Preparation method of simulated spent fuel

Abstract

The invention discloses a preparation method of simulated spent fuel, which comprises the following steps: mixing uranium dioxide powder, simulated fission product metal compound powder and an organic solvent according to a certain proportion, uniformly mixing by wet ball milling to obtain simulated spent fuel mixed slurry, and drying and sieving the slurry to obtain simulated spent fuel powder. Finally, the obtained simulated spent fuel powder is subjected to compression molding and spark plasma sintering in sequence, and the simulated spent fuel is prepared. A discharge plasma rapid densification sintering technology is adopted, the sintering temperature of the simulated spent fuel can be reduced, the sintering time is remarkably shortened, the sintering efficiency is improved, the problem that elements with different properties volatilize inconsistently is effectively avoided, quantitative doping of volatile fission elements is achieved, and the performance of the spent fuel is improved. And the obtained simulated spent fuel element composition is closer to the real spent fuel composition. Meanwhile, the preparation method of the simulated spent fuel avoids the use of reducing atmospheres such as hydrogen and the like, so that the safety performance of the sintering process is remarkably improved.

Description

Technical Field

[0001] The present application relates to the field of nuclear fuel preparation, and in particular to a method for preparing simulated spent fuel. Background Art

[0002] As a high-energy-density, clean, and low-carbon energy, nuclear energy shoulders an important mission in ensuring energy security, alleviating environmental pressure, and thus achieving sustainable economic and social development in my country. The nuclear fuel cycle is the "main artery" of the nuclear energy system, and my country has always adhered to the policy of closed nuclear fuel cycle. Advanced spent fuel reprocessing is one of the important links in achieving the closed nuclear fuel cycle strategy. Spent fuel refers to the nuclear fuel that is unloaded from the reactor after reaching a certain burnup after neutron irradiation in the nuclear reactor. Taking the spent uranium oxide fuel of a nuclear power plant pressurized water reactor with a burnup of 55,000MWd / tU and 8 years of cooling as an example, its composition is about 93% unused uranium and 7% newly generated nuclides (including about 1% plutonium, about 0.2% minor actinides such as neptunium, americium, and curium, and about 5.8% fission products such as strontium-90, cesium-137, technetium-99, and iodine-129). Advanced spent fuel reprocessing is the process of separating and recovering uranium and plutonium for reuse as nuclear fuel, or further recovering long-lived minor actinides (neptunium, americium, and curium) for reuse in fast reactors. This not only maximizes the utilization of spent fuel resources and minimizes waste management, reduces the long-term potential hazards of spent fuel, but is also a key way to achieve a closed cycle of nuclear fuel and ensure the sustainable development of nuclear energy.

[0003] The physical and chemical properties and phase structure of spent fuel samples are important objects for the development and engineering research of advanced spent fuel reprocessing technology. However, due to the extremely strong radioactivity, it is difficult to directly study real spent fuel samples. Simulated spent fuel (SIMFUEL) is composed of uranium dioxide and some simulated fission product metal compounds in proportion. It has similar physical properties (such as density, hardness, particle size, etc.) and chemical composition to real spent fuel but does not involve strong radioactivity. It provides a convenient method for studying spent fuel reprocessing technology in the laboratory.

[0004] At present, the traditional high-temperature sintering method is the main method for preparing simulated spent fuel, that is, uranium dioxide and simulated fission product metal compounds are first ground and mixed in proportion, and then cold pressed and sintered at high temperature in a reducing atmosphere. Germany, Canada, South Korea, China, etc. all use high-temperature sintering technology to prepare simulated spent fuel. However, the preparation conditions of this method are very harsh, the sintering temperature is high, and the sintering temperature generally used is above 1700℃, and the sintering time is long, usually 7h to 9h. Sintering for a long time at a high temperature can easily lead to inconsistent volatilization of elements of different properties, making it difficult to achieve the incorporation of volatile elements (cesium, ruthenium, etc.), so that the elemental composition of the obtained simulated spent fuel is different from that of the real spent fuel. On the other hand, the atmosphere of high-temperature sintering is mostly pure hydrogen, and the lowest hydrogen concentration is 4% H2-Ar, which leads to a high safety risk during the sintering process.

[0005] Chinese patent CN 113488217 discloses a method for preparing simulated spent fuel by mixing raw materials using a chemical method (sol-gel method). The elements are dispersed by means of the coordination ability of citric acid with most metal ions, and the sol-gel property of citric acid and ethylene glycol is further used to disperse the fission product elements that are difficult to coordinate or easy to hydrolyze, thereby effectively reducing the agglomeration of elements, and the sintering temperature can be reduced to below 1500°C, and the preparation conditions are milder. However, the chemical mixing method used in this method is cumbersome to operate and the process is complicated. It is only suitable for small-scale laboratory-scale production and is difficult to achieve industrial promotion. At the same time, this method requires long-term heating and reduction in a hydrogen reducing atmosphere in multiple process links, and the heating time is 3h to 12h. Chinese patent CN 109378097 discloses a method for preparing simulated spent fuel, which generates local high temperature and reducing atmosphere by adding organic additives and roasting in an inert atmosphere or a reducing atmosphere, so that the mixed metal oxides are fully reduced under low external control temperature. The preparation conditions of this method are mild and the firing temperature is low (1400°C to 1640°C). However, the organic additives added by this method are difficult to be completely roasted without residue during the high-temperature sintering process, so that the elemental composition of the obtained sintered body is quite different from the target simulated spent fuel composition. At the same time, the sintering time using this method is relatively long, 2h to 8h.

[0006] In summary, the publicly reported simulated spent fuel preparation methods still have problems such as long high-temperature sintering time, low sintering atmosphere safety, and low efficiency. Therefore, it is very necessary to develop a new simulated spent fuel preparation process that is more efficient, safer, and more energy-saving. Summary of the invention

[0007] In view of this, the object of the present invention is to provide a method for preparing simulated spent fuel with simple preparation conditions, short sintering time and safe sintering atmosphere. The method adopts a spark plasma sintering process, and realizes rapid densification sintering of simulated spent fuel powder materials based on the controllable pulse current of spark plasma under high electric field strength.

[0008] The present invention provides a method for preparing simulated spent fuel, which is characterized by comprising the following steps:

[0009] 1) placing uranium dioxide powder, simulated fission product metal compound powder, organic solvent and zirconium dioxide grinding balls into a ball mill, and then placing the ball mill in a planetary ball mill for grinding and mixing to obtain a uniformly dispersed simulated spent fuel mixed slurry;

[0010] 2) Drying the spent fuel mixed slurry, and then sieving it with a sieving instrument to obtain simulated spent fuel powder;

[0011] 3) loading simulated spent fuel powder into a graphite mold including an upper pressing head and a lower pressing head for compression molding to obtain a simulated spent fuel green body;

[0012] 4) placing the graphite mold containing the simulated spent fuel green body into a spark plasma sintering furnace;

[0013] 5) The upper and lower pressure heads of the graphite mold apply a constant pressure to the simulated spent fuel green body, and at the same time, the furnace chamber of the spark plasma sintering furnace is evacuated and heated. After a certain period of time, the heating is stopped to complete the preparation;

[0014] 6) After the furnace chamber is cooled to below 100°C, the furnace is opened to take out materials to obtain simulated spent fuel.

[0015] Furthermore, the simulated fission product metal compounds described in step 1) include cerium dioxide (CeO2), neodymium trioxide (Nd2O3), molybdenum trioxide (MoO3), cesium iodide (CsI), ruthenium dioxide (RuO2), barium carbonate (BaCO3), strontium oxide (SrO), lanthanum trioxide (La2O3), samarium trioxide (Sm2O3), tellurium dioxide (TeO2), palladium oxide (PdO), and rhodium trioxide (Rh2O3).

[0016] Furthermore, the organic solvent in step 1) is anhydrous ethanol or acetone.

[0017] Furthermore, the rotation speed in step 1) is 100 rpm to 200 rpm, and the grinding time is 3 h to 4 h.

[0018] Furthermore, the aperture size of the sieve described in step 2) is 100 mesh to 200 mesh.

[0019] Furthermore, the compression molding pressure in step 3) is 20 MPa to 30 MPa.

[0020] Furthermore, the graphite mold described in step 4) has a diameter of 8 mm to 20 mm, and the upper pressure head and the lower pressure head are both made of graphite material.

[0021] Furthermore, the constant pressure applied by the upper and lower pressure heads of the graphite mold described in step 5) is 30MPa to 60MPa, the vacuum degree in the furnace chamber is evacuated to below 10Pa, and the furnace chamber is heated to 1500°C to 1700°C at a rate of 50°C / min to 100°C / min, and the holding time is 5min to 10min.

[0022] Furthermore, the furnace chamber heating described in step 5) adopts a step-by-step heating method. When the furnace chamber temperature is below 715°C, the heating rate is 100°C / min, and when the furnace chamber temperature is above 715°C, the heating rate is 50°C / min.

[0023] Furthermore, the furnace chamber cooling described in step 6) adopts step-by-step cooling. When the furnace chamber temperature is above 800°C, the cooling rate is 100°C / min. When the furnace chamber temperature is below 800°C, the cooling is natural cooling. High-purity argon gas is used for protection when opening the furnace and taking out materials.

[0024] The beneficial effect of the present invention is that the discharge plasma rapid densification sintering technology is adopted, which can reduce the sintering temperature of the simulated spent fuel, significantly shorten the sintering time, and improve the sintering efficiency. Since the sintering time is significantly shortened, the problem of inconsistent volatilization of elements of different properties is effectively avoided, and the quantitative incorporation of volatile elements (such as cesium, ruthenium, etc.) is achieved, so that the elemental composition of the obtained simulated spent fuel is closer to the real spent fuel composition. On the other hand, the simulated spent fuel preparation method of the present invention avoids the use of reducing atmospheres such as hydrogen, so that the safety performance of the sintering process is significantly improved. In addition, the simulated spent fuel preparation method of the present invention can quickly prepare high-density simulated spent fuel at low temperature, and the relative density of the simulated spent fuel is 94% to 96%. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a flow chart of a method for preparing simulated spent fuel according to an embodiment of the present invention;

[0026] Figure 2 This is a physical picture of simulated spent fuel with a diameter of 10 mm obtained in an embodiment of the present invention;

[0027] Figure 3 This is a physical picture of simulated spent fuel with a diameter of 20 mm obtained in an embodiment of the present invention;

[0028] Figure 4is an XRD curve analysis diagram of simulated spent fuel obtained in an embodiment of the present invention;

[0029] Figure 5 This is an XPS curve analysis diagram of simulated spent fuel obtained in an embodiment of the present invention. DETAILED DESCRIPTION

[0030] The following examples are used to further illustrate the specific implementation of the present invention. The embodiments of the present invention include but are not limited to the following examples.

[0031] The process of the method for preparing simulated spent fuel of the present invention is as follows: Figure 1 shown.

[0032] The present invention provides a method for preparing simulated spent fuel, which is characterized by comprising the following steps:

[0033] 1) placing uranium dioxide powder, simulated fission product metal compound powder, organic solvent and zirconium dioxide grinding balls into a ball mill, and then placing the ball mill in a planetary ball mill for grinding and mixing to obtain a uniformly dispersed simulated spent fuel mixed slurry;

[0034] 2) Drying the spent fuel mixed slurry, and then sieving it with a sieving instrument to obtain simulated spent fuel powder;

[0035] 3) loading simulated spent fuel powder into a graphite mold including an upper pressing head and a lower pressing head for compression molding to obtain a simulated spent fuel green body;

[0036] 4) placing the graphite mold containing the simulated spent fuel green body into a spark plasma sintering furnace;

[0037] 5) The upper and lower pressure heads of the graphite mold apply a constant pressure to the simulated spent fuel green body, and at the same time, the furnace chamber of the spark plasma sintering furnace is evacuated and heated. After a certain period of time, the heating is stopped to complete the preparation;

[0038] 6) After the furnace chamber is cooled to below 100°C, the furnace is opened to take out materials to obtain simulated spent fuel.

[0039] Furthermore, the simulated fission product metal compounds described in step 1) include cerium dioxide (CeO2), neodymium trioxide (Nd2O3), molybdenum trioxide (MoO3), cesium iodide (CsI), ruthenium dioxide (RuO2), barium carbonate (BaCO3), strontium oxide (SrO), lanthanum trioxide (La2O3), samarium trioxide (Sm2O3), tellurium dioxide (TeO2), palladium oxide (PdO), and rhodium trioxide (Rh2O3).

[0040] Furthermore, the organic solvent in step 1) is anhydrous ethanol or acetone.

[0041] Furthermore, the rotation speed in step 1) is 100 rpm to 200 rpm, and the grinding time is 3 h to 4 h.

[0042] Furthermore, the aperture size of the sieve described in step 2) is 100 mesh to 200 mesh.

[0043] Furthermore, the compression molding pressure in step 3) is 20 MPa to 30 MPa.

[0044] Furthermore, the graphite mold described in step 4) has a diameter of 8 mm to 20 mm, and the upper pressure head and the lower pressure head are both made of graphite material.

[0045] Furthermore, the constant pressure applied by the upper and lower pressure heads of the graphite mold described in step 5) is 30MPa to 60MPa, the vacuum degree in the furnace chamber is evacuated to below 10Pa, and the furnace chamber is heated to 1500°C to 1700°C at a rate of 50°C / min to 100°C / min, and the holding time is 5min to 10min.

[0046] Furthermore, the furnace chamber heating described in step 5) adopts a step-by-step heating method. When the furnace chamber temperature is below 715°C, the heating rate is 100°C / min, and when the furnace chamber temperature is above 715°C, the heating rate is 50°C / min.

[0047] Furthermore, the furnace chamber cooling described in step 6) adopts step-by-step cooling. When the furnace chamber temperature is above 800°C, the cooling rate is 100°C / min. When the furnace chamber temperature is below 800°C, the cooling is natural cooling. High-purity argon gas is used for protection when opening the furnace and taking out materials.

[0048] In the embodiment, the composition of uranium dioxide and simulated fission product metal compounds in the simulated spent fuel is configured according to the following Table 1 (simulated burnup 30GWd / tU, cooling for 3 years).

[0049] Table 1 Composition of simulated spent fuel

[0050]

[0051] Example 1

[0052] Weigh 25.00g of uranium dioxide powder using an electronic balance, and weigh CeO2, Nd2O3, MoO3, CsI, RuO2, BaCO3, SrO, La2O3, Sm2O3, TeO2, PdO, and Rh2O3 according to the proportions in Table 1. Mix the above-mentioned mixture with zirconium dioxide grinding balls and anhydrous ethanol in a mass ratio of 1.5:7:1, and put them into a zirconium dioxide ball mill; wherein the grinding ball particle size is Φ10mm. After the ball mill is sealed, place it in a planetary ball mill for wet mixing, the speed of the ball mill is 100rmp, and the grinding time is 4h to obtain a uniformly dispersed simulated spent fuel mixed slurry; transfer the spent fuel mixed slurry into an oven at 80℃~100℃ and slowly heat it up for drying, and then use a 100-mesh sifter to sieve it to obtain a simulated spent fuel mixed powder. The simulated spent fuel mixed powder was loaded into a Φ10mm graphite mold and molded at a pressure of 25MPa for 2min to obtain a simulated spent fuel green body. The graphite mold containing the simulated spent fuel green body was placed in a spark plasma sintering furnace for spark plasma sintering at a sintering pressure of 50MPa, a vacuum degree of 10Pa, a sintering temperature of 1600℃, and a sintering time of 10min. After sintering, the temperature was lowered in a stepwise manner until the spark plasma furnace chamber was cooled to below 100℃. The furnace was opened under the protection of high-purity argon gas to remove the material for demoulding to obtain the simulated spent fuel.

[0053] Figure 2 The simulated spent fuel with a diameter of 10 mm was prepared by Figure 2 It can be seen that the prepared simulated spent fuel has a complete structure, no cracks, no voids, and no powder falling, indicating that the sintering is sufficient. It has been measured that the density of the simulated spent fuel prepared in this embodiment reaches 94.5% of the theoretical density. After X-ray diffraction analysis (XRD) characterization (see Figure 4 ), proving that the simulated spent fuel prepared by sintering is mainly composed of uranium dioxide material, and no second phase is observed in the simulated fission product compounds due to the small amount of doping, indicating that the above sintering treatment method meets the preparation requirements for the sintering of simulated spent fuel.

[0054] Example 2

[0055] 25.00g of uranium dioxide powder was weighed using an electronic balance, and CeO2, Nd2O3, MoO3, CsI, RuO2, BaCO3, SrO, La2O3, Sm2O3, TeO2, PdO, and Rh2O3 were weighed according to the proportions in Table 1 for batching. The above-mentioned mixture was mixed with zirconium dioxide grinding balls and anhydrous ethanol in a mass ratio of 1.5:7:1, and then loaded into a zirconium dioxide ball mill; wherein the grinding ball particle size was Φ10mm. After the ball mill was sealed, it was placed in a planetary ball mill for wet mixing, the speed of the ball mill was 200rmp, and the grinding time was 3h to obtain a uniformly dispersed simulated spent fuel mixed slurry; the spent fuel mixed slurry was transferred to an oven at 80℃~100℃ for slow heating and drying, and then sieved using a 100-mesh sifter to obtain a simulated spent fuel mixed powder. The simulated spent fuel mixed powder was loaded into a Φ20mm graphite mold and molded at a pressure of 25MPa for 2min to obtain a simulated spent fuel green body. The graphite mold containing the simulated spent fuel green body was placed in a spark plasma sintering furnace for spark plasma sintering at a sintering pressure of 50MPa, a vacuum degree of 10Pa, a sintering temperature of 1650℃, and a sintering time of 5min. After sintering, the temperature was lowered in a stepwise manner until the spark plasma furnace chamber was cooled to below 100℃. The furnace was opened under the protection of high-purity argon gas to remove the material for demoulding to obtain the simulated spent fuel.

[0056] Figure 3 The simulated spent fuel with a diameter of 20 mm was prepared by Figure 3 It can be seen that the prepared simulated spent fuel has a complete structure, no cracks, no voids, and no powder falling, indicating that the sintering is sufficient. It has been measured that the density of the simulated spent fuel prepared in this embodiment reaches 96.0% of the theoretical density. After X-ray photoelectron spectroscopy characterization (see Figure 5 ), proving that the simulated spent fuel prepared by sintering is mainly composed of uranium dioxide material, containing a small amount of Cs and Ru characteristic peaks, indicating that the above sintering treatment method can achieve the quantitative incorporation of volatile elements (cesium, ruthenium, etc.), making the elemental composition of the obtained simulated spent fuel closer to the real spent fuel composition.

[0057] The present invention is described in detail above in combination with specific implementation methods and exemplary examples. The above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments; the above description cannot be understood as limiting the present invention. Those skilled in the art understand that, without departing from the spirit and scope of the present invention, the technical solution of the present invention and its implementation methods may be subjected to a variety of equivalent substitutions, modifications or improvements, all of which fall within the scope of the present invention; the protection scope of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing simulated spent fuel, characterized in that: The following steps are involved: 1) placing uranium dioxide powder, simulated fission product metal compound powder, organic solvent and zirconium dioxide grinding balls into a ball mill, and then placing the ball mill in a planetary ball mill for grinding and mixing to obtain a uniformly dispersed simulated spent fuel mixed slurry; 2) Drying the spent fuel mixed slurry, and then sieving it with a sieving instrument to obtain simulated spent fuel powder; 3) loading simulated spent fuel powder into a graphite mold including an upper pressing head and a lower pressing head for compression molding to obtain a simulated spent fuel green body; 4) placing the graphite mold containing the simulated spent fuel green body into a spark plasma sintering furnace; 5) The upper and lower pressure heads of the graphite mold apply a constant pressure to the simulated spent fuel green body, and at the same time, the furnace chamber of the spark plasma sintering furnace is evacuated and heated. After a certain period of time, the heating is stopped to complete the preparation; 6) After the furnace chamber is cooled to below 100°C, the furnace is opened to take out materials to obtain simulated spent fuel.

2. The method for preparing simulated spent fuel according to claim 1, characterized in that: The simulated fission product metal compounds described in step 1) include cerium dioxide (CeO2), neodymium trioxide (Nd2O3), molybdenum trioxide (MoO3), cesium iodide (CsI), ruthenium dioxide (RuO2), barium carbonate (BaCO3), strontium oxide (SrO), lanthanum trioxide (La2O3), samarium trioxide (Sm2O3), tellurium dioxide (TeO2), palladium oxide (PdO), and rhodium trioxide (Rh2O3).

3. The method for preparing simulated spent fuel according to claim 1, characterized in that: The organic solvent described in step 1) is anhydrous ethanol or acetone.

4. The method for preparing simulated spent fuel according to claim 1, characterized in that: The rotation speed in step 1) is 100 rpm to 200 rpm, and the grinding time is 3 h to 4 h.

5. The method for preparing simulated spent fuel according to claim 1, characterized in that: The mesh size of the sieve described in step 2) is 100-200 meshes.

6. The method for preparing simulated spent fuel according to claim 1, characterized in that: The compression molding pressure in step 3) is 20 MPa to 30 MPa.

7. The method for preparing simulated spent fuel according to claim 1, characterized in that: The graphite mold described in step 4) has a diameter of 8 mm to 20 mm, and the upper pressure head and the lower pressure head are both made of graphite material.

8. The method for preparing simulated spent fuel according to claim 1, characterized in that: The constant pressure applied by the upper and lower pressure heads of the graphite mold described in step 5) is 30MPa to 60MPa, the vacuum degree in the furnace chamber is evacuated to below 10Pa, and the furnace chamber is heated to 1500°C to 1700°C at a rate of 50°C / min to 100°C / min, and the holding time is 5min to 10min.

9. The method for preparing simulated spent fuel according to claim 1, characterized in that: The furnace chamber heating described in step 5) adopts a step-by-step heating method. When the furnace chamber temperature is below 715°C, the heating rate is 100°C / min, and when the furnace chamber temperature is above 715°C, the heating rate is 50°C / min.

10. The method for preparing simulated spent fuel according to claim 1, characterized in that: The furnace chamber cooling described in step 6) adopts step-by-step cooling. When the furnace chamber temperature is above 800°C, the cooling rate is 100°C / min. When the furnace chamber temperature is below 800°C, the cooling is natural cooling. High-purity argon gas is used for protection when opening the furnace and taking out materials.

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