INSTITUTE OF CHEMISTRY AND NUCLEAR TECHNIQUE, Warsaw, PL (43) Application was announced:

10.11.2014 BUP 23/14 (45) The following was announced about the grant of the patent:

29.06.2018 WUP 06/18 (72) Inventor (s):

MARCIN BRYKAŁA, Warsaw, PL ANDRZEJ DEPTUŁA, Warsaw, PL WIESŁAWA ŁADA, Warsaw, PL TADEUSZ OLCZAK, Warsaw, PL MARCIN ROGOWSKI, Warsaw, PL ANDRZEJ G. CHMIELEWSKI, Warsaw, PL (74) Plenipotentiary:

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PL 229 092 B1

Description of the invention

The subject of the invention is a method of obtaining spherical neodymium uranium dioxide grains for the production of fuel for nuclear reactors in the process of recycling of components released by the two-stage extraction method from highly active waste,

Works on the development of new safe reactor technologies have been and are carried out in many research centers. The undisputed advantages of nuclear power, such as low impact on the natural environment, low risk to human health and life, as well as economic profitability mean that an important task for specialists working in this field is the early development of modern technologies not only taking into account the above-mentioned advantages as well as raw material resources, as well as their possible re-use in the so-called recycling of spent fuel. The most important type of nuclear fuel in power reactors are oxides of fissile elements, especially uranium with various degrees of enrichment in ²³⁵ U, and with admixtures of high-energy elements. The spent fuel discharged from the reactor core still contains about 95% of uranium less enriched with an admixture of non-fissile isotopes and the content of uranium-235 ~ 0.8%, plutonium ~ 1% and a whole range of fission products, including minority actinides (MA), which include neptunium- 237, americ-241, cuur-242. All of these isotopes are High Level (HL) and long-lived. Therefore, work is underway to obtain nuclear fuels doped with isolated minority actinides based on classic fuels in order to transmute them to shorter-lived isotopes (e.g. transmutation of americium). Depending on the process of spent fuel processing and the method of handling minority actinides, we obtain "fresh fuel" type (U, Pu, MA) O2, or fuel without plutonium, where 20% are selectively introduced minority actinides - MA to pure uranium fuel (U, MA) O2. Fuels with a higher MA content are called Minor Actinide Bering Blankets (MABB). Both types of fuel are used in fast neutron reactors (J. Somers, Minor Actinide Bearing Fuels: Fabrication and Irradiation Experience in Europe, Energy Proceedia, Asian Nuclear Prospects (2010)). The most common method of synthesizing both types of fuels from MA is the use of aqueous solutions of minority actinides, immediately after their separation and separation from the spent fuel. Then, gelation is carried out to a specific physical form, i.e. to spherical or irregular grains. The last step is thermal conversion to a final product with the properties of a reactor fuel, e.g. (U, Am) O2-x, (U, Am, e.g.) O2-x or (U, Pu, Am) O2-x. Currently, research is being carried out on the selection of a method of producing optimal fuel compositions as well as their physico-chemical properties. Due to the fact that all fission products, including minority actinides, are highly radioactive, research is carried out in laboratories on actinide substitutes. One of the minority actinides from spent fuel is americium formed in nuclear reactors during the bombardment of uranium with neutrons. In chemical compounds, americium occurs in all oxidation states from +2 to +6. Americas in the +3 oxidation state form the most stable compounds, the phase transitions of which occur in the temperature range of 775 ° C - 850 ° C and are analogous to those observed for similar compounds of most lanthanides. For these reasons, the most common as a surrogate for america is neodymium with the oxidation state +3, the most similar to that of america.

As mentioned above, the material used as fuel in the reactors can be obtained in the form of a spherical grained powder. Virtually the only method of obtaining powders with spherical grains is the sol-gel method (V.N. Vaidya, Status of sol-gel process for nuclear fuels, J. Sol-Gel Sci. Technol. (2008) 46; 369-381).

There is a known method of obtaining various types of chemical compounds in the form of spherical grains according to the patented ICHTJ process (Patent PL 83484, 1978) "Methods for Preparing Spherical Grains of Metal Oxides", as well as a second method where, during the synthesis of ceramic materials from solutions, highly complexing compound which is ascorbic acid. This method is called Complex Sol-Gel Process (CSGP - Complex Sol-Gel Process) and has been successfully used in many syntheses, e.g. for the preparation of oxides and oxide compounds (e.g. tungsten oxide and tungstates, titanium dioxide and Li titanates). Ba, bioceramic materials or high-temperature superconductors). The developed methods have been described in the following patents: PL172618 - A method for producing high-temperature superconductors; PL179421 - A method of producing hollow grains of spherical ceramics, cermets and hydrogen-reducible metals; PL198039 - Method for obtaining titanium dioxide and lithium and barium titanates from titanium tetrachloride; PL180602 - A method for obtaining layers of calcium phosphates, in particular hydroxyapatite; PL209170 - Method for the preparation of yttrium-potassium dibungstate and the nanocomposite of this ytterbium-subsidized yttria.

Unexpectedly, it turned out to be a method according to; The invention, thanks to appropriate modifications and the use of the sol-gel and ascorbic acid method, it is possible to obtain spherical grains of uranium-neodymium dioxide powders, containing a reduced amount of nitrate anions, which prevents the destruction of the grains during subsequent thermal conversion.

The method of obtaining uranium-neodymium dioxide powders with spherical grains using the sol-gel method and ascorbic acid by dissolving UO2 (NO3) 2-6H2O in uranyl nitrate solution with intensive stirring, ASC ascorbic acid, while maintaining the ASC: U = 1 molar ratio, according to The invention consists in adding neodymium nitrate Nd (NO3> 6H2O in an amount of 5 to 20 mol% to the ascorbic uranyl sol, then, while stirring, add ammonia solution until the pH is in the range from 4 to 5, and the process of double extraction consists in introducing the sol, to the simultaneous extracting solutions, 2-ethyl-1-hexanol (2EH) with an emulsifier, 1% sorbitan mono oleate -C24H44O6, called SPAN80, and 1% -5% by volume of an aliphatic amine, preferably with C16-22 t-alkyl primary amine During gelation of the sol droplets, simultaneous extraction of water and nitrates is carried out. The gel obtained in this way is subjected to a two-stage thermal treatment at 230 ° C to 260 ° C, for 1 hour at a heating rate of 2 ° C / min and at 575 ° C to 625 ° C for, preferably 2 hours, at a heating rate of 5 ° C / min to obtain a product which are U3O8 powders doped with spherical neodymium oxide which are then reduced, under anaerobic conditions, using a protective gas mixture of 95% N2 or 95% Ar with the addition of a process gas, preferably 5% H2.

In the process according to the invention, the CSGP method for the preparation of ascorbic uranyl sol is used for the synthesis of spherical grains of neodymium uranium dioxide.

In the process of the invention, an americium surrogate, neodymium nitrate, is added to the ascorbic uranyl sol.

The method of obtaining spherical grains of uranium-neodymium dioxide according to the invention is based on the fact that during the gelation of the sol droplets, both the extraction of water and the extraction of nitrate anions are carried out.

In the process according to the invention, the ascorbic uranyl sol is most preferably obtained by dissolving UO2 (NO3> 6H2O) in a solution of uranyl nitrate UO2 (NO3> 6H2O with vigorous stirring for 1 hour at room temperature (25 ° C) by adding the solid form of ascorbic acid ASC, maintaining the ratio molar ASC: U = 1, then a surrogate of americium, preferably neodymium nitrate Nd (NO3> 6H2O in the amount of 10 mol%, is added, then, while stirring for 2 hours, 25% ammonia solution is introduced until pH 4.5 and a double extraction process is carried out consisting in introducing the sol to simultaneous extraction solutions, preferably 2-ethyl-1-hexanol (2EH) with 1% sorbitan mono oleate -C24H44O6 and 1% aliphatic amine, which is Primene JMT. , simultaneous extraction of water and nitrates is carried out.The gel obtained in this way is subjected to a two-stage thermal treatment at 250 ° C for 1h with a heating rate of 2 ° C / min and at 600 ° C for 2h with heating rate of 5 ° C / min to the final product, which are U3O8 powders subsidized with spherical grains of neodymium oxide.

The reduction from the spherical grained neodymium oxide compound U3O8 is carried out under preferably anaerobic conditions using a protective gas mixture of 95% N2 or 95% Ar with the addition of 5% H2, preferably at a flow rate of 1.2 dcm ³ / s.

In the method of obtaining uranium-neodymium dioxide powders with spherical grains according to the invention, simultaneous extraction of water and anions causes a reduction in the amount of nitrate anions in the spherical grains of the produced gels.

In the method according to the invention, simultaneous extraction prevents the destruction of the grains during the thermal conversion.

In the process according to the invention, introducing a two-stage extraction reduces the time of thermal treatment (calcination) from the four-stage process that is usually needed to obtain U3O8 to two-stage.

The undeniable advantage of the method according to the invention is the use of already known methods, such as CSGP and ICHTJ, by simplifying and improving them, which leads not only to shortening the synthesis time but by introducing simultaneous extraction of water and anions in the process

PL 229 092 B1

ICHTJ to reduce the content of nitrates in gels, thus preventing the destruction of grains during thermal conversion and reducing the time needed for the phase change from four-stage to two-stage calcination for gels obtained from uranyl nitrate and neodymium nitrate. In addition, the final product is obtained, which are spherical grains, which ensures a high degree of packing in the production of fuel for reactors. And since in the future this process is to be implemented during routine large-scale production, the costs that will be incurred using this process will be much lower.

The following examples illustrate the invention.

Example 1 3.17 g ascorbic acid was dissolved in 18.0 ml of a 1M UO2 solution (NO3> 6H2O (18 mmol) from Aldrich with intensive stirring (600 rpm) for 1 hour at room temperature 25 ° C. from Aldrich in the molar ratio of ASC: U = 1: 1, and then 2.0 ml of a 1M solution of Nd (NO3> 6H2O (2 mmol) from Aldrich was added while stirring vigorously. The resulting solution was titrated for 2 hours with stirring for 2 hours. % ammonia solution to pH 4.5. The thus prepared sol was dosed into the Sovirel stirred reactor at a rate of 1 ml / 5 minutes using a syringe pump to an intensively stirred solution of 2-ethyl-1-hexanol (Acros Organics), 2900 ml (1% vol. .) SPAN-80 (Fluka) and 29 ml (1 vol.%) Primene-JMT After addition of the sol, the solution was stirred for another hour. The precipitate was then filtered off, washed with acetone and dried at room temperature. two-stage heat treatment at 250 ° C for 1h with rapid heating rate of 2 ° C / min and at 600 ° C for 2 hours with a heating speed of 5 ° C / min to the final product, which are U3O8 powders subsidized with spherical grains neodymium oxide. The reduction to uranium dioxide from the compound U3O8 doped with neodymium oxide with spherical grains was carried out under preferably anaerobic conditions using a mixture of protective and process gases, 95% N2 or 95% Ar with the addition of 5% H2, at a flow of 1.2 dcm ³ / s.

Thermal analysis of the obtained gel in order to select the conditions of thermal treatment was carried out with the use of a Hungarian-made MOM derivatograph. On the other hand, the tests of the physical form of the final product were carried out using a scanning microscope (Zeiss DSM942), which confirmed that the grains of the obtained powder had a spherical shape. X-ray structure analysis performed on a Bruker D8 Advance diffractometer with Cu-Ka radiation confirmed that the obtained spherical grains are made of uranium-neodymium dioxide.

Example II. 3.17 g of Aldrich ascorbic acid were dissolved in a molar ratio of 3.17 g of Aldrich ascorbic acid in 18.0 ml of a 1M solution of UO2 (NO3> 6H2O (18 mmol) from Aldrich with intensive stirring (700 rpm) for 45 minutes at room temperature of 25 ° C ASC: U = 1: 1, then 0.876 g Nd (NO3> 6H2O (2 mmol) from Aldrich was added while stirring vigorously. The resulting solution was titrated with 25% aqueous ammonia solution to pH 4.5 with stirring for 45 minutes. The thus prepared sol was dispensed in 1 ml portions each into the Sovirel stirred reactor at a rate of 1 ml / 5 minutes using a syringe pump into an intensely stirred solution of 2-ethyl-1-hexanol (Acros Organics) 2900 ml containing 29 ml (1 vol. ) SPAN-80 (Fluka) and 29 ml (1% v / v) Primene-JMT After addition of the sol, the solution was stirred for another 45 minutes. The precipitate was then filtered off, washed with acetone and dried at room temperature. two-stage heat treatment at 250 ° C for 1h with heating rate of 2 ° C / min and at 600 ° C for 2 hours with a heating speed of 5 ° C / min to the final product, which are U3O8 powders subsidized with spherical grains neodymium oxide. The reduction to uranium dioxide from the compound U3O8 doped with neodymium oxide with spherical grains was carried out under preferably anaerobic conditions using a mixture of protective and process gases, 95% N2 or 95% Ar with the addition of 5% H2, at a flow of 1.2 dcm ³ / s.

Thermal analysis of the obtained gel in order to select the conditions of thermal treatment was carried out with the use of a Hungarian-made MOM derivatograph. On the other hand, tests of the physical form of the final product were carried out using a scanning microscope (Zeiss DSM942), which confirmed that the obtained powder was spherical grains. X-ray structure analysis performed on a Bruker D8 Advance diffractometer with Cu-Ka radiation confirmed that the obtained spherical grains contain pure uranium-neodymium dioxide.

PL 228 092 B1

Claims (4)

Patent claims 1. The method of obtaining uranium-neodymium dioxide powders with spherical grains, using the sol-gel method and ascorbic acid, where the ascorbic-uranyl sol is dissolved in a solution of uranyl nitrate UO2 (NO3> 6H2O, with intensive stirring, and ASC ascorbic acid is added, while maintaining the molar ratio ASC: U = 1, then an americium-neodymium nitrate surrogate is added, characterized in that neodymium nitrate Nd (NO3> 6H2O is added in an amount of 5 to 20 mol%, then, while stirring, the solution is added ammonia to obtain a pH in the range from 4 to 5, a double extraction process is carried out by introducing the sol, into the simultaneous extracting solutions, 2-ethyl-1-hexanol (2EH) with an emulsifier, preferably with 1% sorbitan mono oleate -C24H44O6, named SPAN-80, and 1% - 5% by volume of an aliphatic amine, preferably a C16-12 t-alkyl primary amine, whereby during the gelation of the sol droplets simultaneous extraction of water and a and the gel obtained in this way is subjected to a two-stage thermal treatment at 230 ° C to 260 ° C, for 1 hour with a heating rate of 2 ° C / min and at 575 ° C to 625 ° C, for preferably 2 hours, with heating rate of 5 ° C / min to obtain a product, which are U3O8 powders subsidized with spherical neodymium oxide, which are then reduced under anaerobic conditions using a protective gas mixture of 95% N2 or 95% Ar with the addition of process gas, preferably 5% H2 . 2. The method according to p. A method according to claim 1, characterized in that the CSGP method is used for the preparation of ascorbic uranyl sol in the synthesis of spherical grains of neodymium uranium dioxide. 3. The method according to p. The process as claimed in claim 1, characterized in that an americium surrogate, neodymium nitrate, is added to the ascorbine-uranyl sol. 4. The method according to p. The method of claim 1, characterized in that during gelation of the sol droplets, simultaneous extraction of water and extraction of nitrate anions with a suitable simultaneous extraction solution, 2-ethyl-1-hexanol (2EH) with 1% mono-oleate C24H44O6 and 1% aliphatic, primary amine is carried out.