Use of barrier material containing molybdenum or molybdenum-based alloy in nuclear reactor

Abstract

To provide a material which exhibits only acceptable levels of swelling effects and neutron embrittlement when exposed to fast neutrons, without experiencing excessive degradation of structural properties of a structural component.SOLUTION: A barrier material for use in a structural component of a nuclear reactor (10) is provided, the barrier material comprising molybdenum or a molybdenum-based alloy and having a molybdenum content of at least 90 wt.% with respect to a total weight of the barrier material.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to the use of barrier materials comprising molybdenum or molybdenum-based alloys in structural components of nuclear reactors. [Background technology]

[0002] Various structural components, such as structural barriers, are used within nuclear reactors that must withstand the harsh conditions experienced during reactor operation. Typical examples of such structural components are the proton beam windows in accelerator-driven reactors or the fuel cladding that encompasses the fuel pellets of a fuel assembly in the reactor core. The inherent safety of a nuclear reactor is closely related to the reliability of such structural components to ensure adequate containment of highly radioactive material.

[0003] In this regard, suitable materials for use in structural components of nuclear reactors must combine several requirements at once. Upon exposure to neutrons, especially fast neutrons, the material experiences swelling effects and neutron embrittlement, which must be limited to acceptable levels without excessive degradation of the structural properties of the structural components. Furthermore, the material must be able to withstand high heat fluxes with acceptable levels of thermal stress and have sufficient fatigue resistance even after numerous thermal cycles. If the material is exposed to the reactor coolant, the corrosive effects of the interaction between the material and the coolant must be minimized.

[0004] In the MEGAPIE experiment (Megawatt Pilot Experiment), characterized by a proton beam power of 1 MW, the structural confinement of the liquid lead-bismuth eutectic spallation target is made of thin-walled ferritic-martensitic stainless steel, which exhibits low sensitivity to neutron swelling. To mitigate liquid metal corrosion and maintain sufficient structural strength of the confinement, the operating temperature of the experiment was limited to 400 °C. However, during post-test inspection, this material was found to have a high susceptibility to lead-bismuth embrittlement. Such a temperature limitation prevents the use of higher proton beam powers. If a higher proton beam power were required or desired, a reduction in the thickness of the proton beam window would be necessary, which would be impractical from a structural standpoint.

[0005] Also, different types of iron-based alloys, such as iron-chromium-aluminum (FeCrAl) alloys, exhibit a drastic loss of mechanical properties when operated at temperatures above 550°C.

[0006] In SPX-type fast reactors, fuel cladding material made of 15-15Ti steel has been used because of its high resistance to neutron swelling and low level of embrittlement. However, this steel exhibits rapid corrosion at temperatures above 480°C when exposed to typical coolants used in nuclear reactors, such as molten lead.

[0007] 1MW / m 2To handle high heat fluxes exceeding 1000 K, tungsten-based alloys appear to be suitable choices due to their high heat resistance and minimal susceptibility to neutron-induced swelling. However, the inherent brittleness of tungsten limits the suitability of these alloys for use in structural components of nuclear reactors, given the cyclic thermomechanical loads experienced during reactor operation.

[0008] Another proposed solution for structural components is the combination of steel components as a primary barrier coated with one or more stable corrosion-resistant metal oxides. However, such designs have an inherent risk of localized breach of the protective coating resulting from elastic or plastic deformation of the structural components over the reactor's lifetime. Such breaches could expose the underlying steel components to the aggressive environment of the reactor core.

[0009] Thus, a need remains for materials suitable for use in structural components of nuclear reactors that simultaneously meet the needs for resistance to neutron-induced swelling and embrittlement, thermal stress and corrosion effects, and mechanical properties. Summary of the Invention

[0010] The object of the present invention is to provide a solution for the structural components of a nuclear reactor that makes it possible to meet these needs.

[0011] The object of the present invention is solved by the use of a barrier material comprising molybdenum or a molybdenum-based alloy in the structural components of a nuclear reactor, the barrier material having a molybdenum content of at least 90% by weight relative to the total weight of the barrier material.

[0012] The present invention is based on the idea of ​​using molybdenum or molybdenum-based alloys containing very high molybdenum contents for structural components of nuclear reactors. Molybdenum and such molybdenum-based alloys offer very high thermal conductivity, a low coefficient of expansion when exposed to neutron flux, strong corrosion resistance, high strength, and excellent strength retention, even when exposed to high temperatures. Until now, molybdenum and molybdenum-based alloys with high molybdenum contents have been used in other demanding applications, such as high-temperature heating elements, evaporation crucibles, sputtering targets, etc. However, it is now believed that the specific property profiles of these materials are also suitable for use in structural components of nuclear reactors, particularly to achieve reliable nuclear reactors.

[0013] In one variation, the barrier material has a molybdenum content of at least 95.0 wt. %, preferably at least 99.0 wt. %, relative to the total weight of the barrier material. That is, any further components forming molybdenum-based alloys are present in the barrier material in rather small or very small amounts. These further components are therefore used to further improve the specific properties of pure molybdenum to suit the intended application scenario of the structural components in nuclear reactors.

[0014] The molybdenum-based alloy may comprise molybdenum and one or more alloying components selected from the group of transition metals, carbon, lanthanum oxide, yttrium oxide, cerium oxide, and combinations thereof, preferably titanium, zirconium, hafnium, carbon, lanthanum oxide, yttrium oxide, cerium oxide, and combinations thereof.

[0015] Typical examples of suitable molybdenum-based alloys are TZM (titanium-zirconium-molybdenum), MHC (molybdenum-hafnium-carbon), ML (molybdenum-lanthanum-oxide), Mo-ILQ (molybdenum-incandescent-lamp-quality), MY (molybdenum-yttrium-cerium-oxide) and LCAC molybdenum (low carbon arc cast molybdenum).

[0016] Of course, the molybdenum-based alloy may further contain unavoidable impurities not explicitly listed in the above alloy component list, so long as the presence of these unavoidable impurities does not substantially interfere with the properties of the barrier material.

[0017] Preferably, the one or more alloying components are selected from the group consisting of titanium, zirconium, carbon, and combinations thereof, such as titanium, zirconium, and combinations thereof. Such molybdenum-based alloys, such as TZM, provide a property profile that is particularly beneficial for applications in nuclear reactors.

[0018] The molybdenum-based alloy may contain 0.03 wt % to 1.3 wt %, preferably 0.3 wt % to 0.75 wt %, and more preferably 0.45 wt % to 0.7 wt %, of one or more alloying components, based on the total weight of the molybdenum-based alloy.

[0019] In one variation, the barrier material consists of molybdenum or a molybdenum-based alloy.

[0020] The structural component may also be made of a barrier material such that the properties of the structural component will be determined solely by the barrier material used.

[0021] To mitigate the effects of radiation embrittlement, structural components can be heated to minimum temperatures in the range of 700°C to 850°C during reactor operation. These minimum temperatures are much lower than the melting and recrystallization points of molybdenum and molybdenum-based alloys according to the present invention, but are high enough to enhance atomic diffusion mechanisms within the barrier material. At these temperatures, molybdenum and molybdenum-based alloys exhibit a thermal recovery or self-healing effect that removes irradiation-induced defects introduced in the barrier material by neutron exposure, improving the reliability and service life of the structural components. As a result of this effect, these high minimum temperatures enable the bonding of structural components at multi-megawatt proton beam powers.

[0022] The minimum temperature, i.e., the minimum temperature during irradiation, is specifically selected to be adjusted to the ductile-brittle transition temperature (DBTT) of the barrier material. If the material is used at a temperature below the DBTT, it becomes brittle and more susceptible to fracture. By selecting a minimum temperature during irradiation of 700°C to 850°C, it is ensured that the DBTT of the barrier material is maintained below the minimum temperature during operation, thus eliminating or at least minimizing the risk of brittle fracture of the structural components.

[0023] Furthermore, during reactor operation, the structural components can be heated to maximum service temperatures of up to 1050°C, limiting the temperature-induced reduction in mechanical properties of the structural components.

[0024] The structural components are designed to withstand 1 MW / m during reactor operation. 2 Heat flux exceeding 2 MW / m 2 Because the barrier material is made of molybdenum or a molybdenum-based alloy, the barrier material can be exposed to a heat flux of 1 MW / m 2The barrier material has a thermal conductivity sufficient to dissipate heat induced by a heat flux exceeding 1000 kJ / cm 2 . Thus, higher reactor operating temperatures and / or proton beam powers can be used, resulting in higher reactor thermodynamic efficiency and better exploitation of the fuel within the reactor core without the risk of failure due to thermally induced effects in the barrier material.

[0025] Additionally, the high thermal conductivity of the barrier material allows the thickness of the structural components to be increased without risking creating localized thermal hot spots, which is particularly beneficial in applications where the structural components must withstand differential pressures.

[0026] Preferably, the nuclear reactor is a fast reactor. In a fast reactor, a nuclear chain reaction is sustained by fast neutrons with an average energy above 1 MeV without the use of a moderator. The operating temperatures of fast reactors are typically much higher than other types of nuclear reactors. The use of barrier materials ensures that these operating temperatures can be handled. Fast reactors also have the advantage that they can be operated as breeder reactors, making it possible to reuse spent fuel obtained, for example, from thermal light water reactors.

[0027] Even more preferably, the fast reactor is a subcritical fast reactor, which requires an additional neutron source to sustain the nuclear chain reaction and thus can be precisely controlled based on the operation of the additional neutron source.

[0028] For example, a subcritical fast reactor can include a spallation neutron source that generates neutrons by irradiation with a proton beam. Thus, by controlling the power of the proton beam, the operation of the reactor can be precisely controlled. One application scenario is the use of barrier materials in a subcritical transmutation accelerator regenerative reactor.

[0029] Structural components may be exposed to coolants, such as liquid metal-based coolants or high-temperature helium, during reactor operation. Barrier materials containing molybdenum or molybdenum-based alloys exhibit low levels of corrosion even when exposed to the coolants used in nuclear reactors at high operating temperatures. The term "high-temperature helium" indicates that helium is used as a coolant having an outlet temperature of at least 700°C.

[0030] In one variant, the coolant is a liquid metal-based coolant, which can be sodium, lead, or lead-bismuth eutectic, preferably lead or lead-bismuth eutectic, more preferably lead. Such coolants can be used in fast reactors, where the metal-based coolant forms the spallation source. The use of barrier materials in structural components can ensure high corrosion resistance even in such application scenarios, further increasing the reliability of the reactor.

[0031] Thus, the present invention may also be understood as a method of operating a nuclear reactor having structural components that include a barrier material, wherein a coolant, for example a liquid metal-based coolant, is contacted with the barrier material, the barrier material comprising or consisting of molybdenum or a molybdenum-based alloy as described above.

[0032] The structural component can be a proton beam window, a spallation target for a spallation neutron source, a structural container for nuclear fuel, e.g., fuel cladding, an emergency container for recovering molten core (also known as "corium") after a severe nuclear accident, a core grid, a reactor vessel housing, e.g., a primary reactor vessel, an emergency decay heat removal system (DHR), a steam or heat treatment unit, e.g., a steam generator, or a heat exchanger in a reactor containment vessel, e.g., a primary or intermediate heat exchanger. Preferably, the structural component is a proton beam window or a fuel cladding.

[0033] Proton beam windows are used in nuclear reactors that rely on an external proton source to generate a proton beam, which is directed through an evacuated proton beam tube to a spallation neutron source to generate neutrons for controlling a nuclear chain reaction. The proton beam window is positioned at the end of the proton beam tube and forms a barrier against the surrounding medium. Depending on the desired proton beam current and power, the proton beam window must withstand significant thermomechanical loads and stresses, which the barrier material can reliably withstand. Due to the high thermal conductivity of molybdenum and molybdenum-based alloys, the thickness of the proton beam window can be increased compared to other materials, such as steel-based materials, thereby improving structural robustness without risking the formation of localized hot spots or exceeding the maximum operating temperature of the proton beam window.

[0034] Fuel cladding material is used to encase the actual fuel, e.g., fuel pellets, used in the nuclear reactor, such that the combination of fuel cladding material and fuel forms the basic structure of a given fuel element within the reactor.

[0035] Further advantages and characteristics of the present invention will become more apparent from the following description of exemplary embodiments thereof, which should not be construed as limiting, and from the accompanying drawings, in which: [Brief explanation of the drawings]

[0036] [Figure 1] FIG. 1 shows a schematic diagram of a nuclear reactor having structural components in which a barrier material according to a first embodiment of the present invention is used. [Figure 2] FIG. 2 shows selected portions of a proton beam tube used in the reactor of FIG. [Figure 3] FIG. 3 shows another schematic diagram of the proton beam tube of FIG. [Figure 4]FIG. 4 shows a schematic diagram of another structural component of a nuclear reactor in which a barrier material is used according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0037] 1 is a schematic diagram of selected portions of a nuclear reactor 10. The reactor 10 includes a reactor core 12 contained within a reactor vessel 14 having a vessel housing 16.

[0038] Reactor vessel 14 contains coolant 18, which flows from below a lower core grid 20 of core 12 toward an upper core grid 22 of core 12, as indicated by the curved arrow in Figure 1. Coolant 18, heated as it flows through core 12 by heat generated in core 12, is transferred to heat exchanger 24, which is also used to control the supply and flow of coolant 18 within reactor vessel 14.

[0039] Of course, as is known in the art, heat exchanger 24 would be connected to additional components (not shown) of reactor 10 for generating electricity, such as a steam generator or additional heat exchangers. These additional components may also be used to measure and / or control the oxygen content in coolant 18.

[0040] For example, an oxygen content control device (not shown) may be used that can control the oxygen content of the coolant 18 by oxygen extraction using hydrogen or a hydrogen-generating substance. Preferably, the oxygen content of the coolant 18 is 10 wt % or less based on the total weight of the coolant 18. -6 It is less than 1 ppmw.

[0041] In the illustrated embodiment, the coolant 18 is a liquid metal coolant, which may be sodium, lead, or lead-bismuth eutectic. Of course, other types of coolant 18 may be used depending on the type of reactor 10, such as high temperature helium with an outlet temperature of at least 700° C., e.g., about 850° C., in a gas-cooled fast reactor.

[0042] Core 12 includes a plurality of fuel elements 26 extending between lower core grid 20 and upper core grid 22. Fuel elements 26 contain the fuel for the nuclear reactor, preferably in the form of fuel pellets 28 encased in fuel cladding material 30 (see FIG. 4). Of course, core 12 may include additional components not shown in FIG. 1, such as control rods.

[0043] Additionally, the nuclear reactor 10 includes a particle accelerator arrangement 31 configured to generate a proton beam that is transported from the particle accelerator arrangement 31 toward the reactor core 12 in an evacuated proton beam tube 32 that extends into the reactor core 12, as indicated by the arrow in Figure 1. The particle accelerator arrangement 31 can be based on a cyclotron or a linear accelerator. Preferably, the particle accelerator arrangement 31 is based on a cyclotron.

[0044] At an end 34 of the proton beam tube 32 located within the reactor core 12 , the proton beam tube 32 is terminated by a proton beam window 36 .

[0045] Figure 2 shows a selected portion of the end 34 of the proton beam tube 32. In Figure 2, it is better visible that the proton beam window 36 is hemispherical and bonded to the substantially cylindrical proton beam tube 32. That is, the proton beam tube 32 and the proton beam window 36 are mechanically connected to one another.

[0046] 3 shows a schematic cross-sectional view of an end 34 of a proton beam tube 32 within the reactor core 12. A proton beam window 36 is disposed between the fuel elements 26 and is immersed in the coolant 18, which in the illustrated embodiment is a liquid metal coolant. The connection between the proton beam tube 32 and the proton beam window 36 seals the evacuated inner part of the proton beam tube from the coolant 18.

[0047] Thus, the proton beam window 36 separates the evacuated proton beam tube interior volume from the coolant 18. However, the high-energy protons produced by the particle accelerator device 31 that forms the proton beam and transported to the reactor core 12 via the proton beam tube 32 at least partially traverse the proton beam window 36 and enter the liquid metal coolant.

[0048] The term "high energy protons" is understood in this context as protons having an energy of at least 500 MeV, e.g., 600 MeV or more, the maximum possible energy of each proton being determined by the type of particle accelerator device 31 used.

[0049] Once the high-energy protons reach the liquid metal coolant, they induce a spallation reaction that produces the number of neutrons needed to power the reactor core 12, i.e., to continue the nuclear fission chain reaction. Thus, the reactor 10 shown in this embodiment is a subcritical fast reactor, and uses the liquid metal coolant as the spallation target. Other types of spallation targets, such as a lead-bismuth target in a gas-cooled fast reactor, can also be used.

[0050] The proton beam current during reactor 10 operation is typically greater than 2.0 mA, and the reactor 10 can operate at multiple MW beam powers and at speeds of up to 1 MW / m. 2 This results in a heat flux exceeding

[0051] The materials used for the proton beam window 36 are selected to withstand the harsh conditions experienced by the proton beam window 36, namely, high heat flux, neutron irradiation, thermomechanical stress, aggressive liquid metal coolant, and high pressure differential between the evacuated interior volume of the proton beam tube 32 and the coolant 18 bath.

[0052] To reliably withstand these conditions, the proton beam window 36 consists of a barrier material comprising molybdenum or a molybdenum-based alloy, the barrier material having a molybdenum content of at least 90% by weight, in particular at least 95.0% by weight, and preferably at least 99.0% by weight, relative to the total weight of the barrier material.

[0053] The molybdenum-based alloy comprises molybdenum and one or more alloying components selected from the group consisting of transition metals, carbon, lanthanum oxide, yttrium oxide, cerium oxide, and combinations thereof, and unavoidable impurities, preferably selected from the group consisting of titanium, zirconium, hafnium, carbon, lanthanum oxide, yttrium oxide, cerium oxide, and combinations thereof, and even more preferably selected from the group consisting of titanium, zirconium, carbon, and combinations thereof, for example, selected from the group consisting of titanium, zirconium, and combinations thereof.

[0054] The one or more alloying elements are especially present in an amount of 0.03 to 1.3 wt. %, preferably 0.3 wt. % to 0.75 wt. %, more preferably 0.45 wt. % to 0.7 wt. %, relative to the total weight of the molybdenum-based alloy.

[0055] For example, the molybdenum-based alloy may be TZM (titanium-zirconium-molybdenum), MHC (molybdenum-hafnium-carbon), ML (molybdenum-lanthanum-oxide), Mo-ILQ (molybdenum incandescent lamp quality), MY (molybdenum-yttrium-cerium oxide) or LCAC molybdenum (low carbon arc cast molybdenum), most preferably TZM.

[0056] These materials have high corrosion resistance to liquid metal coolants such as lead or lead-bismuth eutectic, high strength, and excellent strength retention. For example, the barrier material can be used for 1000 psi or more, e.g., about 300 MPa. 6 It exhibits high cycle fatigue resistance.

[0057] Furthermore, the proton beam window is heated to a minimum temperature of 700°C to 850°C and a maximum temperature of up to 1050°C, for example 1000°C, during operation of the reactor 10.

[0058] At such temperatures, the barrier material exhibits a self-healing mechanism that allows irradiation-induced defects in the barrier material to be repaired, and the mechanical properties of the barrier material are maintained. Furthermore, the barrier material, e.g., TZM, is chemically compatible with liquid metal coolants up to the highest temperatures, minimizing corrosive effects.

[0059] In the embodiment shown, the reactor 10 is a subcritical fast reactor. Of course, the reactor 10 can be a different type of reactor.

[0060] Furthermore, only the proton beam window 36 made of a barrier material is described. However, in addition to or instead of the proton beam window 36, other structural components of the reactor 10 may be made of or include a barrier material. For example, the reactor vessel 14, the lower core grid 20, the upper core grid 22, the heat exchanger 24, the fuel cladding material 30, and / or the fuel plugs may be made of or include a barrier material.

[0061] Further examples of components (not shown) of the reactor 10 that may beneficially consist of or include a barrier material are a spallation target for a spallation neutron source located within the reactor containment vessel of the reactor 10, an emergency vessel for recovering the molten core after a severe nuclear accident, an emergency decay heat removal system, or a steam generator.

[0062] FIG. 4 shows a schematic diagram of another structural component in which a barrier material according to a second embodiment of the present invention is used.

[0063] The second embodiment substantially corresponds to the first embodiment, with only the differences being described below, and the same reference numerals denote the same or functionally identical components, with reference to the above description.

[0064] In a second embodiment, the fuel cladding material 30 of the fuel element 26 is comprised of a barrier material. That is, fuel pellets 28 containing nuclear fuel, e.g., thorium-based nuclear fuel, are contained within a fuel cladding material 30 made from a barrier material that acts as a structural container for the fuel pellets 28.

[0065] The fuel pellets 28 are surrounded by fuel cladding material 30 to form fuel elements 26 located in the core 12 of the nuclear reactor 10. Thus, the fuel cladding material 30 functions as a primary containment barrier for the fuel pellets 28.

[0066] The use of a barrier material as the fuel cladding material 30 allows the fuel element 26 to operate at high temperatures, up to a maximum temperature of 1050°C, without experiencing significant corrosive effects and while providing good mechanical properties, even when using a coolant 18 such as a liquid metal coolant. For example, even at temperatures of 1000°C, molybdenum-based alloys such as TZM have mechanical properties comparable to those of steels used in nuclear application scenarios at temperatures of about 550°C.

[0067] Furthermore, at temperatures of 1000°C and tensile stresses of about 200 MPa, barrier materials according to the present invention, such as molybdenum or TZM, exhibit negligible creep rates, resulting in creep-rupture times in excess of 20,000 operating hours, which is particularly beneficial for fuel cladding materials 30 whose service life is typically determined by creep resistance.

[0068] Generally, the use of barrier materials comprising molybdenum or molybdenum-based alloys in the structural components of the reactor 10 allows the structural components to be resistant to neutron-induced effects such as swelling and embrittlement, to ensure high resistance to thermal stress and corrosion effects, and to provide good mechanical properties, thereby increasing the service life and reliability of the reactor 10.

Claims

1. 1. Use of a barrier material comprising molybdenum or a molybdenum-based alloy in a structural component of a nuclear reactor (10), comprising: The barrier material has a molybdenum content of at least 90% by weight, based on the total weight of the barrier material.

2. 2. Use according to claim 1, wherein the barrier material has a molybdenum content of at least 95.0% by weight, preferably at least 99.0% by weight, relative to the total weight of the barrier material.

3. 3. The use according to claim 1 or 2, wherein the molybdenum-based alloy comprises molybdenum and one or more alloying components selected from the group of transition metals, carbon, lanthanum oxide, yttrium oxide, cerium oxide, and combinations thereof, preferably selected from the group of titanium, zirconium, hafnium, carbon, lanthanum oxide, yttrium oxide, cerium oxide, and combinations thereof.

4. 4. The use of claim 3, wherein the one or more alloying components are selected from the group consisting of titanium, zirconium, carbon and combinations thereof.

5. 5. Use according to claim 3 or 4, wherein the molybdenum-based alloy comprises 0.03% to 1.3% by weight of one or more alloying elements relative to the total weight of the molybdenum-based alloy.

6. 6. The use according to claim 5, wherein the molybdenum-based alloy comprises 0.3% to 0.75% by weight of one or more alloying elements relative to the total weight of the molybdenum-based alloy.

7. Use according to any one of claims 1 to 6, wherein during operation of the nuclear reactor (10), the structural components are heated to a minimum temperature in the range of 700°C to 850°C.

8. Use according to any one of claims 1 to 7, wherein during operation of the nuclear reactor (10), the structural components are heated to a maximum operating temperature of up to 1050°C.

9. During operation of the reactor (10), the structural components ２ The use according to any one of claims 1 to 8, wherein the substrate is exposed to a heat flux of more than

10. Use according to any one of claims 1 to 9, wherein the nuclear reactor (10) is a fast reactor.

11. The structural components are exposed to the coolant (18) during operation of the nuclear reactor. Use according to any one of claims 1 to 10.

12. 12. Use according to claim 11, wherein the coolant (18) is a liquid metal-based coolant or hot helium.

13. 13. Use according to claim 12, wherein the coolant (18) is a liquid metal based coolant, the liquid metal based coolant being selected from sodium, lead or lead bismuth eutectic.

14. 14. The use according to any one of claims 1 to 13, wherein the structural component is a proton beam window (36), a spallation target, a structural container for nuclear fuel, an emergency container, a core grid (20, 22), a vessel housing (16) of a nuclear reactor (10), an emergency decay heat removal system, a steam or heat treatment device or a heat exchanger.

15. The use according to any one of claims 1 to 14, wherein the barrier material consists of molybdenum or a molybdenum-based alloy.

16. The use according to any one of claims 1 to 15, wherein the structural component comprises a barrier material.

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