High-radiation-resistance medium-entropy rare earth zirconate ceramic material for reactor control rod as well as preparation method and application of high-radiation-resistance medium-entropy rare earth zirconate ceramic material

Abstract

The invention relates to a high-radiation-resistance medium-entropy rare earth zirconate ceramic material for a reactor control rod as well as a preparation method and application of the high-radiation-resistance medium-entropy rare earth zirconate ceramic material, and belongs to the technical field of nuclear reactor neutron absorption rod materials. According to the control rod ceramic material provided by the invention, europium oxide, dysprosium oxide, thulium oxide and zirconium oxide are used as raw materials and are proportioned according to a certain proportion, the technological processes of calcination after ball milling, biscuit forming and biscuit sintering are carried out, and then the medium-entropy rare earth zirconate ceramic material capable of being applied to the control rod is prepared through processing. The rare earth zirconate ceramic material has the characteristics of excellent radiation resistance, large neutron absorption cross section and low reactivity value loss, has relatively high density, excellent heat-conducting property and relatively low thermal expansion coefficient, and shows a good application prospect in the field of control rod materials.

Description

Technical Field

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

[0002] Energy is an important cornerstone of social development and scientific and technological progress. As an ideal renewable energy source, the safe operation and sustainable development of nuclear energy are of crucial importance. As a key component in nuclear power generation, the control rod is a key regulating device in a nuclear reactor, which can achieve real-time control of the energy power generated by the fission reaction process of the fuel assembly by absorbing neutrons. Specifically, it realizes the startup, power regulation, shutdown of the nuclear reactor, and key safety control in case of accidents by its lifting and lowering in the reactor core, which is crucial for the safe controllability and long-term stability of the nuclear reactor.

[0003] Since the control rod material needs to be inserted into the active zone of the reactor core for a long time and is irradiated by a high neutron fluence rate, the control rod material is affected as follows: irradiation swelling, irradiation embrittlement, irradiation-induced phase transformation that severely amorphizes the material, and the change of its reactivity value. These irradiation effects will cause serious performance degradation of the control rod neutron absorption material, affect the regulation of the neutron chain reaction by the control rod, and even affect the normal operation of the reactor. Therefore, high anti-irradiation performance is a key index for control rod materials. However, there are some problems with the currently used neutron absorption materials after irradiation, specifically as follows:

[0004] Ag-In-Cd alloy is a commonly used control rod core material, but it will undergo obvious swelling effect due to irradiation after being irradiated in the reactor for a period of time. When the swelling amount of the Ag-In-Cd alloy is too large, the phenomenon of "rod jamming" is likely to occur during the lifting and lowering of the control rod, bringing safety risks to the stable operation of the nuclear reactor. In addition, under high-temperature conditions during service, the thermal expansion of the Ag-In-Cd alloy will cause its structure to deform or fail.

[0005] 10 B has a large neutron absorption cross section (3838 barn), and B 4 C has high hardness, good wear resistance, good corrosion resistance, and stable chemical properties. Therefore, B 4 C has been widely used as a control rod material in early nuclear reactors. However, 10 the (n,α) reaction of B will lead to the generation of He bubbles, which will accumulate and cause amorphization and microcracks.

[0006] Hf is the earliest control rod material, and its reactivity value loss is relatively low, with a long service life. However, irradiation effects may cause embrittlement of this material, resulting in a reduction in its long-term reliability.

[0007] Dy 2 TiO 5 Due to its excellent properties such as good neutron absorption, small swelling at high temperatures, and good thermal stability, it is widely used in control rod materials. However, it is prone to irradiation-induced phase transformation under irradiation conditions. The change in lattice volume caused by the phase transformation will lead to the generation of internal stress in the material and cause changes in its mechanical and thermal properties.

[0008] It can be seen that there are many problems with the above-mentioned currently commonly used control rod materials after being irradiated with a high neutron fluence rate, and they cannot ensure long-term safety and stability in the nuclear reactor environment. They need to be regularly replaced after a certain burnup time, and the economic loss caused by the reactor shutdown during the replacement period is serious. To ensure the long-term safe and effective operation of control rods, it is crucial to explore new control rod materials.

[0009] Some studies have shown that rare earth zirconates with defective fluorite structures (RE 2 Zr 2 O 7 ) exhibit excellent anti-irradiation performance. Even under 100 dpa of irradiation damage, they will not be completely amorphized. In addition, medium and high entropy materials composed of different rare earth element combinations can suppress the aggregation and growth of irradiation defects due to lattice distortion, making them exhibit higher anti-irradiation performance than single-component materials.

[0010] However, at present, zirconate ceramic materials prepared from 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 thermal expansion coefficient, while neutron control rod materials are exactly the opposite. They need to pursue high thermal conductivity and low thermal expansion coefficient. Therefore, applying existing rare earth zirconates used as thermal barrier coating materials to the field of control rods will have the following problems: (1) Due to its low thermal conductivity, thermal stress will be formed 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 thermal expansion coefficient of thermal barrier coating materials will cause the control rod to jam during use, and the reactivity value in the reactor cannot be adjusted by lifting, causing great safety hazards; (3) There are many types of rare earth elements. Developing control rod materials with rare earth elements has extremely complex element compositions and ratios, which have a great impact on the material properties. In particular, it is difficult to obtain materials with extremely low reactivity value losses. The compounding of different types of rare earth elements is difficult to ensure that they simultaneously meet the requirements of low reactivity value loss, high thermal conductivity, and low thermal expansion coefficient. Therefore, it has always been extremely difficult to obtain a rare earth zirconate material with extremely excellent performance suitable for the field of control rods, and the development of such materials faces great difficulties.

[0011] Therefore, how to select appropriate rare earth elements to form a medium-entropy rare earth element combination, so that on the basis of high radiation resistance performance, it can simultaneously meet the stringent requirements such as low reactivity value loss, high thermal conductivity, and low thermal expansion coefficient required for control rods, has become a technical problem to be solved urgently. Summary of the Invention

[0012] The present invention is to solve the above technical problems, and thus proposes a high radiation-resistant medium-entropy rare earth zirconate ceramic material for control rods of a reactor, its preparation method and application, so that its various performances are extremely excellent, so that it can be better applied to neutron control rod materials, to solve the problem that the control rod materials prepared by various material combinations in the prior art are difficult to simultaneously possess a variety of excellent performances, and to provide a medium-entropy rare earth zirconate ceramic material for neutron control rods of a reactor with excellent radiation resistance, low reactivity value loss, high thermal conductivity, and low thermal expansion coefficient.

[0013] To achieve the above technical objectives, the technical solutions adopted by the present invention are as follows:

[0014] The present invention first provides a high radiation-resistant medium-entropy rare earth zirconate ceramic material for control rods of a reactor, and the raw materials for making the material include three rare earth oxides (Eu 2 O 3 , Dy 2 O 3 and Tm 2 O 3 ) and zirconia (ZrO 2 ); the proportions of each oxide are as follows: the content of Eu 2 O 3 is 19.13 wt.%, the content of Dy 2 O 3 is 19.72 wt.%, the content of Tm 2 O 3 is 20.98 wt.%, and the content of ZrO 2 is 40.17 wt.%.

[0015] Since there are many types of rare earth elements, when developing control rod materials with rare earth elements, there are problems that the element composition and ratio are extremely complex and have a great influence on the performance of the materials. As shown in the comparative example of the present invention, the ceramic materials prepared with several rare earth elements adopted by it cannot meet the characteristics of low reactivity value loss. Therefore, through a large amount of exploration and creative labor by the present inventor, a medium-entropy rare earth zirconate ceramic material with the above composition ratio has finally been successfully prepared, which can well meet the use requirements of neutron control rods, can simultaneously possess a variety of excellent performances, and has excellent performances such as excellent radiation resistance, low reactivity value loss, high thermal conductivity, and low thermal expansion coefficient. In addition, the ceramic prepared by the present invention has extremely high density, ensuring its excellent mechanical properties and radiation resistance.

[0016] The second object of the present invention is to provide a preparation method of a high anti-irradiation medium entropy rare earth zirconate ceramic material for reactor control rods as described below. The material preparation method includes the following steps:

[0017] S1. Mix three rare earth oxide powders and zirconia powder according to the elemental molar ratio, and add ethanol and zirconia grinding balls as media for ball milling. After drying, grind, sieve, and calcine to obtain a precursor powder. The rare earth oxides are Eu 2 O 3 , Dy 2 O 3 and Tm 2 O 3 ;

[0018] S2. Dry-press the precursor powder obtained in step S1 into a green body, then take out the green body, evacuate and seal it, and put it into a cold isostatic press for cold isostatic pressing to obtain a dense green body;

[0019] S3. Place the dense green body prepared in step S2 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 reactor neutron control rods is obtained.

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

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

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

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

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

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

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

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

[0028] A third object of the present invention is to provide an application of the rare earth zirconate material for the reactor neutron control rod prepared by the above method, which can be used as a neutron control rod material well and has excellent anti-irradiation ability, low reactivity value loss, high thermal conductivity and low thermal expansion coefficient.

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

[0030] (1) The present invention has successfully realized the preparation of a single-phase dense (Eu 1 / 3 Dy 1 / 3 Tm 1 / 3 ) 2 Zr 2 O 7 ceramic material, which is a medium-entropy rare earth element zirconate ceramic. While having excellent irradiation ability, this ceramic material has a higher thermal conductivity than the current materials, a lower thermal expansion coefficient than the current materials, and a stable low reactivity value loss. Its comprehensive performance in the above aspects is significantly better than that of traditional control rod materials. Therefore, the present invention has developed a new neutron control rod material, which has great practical application potential 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, has a simple treatment process, low preparation cost, and the prepared medium-entropy rare earth zirconate ceramic material has extremely high density, ensuring its excellent mechanical properties and anti-irradiation properties. Description of the Drawings

[0032] Figure 1 It is a comparison of the reactivity value loss of rare earth zirconate ceramic materials prepared by compounding different rare earth elements.

[0033] Figure 2 It is the XRD patterns of the (Eu 1 / 3 Dy 1 / 3 Tm 1 / 3 ) 2 Zr 2 O 7 and (Gd 1 / 3 Dy 1 / 3 Sm 1 / 3 ) 2 Zr 2 O 7 ceramic materials prepared in Example 1 and Comparative Example 1;

[0034] Figure 3 It is the (Eu 1 / 3 Dy 1 / 3 Tm 1 / 3 ) 2 Zr 2 O 7 and (Gd 1 / 3Dy 1 / 3 Sm 1 / 3 ) 2 Zr 2 O 7 Thermal conductivity and coefficient of thermal expansion of the ceramic material at 800 °C. Detailed implementation manners

[0035] The present invention provides a high anti - irradiation medium - entropy rare - earth zirconate ceramic material for control rods of a reactor and a preparation method thereof, and particularly relates to a high anti - irradiation (Eu 1 / 3 Dy 1 / 3 Tm 1 / 3 ) 2 Zr 2 O 7 Control rod ceramic material and its preparation method.

[0036] In order to make the objectives, technical solutions and advantages of the present invention clearer, the following describes the present invention in detail with reference to embodiments. It should be noted 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 inventive content still fall within the protection scope of the present invention.

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

[0038] Eu 2 O 3 (purity 99.99%, China Qixin Chemical Industry);

[0039] Dy 2 O 3 (purity 99.99%, China Qixin Chemical Industry);

[0040] Tm 2 O 3 (purity 99.99%, China Qixin Chemical Industry);

[0041] ZrO 2 (purity 99.99%, China Qixin Chemical Industry)

[0042] Example 1

[0043] Prepare a pure - phase and dense medium - entropy rare - earth zirconate ceramic material by using the solid - phase method with dry - pressing molding and then sintering in a muffle furnace, including the following steps:

[0044] S1. Preparation of precursor powder: Weigh europium oxide, dysprosium oxide, thulium oxide and zirconium oxide according to the molar ratio of 0.33:0.33:0.33:2 respectively, mix them evenly, 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 them through a 200-mesh sieve and calcine them at 1000 °C for 4 h to obtain the precursor powder;

[0045] S2. Green body forming: Add the precursor powder obtained in step S1 into a mold, put the mold into a bench-top powder press, keep the pressure at 5 MPa for 8 min, then take out the green body, seal it under vacuum, and put it into a cold isostatic press, and keep it at a pressure of 350 MPa for 5 minutes to obtain a relatively dense green body;

[0046] S3. Ceramic sintering: Sinter the green body prepared in S2 at 1600 °C for 6 h to obtain a ceramic sample, and polish it to prepare (Eu 1 / 3 Dy 1 / 3 Tm 1 / 3 ) 2 Zr 2 O 7 ceramics.

[0047] Example 2

[0048] Refer to the method of Example 1, the differences are as follows: In step S1, the ball milling time is 18 h; in step S2, the pressure for dry pressing forming is 3 MPa and the pressure holding time is 4 min; in step S3, the sintering temperature is 1500 °C and the sintering time is 4 h.

[0049] Example 3

[0050] Refer to the method of Example 1, the differences are as follows: In step S1, the ball milling time is 24 h; in step S2, the pressure for dry pressing forming is 6 MPa and the pressure holding time is 12 min; in step S3, the sintering temperature is 1700 °C and the sintering time is 12 h.

[0051] Comparative Example 1

[0052] Refer to the method of Example 1, and use rare earth oxides gadolinium oxide, dysprosium oxide and samarium oxide to be compounded with zirconium oxide to prepare (Gd 1 / 3 Dy 1 / 3 Sm 1 / 3 ) 2 Zr 2 O 7 ceramics. The specific method is as follows:

[0053] S1. Preparation of precursor powder: Weigh gadolinium oxide, dysprosium oxide, samarium oxide and zirconium oxide according to the molar ratio of 0.33:0.33:0.33:2 respectively, mix them evenly, 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 and sieve, and calcine at 1000 °C for 4 h to obtain the precursor powder;

[0054] 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, evacuate and seal it, and put it into a cold isostatic press, and keep it at a pressure of 350 MPa for 5 minutes to obtain a relatively dense green body;

[0055] S3. Ceramic sintering: Sinter the green body prepared in S2 at 1600 °C for 6 hours to obtain a ceramic sample, and polish it to obtain (Gd 1 / 3 Dy 1 / 3 Sm 1 / 3 ) 2 Zr 2 O 7 ceramics.

[0056] Comparative Example 2

[0057] Refer to the method of Example 1, and use rare earth oxides europium oxide, holmium oxide and ytterbium oxide to be compounded with zirconium oxide to prepare (Eu 1 / 3 Ho 1 / 3 Yb 1 / 3 ) 2 Zr 2 O 7 ceramics.

[0058] Comparative Example 3

[0059] Refer to the method of Example 1, and use rare earth oxides europium oxide, dysprosium oxide and thulium oxide to be compounded with zirconium oxide to prepare (Eu 1 / 3 Gd 1 / 3 Tm 1 / 3 ) 2 Zr 2 O 7 ceramics.

[0060] Test Example 1

[0061] (1) Characterize the ceramic materials prepared in the examples and comparative examples. The specific characterization methods are as follows:

[0062] Adopt the X-ray diffraction method (XRD, DX-2700, Dongfang Round, China) with Cu-Kα The radiation diffraction pattern is recorded in the range of 2θ (10° - 70°) 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), and graphite was coated on the front and back surfaces of the samples. Under helium protection, the test temperature points of the thermal diffusivity were 25, 100, 200, 300, 350, 400, 500, 600, 650, 700, and 800 °C respectively, and at least three independent measurements were carried out. The thermal conductivity (k) was calculated from the thermal diffusivity, specific heat capacity (C P ), and bulk density (ρ):

[0064] k = λC P ρ where ρ was measured by the Archimedes drainage method, and C P was calculated using Neumann-Kopp's rule. The thermal expansion coefficient of the ceramic was measured using a dilatometer (DIL 402, Netzsch, Germany) up to 800 °C at a heating rate of 5 °C / min.

[0065] (II) The obtained results are characterized 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 zirconate ceramic materials prepared in Example 1 and Comparative Example 1 (chemical formulas are (Eu 1 / 3 Dy 1 / 3 Tm 1 / 3 ) 2 Zr 2 O 7 and (Gd 1 / 3 Dy 1 / 3 Sm 1 / 3 ) 2 Zr 2 O 7 ) have extremely high density, indicating that the material has very few pores and is very dense, suitable for characterization by the test method. However, the density of the ceramic obtained in the present invention is higher, and its mechanical properties and radiation resistance are more excellent.

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

[0068] Material Relative density Example 1 99.58％ Comparative example 1 98.72％

[0069] (2) Figure 1For the reactivity value loss of the control rod made of different zirconate materials with all RE bits calculated by RMC being three rare earth elements, it can be seen that the reactivity value loss of Example 1 is only 8.51% at a burnup of 70 GWd / tU, meeting the requirement of low reactivity value loss of the control rod. However, for the ceramic materials obtained by compounding other rare earth elements, their reactivity value losses are significantly higher than that of the ceramic obtained in Example 1. Therefore, these materials will cause a significant decrease in neutron absorption capacity during long-term use, affecting the regulation of core neutrons by the control rod and the safe operation of the reactor.

[0070] (3) Figure 2 The diffraction patterns of the ceramic samples of Example 1 and Comparative Example 1 tested by XRD are shown, specifically the diffraction patterns from 10° to 70°. By comparing with the PDF standard card 78 - 1293 of the defective fluorite structure (F), it is found that both have a defective fluorite structure, which helps to improve their radiation resistance performance and effectively avoid the reduction of neutron absorption performance caused by the degradation of structure and performance during long-term exposure to a high-irradiation environment.

[0071] (4) Figure 3 The left figure in the middle shows the thermal conductivity of Example 1 and Comparative Example 1 tested. The results show that the thermal conductivity of the samples ranges from 1.60 - 2.10 W·m -1 ·K -1 from room temperature to 800 °C, which is much higher than the thermal conductivity range of 1.11 - 1.13 W·m 2 TiO 5 of the currently commonly used control rod material Dy -1 ·K -1 ; Figure 3 The right figure in the middle shows the thermal expansion coefficients of Example 1 and Comparative Example 1. The thermal expansion coefficients measured under the test condition of 350 °C are 9.15×10 -6 K -1 and 10.12×10 -6 K -1 , respectively, both of which are lower than the thermal expansion rate (10.40×10 2 TiO 5 K -6 ) of Dy -1 ceramics at 350 °C, indicating 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 during the service and replacement of the material. The element composition ratios in Examples 2 and 3 remain unchanged, and only the forming process is slightly different. Therefore, their properties are similar to the results of Example 1.

[0072] In summary, the ((Eu 1 / 3 Dy 1 / 3 Tm 1 / 3 ) prepared in the present invention2 Zr 2 O 7 ) While having excellent anti-irradiation performance, the ceramic material can also have excellent thermal conductivity, a low coefficient of thermal expansion, and a stable low reactivity value loss. In the above aspects, its comprehensive performance is significantly superior to that of traditional control rod materials.

[0073] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A highly radiation-resistant medium-entropy rare earth zirconate ceramic material for reactor control rods, characterized in that: The ceramic material is composed of the following raw materials by weight percentage: Eu2O3 19.13 wt%, Dy2O3 19.72 wt%, Tm2O3 20.98 wt%, and ZrO2 40.17 wt%.

2. A method for preparing the high radiation resistant medium entropy rare earth zirconate ceramic material for reactor control rods 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 molar ratio of the elements, then adding ethanol and zirconium oxide grinding balls as the medium for ball milling, drying, grinding, sieving and calcining to obtain a precursor powder; S2, dry-pressing the precursor powder obtained in step S1 into a green blank, taking out the green blank, vacuum-sealing it, and then placing it in a cold isostatic press to obtain a dense green blank by cold isostatic pressing; S3, placing the dense green blank obtained in step S2 in a muffle furnace for high-temperature sintering to obtain a dense pure-phase ceramic, and processing and polishing to obtain the high-irradiation-resistant medium-entropy rare earth zirconate ceramic material for stacking.

3. The preparation method according to claim 2, characterized in that: 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 preparation method according to claim 2, characterized in that: The calcination temperature in step S1 is 1000° C. and the calcination time is 4 hours.

5. The preparation method according to claim 2, characterized in that: In step S1, the size of the zirconia grinding balls is 2 mm, and the ball milling time is 18 to 24 hours; preferably, the sieving is through a 200-mesh sieve.

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

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

8. The preparation method according to claim 2, characterized in that: The sintering temperature in step S3 is 1500-1700°C, preferably 1600°C.

9. The preparation method according to claim 2, characterized in that: The sintering time in step S3 is 4-12 hours, preferably 6 hours.

10. Use of the highly radiation-resistant medium-entropy rare earth zirconate ceramic material for reactor control rods obtained by the method according to claim 1 or any one of claims 2 to 9 in preparing neutron absorption rod materials.

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