A boron carbide dispersion neutron absorbing material and a method of manufacturing the same and a safety rod

Abstract

A boron carbide dispersed neutron absorbing material comprises a stainless steel base, boron carbide particles and Fe2B particles, wherein the stainless steel base comprises 15-18% of Cr, 13-15% of Ni, 1.5-2.5% of Mo, Co≤0.02% and Fe as the balance by weight; the boron carbide particles are dispersed in the stainless steel base with a volume fraction of 10-40%; and the Fe2B particles are precipitated in the grains of the stainless steel base. The boron carbide dispersed neutron absorbing material has good high-temperature mechanical properties and structural stability, can effectively inhibit the corrosion of boron carbide on the stainless steel structural material at 700 DEG C or above, and can maintain stable neutron absorbing capacity for a long time. The application further provides a manufacturing method of the boron carbide dispersed neutron absorbing material and a safety rod.

Description

Technical Field

[0001] This invention belongs to the field of nuclear power, specifically relating to a boron carbide dispersed neutron absorbing material, its manufacturing method, and a safety rod. Background Technology

[0002] A heat pipe microreactor (HBR) is a novel type of reactor that utilizes heat pipe elements to transfer heat from the reactor core to the thermoelectric conversion device. It features a compact core, small size, and advantages such as safety, reliability, and flexible deployment. This reactor requires the introduction of materials with neutron absorption capabilities to control the reaction rate. Boron carbide, with its excellent neutron absorption performance, radiation resistance, and chemical stability, is one of the most commonly used neutron-absorbing materials. Currently, the commonly used reaction control component is a safety rod, clad in stainless steel, housing a neutron-absorbing core made of boron carbide to absorb fast neutrons in the reactor at temperatures not exceeding 700°C. Below 650°C, boron carbide and stainless steel cladding materials exhibit good compatibility and almost no reaction. However, above 650°C, boron diffusion accelerates, readily reacting with elements such as Fe, Cr, and Ni in the stainless steel cladding to form borides. This reduces the load-bearing area of ​​the stainless steel structure, increases stress, and raises the risk of failure. Furthermore, the absorption of neutrons by the boron carbide core produces helium (He), which causes the boron carbide core to swell, break, or even pulverize. This prevents the core from maintaining its original reactivity control structure, threatening reactor safety. Therefore, providing a stable neutron-absorbing material is of great practical value for improving the safety of nuclear reactors. Summary of the Invention

[0003] The purpose of this invention is to provide a boron carbide dispersed neutron absorbing material that reduces the corrosion of stainless steel cladding by boron carbide under high-temperature conditions. This invention also provides a method for manufacturing the boron carbide dispersed neutron absorbing material and a safety rod.

[0004] According to one aspect of the present invention, a boron carbide dispersed neutron absorber is provided, comprising a stainless steel matrix, boron carbide particles, and Fe2B particles, wherein: the composition of the stainless steel matrix, by weight ratio, includes: Cr: 15-18%; Ni: 13-15%; Mo: 1.5%-2.5%; Co ≤ 0.02%; Fe: balance; the boron carbide particles are dispersed in the stainless steel matrix, and their volume fraction is 10%-40%; the Fe2B is precipitated within the grains of the stainless steel matrix.

[0005] This boron carbide dispersed neutron absorber uses stainless steel as its matrix. When in service in a reactor, the stainless steel matrix can effectively support the boron carbide, preventing the boron carbide structure from breaking or pulverizing after neutron absorption, thus avoiding failure of the reactivity control structure. On the other hand, under high temperature conditions, the Fe element in the stainless steel matrix can react with the B element to form Fe2B with even lower energy. Even if the B element diffuses above 700°C, it can be trapped inside the stainless steel matrix, preventing it from diffusing and corroding the external stainless steel cladding.

[0006] Furthermore, in some embodiments, the boron carbide particles have a particle size of 3nm-20nm.

[0007] Furthermore, in some embodiments, the B element in the boron carbide particles... 10 The enrichment degree of B is not less than 95%. 10 B has a higher neutron capture capability, high 10 The enrichment of B enables this boron carbide dispersed neutron absorber to possess neutron absorption capabilities similar to those of pure boron carbide.

[0008] According to another aspect of the present invention, a method for manufacturing a boron carbide dispersed neutron absorber material is provided, comprising the following steps: providing stainless steel powder, wherein the composition of the stainless steel powder, by weight ratio, includes: Cr: 15-18%; Ni: 13-15%; Mo: 1.5%-2.5%; Co≤0.02%; Fe: balance; and the particle size of the stainless steel powder is 50 nm-15 μm. Providing boron carbide powder, wherein the particle size of the boron carbide powder is 1 μm-30 μm. Mixing the stainless steel powder and the boron carbide powder uniformly to obtain a mixed powder, wherein the volume ratio of the boron carbide powder in the mixed powder is 10%-40%. Sintering the mixed powder under a pressure of 100-600 MPa at 1100℃-2000℃ for 2-6 h to obtain the boron carbide dispersed neutron absorber material.

[0009] Furthermore, in some embodiments, the mixed powder is obtained by mixing the stainless steel powder and the boron carbide powder through ball milling, with a ball milling speed of 400-600 r / min and a ball milling time of 24h-120h.

[0010] Furthermore, in some embodiments, during hot isostatic pressing sintering, GdB6 or Si3N4 is added to the mixed powder as a sintering aid, wherein the sintering aid accounts for 0.1%-1.5% of the mass percentage of the mixed powder. The addition of the sintering aid can enhance the sintering activity of the mixed powder during the sintering process and improve the density of the sintered product.

[0011] Furthermore, before performing the hot isostatic pressing sintering, the mixture is further comprising a step of placing the mixed powder under vacuum or inert gas protection and holding it at 200℃-300℃ for 1h-4h.

[0012] Furthermore, in some embodiments, the B element in the boron carbide... 10 The enrichment degree of B is not less than 95%.

[0013] Furthermore, in some embodiments, the hot isostatic pressing sintering employs a graphite mold.

[0014] According to another aspect of the present invention, a safety rod is provided, comprising a stainless steel shell and a core, wherein the core is made of boron carbide diffuse neutron absorbing material provided in any of the foregoing embodiments, and the boron carbide diffuse neutron absorbing material is manufactured using the manufacturing method of boron carbide diffuse neutron absorbing material provided in any of the foregoing embodiments. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the microstructure of a dispersed boron carbide neutron absorber in one embodiment;

[0016] Figure 2 This is a schematic diagram of the safety bar structure in one embodiment.

[0017] The above-described drawings are intended to provide a detailed description of the invention so that those skilled in the art can understand the technical concept of the invention, and are not intended to limit the invention. For the sake of brevity, the above-described drawings only schematically illustrate the structures related to the technical features of the invention, and do not depict the complete device and all details strictly according to actual scale. Detailed Implementation

[0018] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings.

[0019] The term "embodiment" as used herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment herein. The phrase appearing in various places in the specification does not necessarily refer to the same embodiment, nor is it limited to mutually exclusive, independent, or alternative embodiments. Those skilled in the art will understand that the embodiments herein can be combined with other embodiments without structural conflict. In the description herein, "a plurality of" means at least two.

[0020] A heat pipe microreactor (HMR) is a novel type of reactor that utilizes heat pipe heat transfer elements to conduct core heat to the thermoelectric conversion device. It features a compact core, small size, and advantages such as safety, reliability, and flexible deployment. Internationally, HMRs typically employ reactivity control components to regulate core reactivity. Through different maneuvers such as insertion and rotation, different neutron absorption values ​​are introduced to achieve reactor power regulation and shutdown. The materials used in the reactivity control components of HMRs face extremely demanding operating conditions, including high temperatures (700°C).

[0021] The effects of ℃), neutron irradiation, oxidation, and long-term thermal aging of 5-10 years pose significant challenges to the design and selection of materials.

[0022] Currently, internationally, fast neutron spectrum reactor cores are commonly used, with drum-shaped or rod-shaped components serving as reactivity control devices. These components are clad in stainless steel to provide high-temperature support and load-bearing capacity at 700°C. The neutron absorber material is selected from high-abundance materials with strong fast neutron absorption capacity and high maturity. 10 Boron carbide (B4C), through 10 B(n,α) 7 The Li reaction traps neutrons, controlling reactivity. Below 650℃, boron carbide exhibits good compatibility with stainless steel cladding materials.

[0023] The reaction rate is low, and it hardly corrodes the cladding, reducing its thickness. However, when the temperature exceeds 650℃, boron diffusion accelerates, reacting with the main metallic elements in stainless steel such as Fe, Cr, and Ni to form borides like Fe₂B, Cr₂B, and Ni₃B. This reduces the thickness of the stainless steel cladding, decreases the load-bearing area, and increases stress, thereby increasing the risk of cladding failure and seriously threatening reactor safety. On the other hand, the helium gas produced by the nuclear reaction between boron carbide and neutrons causes the boron carbide core to swell. At high burnup levels, this can lead to core breakage or even pulverization, altering the original reactivity control structure and causing it to lose its original geometric reactivity control value, severely threatening reactor safety.

[0024] However, the power of a heat pipe microreactor is directly proportional to its core temperature. To ensure that the power of the heat pipe reactor meets application requirements, the core temperature must be raised to above 700°C. Based on the current state of research and development of structural materials and neutron-absorbing materials, and considering the material design principles and performance requirements such as mechanics, radiation resistance, oxidation resistance, and machinability, stainless steel and boron carbide are the only choices for structural materials and neutron-absorbing materials, with no other mature alternatives. However, above 700°C, the reaction rate of boron carbide and stainless steel accelerates, inevitably leading to corrosion of the cladding material over the full lifespan of the heat pipe reactor (approximately 5-10 years).

[0025] To address the aforementioned problems, embodiments of the present invention provide a boron carbide neutron dispersion-enhanced material and a method for manufacturing the same. The microstructure of this material is as follows: Figure 1 As shown, with stainless steel grains 1 as the matrix, boron carbide particles 2, accounting for 10%-40% of the total content, are dispersed in the matrix of stainless steel grains 1. The boron carbide particles 2 are dispersed within the grains and grain boundaries of the stainless steel grains 1, while a small amount of Fe2B particles 3 exist within the stainless steel grains 1 as precipitates after the reaction of B and Fe during sintering. The stainless steel composition, by weight, includes: 15-18% Cr, 13-15% Ni, 1.5%-2.5% Mo, Co ≤ 0.02%, and Fe as the balance. In a preferred embodiment, the particle size of the boron carbide particles is 1μm-30μm. In a further preferred embodiment, the B element in the boron carbide particles 2... 10 The enrichment degree of B is not less than 95%.

[0026] In the first embodiment of the present invention, the preparation process of the material is as follows:

[0027] Nuclear-grade boron carbide powder with a particle size of 3 μm and stainless steel powder with a particle size of 10 μm were loaded into a nylon ball mill at a mass ratio of 1:15 and ball-milled for 96 hours using 95% zirconia beads at a milling speed of 400 r / min. The boron carbide powder contained... 10 The enrichment of boron is 95.8%. The composition of stainless steel powder is 17.6% Cr, 15.2% Ni, 2% Mo and no more than 0.02% Co, with Fe as the balance.

[0028] The ball-milled powder is placed in a vacuum protective atmosphere and kept at 250℃ for 2 hours for preheating and drying. The inert gas can be nitrogen or argon.

[0029] The dried mixed powder was loaded into a graphite mold and sintered under hot isostatic pressing at 1300℃ for 4 hours under a pressure of 600MPa to obtain the finished boron carbide dispersed neutron absorber material, in which the volume fraction of boron carbide particles was about 20% and the size of the dispersed boron carbide particles was 3nm-20nm.

[0030] In the second embodiment of the present invention, the preparation process of the material is as follows:

[0031] Nuclear-grade boron carbide powder with a particle size of 30 μm and stainless steel powder with a particle size of 15 μm were loaded into a nylon ball mill at a mass ratio of 1:15 and ball-milled for 120 hours using 95% zirconia beads at a milling speed of 480 r / min. The boron carbide powder contained... 10The enrichment of boron is 97.2%, and the stainless steel powder composition is 17.6% Cr, 15.2% Ni, 2% Mo, and no more than 0.02% Co, with Fe as the balance. In a preferred embodiment, 0.1%-1.5% by mass of GdB6 or Si3N4 can be added as a sintering aid to improve the sintering activity of the mixed powder and promote densification during sintering.

[0032] The ball-milled powder is placed in a vacuum protective atmosphere and kept at 250℃ for 2 hours for preheating and drying. The inert gas can be nitrogen or argon.

[0033] The dried mixed powder was loaded into a graphite mold and sintered at 1800℃ for 3 hours under a pressure of 100MPa to obtain the finished boron carbide dispersed neutron absorber material, in which the volume fraction of boron carbide particles was about 20% and the size of the dispersed boron carbide particles was 3nm-20nm.

[0034] In the third embodiment of the present invention, the preparation process of the material is as follows:

[0035] Nuclear-grade boron carbide powder with a particle size of 1 μm and stainless steel powder with a particle size of 50 μm were loaded into a nylon ball mill at a mass ratio of 1:15 and ball-milled for 24 hours using 95% zirconia beads at a milling speed of 600 r / min. The boron carbide powder contained... 10 The enrichment of boron is 97.2%. The stainless steel powder composition is 17.6% Cr, 15.2% Ni, 2% Mo and no more than 0.02% Co, with Fe as the balance.

[0036] The ball-milled powder is placed in a vacuum protective atmosphere and kept at 250℃ for 2 hours for preheating and drying. The inert gas can be nitrogen or argon.

[0037] The dried mixed powder was placed into a graphite mold and sintered under hot isostatic pressing at 1500℃ for 4 hours under a pressure of 600 MPa to obtain the finished boron carbide dispersed neutron absorber material, in which the volume fraction of boron carbide particles was approximately 20%, and the size of the dispersed boron carbide particles was 3 nm-20 nm.

[0038] Another embodiment of the present invention provides a safety bar, the structure of which is as follows: Figure 2 As shown, the safety rod includes a stainless steel cladding 4 and a core 5 made of neutron-absorbing material housed within the stainless steel cladding 4. The stainless steel cladding 4 is tubular, and the cylindrical core 5 is enclosed within the cavity of the stainless steel cladding 4 by an upper plug 6 and a lower plug 9, and is compressed by a gas spring 7. The core 5 is manufactured using the boron carbide neutron-dispersing material provided in any of the aforementioned embodiments. This safety rod can be used as a reactivity control component in heat pipe microreactors or other types of reactors.

[0039] In a pair, it provides a density of 90%. 10 Pure boron carbide neutron absorber material with 90% boron enrichment.

[0040] The neutron-absorbing materials provided in the examples and comparative examples were tightly bonded to 316 stainless steel cladding and placed in a high-temperature furnace at 750°C for 90 days for chemical compatibility testing. Furthermore, the examples and comparative examples were subjected to He ion irradiation, and the mechanical properties at 750°C and the thermal conductivity after He ion irradiation are shown in Table 1.

[0041]

[0042] Table 1. Results of 90-day chemical compatibility test

[0043] As shown in Table 1, the boron carbide dispersed neutron absorber provided in this embodiment of the invention did not cause corrosion to the stainless steel cladding after 90 days of testing, while the pure boron carbide neutron absorber caused significant corrosion to the stainless steel cladding. After He ion irradiation, the thermal conductivity of the boron carbide dispersed neutron absorber provided in this embodiment is also significantly better than that of the pure boron carbide neutron absorber.

[0044] Compared to pure boron carbide neutron absorbers, the boron carbide particles in the dispersed neutron absorber provided in this embodiment of the invention are dispersed within a stainless steel matrix, avoiding direct contact with the external stainless steel cladding. Furthermore, at temperatures above 700°C, Fe₂B has a lower formation energy, allowing B to diffuse and remain within the core as Fe₂B, effectively preventing corrosion of the stainless steel cladding by B at temperatures above 700°C, thus ensuring the safety of reactivity control components in the nuclear reactor. Simultaneously, it improves… 10 The enrichment of boron (B) can further enhance neutron absorption capacity, compensating for the impact of the reduced boron carbide volume fraction.

[0045] Because the boron carbide dispersed neutron absorber material provided in this embodiment of the invention uses stainless steel as the matrix, the core made of this material exhibits good structural stability and a certain degree of plastic deformation capability under high burnup conditions. Even when the core produces a large amount of He due to neutron absorption under high burnup conditions, the core structure itself can remain stable, avoiding the loss of geometric reactivity control value caused by core pulverization. Furthermore, boron carbide particles dispersed in the stainless steel matrix can also act as trapping traps for mutable gases such as He. The dispersion of boron carbide in the stainless steel matrix can promote grain refinement and increase grain boundary area, thereby effectively trapping radiation-induced defects such as dislocation loops and precipitation phases, thus effectively reducing the number of radiation-induced defects and improving the radiation resistance of the core.

[0046] The purpose of the above embodiments is to provide a further detailed description of the present invention in conjunction with the accompanying drawings so that those skilled in the art can understand the technical concept of the present invention. Within the scope of the present invention, optimization or equivalent substitution of the components or method steps involved, as well as combination of implementation methods in different embodiments without causing structural or principle conflicts, all fall within the protection scope of the present invention.

Claims

1. A boron carbide dispersed neutron absorber, characterized in that, Includes a stainless steel matrix, boron carbide particles, and Fe2B particles. The stainless steel matrix comprises, by weight: Cr: 15%~18%; Ni: 13%~15%; Mo: 1.5%~2.5%; Co≤0.02%; Fe: balance; The boron carbide particles are dispersed in the stainless steel matrix, with a volume fraction of 10%-40%. The Fe2B precipitates within the grains of the stainless steel matrix; The boron carbide dispersed neutron absorber material is manufactured by the following method: Stainless steel powder is provided, wherein the composition of the stainless steel powder by weight includes: Cr: 15~18%; Ni: 13%~15%; Mo: 1.5%~2.5%; Co≤0.02%; Fe: balance; and the particle size of the stainless steel powder is 50nm-15μm. Boron carbide powder is provided, wherein the particle size of the boron carbide powder is 1μm-30μm; The stainless steel powder and the boron carbide powder are mixed evenly to obtain a mixed powder, wherein the volume ratio of the boron carbide powder in the mixed powder is 10%-40%. The mixed powder was subjected to hot isostatic pressing sintering at 1100℃-2000℃ under a pressure of 100-600MPa for 2-6 hours to obtain boron carbide dispersed neutron absorber material. During hot isostatic pressing sintering, GdB6 or Si3N4 is added to the mixed powder as a sintering aid, and the sintering aid accounts for 0.1%-1.5% of the mass percentage of the mixed powder.

2. The boron carbide dispersed neutron absorber material according to claim 1, characterized in that, The boron carbide particles have a particle size of 3nm-20nm.

3. The boron carbide dispersed neutron absorber material according to claim 1 or 2, characterized in that, The B element in the boron carbide particles 10 The enrichment degree of B is not less than 95%.

4. A method for manufacturing a boron carbide dispersed neutron absorber, characterized in that, The method for manufacturing boron carbide dispersed neutron absorber material as described in any one of claims 1 to 3 includes the following steps: Stainless steel powder is provided, wherein the composition of the stainless steel powder by weight includes: Cr: 15%~18%; Ni: 13%~15%; Mo: 1.5%~2.5%; Co≤0.02%; Fe: balance; and the particle size of the stainless steel powder is 50nm-15μm. Boron carbide powder is provided, wherein the particle size of the boron carbide powder is 1μm-30μm; The stainless steel powder and the boron carbide powder are mixed evenly to obtain a mixed powder, wherein the volume ratio of the boron carbide powder in the mixed powder is 10%-40%. The mixed powder was subjected to hot isostatic pressing sintering at 1100℃-2000℃ under a pressure of 100-600MPa for 2-6 hours to obtain boron carbide dispersed neutron absorber material.

5. The method for manufacturing boron carbide dispersed neutron absorber material according to claim 4, characterized in that, The mixed powder is obtained by mixing the stainless steel powder and the boron carbide powder through ball milling. The ball milling speed is 400-600 r / min and the ball milling time is 24h-120h.

6. The method for manufacturing boron carbide dispersed neutron absorber material according to claim 4, characterized in that, Before performing the hot isostatic pressing sintering, the process also includes placing the mixed powder in a vacuum or inert gas protective atmosphere and holding it at 200℃-300℃ for 1h-4h.

7. The method for manufacturing the boron carbide dispersed neutron absorber material according to any one of claims 4 to 6, characterized in that, In the boron carbide, the B element 10 The enrichment degree of B is not less than 95%.

8. The method for manufacturing the boron carbide dispersed neutron absorber material according to any one of claims 4 to 6, characterized in that, The hot isostatic pressing sintering process uses a graphite mold.

9. A safety bar, comprising a stainless steel shell and a core, characterized in that, The core is made of boron carbide dispersed neutron absorbing material as described in any one of claims 1 to 3, and the boron carbide dispersed neutron absorbing material is manufactured using the manufacturing method of boron carbide dispersed neutron absorbing material as described in any one of claims 5 to 8.

Images