Double-rare-earth zirconate ceramic material for reactor control rod as well as preparation method and application of double-rare-earth zirconate ceramic material

Abstract

The invention relates to a high-radiation-resistance double-rare-earth zirconate ceramic material for a reactor control rod as well as a preparation method and application of the high-radiation-resistance double-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, gadolinium oxide and zirconium oxide are used as raw materials and are proportioned according to a certain stoichiometric ratio, and the double-rare-earth zirconate ceramic material which can be well applied to the control rod is prepared through the technological processes of ball-milling, calcining, biscuit forming and biscuit sintering. The ceramic material provided by the invention is excellent in radiation resistance, high in reactivity value, low in loss, relatively high in density, excellent in heat-conducting property and relatively high in hardness, shows a good control rod application prospect, and can be well applied to a nuclear reactor control rod material.

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 double rare earth zirconate ceramic material for reactor control rods, a preparation method thereof, and an application thereof. Background Technique

[0002] The control rod is one of the key components of a nuclear reactor. By inserting or withdrawing it from the reactor core, the reactivity of the reactor core is adjusted to regulate and control the rate of the chain fission reaction, ensuring the safe and stable operation of the reactor. The control rod needs to be in the long-term core active area and faces irradiation with a high neutron fluence rate, resulting in the change of reactivity value with burnup being non-negligible. Therefore, the control rod material needs to meet stringent conditions such as high reactivity value, low loss, high thermal conductivity, and strong anti-irradiation. In recent years, in order to improve the operation life and economy of the reactor, more stringent requirements have been put forward for the control rod material, and the currently commonly used neutron absorption materials can no longer meet these performance requirements simultaneously.

[0003] The Ag-In-Cd alloy has great advantages in industrial production, material acquisition, and neutron absorption performance. However, after being used for five years, its reactivity value drops to about 80% of the initial value, and it can no longer be used and needs to be replaced. In addition, its unexpected swelling during use has led to the phenomenon of rod jamming many times, greatly affecting the free movement of the control rod and posing a safety hazard to nuclear power plants.

[0004] B4C has a high melting point, stable chemical properties, and excellent neutron absorption performance. However, 10 After B absorbs neutrons, He bubbles will be generated, resulting in serious volume expansion during use and even a large number of microcracks leading to failure.

[0005] The reactivity value of the Hf material is relatively stable after absorbing neutrons, and it has excellent corrosion resistance. However, its extremely high requirement for chemical purity and the decrease in mechanical properties and geometric stability after neutron irradiation are still the key problems affecting the service life of Hf control rods.

[0006] Dy2TiO5 is a preferred control rod material due to its excellent properties such as good neutron absorption, small swelling at high temperatures, and good thermal stability. 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 the above several currently commonly used control rod materials will have many problems after being irradiated with a high neutron fluence rate, and 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 benefit loss caused by the reactor shutdown during the replacement period is serious. To ensure the long-term safe and effective operation of the control rod, it is crucial to explore new control rod materials.

[0008] Gd2Zr2O7 is considered to be one of the oxides with the most excellent anti-irradiation performance. Under the irradiation damage of 100 dpa, it will not be completely amorphized, and it also has properties required for control rods such as high melting point, high temperature stability, and low thermal expansion, showing great application potential. However, the relatively large reactivity value loss of Gd makes it have certain limitations. However, even by combining the different properties of multiple rare earth elements and combining multiple rare earth elements, it is still extremely difficult to develop a control rod material with excellent performance.

[0009] Therefore, how to select appropriate rare earth elements for combination so that they can exert their own properties and at the same time meet the stringent requirements such as low reactivity value loss, high thermal conductivity, and high hardness required for control rods has become a technical problem to be solved urgently. Summary of the Invention

[0010] The present invention is to solve the problems existing in the above-mentioned prior art, and thus proposes a high anti-irradiation double rare earth zirconate ceramic material for reactor control rods, its preparation method and application. The technical purpose of the present invention is to solve the problem that the anti-irradiation ability of control rods made of various materials in the prior art is weak, and to solve the problem that the control rod materials prepared by the existing methods cannot meet the requirements of low reactivity value loss, high thermal conductivity, and high hardness.

[0011] In order to achieve the above technical purpose, the specific technical solutions adopted by the present invention are as follows:

[0012] The present invention first provides a preparation method of a high anti-irradiation double rare earth zirconate ceramic material for reactor control rods, which is characterized in that the preparation method includes the following steps:

[0013] S1. Mix europium oxide and gadolinium oxide powders with zirconium oxide powder according to the elemental molar ratio, add them to a ball milling device, and then add ethanol and zirconium oxide grinding balls as media for ball milling. After ball milling is completed, it is dried, ground, sieved, and calcined to obtain a precursor powder.

[0014] S2. Dry-press the precursor powder obtained in step S1 into a green body, then vacuum-seal the green body and put it into a cold isostatic press, and perform cold isostatic pressing to obtain a dense green body.

[0015] 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, and after processing and polishing, the high anti-irradiation double rare earth zirconate ceramic material for reactor is obtained.

[0016] Existing research shows that the rare earth element Eu has a high reactivity value and low loss, and Eu will transmute to produce Gd. However, there have been many failures in how to make the rare earth elements be compounded to solve the problem that the existing control rod materials cannot simultaneously meet the stringent requirements of low reactivity value loss, high thermal conductivity, and high hardness. Currently, very few ceramic materials that can meet the requirements of neutron control rods have been developed. The inventor of the present invention unexpectedly found that by using the above preparation method of the present invention and combining two rare earth elements, Eu and Gd, in rare earth zirconate, high radiation resistance performance and low reactivity value loss can be taken into account. In addition, when Eu and Gd are combined, a single-structured rare earth zirconate can be formed, which is beneficial to the improvement of density and the stability of performance. Therefore, the (Eu x Gd 1-x )2Zr2O7 material prepared by the method of the present invention has excellent radiation resistance performance, high reactivity value, high melting point, excellent thermal stability, and low thermal expansion performance, and is expected to be a candidate material for control rods.

[0017] Furthermore, the calcination temperature in step S1 is 1000 °C, and the calcination time is 4 h.

[0018] Furthermore, the size of the zirconia grinding balls in step S1 is 2 mm, and the ball milling time is 18 - 24 h.

[0019] Furthermore, the sieving in step S1 is sieving through a 200-mesh sieve.

[0020] Furthermore, the pressure of dry pressing in step S2 is 3 - 6 Mpa, and the pressure holding time is 4 - 12 min.

[0021] Furthermore, the pressure of cold isostatic pressing in step S2 is 300 MPa, and the pressure holding time is 10 minutes.

[0022] Furthermore, the sintering temperature in step S3 is 1500 - 1700 °C, preferably 1600 °C.

[0023] Furthermore, the heat preservation time in step S3 is 4 - 12 h, preferably 8 h.

[0024] Furthermore, the molar ratio of the elements in each raw material in step S1 is europium:gadolinium:zirconium = x:(1 - x):1, where x = 0.6 - 0.9.

[0025] The second object of the present invention is to provide a rare earth zirconate material for a reactor neutron control rod prepared by the above method. The use performance of this material is extremely excellent, meeting the requirements of low reactivity value loss, high thermal conductivity, and high hardness, and can meet the use requirements of neutron control rods for a long time.

[0026] A third object of the present invention is to provide an application of the above-described material in the field of neutron control rods.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] (1) The preparation method provided by the present invention can obtain a single-phase dense (Eu x Gd 1-x )2Zr2O7 zirconate ceramic material. While having excellent irradiation resistance, this ceramic material has a higher thermal conductivity and a stable reactivity value than the current materials. Its comprehensive performance in the above aspects is significantly better than that of traditional control rod materials. Therefore, it has great practical application potential in the field of control rod materials;

[0029] (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 prepared rare earth zirconate ceramic material has extremely high density and a pure phase structure, ensuring its excellent mechanical properties and radiation resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 XRD patterns of the (Eu x Gd 1-x )2Zr2O7 (x = 0.6, 0.7, 0.8, 0.9) ceramic materials prepared in Example 1;

[0031] Figure 2 Thermal conductivities of the (Eu x Gd 1-x )2Zr2O7 (x = 0.6, 0.7, 0.8, 0.9) prepared in Example 1 at 800 °C;

[0032] Figure 3 Comparison of the reactivity value change with burnup and the reactivity value loss percentage change with burnup of the (Eu 0.6 Gd 0.4 )2Zr2O7 and (RE 0.6 Gd 0.4 )2Zr2O7 (RE = Tm, Sm, Er, Dy) prepared in Example 1;

[0033] Figure 4 Hardness of the (Eu x Gd 1-x )2Zr2O7 (x = 0.6, 0.7, 0.8, 0.9) prepared in Example 1 and comparison with the hardness of the xEu2O3-(1-x)Gd2Zr2O7 (x = 0.6, 0.7, 0.8, 0.85) ceramic materials of the same raw materials in the literature;

[0034] Figure 5For the reactivity value and loss of (Eu x Gd 1-x )2Zr2O7 (x = 0.6, 0.7, 0.8, 0.9) prepared in Example 1, the reactivity value and loss of Gd2Zr2O7 material were calculated and compared. Detailed implementation manners

[0035] The present invention provides a high anti-irradiation dual 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 x Gd 1-x )2Zr2O7 control rod ceramic material and a preparation method thereof.

[0036] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be specifically described below in conjunction with 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 according to the above invention content still fall within the protection scope of the present invention.

[0037] The powder raw materials involved in all embodiments of this patent are as follows:

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

[0039] Gd2O3 (purity 99.99%, China Qixin Chemical Industry);

[0040] ZrO2 (purity 99.99%, China Qixin Chemical Industry).

[0041] Example 1

[0042] A pure-phase and dense dual rare earth zirconate ceramic material is prepared by using the solid-phase method for dry pressing and sintering in a muffle furnace, including the following steps:

[0043] S1. Preparation of precursor powder: Europium oxide, gadolinium oxide and zirconium oxide are weighed and mixed evenly according to the molar ratio respectively, and ball-milled for 20 h with ethanol and zirconium oxide grinding balls (diameter size 2 mm) as the medium. After drying, it is ground through a 200-mesh sieve and calcined at 1000 °C for 4 h to obtain the precursor powder;

[0044] S2. Green body forming: The precursor powder obtained in step S1 is added to a mold, the mold is placed in a bench-top powder press, and the pressure is maintained at 5 MPa for 8 minutes. Then the green body is taken out, vacuum-sealed and placed in a cold isostatic press, and maintained at 300 MPa for 10 minutes to obtain a relatively dense green body;

[0045] S3, Ceramic sintering: The green body obtained in S2 is sintered at 1600 °C for 6 hours to obtain a ceramic sample, and it is polished.

[0046] By setting the molar ratio of oxides in each raw material as europium oxide: gadolinium oxide: zirconium oxide = (), a double rare earth zirconate ceramic material is prepared, and its chemical element combination is (Eu x Gd 1-x )2Zr2O7 (x = 0.6, 0.7, 0.8, 0.9).

[0047] Example 2

[0048] Referring to the method of Example 1, adjust the ball milling time in step S1 above to 18 - 24 h, adjust the pressure of dry pressing forming in step S2 to 3 - 6 Mpa, adjust the pressure holding time to 4 - 12 min, adjust the sintering temperature in step S3 to 1500 - 1700 °C, and adjust the heat preservation time of sintering to 4 - 12 h. The double rare earth zirconate ceramic material of the present invention can be obtained, and its performance is generally similar to that of Example 1, except that a certain performance changes slightly.

[0049] Test Example 1

[0050] (1) Characterize the control rod ceramic material prepared in the example. The specific characterization method is as follows:

[0051] 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.

[0052] Adopt 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):

[0053]

[0054] Among them, ρ is measured by the Archimedes drainage method, φ is the porosity of the ceramic sample, and C P Adopt the Neumann-Kopp rule to calculate.

[0055] The hardness test was obtained by using a hardness tester with a load of 9.8 N and holding the pressure for 10 s, and at least three indentation tests were performed on each sample.

[0056] Using the AP1000 reactor model through RMC software, the reactivity value and its loss of the sample at a burnup of 70 GWd / tU were calculated.

[0057] (2) The characterization results are as follows (taking Example 1 as an example):

[0058] Figure 1 It shows the XRD diffraction patterns of (Eu x Gd 1-x )2Zr2O7 (x = 0.6, 0.7, 0.8, 0.9) ceramics. By comparing the obtained results with the PDF standard card 80 - 0470 of the pyrochlore structure (P), it was found that they are all of the pyrochlore structure and no second phase was observed. This experimental result proves that the present invention has prepared a double rare earth zirconate ceramic material with a single-phase structure, and this single-phase structure helps to improve its density and maintain the stability of its performance.

[0059] Figure 2 It is the thermal conductivity of (Eu x Gd 1-x )2Zr2O7 (x = 0.6, 0.7, 0.8, 0.9) ceramics tested. The results show that the thermal conductivity of the samples ranges from 1.59 - 2.07 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 -1 ·K -1 of the currently commonly used control rod material Dy2TiO5.

[0060] Comparative Example 1

[0061] Prepare (Eu 0.6 Gd 0.4 )2Zr2O7 ceramics according to the method of Example 1, and compare it with (RE 0.6 Gd 0.4 )2Zr2O7 (RE = Tm, Sm, Er, Dy) prepared by combining it with other rare earth elements, and examine the reactivity value loss of the ceramic materials obtained by different rare earth element combinations. The results are shown in Figure 3 .

[0062] From Figure 3It can be seen that the initial reactivity value of the ceramic obtained in Example 1 is the highest and remains stable with burnup. The reduction rate of the reactivity value at a burnup of 70 GWd / tU is only 9.05%, far lower than the losses of other various double rare earth element zirconate ceramic materials (80.62%, 53.47%, 38.33%, 24.69% from largest to smallest).

[0063] Comparative Example 2

[0064] Referring to the method of the examples in Patent Document CN117326869A, xEu2O3-(1-x)Gd2Zr2O7 (x = 0.6, 0.7, 0.8, 0.85) control rod ceramics were prepared, and the hardness of the two was compared. The results are as Figure 4 . From Figure 4 It can be seen that the hardness of (Eu x Gd 1-x )2Zr2O7 (x = 0.6, 0.7, 0.8, 0.9) is twice as high as that of xEu2O3-(1-x)Gd2Zr2O7 (x = 0.6, 0.7, 0.8, 0.85). Therefore, the ceramic with higher hardness obtained in the present invention is more conducive to improving the anti-irradiation performance and is more suitable for use as a control rod under extreme conditions, while the control rod ceramics prepared in the existing patent documents cannot meet the high hardness index.

[0065] Comparative Example 3

[0066] The reactivity value and loss of the (Eu x Gd 1-x )2Zr2O7 (x = 0.6, 0.7, 0.8, 0.9) ceramics prepared in the examples were calculated and compared with the Gd2Zr2O7 ceramic material obtained by compounding gadolinium oxide and zirconia in a ratio of 1:1. The results are as Figure 5 shown. From Figure 5 It can be seen that the initial reactivity value of the ceramic in the example is higher than that of Gd2Zr2O7, and the loss of its reactivity value does not exceed 10% at a burnup of 70 GWd / tU, which can well meet the requirement of low reactivity value loss of the control rod, while the loss of the reactivity value of the Gd2Zr2O7 ceramic is as high as 86%, far exceeding the low reactivity value loss index of the present invention.

[0067] In summary, the (Eu x Gd 1-x )2Zr2O7 (x = 0.6, 0.7, 0.8, 0.9) ceramic material prepared in the present invention not only has excellent anti-irradiation performance, but also has a higher thermal conductivity and a stable reactivity value than the current materials, and its comprehensive performance is significantly better than that of traditional control rod materials in the above aspects.

[0068] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing radiation-resistant double rare earth zirconate ceramic material for reactor control rods, characterized in that: The preparation method comprises the following steps: S1, mixing europium oxide and gadolinium oxide powder with zirconium oxide powder according to the element molar ratio, adding them into a ball mill, then adding ethanol and zirconium oxide grinding balls as media for ball milling, and after the ball milling is completed, drying, grinding, sieving, and calcining to obtain a precursor powder; S2, dry-pressing the precursor powder obtained in step S1 into a green blank, vacuum-sealing the green blank, and 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 highly radiation-resistant double rare earth zirconate ceramic material for stacking.

2. The preparation method according to claim 1, characterized in that: The calcination temperature in step S1 is 1000° C. and the calcination time is 4 hours.

3. The preparation method according to claim 1, characterized in that: The size of the zirconia grinding balls in step S1 is 2 mm, and the ball milling time is 18 to 24 hours.

4. The preparation method according to claim 1, characterized in that: The sieving in step S1 is through a 200-mesh sieve.

5. The preparation method according to claim 1, characterized in that: The pressure of the dry pressing in step S2 is 3-6 MPa, and the holding time is 4-12 min; the pressure of the cold isostatic pressing is 300 MPa, and the holding time is 10 minutes.

6. The preparation method according to claim 1, characterized in that: The sintering temperature in step S3 is 1500-1700°C, preferably 1600°C.

7. The preparation method according to claim 1, characterized in that: The sintering time in step S3 is 4-12 hours, preferably 6 hours.

8. The preparation method according to claim 1, characterized in that: In step S1, the molar ratio of the raw materials is europium: gadolinium: zirconium = x: (1-x): 1, wherein x = 0.6 to 0.

9.

9. A highly radiation-resistant double rare earth zirconate ceramic material for reactor control rods prepared by the method according to any one of claims 1 to 8.

10. Use of the highly radiation-resistant double rare earth zirconate ceramic material for reactor control rods as claimed in claim 9 in the preparation of neutron absorption rod materials.

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