High temperature resistant composite neutron moderating material and method of making

Abstract

The application relates to a high-temperature-resistant composite neutron moderator material and a manufacturing method thereof, and belongs to the nuclear power field. The manufacturing method of the high-temperature-resistant composite neutron moderator material comprises the following steps: determining the hydrogen partial pressure of a metal hydride at a working temperature, establishing a moderator material particle model comprising a metal hydride core, a buffer layer and a SiC sealing layer and calculating the stress borne by the SiC sealing layer at the working temperature; calculating the allowable stress of the SiC sealing layer at the working temperature and adjusting the moderator material particle model according to the allowable stress to obtain a corrected moderator material particle model; and manufacturing a high-temperature-resistant composite neutron moderator material finished product based on the corrected moderator material particle model. The method can be used for manufacturing a neutron moderator material with good stability and reliability at a high temperature, and improves the safety and reliability of a commercial nuclear power plant reactor.

Description

Technical Field

[0001] This invention belongs to the field of nuclear power, specifically relating to a high-temperature resistant composite neutron moderator material and its manufacturing method. Background Technology

[0002] Fourth-generation reactors, such as high-temperature gas-cooled reactors, molten salt reactors, microreactors, and space reactors, operate at much higher temperatures than traditional pressurized water reactors. This places higher demands on the heat resistance of neutron moderators, with some solutions requiring them to operate stably at 600°C for extended periods. Among existing neutron moderators, metal hydrides exhibit good high-temperature tolerance, maintaining a high hydrogen atom density at high temperatures. However, even metal hydrides, such as yttrium hydride, are at risk of thermal decomposition at high temperatures. As temperature increases, the equilibrium partial pressure of hydrogen released by the metal hydride rises rapidly, leading to a decline in moderation performance and structural instability. Therefore, providing a method for manufacturing moderators that improves the stability of metal hydrides under high-temperature conditions is of high practical value. Summary of the Invention

[0003] The purpose of this invention is to provide a method for manufacturing a high-temperature resistant composite neutron moderator, thereby improving the high-temperature stability of the neutron moderator. This invention also provides a high-temperature resistant composite neutron moderator.

[0004] According to one embodiment of the present invention, a method for manufacturing a high-temperature resistant composite neutron moderator material is provided, the method comprising the following steps: Step a): Provide the operating temperature T1 of the high-temperature resistant composite neutron moderator material and determine the hydrogen partial pressure of the metal hydride at T1; Step b): Establish a moderating material particle model, which includes a metal hydride core, a buffer layer, and a SiC sealing layer from the inside out; calculate the stress generated by the hydrogen partial pressure on the SiC sealing layer under T1 based on the outer diameter of the moderating material particle model, the initial thickness of the SiC sealing layer, and the size of the metal hydride core. Step c): Calculate the allowable stress σ of the SiC sealing layer at T1, where σ = σ0[-ln(1-P)]. 1 / m Calculations are performed, where σ0 is the characteristic strength of SiC, P is the failure rate, and m is the Weibull modulus. Based on the calculated allowable stress, the thickness of the SiC sealing layer and the size of the metal hydride core are adjusted to obtain a modified model for the moderating material particles. Step d): Based on the modified model of the moderating material particles, manufacture the finished high-temperature resistant composite neutron moderating material.

[0005] This method encloses hydrogen gas inside each moderator material particle by setting a SiC sealing layer, which enables the moderator material particles to maintain the stability of the overall structure at high temperatures. This avoids changes in the spatial distribution of the moderator material caused by the decomposition and breakage of metal hydrides, effectively increases the service temperature of the neutron moderator material, reduces the risk of hydrogen leakage or migration, and improves the overall safety of the reactor.

[0006] Furthermore, in some embodiments, in step d), metal hydride particles are provided as the metal hydride core, and the buffer layer and the SiC sealing layer are sequentially deposited on the metal hydride core using a chemical vapor deposition process.

[0007] Furthermore, in some embodiments, step d) further includes the step of depositing a pyrolytic carbon layer on the surface of the SiC sealing layer.

[0008] Furthermore, in some embodiments, in step a), the hydrogen partial pressure p1 of the metal hydride at T1 is determined by the following method: Provide the hydrogen partial pressure p2 of the metal hydride at a reference temperature T2, according to The solution ln(p1 / p2) = -(1 / T1 - 1 / T2)ΔH / R is used to obtain p1, where R is the ideal gas constant and ΔH is the enthalpy of formation.

[0009] Furthermore, in some embodiments, 800°C <T2<1100℃。

[0010] Furthermore, in some embodiments, the metal hydride is yttrium hydride or zirconium hydride, and the buffer layer is made of porous pyrolytic carbon.

[0011] According to another embodiment of the present invention, a high-temperature resistant composite neutron moderator material is provided, comprising, from the inside out, a metal hydride core, a buffer layer and a SiC sealing layer, and is manufactured using the manufacturing method of the high-temperature resistant composite neutron moderator material provided in any of the foregoing embodiments.

[0012] Furthermore, in some embodiments, the metal hydride core is composed of YH. x , where 1.7≤x≤2.

[0013] Furthermore, in some embodiments, the buffer layer is porous pyrolytic carbon.

[0014] Furthermore, in some embodiments, the surface of the SiC sealing layer is further provided with a pyrolytic carbon layer. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the particle structure of the composite neutron moderator material in one embodiment.

[0016] Meaning of the reference numerals in the attached figures: 1-Metal hydride core; 2-Buffer layer; 3-SiC sealing layer.

[0017] The purpose of the above figures is to provide a detailed description of the invention so that those skilled in the art can understand the technical concept of the invention, and not to limit the invention. 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 causing structural conflicts.

[0020] In this article, "multiple" means at least two.

[0021] Metal hydrides, such as yttrium hydride, are among the most promising neutron moderator materials for commercial nuclear power plants. Under normal operating conditions in pressurized water reactors, metal hydrides exhibit good thermal stability and can maintain a high hydrogen atom density, thus ensuring effective neutron moderation over extended periods. However, with the development of Generation IV nuclear reactor technology, the design operating temperature of new reactors is significantly higher than that of existing pressurized water reactors, leading to significant instability in metal hydrides. At high temperatures, the equilibrium partial pressure of hydrogen released from the decomposition of metal hydrides increases significantly. Hydrogen loss and decomposition of metal hydrides affect the uniformity of hydrogen atom distribution, causing a decline in moderation performance, and can also lead to damage to the moderator material, affecting its structural stability. The lack of neutron moderator materials suitable for the high-temperature operating conditions of Generation IV reactors has become a significant factor restricting the construction of new commercial nuclear power plants.

[0022] To address the aforementioned problems in the prior art, one embodiment of the present invention provides a high-temperature resistant composite neutron moderator material, the structure of which is as follows: Figure 1As shown, the entire structure is granular, with an inner layer of metal hydride core 1 and an outer layer of SiC sealing layer 3. A buffer layer 2 fills the space between the metal hydride core 1 and the SiC sealing layer 3. The metal hydride core 1 plays a primary role in neutron moderation; while the SiC sealing layer 3 encapsulates the metal hydride core 1, providing sealing and support. Under high-temperature conditions, the ceramic SiC sealing layer 3 maintains its structural stability. Even if the metal hydride core 1 pulverizes or dehydrogenates after long-term service, the broken metal hydride and escaped hydrogen are confined within the SiC sealing layer 3, preventing changes in the spatial distribution of the metal hydride from affecting the overall moderation effect. The buffer layer 2 provides a buffer space for the escaped hydrogen and the thermal deformation difference between the metal hydride core 1 and the SiC sealing layer 3. When the metal hydride core 1 undergoes dehydrogenation at high temperatures, the pressure within the SiC sealing layer 3 increases rapidly. If the thickness of the SiC sealing layer 3 is too low, there is a risk of breakage and failure; conversely, if the SiC sealing layer 3 is too thick, the hydrogen atom density will be insufficient, affecting the neutron moderation performance. Therefore, this high-temperature resistant composite neutron moderator material needs to be manufactured using the manufacturing method for high-temperature resistant composite neutron moderator material provided in another aspect of this application. The specific steps are as follows: Step a): Provide the operating temperature T1 of the neutron moderator material and determine the hydrogen partial pressure p1 of the metal hydride at that temperature. In some embodiments, the hydrogen partial pressure of the metal hydride at T1 can be calculated directly based on common knowledge of materials thermodynamics or measured directly experimentally; in other embodiments where experimental measurement is difficult at higher temperatures, the hydrogen partial pressure p2 at a lower reference temperature T2 can be determined experimentally first, and the hydrogen partial pressure at the operating temperature T1 can be calculated based on the van der Hoff equation: ln(p1 / p2) = -(1 / T1 - 1 / T2)ΔH / R, where R is the ideal gas constant and ΔH is the enthalpy of formation. In a preferred embodiment, T2 is in the range of 800℃-1100℃.

[0023] Step b): Establish a particle model of the moderating material, the model structure of which is as follows: Figure 1 As shown, the structure includes a metal hydride core 1 with an initial diameter, a SiC sealing layer 3 with an initial outer diameter and an initial thickness, and a porous buffer layer 2 between the metal hydride core 1 and the SiC sealing layer 3. The initial outer diameter of the SiC sealing layer 3 is determined according to the design requirements of the moderating material particles. The stress σ1 = p1r / 2t is calculated using the thin-walled spherical shell stress formula when the internal pressure of the SiC sealing layer 3 is p1, where r is the radius and t is the thickness of the SiC sealing layer 3.

[0024] Step c): The allowable stress of SiC sealing layer 3 at temperature T1 is calculated using the Weibull distribution formula: σ = σ0[-ln(1-P)]. 1 / mThe calculations are performed, where σ0 is the characteristic strength of SiC, P is the failure rate, and m is the Weibull modulus. The thickness of the SiC sealing layer 3 and the size of the metal hydride core are adjusted based on the difference between the allowable stress σ and the stress σ1 at the initial model temperature T1: when σ is significantly greater than σ1, the thickness t is reduced and the size of the metal hydride core is increased; when σ is less than σ1, the thickness t is increased and the size of the metal hydride core 1 is appropriately reduced. Ultimately, the modified model for the moderating material particles is obtained when σ ≥ σ1 and the difference is less than a small given threshold, such as 5 MPa. In a preferred embodiment, uncertainty should also be considered when comparing σ and σ1. When the uncertainty is a%, σ(1-a%) ≥ σ1 should be satisfied.

[0025] Step d): Fabricate a high-temperature resistant composite neutron moderator material based on a modified model of the moderator material particles. Metal hydride particles of appropriate size are provided as the metal hydride core 1. A porous buffer layer 2 is deposited on the surface of the metal hydride core 1 using chemical vapor deposition. In a preferred embodiment, the porous buffer layer 2 is a pyrolytic carbon layer. Subsequently, a SiC sealing layer 3 is deposited on the surface of the buffer layer 2 to obtain the finished moderator material particles. In different embodiments, the composition of the metal hydride core 1 can be YH... x or ZrH x Depending on the design requirements, x ranges from 1.7 to 2.

[0026] The finished moderator material particles produced by the above method can be directly filled into containers as neutron moderator components and arranged in the reactor, or they can be further mixed with other materials and solidified into block materials for reactor structure construction.

[0027] In a preferred embodiment, a layer of pyrolytic carbon can be further deposited on the surface of the SiC sealing layer 3 to further improve the mechanical strength of the particles and enhance the interfacial bonding strength and compatibility when the moderating material particles need to be combined with other matrix materials.

[0028] In a preferred embodiment, the manufacturing process of the high-temperature resistant composite neutron moderator material is as follows: First, the service temperature of the neutron moderator was determined to be 1300℃, and YH was used. 1.8 The material used as the core of the metal hydride. The YH content at 1000℃ was experimentally determined. 1.8 The equilibrium hydrogen partial pressure p2 is 40 kPa, and the enthalpy of formation ΔH is 252.3 kJ / mol. The characteristic strength of SiC is 350 MPa, and its Weibull modulus is 7. Based on the van der Hoff equation, the equilibrium hydrogen partial pressure p1 at 1300 °C is calculated to be 3720 kPa.

[0029] Next, a model of the moderating material particles was established: the initial radius of the moderating material particles (outer radius of SiC sealing layer 3) was 460 μm, and the thickness was 20 μm; the buffer layer 2 was porous pyrolytic carbon with a porosity of 50% and a thickness of 40 μm; the metal hydride core 1 had a radius of 400 μm. When the SiC spherical shell was subjected to an internal pressure of 3720 kPa, the stress borne by the SiC sealing layer 3 was calculated to be 40.92 MPa according to the thin-walled spherical shell stress formula. Based on the Weibull distribution formula, the allowable stress of the SiC spherical shell structure was calculated to be 94 MPa when the failure rate P was 0.01%. Considering a 30% uncertainty, the upper limit of the stress borne by the SiC spherical shell structure was 65.8 MPa, significantly greater than the initial stress of 40.92 MPa borne by the SiC sealing layer 3 in the model. Therefore, the parameters in the moderating material particle model were adjusted. The radius of the metal hydride core 1 was increased to 550 μm, and the thickness of the SiC sealing layer 3 was reduced to 17 μm while keeping the thickness of the buffer layer 2 unchanged. This increased the overall radius of the moderating material particles to 607 μm, thereby improving the volume ratio of the metal hydride core 1 and obtaining the modified moderating material particle model. Calculations showed that in the modified model, the stress borne by the SiC sealing layer at 1300℃ was 64.6 MPa, which did not exceed the upper limit of 65.8 MPa under 30% uncertainty. Compared to the initial state of the moderating material particles, the stress of the metal hydride core 1 was significantly lower. 1.8 The volume ratio was increased from 65.7% to 74.4%, effectively improving the neutron moderation capability.

[0030] Finally, based on the moderated material particle correction model, YH with corresponding size is provided. 1.8 The particles serve as the metal hydride core 1, and a buffer layer 2 and a SiC sealing layer 3 are deposited sequentially on their surface to obtain the finished moderating material particles.

[0031] In another preferred embodiment, the manufacturing process of the high-temperature resistant composite neutron moderator material is as follows: First, the service temperature of the neutron moderator was determined to be 900℃, using ZrH2O. 1.8 ZrH is used as the material for the metal hydride core 1. Experimental measurements show that ZrH... 1.8 The equilibrium hydrogen partial pressure p1 at 900℃ is 25.6 MPa. The characteristic strength of SiC is 350 MPa, and the Weibull modulus is 7.

[0032] Next, a moderating material particle model was established: the initial radius of the moderating material particle model (outer radius of SiC sealing layer 3) was 460 μm, and the thickness was 20 μm; the buffer layer 2 was porous pyrolytic carbon with a porosity of 50% and a thickness of 40 μm; the metal hydride core 1 had a radius of 400 μm. When the SiC spherical shell was subjected to an internal pressure of 25.6 MPa, the stress borne by the SiC sealing layer 3 was calculated to be 70.4 MPa according to the thin-walled spherical shell stress formula. According to the Weibull distribution formula, the allowable stress of the SiC spherical shell structure was calculated to be 94 MPa when the failure rate P was 0.01%. Considering a 30% uncertainty, the upper limit of the stress borne by the SiC spherical shell structure was 65.8 MPa, which was less than the stress borne by the SiC sealing layer 3 in the initial model of 70.4 MPa. Therefore, the parameters in the moderating material particle model were adjusted, and the thickness of the SiC sealing layer was increased to 22 μm while keeping the thickness of the buffer layer 2 unchanged, resulting in a modified moderating material particle model. Calculations show that in the modified model for moderating material particles, the stress borne by the SiC sealing layer at 900℃ is 64MPa, which does not exceed the upper limit of stress of 65.8MPa under 30% uncertainty, effectively improving the reliability of the moderating material particles at 900℃.

[0033] Finally, based on the moderated material particle correction model, ZrH with corresponding dimensions is provided. 1.8 The particles serve as the metal hydride core 1, and a buffer layer 2 and a SiC sealing layer 3 are deposited sequentially on their surface to obtain the finished moderating material particles.

[0034] Calculations of the equilibrium hydrogen partial pressure at the operating temperature in the above embodiments show that conventional metal hydride materials undergo significant dehydrogenation at the corresponding temperatures, leading to a significant change in the hydrogen atom distribution under long-term service conditions and severely affecting neutron moderation performance. The manufacturing method for the high-temperature resistant composite neutron moderator material provided in the above embodiments can be used to manufacture neutron moderator material particles with good stability and reliability at high temperatures. This effectively confines the hydrogen gas generated by the decomposition of metal hydrides within the SiC spherical shell, ensuring that the macroscopic hydrogen atom distribution of the neutron moderator absorber remains stable during service, effectively improving the safety and reliability of nuclear power plants, especially new commercial nuclear power facilities using fourth-generation reactors.

[0035] 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 technical features involved, as well as combination of implementation methods in different embodiments without causing structural and principle conflicts, all fall within the protection scope of the present invention.

Claims

1. A method for manufacturing a high-temperature resistant composite neutron moderator material, characterized in that, Includes the following steps: Step a): Provide the operating temperature T1 of the high-temperature resistant composite neutron moderator material and determine the hydrogen partial pressure of the metal hydride at T1; Step b): Establish a moderating material particle model, which includes a metal hydride core, a buffer layer, and a SiC sealing layer from the inside out; calculate the stress generated by the hydrogen partial pressure on the SiC sealing layer under T1 based on the outer diameter of the moderating material particle model, the initial thickness of the SiC sealing layer, and the size of the metal hydride core. Step c): Calculate the allowable stress σ of the SiC sealing layer at T1, where σ = σ0[-ln(1-P)]. 1 / m Calculations are performed, where σ0 is the characteristic strength of SiC, P is the failure rate, and m is the Weibull modulus. Based on the calculated allowable stress, the thickness of the SiC sealing layer and the size of the metal hydride core are adjusted to obtain a modified model for the moderating material particles. Step d): Based on the modified model of the moderating material particles, manufacture the finished high-temperature resistant composite neutron moderating material.

2. The method for manufacturing the high-temperature resistant composite neutron moderator material according to claim 1, characterized in that, In step d), metal hydride particles are provided as the metal hydride core, and the buffer layer and the SiC sealing layer are sequentially deposited on the metal hydride core using a chemical vapor deposition process.

3. The method for manufacturing the high-temperature resistant composite neutron moderator material according to claim 2, characterized in that, Step d) further includes the step of depositing a pyrolytic carbon layer on the surface of the SiC sealing layer.

4. The method for manufacturing the high-temperature resistant composite neutron moderator material according to claim 1, 2, or 3, characterized in that, In step a), the hydrogen partial pressure p1 of the metal hydride at T1 is determined by the following method: Provide the hydrogen partial pressure p2 of the metal hydride at a reference temperature T2, according to The solution ln(p1 / p2) = -(1 / T1 - 1 / T2)ΔH / R is used to obtain p1, where R is the ideal gas constant and ΔH is the enthalpy of formation.

5. The method for manufacturing the high-temperature resistant composite neutron moderator material according to claim 4, characterized in that, 800℃<T2<1100℃。 6. The method for manufacturing high-temperature resistant composite neutron moderator material according to claim 1, 2 or 3, wherein the metal hydride is yttrium hydride or zirconium hydride, and the buffer layer is made of porous pyrolytic carbon.

7. A high-temperature resistant composite neutron moderator material, characterized in that, The high-temperature resistant composite neutron moderator material comprises, from the inside out, a metal hydride core, a buffer layer, and a SiC sealing layer, and is manufactured using the manufacturing method of the high-temperature resistant composite neutron moderator material as described in any one of claims 1 to 6.

8. The high-temperature resistant composite neutron moderator material according to claim 7, characterized in that, The metal hydride core is composed of YH. x or ZrH x , where 1.7≤x≤2.

9. The high-temperature resistant composite neutron moderator material according to claim 7 or 8, characterized in that, The buffer layer is porous pyrolytic carbon.

10. The high-temperature resistant composite neutron moderator material according to claim 7 or 8, characterized in that, The surface of the SiC sealing layer is also provided with a pyrolytic carbon layer.

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