Zirconic acid rare earth-based high-entropy ceramic material for nuclear reactor neutron absorption rod as well as preparation method and application of zirconic acid rare earth-based high-entropy ceramic material

Abstract

The invention belongs to the technical field of nuclear reactor neutron absorption rod materials, and relates to a zirconic acid rare earth based high-entropy ceramic material for a nuclear reactor neutron absorption rod as well as a preparation method and application of the zirconic acid rare earth based high-entropy ceramic material. The chemical formulas of the two high-entropy ceramic materials provided by the invention are respectively four-component element high-entropy ceramic (Eu < 1 / 4 > Dy < 1 / 4 > Yb < 1 / 4 > Tm < 1 / 4 >) 2Zr2O7 and five-component element high-entropy ceramic (Eu < 1 / 5 > Dy < 1 / 5 > Yb < 1 / 5 > Tm < 1 / 5 > Er < 1 / 5 >) 2Zr2O7. According to the prepared high-entropy zirconate neutron absorption rod material, the rare earth element RE with excellent neutron absorption performance is selected at the A site by adopting a high-entropy strategy on the basis of rare earth zirconate (RE2Zr2O7), design is performed in combination with mechanical properties, and the control rod material with excellent radiation resistance, high fracture toughness and high hardness is obtained.

Description

Technical Field

[0001] The present invention belongs to the technical field of control rod materials, and particularly relates to a rare earth zirconate-based high-entropy ceramic material for neutron absorber rods in nuclear reactors, a preparation method thereof, and an application thereof. Background Art

[0002] With the rapid development of the nuclear power industry, nuclear safety issues have become increasingly important, especially the risks of radiation leakage, core overheating, etc. that may occur during the long-term operation of nuclear reactors. Nuclear safety is not only an important part of national security but also the fundamental guarantee for the development of the nuclear industry. To achieve the sustainable and healthy development of nuclear power, nuclear safety must be given top priority. As the core component of the nuclear reactor safety system, control rods play a crucial role in ensuring the safe operation of nuclear reactors. By raising and lowering in the core to adjust neutron absorption in the core, control rods can achieve the startup, power regulation, shutdown of nuclear reactors, and critical safety operations in case of accidents. Compared with the traditional method of adjusting reactor reactivity by changing the boric acid concentration, using control rods to automatically adjust the reactivity value mainly effectively avoids the defects of slow reaction, a large amount of wastewater, and complex supporting facilities, and has a faster response speed and higher accuracy. In addition to flexibly adjusting reactivity, control rods can also quickly and effectively stop the fission reaction of the reactor in case of emergencies, thus preventing accidents in a timely manner. Therefore, the design and operating performance of control rods directly affect the safety of nuclear reactors. Developing neutron absorption materials with higher neutron absorption efficiency and longer service life has become the key direction for improving the performance of control rods and ensuring the safety of nuclear reactors.

[0003] 10 B has a relatively large neutron absorption cross-section and is therefore commonly used as a neutron absorption material. As the most commonly used material in the boron-containing neutron absorption system, B4C has a melting point as high as 2450 °C, stable chemical properties, and excellent neutron absorption performance. However, 10 After B absorbs thermal neutrons, it will undergo α decay, and the released helium gas generates He bubbles inside the material, resulting in irradiation swelling, causing serious volume expansion during service, damaging the material density, and even generating a large number of microcracks, leading to failure.

[0004] Ag-In-Cd alloy is widely used in pressurized water reactor control rods due to its easy processability (hot forging temperature 650 °C) and high neutron absorption cross-section, but there is an irreversible attenuation of irradiation performance: when using this material as a control rod for five years of service, its reactivity value drops to about 80% of the initial value, and it needs to be shut down and replaced, resulting in huge economic losses. In addition, its irradiation swelling during actual service is much higher than the design expectation, resulting in the phenomenon of rod jamming occurring many times, posing a safety hazard to nuclear power plants.

[0005] Hf has excellent corrosion resistance, and its reactivity value remains relatively stable after neutron absorption. However, the ability of Hf materials to resist impact loads decreases after neutron irradiation, which may also lead to brittle fracture of the materials. Therefore, although Hf materials exhibit excellent performance in neutron absorption, the extremely high requirements for chemical purity and the degradation of mechanical properties and geometry after neutron irradiation are still the key issues affecting the service life of Hf control rods.

[0006] Dy2TiO5 meets the performance indicators such as good neutron absorption, low swelling at high temperatures, and good thermal stability through fluorite structure stabilization and high-density sintering methods. However, the preparation of its stable cubic structure is extremely difficult, and it is prone to phase transformation under irradiation conditions, resulting in changes in volume and performance.

[0007] It can be seen that after irradiation with high neutron fluence, the above several commonly used traditional control rod materials cannot ensure long-term safe and stable service in the nuclear reactor environment. They need to be replaced regularly after a certain burnup time, and the economic losses caused by reactor shutdown during the replacement period are serious. To ensure the long-term safe and effective operation of control rods, it is crucial to explore new control rod materials.

[0008] The concept of high-entropy ceramics was proposed in 2015. Due to the relatively high mixing entropy of high-entropy ceramics, they have thermal stability, higher defect formation energy. In addition, medium and high-entropy materials composed of different rare earth element combinations can inhibit the aggregation and growth of irradiation defects due to lattice distortion, making them exhibit higher anti-irradiation performance than single-component materials. Therefore, they are less likely to generate defects when irradiated. In addition, the high-density dislocations formed by the high-entropy effect will significantly improve the fracture toughness of the materials, ensuring excellent mechanical properties. On this basis, studies have shown that defect fluorite structure rare earth zirconates (RE2Zr2O7) have excellent anti-irradiation performance, and even under 100 dpa of irradiation damage, they will not be completely amorphized.

[0009] At present, there is little research on high-entropy ceramic materials for neutron absorber rods applied in the strong irradiation environment of nuclear reactors at home and abroad. Therefore, how to select appropriate rare earth elements for combination to make them fully exert their own properties and at the same time meet the strict requirements such as low reactivity value loss, high anti-irradiation, and high fracture toughness required for control rod materials has become a technical problem to be solved urgently.

[0010] Among the existing selectable rare earth elements, Eu has a relatively high reactivity value and low loss. The thermal neutron absorption cross-section of Dy is significantly higher than that of the traditional material Hf, and the 164 Dy generated after neutron capture has high stability. Although the thermal neutron cross-section of Yb is lower than that of the isotopes generated after the two capture neutrons 176Yb has a short half-life and rapid radioactive decay, which is beneficial for reducing the post-retirement treatment cost. In addition, Yb has a high neutron scattering cross-section and can effectively slow down neutrons to assist in controlling the reaction rate. Therefore, the present invention adds other rare earth elements on the basis of Eu, Dy, and Yb, and synergizes with other elements through the "cocktail effect" of high entropy. By using the above preparation method of the present invention, by combining various rare earth elements at the A site in rare earth zirconate, both high radiation resistance and excellent mechanical properties can be achieved. Therefore, the high-entropy rare earth zirconate material prepared by the method of the present invention has excellent radiation resistance, excellent neutron absorption ability, and high hardness and fracture toughness, and has great potential as a candidate material for control rods. Summary of the Invention

[0011] To improve the deficiencies of the existing technology, the present invention proposes a rare earth zirconate-based high-entropy ceramic material for neutron absorber rods in nuclear reactors, its preparation method, and application. In the present invention, based on rare earth zirconate (RE2Zr2O7), a high-entropy strategy is adopted to select rare earth elements RE with excellent neutron absorption performance at the A site, and design is carried out in combination with mechanical properties to obtain a control rod material with excellent radiation resistance, high fracture toughness, and high hardness.

[0012] In the first aspect, the present invention provides a rare earth zirconate-based high-entropy ceramic material for neutron absorber rods in nuclear reactors. The chemical formula of the ceramic material is: the high entropy of four-component elements is (Eu 1 / 4 Dy 1 / 4 Yb 1 / 4 RE 1 / 4 )2Zr2O7 and the high entropy of five-component elements is (Eu 1 / 5 Dy 1 / 5 Yb 1 / 5 RE1 1 / 5 RE2 1 / 5 )2Zr2O7; wherein, RE is selected from any one or two of Tm, Sm, Gd, or Er according to the number of components. For example, RE is Gd, and RE1 and RE2 are Sm and Gd respectively.

[0013] According to the embodiment of the present invention, the ceramic material has an XRD pattern substantially as Figure 1 .

[0014] According to the embodiment of the present invention, the ceramic material has a thermal conductivity substantially as Figure 2 .

[0015] According to the embodiment of the present invention, the ceramic material has a reactivity value change diagram substantially as Figure 3 .

[0016] According to the embodiment of the present invention, the ceramic material has a certain property substantially as Figure 4Hardness.

[0017] According to an embodiment of the present invention, the ceramic material has substantially as Figure 5 Fracture toughness.

[0018] According to an embodiment of the present invention, the ceramic material has substantially as Figure 6 Coefficient of thermal expansion diagram.

[0019] In a second aspect, the present invention provides a method for preparing the above-mentioned ceramic material to obtain a rare earth zirconate-based high-entropy ceramic material for a neutron absorber rod in a nuclear reactor. The material has excellent service performance, excellent anti-irradiation performance, excellent neutron absorption ability, high hardness and fracture toughness, and can meet the performance index requirements for serving as a neutron absorber rod for a long time. The method includes the following steps:

[0020] Solid-phase sintering of the RE source and the Zr source to obtain a ceramic material.

[0021] According to an embodiment of the present invention, the solid-phase sintering includes pre-sintering and secondary sintering.

[0022] According to an embodiment of the present invention, the preparation method includes the following steps:

[0023] S1. Mix the RE source and the Zr source, add anhydrous ethanol and ball mill to obtain compound A;

[0024] S2. Dry, screen and calcine the mixture A to obtain a precursor powder;

[0025] S3. Dry-press the precursor powder, vacuum-seal, cold isostatic press, and sinter at high temperature in a muffle furnace to obtain a dense pure-phase ceramic;

[0026] S4. Process and polish the pure-phase ceramic to obtain the rare earth zirconate-based high-entropy ceramic material.

[0027] According to an embodiment of the present invention, the Zr source is provided by an oxide containing Zr element, preferably ZrO2.

[0028] According to an embodiment of the present invention, the RE source is provided by a compound containing RE element, and the RE element is selected from Eu, Dy, Tb, Tm, Sm, Er and Gd; preferably, the compound containing RE element is selected from the corresponding rare earth oxides RE2O3.

[0029] According to an embodiment of the present invention, the molar contents of the rare earth ions in the RE source are the same.

[0030] According to an embodiment of the present invention, the dosage ratio of the rare earth cations in the Zr source and the RE source satisfies Zr 4+ To total RE3 + The molar ratio is 1:1.

[0031] According to an embodiment of the present invention, the calcination temperature in step S1 is 1000 °C, and the calcination time is 4 h.

[0032] According to an embodiment of the present invention, the size of the zirconia grinding balls in step S1 is 2 mm, and the ball milling time is 18 - 24 h.

[0033] According to an embodiment of the present invention, the sieving in step S1 is through a 200 - mesh sieve.

[0034] According to an embodiment of the present invention, the pressure of dry pressing forming in step S2 is 3 - 6 Mpa, and the pressure holding time is 4 - 12 min.

[0035] According to an embodiment of the present invention, the pressure of cold isostatic pressing forming in step S2 is 300 MPa, and the pressure holding time is 10 minutes.

[0036] According to an embodiment of the present invention, the sintering temperature in step S3 is 1500 - 1700 °C, preferably 1600 °C.

[0037] According to an embodiment of the present invention, the heat preservation time in step S3 is 4 - 12 h, preferably 8 h.

[0038] In a third aspect, the present invention also provides a neutron absorber rod, including the application of the above - mentioned material in the field of neutron control rods.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0040] (1) The present invention prepares a rare - earth zirconate - based high - entropy ceramic material through a short - process technology combining pre - sintering and muffle furnace sintering. This method significantly shortens the sintering cycle while maintaining the simplicity of the process. The density of the prepared ceramics is greater than 99%, far exceeding the current density requirements for neutron - absorbing materials. And due to the dense structure, it endows excellent mechanical properties. This low - temperature and high - efficiency sintering process breaks through the limitations of traditional preparation methods and provides a new path for the large - scale production of highly reliable ceramic materials for nuclear use.

[0041] (2) While having excellent irradiation ability, this ceramic material has mechanical properties and thermal conductivity higher than those of existing materials, as well as relatively low reactivity value loss and a thermal expansion coefficient lower than that of other component ratios. Its comprehensive performance in the above aspects is significantly superior to traditional control rod materials, so it has great practical application potential in the field of control rod materials; Brief Description of the Drawings

[0042] Figure 1XRD pattern of the rare earth zirconate-based high-entropy ceramic material prepared in Example 1;

[0043] Figure 2 Comparison chart of the thermal conductivity of the rare earth zirconate-based high-entropy ceramic material prepared in Example 1 measured under different temperature conditions with the commonly used control rod material Dy2TiO5;

[0044] Figure 3 Comparison of the change of the reactivity value of the rare earth zirconate-based high-entropy ceramic material prepared in Example 1 with the burnup and the zirconates of other rare earth elements;

[0045] Figure 4 Hardness of the rare earth zirconate-based high-entropy ceramic material prepared in Example 1 at room temperature, and comparison with the zirconates of other rare earth elements;

[0046] Figure 5 Fracture toughness of the rare earth zirconate-based high-entropy ceramic material prepared in Example 1, and comparison with the zirconate ceramic materials of other rare earth elements;

[0047] Figure 6 Thermal expansion coefficient of the rare earth zirconate-based high-entropy ceramic material prepared in Example 1. Detailed implementation manners

[0048] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be specifically described below in conjunction with embodiments and the accompanying drawings. It is necessary to point out that the following embodiments are only used to explain and illustrate the present invention, and are not used to limit the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above-mentioned invention content still fall within the protection scope of the present invention.

[0049] Unless otherwise specified, the raw materials and reagents used in the following embodiments are all commercially available products, or can be prepared by known raw materials and methods.

[0050] Example 1

[0051] In this example, a four-component rare earth zirconate-based high-entropy ceramic (Eu 1 / 4 Dy 1 / 4 Yb 1 / 4 Tm 1 / 4 )2Zr2O7 and a five-component rare earth zirconate-based high-entropy ceramic (Eu 1 / 5 Dy 1 / 5 Yb 1 / 5 Tm 1 / 5 Er 1 / 5 )2Zr2O7 were prepared. The specific preparation method is as follows:

[0052] S1. Preparation of precursor powder: Weigh and mix the four / five rare earth oxides and zirconia involved in the chemical formula evenly according to the above molar ratio, and use ethanol and zirconia grinding balls (with a diameter of 2 mm) as the medium for ball milling for 20 h. After drying, grind it through a 200-mesh sieve and calcine it at 1000 °C for 4 h to obtain the precursor powder.

[0053] S2. Green body forming: Add the precursor powder obtained in step S1 into the mold, put the mold into a bench-top powder press, keep the pressure at 5 MPa for 8 minutes, then take out the green body, perform vacuum packaging, and put it into a cold isostatic press, and keep it at 300 MPa for 10 minutes to obtain a relatively dense green body.

[0054] S3. Ceramic sintering: Sinter the green body prepared in step S2 at 1600 °C for 6 hours to obtain a ceramic sample, and polish it.

[0055] Comparative Example 1

[0056] Referring to the method steps of Example 1, other rare earth elements (represented by RE) are used to prepare rare earth zirconate ceramic materials with the general chemical formula of RE2Zr2O7 to examine the advantages of the control rod material prepared by the present invention compared with other existing rare earth control rod materials. Specifically, Yb2Zr2O7, Gd2Zr2O7, Sm2Zr2O7, and the ternary (Dy 1 / 3 Gd 1 / 3 Sm 1 / 3 )2Zr2O7 control rod materials are compared.

[0057] Test Example 1

[0058] (1) Characterize the control rod ceramic material prepared in the example. The specific characterization methods are as follows:

[0059] Use X-ray diffraction method (XRD, DX-2700, Dandong Fangyuan, China) with Cu-Kα Record the radiation diffraction pattern in the range of 2θ (10° - 70°) with a resolution of 0.05° / step.

[0060] Use a laser thermal conductivity meter (LINSEIS, LFA 1000, Germany) to measure the thermal diffusivity (λ) of the sample, and coat graphite on the front and back surfaces of the sample. Under helium protection, the test temperature points of the thermal diffusivity are 25, 100, 200, 300, 350, 400, 500, 600, 650, 700, and 800 °C respectively, and at least three independent measurements are carried out. The thermal conductivity (k) is calculated from the thermal diffusivity, specific heat capacity (C P ) and bulk density (ρ):

[0061]

[0062] Among them, ρ is measured by the Archimedes drainage method (distilled water under the condition of 25 °C); φ is the porosity of the ceramic sample, which is determined by the actual density and the theoretical density; C P It is calculated according to the molar ratio of each component by adopting the Neumann-Kopp rule.

[0063] For the hardness test, a hardness tester is used to hold the pressure for 10 s under a load of 9.8 N, and at least 3 defect-free areas are selected for each sample for indentation test, and the average value is taken to obtain the result.

[0064] Based on the AP1000 reactor physics model, the RMC (Reactor Monte Carlo) program is used to calculate the reactivity value change and loss of the material under a burnup of 70 GWd / tU.

[0065] (2) The characterization results are as follows (taking Example 1 as an example):

[0066] Figure 1 The XRD diffraction pattern of the ceramic as described above is shown. The obtained result is compared with the PDF standard card 78-1293 of the defective fluorite structure (F), and it is found that it is all a defective fluorite structure and no second phase is observed. This experimental result proves that the rare earth zirconate-based high-entropy ceramic material prepared by the present invention has a single phase structure, and this single-phase structure helps to improve its density and maintain the high-temperature stability of its performance.

[0067] Figure 2 is the thermal conductivity measured for the above ceramic material. The results show that the thermal conductivity of the sample ranges from 1.55 - 1.98 W·m -1 ·K -1 in the range from room temperature to 800 °C, which is much higher than that of the currently commonly used control rod material Dy2TiO5, which is 1.11 - 1.13 W·m -1 ·K -1 thermal conductivity range.

[0068] Figure 3 is the trend of the reactivity value change of the ceramic materials obtained by RMC calculation for the above and the comparative example under a burnup of 70 GWd / tU. It can be seen that the reactivity value of the material obtained by the method described in Example 1 is much higher than that of Yb2Zr2O7, and the loss is lower than that of Gd2Zr2O7, and it overcomes the disadvantage that the reactivity value of Sm2Zr2O7 changes unstably with burnup. In addition, its stability is also higher than that of the ternary (Dy 1 / 3 Gd 1 / 3 Sm 1 / 3 )2Zr2O7.

[0069] Figure 4 and Figure 5The figure below shows the comparison of the hardness and fracture toughness of the above materials measured under room temperature and atmospheric pressure conditions with those of other component zirconate ceramic materials. It can be seen that due to the lattice distortion and increased dislocation density caused by the high-entropy effect, the mechanical properties of the materials are significantly enhanced, forming the characteristics of high hardness and high fracture toughness superior to those of low-entropy element component ceramics. For nuclear neutron absorber rods, this mechanical optimization has double engineering value: the increase in hardness directly enhances the anti-wear ability of the control rod in the reactor core, and the breakthrough in fracture toughness significantly reduces the risk of brittle fracture induced by irradiation swelling, providing a new material design scheme for the long-term safe operation of neutron absorber rods.

[0070] Figure 6 The figure below shows the comparison of the thermal expansion coefficients of the above materials with those of other component zirconate ceramic materials. It can be seen that the thermal expansion coefficient of the material described in this patent is significantly lower than that of other component zirconate ceramic materials, which can effectively reduce the probability of rod jamming during service, and at the same time improve the dimensional stability of the material in the irradiation-thermal coupling environment, providing a key guarantee for extending the service life of the control rod.

[0071] In summary, the rare earth zirconate-based high-entropy ceramic material prepared by the present invention has a single phase structure and excellent anti-irradiation performance, and at the same time has a higher thermal conductivity, a stable change in reactivity value, and higher hardness and fracture toughness than the current materials. Its comprehensive performance in the above aspects is significantly superior to that of traditional control rod materials and has service characteristics.

[0072] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A rare earth zirconate-based high entropy ceramic material for neutron absorption rods in nuclear reactors, characterized in that: The chemical formulas of the high entropy ceramic materials are: four-component element high entropy ceramic (Eu 1 / 4 Dy 1 / 4 Yb 1 / 4 Tm 1 / 4 )2Zr2O7, and five-component element high entropy ceramics (Eu 1 / 5 Dy 1 / 5 Yb 1 / 5 Tm 1 / 5 Er 1 / 5 )2Zr2O7.

2. The rare earth zirconate-based high entropy ceramic material for neutron absorption rods in nuclear reactors according to claim 1, characterized in that: The density of the ceramic material is greater than 95%; preferably, the density of the ceramic material is greater than 99%.

3. The rare earth zirconate-based high entropy ceramic material for neutron absorption rods in nuclear reactors according to claim 1 or 2, characterized in that: The ceramic material has a hardness greater than 10 GPa and a fracture toughness greater than 1.5 MPa·m at room temperature and standard atmospheric pressure. 1 / 2 Preferably, the hardness of the ceramic material at room temperature is greater than 12 GPa, and the fracture toughness is greater than 2 MPa·m 1 / 2 .

4. A method for preparing a ceramic material according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: S1, mixing oxide raw materials of RE source and Zr source, adding anhydrous ethanol and ball milling to obtain compound A; S2, drying, sieving, and calcining the mixture A to obtain a precursor powder; S3, dry pressing the precursor powder, vacuum sealing, cold isostatic pressing, and high-temperature sintering in a muffle furnace to obtain dense pure phase ceramics; S4, processing and polishing the pure phase ceramic to obtain the rare earth zirconate-based high entropy ceramic material.

5. The method for preparing the ceramic material according to claim 4, characterized in that: The Zr source is ZrO2, and the RE element in the RE source is selected from Tm and Er; preferably, the compound containing the RE element is selected from the corresponding rare earth oxide RE2O3.

6. The method for preparing a ceramic material according to claim 4, characterized in that: The molar content of each rare earth ion in the RE source is the same, and the amount ratio of the rare earth cations in the Zr source and the RE source satisfies Zr 4+ With total RE 3+ The molar ratio is 1:

1.

7. The method for preparing a ceramic material according to claim 4, characterized in that: The size of the zirconia grinding balls in step S1 is 2 mm, and the ball milling time is 22 h.

8. The method for preparing a ceramic material according to claim 4, characterized in that: In step S2, the mixture A is dried at a temperature of 70° C. for 24 hours, the sieving is through a 200-mesh sieve, the calcination temperature is 1000° C. for 4 hours.

9. The method for preparing a ceramic material according to claim 4, characterized in that: In step S3, the pressure of dry pressing is 3-6 MPa, and the holding time is 4-12 min; the pressure of cold isostatic pressing is 300 MPa, and the holding time is 10 min; the sintering temperature is 1500-1700° C., preferably 1600° C. The sintering time is 4-12 h, preferably 6 h.

10. Use of the rare earth zirconate-based high entropy ceramic material according to any one of claims 1 to 3 or the rare earth zirconate-based high entropy ceramic material prepared by the method according to any one of claims 4 to 9 in preparing neutron absorption rod materials.

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