A high-irradiation-resistant cerium-zirconate ceramic material for nuclear reactor control rods and a preparation method and application thereof

Abstract

The present application relates to a kind of high radiation resistance of control rod for stack entropy rare earth zirconate ceramic material and its preparation method and application, belong to nuclear reactor neutron absorption rod material technical field.The control rod ceramic material provided by the present application is prepared by using europium oxide, dysprosium oxide, thulium oxide and zirconium oxide as raw materials, according to certain proportion, after ball milling, calcination, green body forming and green body sintering process, and then processing to obtain the middle entropy rare earth zirconate ceramic material that can be applied to control rod.The rare earth zirconate ceramic material has excellent radiation resistance, large neutron absorption cross section and low reactivity value loss, and has high density, excellent thermal conductivity and low thermal expansion coefficient, and shows good application prospect in the field of control rod materials.

Description

Technical Field

[0001] This invention belongs to the technical field of neutron control rod materials for nuclear reactors, specifically relating to a high radiation-resistant intermediate-entropy rare-earth zirconate ceramic material for reactor control rods, its preparation method, and its application. Background Technology

[0002] Energy is a crucial cornerstone of social development and technological progress. Nuclear energy, as an ideal renewable energy source, is of paramount importance for its safe operation and sustainable development. As a key component of nuclear power generation, control rods are critical regulatory devices in nuclear reactors. They enable real-time control of the energy and power generated during the fission reaction of fuel assemblies by absorbing neutrons. Specifically, their raising and lowering within the reactor core enables crucial safety controls for reactor startup, power regulation, shutdown, and accident scenarios, which are essential for the safety, controllability, and long-term stability of nuclear reactors.

[0003] Because control rod materials need to be inserted into the reactor core active region for extended periods and subjected to high neutron flux irradiation, they suffer the following effects: irradiation swelling, irradiation embrittlement, irradiation-induced phase transitions leading to severe amorphization, and changes in their reactivity. These irradiation effects cause severe performance degradation in the neutron-absorbing materials of the control rods, affecting their regulation of neutron chain reactions and even impacting the normal operation of the reactor. Therefore, high radiation resistance is a key indicator for control rod materials. Currently used neutron-absorbing materials exhibit several problems after irradiation, as detailed below:

[0004] Ag-In-Cd alloy is a commonly used control rod core material, but after being irradiated in the reactor for a period of time, it will exhibit a significant swelling effect due to irradiation. When the swelling of Ag-In-Cd alloy is too large, "stick jamming" can easily occur during the raising and lowering of control rods, posing a safety risk to the stable operation of the nuclear reactor. In addition, under the high-temperature conditions during service, the thermal expansion of Ag-In-Cd alloy can lead to structural deformation or failure.

[0005] 10 Due to its large neutron absorption cross section (3838 barn), high hardness, good wear resistance, corrosion resistance, and chemical stability, B4C was widely used as a control rod material in early nuclear reactors. However, 10 The (n,α) reaction of B leads to the formation of He bubbles, which in turn accumulate and cause amorphization and microcracks.

[0006] Hf was one of the earliest control rod materials, exhibiting low reactivity loss and a long service life. However, irradiation can cause this material to become embrittled, leading to a decrease in its long-term reliability.

[0007] Dy2TiO5 is widely used in control rod materials due to its excellent properties such as good neutron absorption, low swelling at high temperatures, and good thermal stability. However, it is prone to phase transition under irradiation. The change in lattice volume caused by the phase transition will lead to stress inside the material and cause changes in its mechanical and thermal properties.

[0008] It is evident that the aforementioned commonly used control rod materials all exhibit numerous problems after high neutron flux irradiation, failing to guarantee long-term safety and stability in a nuclear reactor environment. They require periodic replacement after a certain burnup period, resulting in significant economic losses due to reactor shutdowns during replacement. Therefore, exploring new control rod materials is crucial to ensuring the long-term safe and effective operation of control rods.

[0009] Studies have shown that rare earth zirconates with defective fluorite structures (RE2Zr2O7) exhibit excellent radiation resistance, and do not become completely amorphous even under irradiation damage of 100 dpa. In addition, medium- and high-entropy materials composed of different rare earth elements exhibit higher radiation resistance than single-component materials because the lattice distortion can suppress the aggregation and growth of irradiation defects.

[0010] However, currently, zirconate ceramic materials prepared with rare earth elements are only used in fields such as thermal barrier coatings, and cannot be applied to control rod materials. This is because thermal barrier coating materials generally have the characteristics of low thermal conductivity and high coefficient of thermal expansion, while neutron control rod materials are exactly the opposite, requiring high thermal conductivity and low coefficient of thermal expansion. Therefore, applying existing rare earth zirconates as thermal barrier coating materials to the field of control rods will have the following problems: (1) Due to their low thermal conductivity, thermal stress will be generated inside the ceramic, leading to a decrease in the mechanical properties of the ceramic and the generation of cracks, which cannot meet the long-term use requirements of nuclear reactor control rods; (2) The large coefficient of thermal expansion of thermal barrier coating materials will cause the control rod to jam during use, making it impossible to adjust the reactivity value in the reactor by lifting, causing a large safety hazard; (3) There are many types of rare earth elements. Developing control rod materials with rare earth elements involves extremely complex elemental composition and proportions, which have a great impact on the performance of the materials, especially making it difficult to obtain materials with extremely low reactivity value loss. Combining different rare earth elements makes it difficult to simultaneously guarantee low reactivity loss, high thermal conductivity, and low coefficient of thermal expansion. Therefore, it has been difficult to obtain a rare earth zirconate material with excellent performance suitable for the field of control rods. The development of such materials is extremely challenging.

[0011] Therefore, how to select suitable rare earth elements to form a medium-entropy rare earth element combination, so that it can meet the stringent requirements of low reactivity value loss, high thermal conductivity and low coefficient of thermal expansion required by the control rod while having high radiation resistance, has become an urgent technical problem to be solved. Summary of the Invention

[0012] This invention aims to solve the aforementioned technical problems by proposing a high-irradiation-resistant medium-entropy rare-earth zirconate ceramic material for reactor control rods, its preparation method, and its application. This material exhibits excellent performance in all aspects, making it better suited for use as a neutron control rod material. It addresses the challenge of existing technologies where control rod materials prepared from various material combinations often lack multiple superior properties simultaneously. This invention provides a medium-entropy rare-earth zirconate ceramic material for reactor neutron control rods that offers excellent radiation resistance, low reactive value loss, high thermal conductivity, and a low coefficient of thermal expansion.

[0013] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0014] This invention first provides a high-radiation-resistant intermediate-entropy rare-earth zirconate ceramic material for reactor control rods. The raw materials for manufacturing this material include three rare-earth oxides (Eu2O3, Dy2O3, and Tm2O3) and zirconium oxide (ZrO2). The proportions of each oxide are as follows: Eu2O3 content is 19.13 wt.%, Dy2O3 content is 19.72 wt.%, Tm2O3 content is 20.98 wt.%, and ZrO2 content is 40.17 wt.%.

[0015] Due to the vast variety of rare earth elements, developing control rod materials using rare earth elements presents a significant challenge: the elemental composition and ratios are extremely complex, greatly impacting material performance. As shown in the comparative example of this invention, the ceramic materials prepared using several rare earth elements fail to meet the requirement of low reactive value loss. Therefore, through extensive exploration and creative effort, the inventors have successfully prepared a medium-entropy rare earth zirconate ceramic material with the aforementioned composition and ratio. This material effectively meets the requirements for neutron control rod applications, possessing multiple excellent properties simultaneously, including excellent radiation resistance, low reactive value loss, high thermal conductivity, and a low coefficient of thermal expansion. Furthermore, the ceramic prepared in this invention exhibits extremely high density, ensuring its superior mechanical properties and radiation resistance.

[0016] The second objective of this invention is to provide a method for preparing a high-irradiation-resistant intermediate-entropy rare-earth zirconate ceramic material for stack control rods, as described below. This method includes the following steps:

[0017] S1. Mix three rare earth oxide powders and zirconium oxide powder according to the elemental molar ratio, add ethanol and zirconium oxide grinding balls as media for ball milling, dry, grind, sieve, and calcine to obtain precursor powder; the rare earth oxides are Eu2O3, Dy2O3 and Tm2O3.

[0018] S2. The precursor powder obtained in step S1 is dry-pressed into a green blank. Then, the green blank is taken out, vacuum-sealed and placed in a cold isostatic press. After cold isostatic pressing, a dense green blank is obtained.

[0019] S3. The dense green blank obtained in step S2 is placed in a muffle furnace for high-temperature sintering to obtain a dense pure phase ceramic. After processing and polishing, the rare earth zirconate material for neutron control rods for piles is obtained.

[0020] Furthermore, the calcination temperature in step S1 is 1000℃, and the calcination time is 4h.

[0021] Furthermore, the molar ratio of the three rare earth oxides and zirconium oxide in step S1 is 0.33:0.33:0.33:2.

[0022] Furthermore, the size of the zirconia grinding ball in step S1 is 2 mm, and the grinding time is 18-24 hours.

[0023] Furthermore, the sieving in step S1 is sieving through a 200-mesh sieve.

[0024] Furthermore, the pressure for dry pressing in step S2 is 3-6 MPa, and the holding time is 4-12 min.

[0025] Furthermore, the pressure for cold isostatic pressing in step S2 is 350 MPa, and the holding time is 5 minutes.

[0026] Furthermore, the sintering temperature in step S3 is 1500–1700°C, preferably 1600°C.

[0027] Furthermore, the heat preservation time in step S3 is 4-12 hours, preferably 8 hours.

[0028] The third objective of this invention is to provide the application of rare earth zirconate materials for neutron control rods in reactors prepared by the above method. These materials can serve as excellent neutron control rod materials, possessing superior radiation resistance, low reactive value loss, high thermal conductivity, and low coefficient of thermal expansion.

[0029] The beneficial effects of this invention are as follows:

[0030] (1) This invention is the first to successfully prepare a single-phase dense (Eu) material. 1 / 3 Dy 1 / 3 Tm 1 / 3)2Zr2O7 ceramic material is a medium-entropy rare earth element zirconate ceramic. This ceramic material has excellent irradiation capability, and at the same time, it has higher thermal conductivity than existing materials, lower thermal expansion coefficient than existing materials, and stable low reactivity value loss. In these aspects, its comprehensive performance is significantly better than that of traditional control rod materials. Therefore, this invention has developed a new neutron control rod material, which has great potential for practical application in the field of control rod materials.

[0031] (2) The preparation method provided by the present invention does not require the addition of sintering aids, its processing technology is simple, the preparation cost is low, and the medium entropy rare earth zirconate ceramic material prepared has extremely high density, which ensures its excellent mechanical properties and radiation resistance. Attached Figure Description

[0032] Figure 1 This study compares the reactive value loss of rare earth zirconate ceramic materials prepared by compounding different rare earth elements.

[0033] Figure 2 The (Eu) prepared for Example 1 and Comparative Example 1 1 / 3 Dy 1 / 3 Tm 1 / 3 )2Zr2O7 and (Gd 1 / 3 Dy 1 / 3 Sm 1 / 3 XRD pattern of Zr2O7 ceramic material;

[0034] Figure 3 The (Eu) prepared for Example 1 and Comparative Example 1 1 / 3 Dy 1 / 3 Tm 1 / 3 )2Zr2O7 and (Gd 1 / 3 Dy 1 / 3 Sm 1 / 3 Thermal conductivity and coefficient of thermal expansion of Zr2O7 ceramic material at 800℃. Detailed Implementation

[0035] This invention proposes a high radiation-resistant intermediate-entropy rare-earth zirconate ceramic material for stack control rods and its preparation method, particularly relating to a high radiation-resistant (Eu) rare-earth zirconate ceramic material. 1 / 3 Dy 1 / 3 Tm 1 / 3 )2Zr2O7 control rod ceramic material and its preparation method.

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is described in detail below with reference to embodiments. It should be noted that the following embodiments are for explanation and illustration only and are not intended to limit the invention. Non-essential improvements and adjustments made by those skilled in the art based on the above description are still within the scope of protection of this invention.

[0037] The sources of rare earth oxides and raw material powders involved in all embodiments of this patent are as follows:

[0038] Eu2O3 (99.99% purity, Qixin Chemical, China);

[0039] Dy2O3 (99.99% purity, Qixin Chemical, China);

[0040] Tm2O3 (99.99% purity, China Qixin Chemical);

[0041] ZrO2 (99.99% purity, Qixin Chemical, China)

[0042] Example 1

[0043] Pure-phase and dense medium-entropy rare-earth zirconate ceramic materials are prepared by solid-state dry pressing followed by muffle furnace sintering, including the following steps:

[0044] S1. Preparation of precursor powder: Europium oxide, dysprosium oxide, thulium oxide and zirconium oxide were weighed and mixed evenly in a molar ratio of 0.33:0.33:0.33:2 and ball-milled for 20 hours with ethanol and zirconium oxide grinding balls (diameter size 2 mm) as the medium. After drying, the powder was ground through a 200-mesh sieve and calcined at 1000℃ for 4 hours to obtain precursor powder.

[0045] S2. Green preform forming: Add the precursor powder obtained in step S1 into the mold, place the mold into a benchtop powder press, hold it under 5MPa pressure for 8 minutes, then take out the green preform, vacuum seal it, and place it into a cold isostatic press, and hold it under 350MPa pressure for 5 minutes to obtain a relatively dense green preform.

[0046] S3. Ceramic Sintering: The green body obtained in S2 was sintered at 1600℃ for 6 hours to obtain a ceramic sample, which was then polished to prepare (Eu) 1 / 3 Dy 1 / 3 Tm 1 / 3 )2Zr2O7 ceramics.

[0047] Example 2

[0048] The method is the same as in Example 1, except that: the ball milling time in step S1 is 18h, the dry pressing pressure in step S2 is 3MPa and the holding time is 4min, and the sintering temperature in step S3 is 1500℃ and the sintering time is 4h.

[0049] Example 3

[0050] The method is the same as in Example 1, except that: the ball milling time in step S1 is 24h, the dry pressing pressure in step S2 is 6MPa and the holding time is 12min, and the sintering temperature in step S3 is 1700℃ and the sintering time is 12h.

[0051] Comparative Example 1

[0052] Referring to the method in Example 1, (Gd) was prepared by combining rare earth oxides gadolinium oxide, dysprosium oxide, and samarium oxide with zirconium oxide. 1 / 3 Dy 1 / 3 Sm 1 / 3 The specific method for preparing Zr₂O₇ ceramics is as follows:

[0053] S1. Preparation of precursor powder: Gadolinium oxide, dysprosium oxide, samarium oxide and zirconium oxide were weighed and mixed evenly in a molar ratio of 0.33:0.33:0.33:2 and ball-milled for 20 hours with ethanol and zirconium oxide grinding balls (2 mm in diameter) as the medium. After drying, the powder was ground and sieved, and then calcined at 1000℃ for 4 hours to obtain precursor powder.

[0054] S2. Green preform forming: Add the precursor powder obtained in step S1 into the mold, place the mold into a benchtop powder press, hold it under 5MPa pressure for 8 minutes, then take out the green preform, vacuum seal it, and place it into a cold isostatic press, and hold it under 350MPa pressure for 5 minutes to obtain a relatively dense green preform.

[0055] S3. Ceramic Sintering: The green body obtained in S2 is sintered at 1600℃ for 6 hours to obtain a ceramic sample, which is then polished to obtain (Gd) 1 / 3 Dy 1 / 3 Sm 1 / 3 )2Zr2O7 ceramics.

[0056] Comparative Example 2

[0057] Referring to the method in Example 1, rare earth oxides europium oxide, holmium oxide, and ytterbium oxide were combined with zirconium oxide to prepare (Eu) 1 / 3 Ho 1 / 3 Yb 1 / 3 )2Zr2O7 ceramics.

[0058] Comparative Example 3

[0059] Referring to the method in Example 1, rare earth oxides europium oxide, dysprosium oxide, and thulium oxide were combined with zirconium oxide to prepare (Eu) 1 / 3 Gd 1 / 3 Tm 1 / 3 )2Zr2O7 ceramics.

[0060] Test Example 1

[0061] (I) The ceramic materials prepared in the examples and comparative examples were characterized using the following specific methods:

[0062] Cu-Kα was analyzed using X-ray diffraction (XRD, DX-2700, Dongfang Yuan, Dandong, China). The radiation diffraction patterns were recorded in the 2θ (10°–70°) range with a resolution of 0.05° / step.

[0063] The thermal diffusivity (λ) of the samples was measured using a laser thermal conductivity meter (LINSEIS, LFA 1000, Germany), with graphite coated on both the front and back surfaces of the samples. Under helium protection, the thermal diffusivity was measured at temperatures of 25, 100, 200, 300, 350, 400, 500, 600, 650, 700, and 800 °C, with at least three independent measurements performed. Thermal conductivity (k) is derived from the thermal diffusivity and specific heat capacity (C). P The results were calculated from the bulk density (ρ):

[0064] k=λC P ρ, where ρ is measured using Archimedes' displacement method, and C P The von Neumann-Kop rule was used for calculation. The coefficient of thermal expansion of the ceramic was measured up to 800°C using a thermal expansion meter (DIL 402, Netzsch, Germany) at a heating rate of 5°C / min.

[0065] (II) The results obtained from the characterization are as follows:

[0066] (1) Table 1 shows the density characterization of the prepared ceramic materials using Example 1 and Comparative Example 1 as examples. As can be seen from Table 1, the medium-entropy rare earth element zirconate ceramic materials (chemical formulas) prepared in Example 1 and Comparative Example 1 are respectively (Eu... 1 / 3 Dy 1 / 3Tm 1 / 3 )2Zr2O7 and (Gd 1 / 3 Dy 1 / 3 Sm 1 / 3 Zr₂O₇ has extremely high density, indicating that the material has very few pores and is very dense, making it suitable for characterization by testing methods. However, the ceramic obtained by this invention has even higher density, and its mechanical properties and radiation resistance are superior.

[0067] Table 1 Density of ceramic materials prepared by different methods

[0068] Material Density Example 1 99.58％ Comparative Example 1 98.72％

[0069] (2) Figure 1The reactivity value loss of different zirconate materials with three rare earth elements as control rods was calculated by RMC. It can be seen that the reactivity value loss of Example 1 is only 8.51% under a burnup of 70 GWd / tU, which meets the low reactivity value loss requirement of control rods. However, the ceramic materials obtained with other rare earth elements have significantly higher reactivity value losses than the ceramics obtained in Example 1. Therefore, these materials will cause a significant decrease in neutron absorption capacity during long-term use, affecting the control rod's regulation of neutrons in the reactor core and the safe operation of the reactor.

[0070] (3) Figure 2 The diffraction patterns of the ceramic samples from Example 1 and Comparative Example 1, obtained by XRD testing, are shown, specifically the diffraction patterns from 10° to 70°. Comparison with the PDF standard card 78-1293 for defective fluorite structures (F) reveals that both exhibit defective fluorite structures. This helps improve their radiation resistance and effectively avoids the reduction in neutron absorption performance caused by long-term structural and performance degradation under high radiation environments.

[0071] (4) Figure 3 The left-middle figure shows the thermal conductivity obtained from tests of Example 1 and Comparative Example 1. The results show that the thermal conductivity of the samples ranges from 1.60 to 2.10 W·m from room temperature to 800°C. -1 ·K -1 The range is far greater than the 1.11-1.13 W·m⁻² of Dy₂TiO₅, a commonly used control rod material. -1 ·K -1 Thermal conductivity range; Figure 3 The right-hand figure shows the coefficients of thermal expansion for Example 1 and Comparative Example 1. The coefficients of thermal expansion measured at 350°C for both are 9.15 × 10⁻⁶. -6 K -1 10.12×10 -6 K -1 All are lower than the thermal expansion coefficient of Dy2TiO5 ceramic at 350℃ (10.40×10). -6 K -1 The results indicate that the ceramic material prepared in Example 1 can effectively reduce the deformation of the control rod during use, significantly reduce the risk of rod jamming during the lifting process, and ensure the safety of the material during service and replacement. The elemental composition ratios in Examples 2 and 3 remain unchanged, with only slight differences in the molding process; therefore, their performance is similar to that of Example 1.

[0072] In summary, the ((Eu) prepared by this invention 1 / 3 Dy 1 / 3 Tm 1 / 3In addition to excellent radiation resistance, 2Zr2O7 ceramic materials also possess superior thermal conductivity, a low coefficient of thermal expansion, and stable low reactive energy loss. In these aspects, their overall performance is significantly better than that of traditional control rod materials.

[0073] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high irradiation resistant cermet material for control rods for nuclear reactors, characterized in that it comprises a ceramic matrix of zirconate of a rare earth with a high entropy, and a dispersion of zirconium particles in the matrix, the zirconium particles having a size of less than 100 nm. The ceramic material consists of the following raw materials in percentage by weight: Eu2O319.13 wt %, Dy2O319.72 wt %, Tm2O3 20.98 wt %, ZrO2 40.17 wt %.

2. A method of producing a high-irradiation-resistant cermet material for a control rod of a nuclear reactor, as claimed in claim 1, characterized in that, The preparation method comprises the following steps: S1, mixing europium oxide, dysprosium oxide, thulium oxide and zirconium oxide powders according to the element molar ratio, then adding ethanol and zirconium oxide grinding balls as medium for ball milling, drying, grinding and sieving, and calcining to obtain a precursor powder; S2, dry pressing the precursor powder obtained in step S1 into a green body, taking out the green body, vacuumizing and sealing, and then placing it into a cold isostatic pressing machine for cold isostatic pressing to obtain a dense green body; S3, placing the dense green body obtained in step S2 into a muffle furnace for high-temperature sintering to obtain a dense pure-phase ceramic, and polishing after processing to obtain the high-irradiation-resistance meso-entropy rare earth zirconate ceramic material for nuclear reactors.

3. The production method according to claim 2, characterized by, The molar ratio of the three rare earth oxides and zirconium oxide in step S1 is 0.33:0.33:0.33:

2.

4. The production method according to claim 2, characterized by, The calcination temperature in step S1 is 1000℃, and the calcination time is 4 h.

5. The preparation method according to claim 2, characterized in that, The size of the zirconium oxide grinding balls in step S1 is 2mm, and the ball milling time is 18-24 h; the sieving is 200 mesh.

6. The preparation method according to claim 2, characterized in that, The dry pressing forming pressure in step S2 is 3-6 Mpa, and the pressure holding time is 4-12 min.

7. The preparation method according to claim 2, characterized in that, The cold isostatic pressing forming pressure in step S2 is 350 MPa, and the pressure holding time is 5 min.

8. The method of claim 2, wherein, The sintering temperature in step S3 is 1500-1700℃.

9. The production method according to claim 8, characterized by, The sintering temperature in step S3 is 1600℃.

10. The method of claim 2, wherein, The sintering time in step S3 is 4-12 h.

11. The method of claim 10, wherein, The sintering time in step S3 is 6 h.

12. The high-irradiation-resistance meso-entropy rare earth zirconate ceramic material for nuclear reactors of claim 1 in the preparation of neutron absorbing rod materials.

13. The high-irradiation-resistance meso-entropy rare earth zirconate ceramic material for nuclear reactors prepared by the method of any one of claims 2-9 in the preparation of neutron absorbing rod materials.

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