A low-reactivity, value-loss single-component rare-earth hafnium salt ceramic material and its preparation method

Abstract

This invention provides a low-reactivity-value-loss single-component rare-earth hafnium salt ceramic material and its preparation method, belonging to the technical field of nuclear reactor control rod materials. This invention uses a solid-state method to prepare the powder, solving the cumbersome process problems of previous methods for preparing highly sintered active powders, and has the advantages of wide application range, simple operation, and favorable application scenarios. The invention also uses vacuum sintering technology to prepare a hafnium salt ceramic material with high density, high transmittance, and excellent mechanical and thermal properties, showing good application prospects in reactor control rod materials, magneto-optical deflectors, and other fields. The single-component rare-earth hafnium salt ceramic material developed in this invention has the advantage of extremely low reactivity-value-loss, while also possessing high transmittance, a simple preparation method, and a long service life, making it well-suited for use in the field of nuclear reactor control rod materials.

Description

Technical Field

[0001] This invention belongs to the field of nuclear reactor control rod materials technology, specifically relating to a low-reactivity, value-loss single-component rare-earth hafnium salt ceramic material and its preparation method. Background Technology

[0002] Nuclear energy is a major contributor to clean energy, particularly in the development of low-carbon energy technologies and the global goal of world economic prosperity and stability. The safe and economical operation of current advanced nuclear energy systems largely depends on the performance of fuels and materials. Among nuclear engineering materials, control rods are key components used in nuclear power reactors to compensate for and regulate core reactivity, ensuring the long-term safe operation of the core. For control rod materials, firstly, they are required to have a large neutron absorption cross-section and a high initial reactivity value. Secondly, control rod materials are required to have a long lifetime, which necessitates a high number of absorber nucleons per unit volume, low reactivity value loss, and the daughter nuclei formed after neutron absorption also need to have a large absorption cross-section, so that their neutron absorption capacity is not affected by their own "burnup." Finally, control rod materials are required to have radiation resistance, corrosion resistance, and good mechanical and thermal properties.

[0003] In recent years, some rare earth elements have attracted much attention due to their high neutron absorption cross section and long neutron burnup chain, and researchers have long sought to utilize the (n, γ) reaction absorption of thermal neutrons in rare earth-based materials to replace boron materials. 10 The (n, α) reaction of B.

[0004] Traditional control rod materials are mainly made of boron carbide (B4C) or boron steel, silver-indium-cadmium alloys, and hafnium. Boron carbide (B4C) or boron steel has high neutron absorption capacity and does not produce secondary radiation pollution, but... 10 The (n,α) reaction of boron accumulates a large number of irradiation defects, leading to the formation of He bubbles and causing material swelling, resulting in rod jamming. Furthermore, boron carbide control rods experience a reactivity value loss exceeding 50% within five years, indicating excessive loss and a short service life. Silver-indium-cadmium (Ag-In-Cd) alloys also possess highly efficient neutron absorption performance and can rapidly introduce negative reactivity, enabling emergency reactor shutdown and ensuring nuclear safety. However, Ag and In undergo transmutation after neutron absorption, producing a low-density second phase that precipitates, causing swelling. Silver-indium-cadmium materials also experience a reactivity value loss exceeding 15% within five years of service, and are expensive, resulting in excessive cost. Metallic hafnium has a high thermal neutron trapping cross-section and is resistant to high temperatures and corrosion. However, under irradiation, hafnium alloys are prone to vacancies and defects, leading to irradiation swelling and fatigue fracture, significantly reducing the service life and reliability of hafnium alloy control rods.

[0005] For example, patent document CN 114988869 A (publication date: September 2, 2022) provides a rare-earth high-entropy hafnium salt-based ceramic material and its preparation method. The chemical formula of this high-entropy rare-earth hafnium salt ceramic material is: (RE a Tm b Dy c M d )4Hf3O 12 RE is selected from at least one of Tb, Ho, and Gd; M is selected from Eu and / or Er. This hafnium-based ceramic material is prepared by the sol-gel method and is mainly used to improve the radiation resistance of neutron absorber materials. However, this hafnium-based ceramic material suffers from high reactive value loss, which affects its service life. At the same time, its transmittance is low, making it impossible to prepare hafnium-based ceramic materials with high transparency.

[0006] A₂B₂O₇ oxide is considered a promising radiation-resistant material for current and advanced nuclear systems due to its flexible crystal structure, ability to accommodate actinides, and excellent thermal stability and chemical durability under extreme conditions. Rare-earth hafnium salts, such as RE₂Hf₂O₇, possess high melting points and excellent high-temperature stability. The Hf element has a high neutron absorption cross section, and its daughter nuclei also have high neutron absorption cross sections, for example... 177 Hf, which forms after capturing neutrons 178 Hf, the latter forms 179 Hf and others all have large resonant absorption cross sections, and as neutron absorbers, they have the potential for long-life service.

[0007] For example, patent document CN 115572162 A (publication date: January 6, 2023) provides a rare-earth high-entropy hafnium carbonate ceramic material for neutron control in reactors. The chemical formula of the rare-earth high-entropy hafnium carbonate ceramic material is: (RE 0.2 Sm 0.2 Eu 0.2 Dy 0.2 Er 0.2 )2Hf2O7, where RE is Nd or Gd. The chemical formula of rare earth entropy hafnium salt ceramics is: (Sm 1 / 3Eu 1 / 3 Gd 1 / 3 )2Hf2O7. However, this hafnium salt ceramic material suffers from high reactive value loss and low transmittance, making it impossible to prepare hafnium salt ceramic materials with high transparency.

[0008] Therefore, how to prepare a ceramic control rod material based on hafnium salts that has a simple preparation process, low reactive value loss, good neutron absorption performance, excellent mechanical and thermal properties, corrosion resistance and long service life, and high transmittance, so as to prepare high-transparency hafnium salt ceramic materials, has become an important problem that urgently needs to be solved. Summary of the Invention

[0009] This invention aims to solve the aforementioned technical problems by providing a low-reactivity-value-loss single-component rare-earth hafnium carbonate ceramic material and its preparation method. The technical objective of this invention is to combine rare-earth elements with good neutron absorption properties (such as Eu, Gd, Tb, Dy, Tm) with radiation-resistant RE2M2O7 (M=Hf) type oxide substrates to prepare a single-component hafnium carbonate ceramic control rod material with lower reactivity-value-loss than existing materials and meeting reactor service requirements, while also achieving high transparency in this material.

[0010] To achieve the above objectives, the technical solution adopted by this invention is as follows: a method for preparing highly dense single-component rare earth hafnium salts by solid-state molding combined with vacuum sintering, comprising the following steps:

[0011] (1) Rare earth oxide (Eu2Hf2O7, Gd2Hf2O7, Tb2Hf2O7, Dy2Hf2O7, Tm2Hf2O7) powder and hafnium oxide powder are dried to remove crystal water, mixed in a certain stoichiometric ratio, ball-milled, dried, ground and sieved to obtain fine powder. The fine powder is calcined at 1300-1600℃ for 4 hours to obtain pure phase mixed powder. After cooling to room temperature, the pure phase powder is ball-milled, dried, ground and sieved to finally obtain uniform single-component hafnium salt (Eu2Hf2O7, Gd2Hf2O7, Tb2Hf2O7, Dy2Hf2O7, Tm2Hf2O7) precursor powder with good sintering activity;

[0012] (2) Add the precursor powder obtained in step (1) into the mold, press it for 2-5 minutes under a pressure of 2-6 MPa, press it to form a blank, place the blank in a cold isostatic press, and hold it under a pressure of 250-300 MPa for 10-15 minutes to obtain a dense blank.

[0013] (3) The dense green blank obtained in step (2) is placed in a vacuum environment and sintered at 1850°C for 8 hours to obtain pure phase ceramic. The obtained pure phase ceramic is annealed and polished to finally obtain a highly dense single-component hafnium salt ceramic material.

[0014] To investigate the reactive value loss of the selected materials, this invention conducted theoretical preliminary studies on single-component, two-component, and multi-component rare earth hafnium salt systems, calculating the reactive value loss of single-component Eu₂Hf₂O₇ and two-component (Eu₂Hf₂O₇) hafnium salt systems. 1 / 2 ,Gd 1 / 2)2Hf2O7, three-component (Eu) 1 / 3 ,Gd 1 / 3 ,Tb 1 / 3 )2Hf2O7, four-component (Eu) 1 / 4 ,Gd 1 / 4 ,Tb 1 / 4 ,Dy 1 / 4 )2Hf2O7 and the five-component (Eu) 1 / 5 ,Gd 1 / 5 ,Tb 1 / 5 ,Dy 1 / 5 ,Tm 1 / 5 The five-year reactive value loss of hafnium 2Hf2O7 ceramic materials was investigated. The results showed that the initial reactive value loss of hafnium 2Hf2O7 ceramic materials decreased with increasing component concentration, while the five-year loss increased with increasing component concentration. The experimental results indicate that single-component hafnium esters exhibit superior initial performance and lower value loss compared to multi-component materials, with Eu2Hf2O7 and Dy2Hf2O7 showing a five-year loss of only about 5%.

[0015] Therefore, the inventors designed five single-component rare-earth hafnium salt ceramic materials using a single-component RE₂Hf₂O₇ type rare-earth hafnium salt as the structural framework, and selected rare-earth elements Eu, Gd, Tb, Dy, and Tm at the RE sites based on the high neutron absorption cross-section. They successfully prepared hafnium salt ceramic materials with high transmittance, which not only fills the gap in the application research of single-component rare-earth hafnium salt ceramics, but also successfully achieved a transmittance of over 92% of the theoretical transmittance. Therefore, the method of this invention provides an important material for the future use of control rods, obtaining a class of neutron absorbing materials with high density, low reactive value loss, high transparency, and promising long service life.

[0016] The preparation method provided by this invention successfully prepared single-component rare earth hafnium salts (Eu₂Hf₂O₇, Gd₂Hf₂O₇, Tb₂Hf₂O₇, Dy₂Hf₂O₇, Tm₂Hf₂O₇) ceramic materials with high density, high transmittance, and low reactive value loss. Specifically, the reactive value loss of europium hafnium oxide (Eu₂Hf₂O₇) and dysprosium hafnium oxide (Dy₂Hf₂O₇) is as low as approximately 5% over 5 years. This is expected to meet the requirement of less than 10% reactive value loss over 15 years proposed by novel control strategies and satisfy the long service life of control rods. Furthermore, the preparation method of this invention has advantages such as simple process, no need for sintering aids, ease of operation, and no gas pollution.

[0017] The preparation method of the single-component RE2Hf2O7 type rare earth hafnium salt ceramic material provided by this invention is not inspired by existing technologies. Currently developed hafnium salt ceramic materials are generally multi-component materials, and there is no discussion on how to develop single-component materials. Therefore, those skilled in the art are unaware of the specific process conditions required for the development of single-component materials. However, the method provided by this invention, when preparing single-component ceramic materials, has been found to have extremely low reactivity loss compared to multi-component hafnium salt ceramic materials, a characteristic that multi-component ceramic materials cannot possess. Furthermore, the method of this invention yields hafnium salt ceramic materials with extremely high transparency, which exceeds expectations. Existing methods generally do not possess high transparency and are essentially opaque ceramic materials.

[0018] Furthermore, in step (1), both the rare earth oxide and hafnium oxide are high-purity oxides with a purity >99.9%, and the molar ratio of the rare earth oxide to hafnium oxide is 1:2.

[0019] Furthermore, the ball milling process in step (1) is as follows: the oxide mixed powder is added to a nylon ball milling jar with alcohol as the medium and milled for 20 hours, the ball-to-material ratio is controlled to be 27:1 (mass ratio) and the ball milling speed is 300 r / min.

[0020] Furthermore, the drying process in step (1) is as follows: the slurry obtained after ball milling is poured into a glass container and dried at 70-80°C for 24 hours.

[0021] Furthermore, the sieving in step (1) is sieving through a 300-mesh sieve.

[0022] Furthermore, the vacuum environment in step (3) is a vacuum degree of 10. -2 ~10 -4 Pa; the annealing temperature is 1300-1400℃, and the annealing time is 3-4h.

[0023] This invention also provides five single-component rare earth hafnium salt ceramics prepared by the above method. These ceramic pillars have the characteristics of high density, low reactive value loss, and long service life.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] (1) This invention prepares powder by solid-state method, which solves the cumbersome process problem of preparing high sintering active powder in the past. It has the advantages of wide application range, simple operation and good application scenarios.

[0026] (2) The method of the present invention has obtained a single-component hafnium salt with excellent low loss performance and prepared a hafnium salt ceramic material with high density, high transmittance and excellent mechanical and thermal properties, which has good application prospects in reactor control rod materials, magneto-optical deflectors and other fields.

[0027] (3) By using single-component hafnium salt pure phase powder as precursor powder, this invention avoids the effects caused by phase transformation during sintering, and vacuum sintering has no gas pollution, so it is very harmless to the human body and the environment. Attached Figure Description

[0028] Figure 1 The initial reactivity value and five-year loss of five different hafnium salt components were theoretically calculated: (a) the value loss of the five hafnium salt components over time; (b) the rate of change of the value loss of the five hafnium salt components over time.

[0029] Figure 2 Images of five single-component rare earth hafnium salt (Eu2Hf2O7, Gd2Hf2O7, Tb2Hf2O7, Dy2Hf2O7, Tm2Hf2O7) ceramic samples.

[0030] Figure 3 XRD patterns of five single-component rare earth hafnium salts (Eu2Hf2O7, Gd2Hf2O7, Tb2Hf2O7, Dy2Hf2O7, Tm2Hf2O7).

[0031] Figure 4 Mechanical properties of five single-component rare earth hafnium salts (Eu2Hf2O7, Gd2Hf2O7, Tb2Hf2O7, Dy2Hf2O7, Tm2Hf2O7): (a) hardness and fracture toughness; (b) bulk modulus, Young's modulus and shear modulus.

[0032] Figure 5 Thermal conductivity and coefficient of thermal expansion of five single-component rare earth hafnium salts (Eu2Hf2O7, Gd2Hf2O7, Tb2Hf2O7, Dy2Hf2O7, Tm2Hf2O7): (a) thermal conductivity; (b) coefficient of thermal expansion. Detailed Implementation

[0033] 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.

[0034] Example 1

[0035] The sources of the powder raw materials involved in all embodiments of the present invention are as follows:

[0036] Eu2O3 (purity 99.99%, Shanghai Aladdin Biochemical Technology Co., Ltd.);

[0037] Gd2O3 (purity 99.99%, Shanghai Aladdin Biochemical Technology Co., Ltd.);

[0038] Tb2O3 (purity 99.99%, Shanghai Aladdin Biochemical Technology Co., Ltd.);

[0039] Dy2O3 (purity 99.99%, Shanghai Aladdin Biochemical Technology Co., Ltd.);

[0040] Tm2O3 (purity 99.99%, Shanghai Aladdin Biochemical Technology Co., Ltd.);

[0041] HfO2 (purity 99.9%, Beijing Huawiruike Chemical Co., Ltd.).

[0042] This embodiment prepares single-component rare earth hafnium salt ceramics by solid-state method combined with vacuum sintering, including the following steps:

[0043] (1) Preparation of precursor powder: Europium oxide and hafnium oxide, gadolinium oxide and hafnium oxide, terbium oxide and hafnium oxide, dysprosium oxide and hafnium oxide, and thulium oxide and hafnium oxide were weighed according to a stoichiometric ratio of 1:2 and added to a nylon ball mill jar with alcohol as the medium for ball milling (ball milling in ethanol at a speed of 300 r / min for 20 hours to obtain a uniformly mixed slurry, with a ball-to-powder mass ratio of 27:1). The obtained slurry was filtered into a glass container and dried at 70°C for 24 hours. The dried powder was then... After sieving (300 mesh), the powder was placed in a muffle furnace and calcined at 1300℃ for 4 hours to obtain a single-component rare earth hafnium salt precursor powder. The heating rate was 3℃ / min, and after cooling to room temperature, the cooling rate was 4℃ / min. The obtained powder was then subjected to the same ball milling, drying, and sieving as described above to obtain a uniform single-component rare earth hafnium salt (Eu2Hf2O7,Gd2Hf2O7,Tb2Hf2O7,Dy2Hf2O7,Tm2Hf2O7) pure phase precursor powder with good sintering activity.

[0044] (2) Molding: The dry pressing method combined with the cold isostatic pressing process is used to obtain a single-component rare earth hafnium salt ceramic blank. The specific process is as follows: the precursor powder obtained in step (1) is added into a customized metal mold, the mold is placed in a dry press, and the pressure is maintained at 2MPa for 2 minutes. Then the blank is taken out, vacuum sealed and placed in a cold isostatic press, and maintained at 250MPa for 10 minutes to obtain a relatively dense blank.

[0045] (3) Sintering: The prepared single-component rare earth hafnium salt dense green blank is placed in a vacuum of 10 -4 The ceramic sample was obtained by sintering at 1850℃ for 8 hours under a vacuum of Pa.

[0046] (4) Processing: The sintered ceramics are processed into columnar bodies with a diameter of 8.5 mm and a height of 15 mm and circular pieces with a diameter of 12.5 mm and a thickness of 2 mm.

[0047] Example 2

[0048] Single-component rare earth hafnium salt ceramics were prepared according to the method in Example 1, with the following difference:

[0049] In step (1), the product is dried at 80°C for 24 hours and then calcined in a muffle furnace at 1600°C for 4 hours.

[0050] In step (2), the blank is held under 6MPa pressure for 5 minutes and under 300MPa pressure for 15 minutes to obtain a relatively dense green blank;

[0051] In step (3), at a vacuum degree of 10 -3 Under a vacuum of Pa, it was annealed at 1400℃ for 4 hours.

[0052] Example 3

[0053] Single-component rare earth hafnium salt ceramics were prepared according to the method in Example 1, with the following difference:

[0054] In step (1), the product is dried at 80°C for 24 hours and then calcined in a muffle furnace at 1400°C for 4 hours.

[0055] In step (2), the blank is held at 3 MPa for 3 minutes and at 280 MPa for 12 minutes to obtain a relatively dense green blank;

[0056] In step (3), at a vacuum degree of 10 -2 Sintered under vacuum at Pa and annealed at 1350°C for 3.5 hours.

[0057] Test Example 1

[0058] The ceramic samples prepared in Examples 1-3 were subjected to performance tests, and the test methods are as follows:

[0059] X-ray diffraction (XRD, X-2700, Dandong Oriental, China) was performed using nickel-filtered Cu Kα1 radiation. The diffraction pattern is recorded in the range of 2θ (10° to 70°) with a resolution of 0.05° / step.

[0060] Vickers hardness (H) VThe Vickers indentation method (Buehler, Omnimet MHT, Lake Bluff, USA) was used to measure the hardness under a load of up to 2 N. Before measurement, the sample surface was carefully polished with diamond abrasive. The Vickers hardness was calculated according to equation (1):

[0061]

[0062] In equation (1), F is the indentation load and d is the length of the indentation diagonal; each sample is measured 7 times to reduce experimental uncertainty, and then the average value is calculated.

[0063] The longitudinal (V) of each component of hafnium salt ceramic samples was measured using an ultrasonic pulse generator / receiver device (TECLAB, UMS-100, Chelles, France). L ) and lateral (V) T Speed ​​of sound.

[0064] V L and V T Calculate the following different parameters:

[0065] bulk modulus:

[0066] Young's modulus:

[0067] Shear modulus:

[0068] The thermal expansion coefficient of sintered ceramics was measured using a thermal analyzer (DIL 402 Expedis Supreme, NETZSCH, Germany), and the thermal diffusivity (α) of the samples was measured using a laser thermal conductivity meter (LFA 457, NETZSCH, Germany). The thermal conductivity was calculated from the thermal diffusivity, specific heat, and bulk density. The bulk density ρ was measured using the Archimedes method, and all measured densities were >97%. Cp is the specific heat, calculated using the Neumann-Kop rule.

[0069] k=αρCp(5)

[0070] Example 1

[0071] Taking Example 1 as an example (the results of other examples are not significantly different), the reactivity value and loss rate of the single-component rare earth hafnium salt ceramics prepared in the examples are as follows: Figure 1 As shown, the initial reactivity value can reach a maximum of 44 × 10⁻⁶. 3The pcm is 1.3 times the initial value of existing materials such as silver-indium-cadmium (Ag-In-Cd) alloy and dysprosium titanate material. The reactive value loss rate is the lowest at about 5% within 5 years, which is far lower than that of existing materials such as B4C (5-year loss >50%), silver-indium-cadmium alloy (5-year loss >15%), and dysprosium titanate material (5-year loss >10%). According to the above calculation results, it is confirmed that the reactive value loss of the single-component hafnium salt material in Example 1 is better than that of two-component and multi-component high-entropy hafnium salt materials, and it has a longer service life.

[0072] The physical image of the single-component hafnium salt (Eu2Hf2O7, Gd2Hf2O7, Tb2Hf2O7, Dy2Hf2O7, Tm2Hf2O7) ceramic bulk prepared in the example is shown below. Figure 2 As shown in the figure, the sample surface is flat and smooth without any damage, and the ceramic sample has achieved high transmittance. Among them, the transmittance of Tb2Hf2O7 material reached 92% of the theoretical transmittance, while the transmittance of other ceramic samples was slightly lower, but the difference was not significant.

[0073] The XRD pattern of the single-component hafnium salt prepared in the example is shown below. Figure 3 As shown, the Eu2Hf2O7, Gd2Hf2O7, and Tb2Hf2O7 in the prepared single-component rare earth hafnium oxide ceramics have pyrochlore structures, while Dy2Hf2O7 and Tm2Hf2O7 have defective fluorite structures. At the same time, the characteristic peaks of the five samples are free of impurity peaks and have good crystallinity, indicating that the prepared products have complete crystal forms.

[0074] The mechanical properties of the single-component hafnium salts prepared in the examples are as follows: Figure 4 As shown, the single-component hafnium salt (Eu2Hf2O7,Gd2Hf2O7,Tb2Hf2O7,Dy2Hf2O7,Tm2Hf2O7) ceramics have high hardness and low toughness, and are classified as brittle materials.

[0075] The thermal properties of the single-component hafnium salts prepared in the examples are as follows: Figure 5 As shown, the thermal expansion coefficient of the single-component rare earth hafnium oxide ceramic increases linearly with increasing temperature, indicating that the prepared sample has excellent high-temperature phase stability, high density, and its thermal conductivity is significantly higher than that of the existing material dysprosium titanate. It is evident that it is an important material that can be used in the future reactor control rod material system.

[0076] Comparative Example 1

[0077] Testing of various ceramic materials prepared in patent CN 114988869 A revealed that their transmittance was only 32-43% of the theoretical transmittance.

[0078] Comparative Example 2

[0079] Tests on various ceramic materials prepared in patent CN 115572162 A revealed that their transmittance was only 30-35% of the theoretical transmittance.

Claims

1. A method for preparing a low-reactivity, value-loss-inefficient single-component rare-earth hafnium salt ceramic control rod material, characterized in that, Includes the following steps: (1) Take rare earth oxide and hafnium oxide raw material powder, mix them at a molar ratio of rare earth oxide to hafnium oxide of 1:2, grind them, and then calcine the refined powder at 1300-1600℃ for 4 hours to obtain pure phase powder. After cooling to room temperature, ball mill, dry, grind and sieve the pure phase powder to obtain uniform, single-component hafnium salt precursor powder with good sintering activity; the rare earth oxide is europium oxide, gadolinium oxide, dysprosium oxide or thulium oxide, and the purity of the rare earth oxide is greater than 99%. 0.9%; the single-component hafnium salt precursor powder is Eu2Hf2O7, Gd2Hf2O7, Dy2Hf2O7 or Tm2Hf2O7; the ball milling process of the pure phase powder is as follows: the pure phase powder is added to a nylon ball milling jar with alcohol as the medium and ball milled for 20 hours, the ball-to-material weight ratio is controlled at 27:1 and the ball milling speed is 300 r / min; (2) Add the precursor powder obtained in step (1) into the mold, press it for 2-5 minutes under a pressure of 2-6 MPa, press it to form a preform, place the preform in a cold isostatic press, and hold it under a pressure of 250-300 MPa for 10-15 minutes to obtain a dense preform. (3) The dense green blank obtained in step (2) is placed in a vacuum environment and sintered at 1850°C for 8 hours to obtain pure phase ceramic. The obtained pure phase ceramic is annealed and polished to finally obtain a highly dense single-component hafnium salt ceramic control rod material.

2. The preparation method according to claim 1, characterized in that, The rare earth oxide powder and hafnium oxide powder mentioned in step (1) are dried to remove the water of crystallization.

3. The preparation method according to claim 1 or 2, characterized in that, The rare earth oxide and hafnium oxide raw material powders mentioned in step (1) are ball-milled, dried, ground and sieved to obtain fine powders.

4. The preparation method according to claim 1 or 2, characterized in that, The drying process in step (1) is as follows: the slurry obtained after ball milling is poured into a glass container and dried at 70-80°C for 24 hours; the sieving is done through a 300-mesh sieve.

5. The preparation method according to claim 1 or 2, characterized in that, The vacuum environment mentioned in step (3) is a vacuum degree of 10. -2 ~10 -4 Pa.

6. The preparation method according to claim 1 or 2, characterized in that, The annealing temperature in step (3) is 1300-1400℃, and the annealing time is 3-4h.

7. A low-reactivity, value-loss single-component rare-earth hafnium salt ceramic control rod material prepared by the method according to any one of claims 1-6.

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