Coating of plasma-wall interacting components in nuclear power generators

Abstract

A coating for a plasma-wall interaction component in a machine for magnetic confinement of thermonuclear plasma, the coating including a capillary holding structure defining a predetermined containment volume, the containment volume adapted to hold at least one liquid metal, the capillary holding structure including at least one metallic multi-wire cable arranged according to an intertwining pattern.

Description

[Technical Field]

[0001] The present invention relates to the field of research and applications related to nuclear fusion, and in particular to the problem of suitable coating materials for structural components present in machines involved in the confinement of thermonuclear plasmas (e.g., "tokamak" machines), and more particularly to the structure of the so-called "divertors" present in such machines. [Background technology]

[0002] A diverter, in the technical field related to the present invention, can be thought of as a part of the wall where the plasma is redirected (naturally diffusing perpendicular to the magnetic field lines), typically found in nuclear fusion reactors, circulating and generally forming the "first wall" directly interfaced with the plasma to be fused.

[0003] In the field of fusion, the idea of ​​using liquid metals as materials directly facing the plasma is increasingly emerging to mitigate the effects of plasma on conventional solid materials such as tungsten (erosion, fusion, damage, neutron embrittlement). When used in magnetic confinement fusion devices, liquid metals must be confined. Currents induced on the metal's surface (mainly by magnetic flux fluctuations or thermoelectric effects) couple with existing magnetic fields and cause the formation of liquid droplets. There are many approaches to confinement, including "static" types (i.e., no forced circulation of the liquid metal), but capillary confinement is gaining attention. This involves holding the metal in a porous structure that allows it to resist the forces acting on the liquid that would otherwise disperse it within the device. Summary of the Invention [Problem to be solved by the invention]

[0004] Approaches known to date (and in the literature) have little emphasis on the associated strands, such as creating them from wire, sintering materials with variable porosity, or creating surface castings. The latter option has proven to be the least effective due to the very small capillary forces relative to the considerable implementation effort. The second technique theoretically allows for very high capillary pressures, but its main drawback is the lack of control over the proportion of open and closed capillaries, which significantly reduces the product's viability. The final solid object is typically brittle. The very wide distribution of equivalent capillary radii can cause considerable variations in the confinement force as the surface changes. [Means for solving the problem]

[0005] The main objective of the present invention is to overcome the aforementioned problems by providing tungsten capillary structures made by braiding pure tungsten multi-wire cables (yarns), where the fabrication parameters are designed to obtain high capillary pressures with the aim of using these structures with liquid metal in machines of fusion interest (such as so-called "tokamak" machines), especially in relation to plasma-wall interactions.

[0006] This has been achieved according to the present invention by providing a coating of plasma-wall interaction components in the machine for magnetic confinement of thermonuclear plasma, as defined in the claims appended hereto.

[0007] The coating includes a capillary retention structure defining a predetermined containment volume adapted to hold at least one liquid metal, the capillary retention structure including at least one metallic multi-wire cable arranged according to an intertwining pattern.

[0008] A better understanding of the invention will be attained from the following detailed description and by reference to the accompanying drawings which show preferred embodiments by way of non-limiting example. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram illustrating a preferred "entanglement pattern" of a coating having a capillary structure according to the present invention. [Figure 2] 1 shows an electron microscope photograph of the structural components of a coating according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] Referring to FIG. 1, the braided wire based technology according to the present invention is the most promising due to both the simplicity of manufacturing and the possibility of process industrialization, as well as its inherent strength and flexibility.

[0011] The inventive concept underlying the present invention consists in using a multi-wire cable with a material containing tungsten to weave a material characterized by a porous structure capable of retaining liquid metal against hydrostatic pressure and other forces of various nature (for example, electromagnetic forces that may occur inside a tokamak).

[0012] In accordance with the present invention, tungsten is selected because it is resistant to corrosion by liquid metals, is largely unaffected by neutron characterization challenges, and has a very high fusion temperature.

[0013] One of the unique features of this invention is the innovative use of multi-wire cables, which significantly reduces the effective radius at which capillary action occurs. The effective radius of a structure is inversely proportional to the capillary pressure, i.e., its performance with respect to the pressure of the object itself. In tests, this has enabled hydrostatic liquid column heights to be reached that have not previously been seen in the literature or in other currently known experiments.

[0014] The research that led to the aforementioned test was based on the capillary pressure P c The following formula specifies how is determined:

number

[0015] It is important to note that the mesh obtained by weaving the multi-wire cable according to the invention preferably has the entanglement pattern shown in Figure 1, and therefore such a mesh can be used as a material directly exposed to plasma in machines of interest for controlled thermonuclear fusion. In this case, the use of a solution based on the concept of a porous structure confining a liquid metal advantageously has an inherent insensitivity to damage induced by fast neutrons (DPA) and the ability to regenerate the surface in transient or accidental events (e.g., ELM or fracture).

[0016] Experiments in tokamaks (including the Frascati Tokamak Upgrade - FTU) have demonstrated the existence of a "vapor shield" process, which occurs when plasma breakdown involves liquid metal contained in the structure. Indeed, liquid metal subjected to very high heat fluxes forms a thin layer of vapor, which ionizes and redistributes thermal energy in the form of radiation over the entire solid angle. This phenomenon did not cause damage to the porous structure (always resulting in the entanglement pattern shown in Figure 1), even in transient events with very high heat load values.

[0017] The flexibility of the coating obtained according to the invention, as well as the possibility of shaped weaving, allows for optimal adaptation of the coating to the supporting and cooling structures of the diverter.

[0018] The material in contact with the plasma can benefit from a very thin thickness, facilitating heat exchange with the cooling structure and increasing its steady-state heat load removal capacity. Material consumption by sputtering and / or evaporation can be quickly replaced by a liquid metal tank placed in direct contact with the sponge material described above, much like an oil lamp works with its wick.

[0019] The coated mesh thus produced can be easily immersed in liquid metal and molded for optimal adhesion to any support structure. The support structure is provided with a corrosion-resistant surface coating that is wetted by the liquid metal (for example, as shown in Figure 2). This ensures optimal heat exchange between the capillary structure of the coating and the heat removal system.

[0020] In the same Figure 2, it can be seen that the image shown therein shows the coating of the invention made of tungsten, which protects the copper of the cooling base from the corrosive attack of the tin in which the product is immersed.

[0021] Another unique feature of the present invention is the innovative use of multi-wire cables, essentially consisting of very small capillaries, to create porous tungsten structures that can be used to confine liquid metal (particularly in tokamak-type applications).

[0022] Furthermore, it is noted that the present invention preferably includes the following geometric / dimensional features related to the capillary retention structure and the material forming it: The wires forming the multi-wire cable can be identical to each other or different, each of them having -pure tungsten, - metal alloys containing a certain weight and / or mass percentage of tungsten (e.g., 80% to 99.999%), - chemical compositions containing tungsten and "doped" with other elements or substances such as potassium (K) or rhenium (Re); -Tungsten compounds can be produced from -10 -4 mm~10 -2 the average diameter of the cavities present in the capillary holding structure (e.g., "equivalent diameter" if such cavities approximate cylindrical spaces or, in either case, have a circular cross section), in mm; - the average diameter of the single wires forming the multi-wire cable, between 0.005 and 0.020 mm; - the total number of single wires forming the multi-wire cable, which may range from 5 to 25, preferably equal to, for example, 14; -All diameters of multi-wire cables from 0.050mm to 0.500mm.

[0023] It is worth noting that the present invention can also be adapted to hold a wide range of liquid metals (even if highly corrosive), e.g., tin, lithium, indium, gallium, as long as the liquid metal is adapted to effectively perform its insulating function against the plasma ring extending inside a machine using controlled thermonuclear fusion.

[0024] During the present experiments, several porous structures of pure tungsten were fabricated, which successfully passed wetting tests and effectively trapped liquid metal. Furthermore, tests with tin showed that liquid columns could exceed tens of centimeters, corresponding to capillary pressures never before reached in previous experiments in the field.

[0025] Advantageously, it is also possible to compress / sinter the porous structure in a mold having the same geometric shape as the component to be coated, which increases the ease of application of the invention and improves the adhesion and consequent heat exchange between the porous structure and the substrate when applied to a liquid metal diverter; in other words, the subsequent formation of the porous structure (in a mold having the same geometric shape as the component to be coated) also makes it possible to provide a smooth and continuous surface in view of the plasma.

[0026] Finally, the aforementioned intertwining or braiding patterns can be combined with the following weaving patterns: -plain weave, -Smooth herringbone fabric, -Mixed woven fabric It is useful to note that the sine wave is defined by at least one of:

Claims

1. 1. A coating for a plasma-wall interacting component in a machine for magnetic confinement of thermonuclear plasma, the machine being adapted to perform controlled thermonuclear fusion phenomena, the coating comprising a capillary retention structure including at least one metallic multi-wire cable, the metallic multi-wire cable being woven according to an intertwining pattern configured to define a predetermined containment volume, the containment volume being adapted to hold at least one liquid metal.

2. The intertwining or weaving pattern may be a weave pattern of: Plain weave, Smooth herringbone fabric, Mixed woven fabric The coating of claim 1 , characterized in that it is defined by at least one of:

3. Each of the wires forming the at least one metallic multi-wire cable is made of the following material: pure tungsten, present in a purity percent of 99,000% to 99.999%; a metal alloy containing 80% to 99.999% tungsten by weight and / or mass; a steel adapted to interact with said liquid metal, comprising steel of type AISI 304 and / or AISI 316; a superalloy adapted to interact with said liquid metal The coating of claim 1 , characterized in that it is made from at least one of:

4. The superalloy is made of the following material: INCONEL, preferably INCONEL 600 / 625; Incoloy 800 / 825 / A286, Fecralloy, Hastelloy, Constantan, Monel, nickel, Duplex / Super Duplex The coating of claim 3, comprising at least one of:

5. The coating of claim 1 , wherein the capillary retention structure defines a plurality of cavities adapted to retain the liquid metal.

6. The average diameter of the cavities present in the capillary holding structure is 10 －４ mm to 10 －２ 6. The coating of claim 5, wherein the thickness is 1 / 2 mm.

7. The at least one multi-wire cable comprises a bundle of wires or cables or bands, the wires or cables or bands comprising: - parallel to each other, or Twisted together 2. The coating of claim 1 .

8. 8. The coating of claim 7, wherein the average diameter of each of the wires or cables or bands forming the multi-wire cable is between 0.005 mm and 0.030 mm.

9. Coating according to claim 7, characterized in that the total number of wires forming said at least one multi-wire cable is between 5 and 30, preferably equal to 14.

10. 8. The coating of claim 7, wherein the at least one multi-wire cable has an overall diameter of 0.050 mm to 0.500 mm.

11. The coating of claim 1, wherein the capillary retention structure defines a surface roughness of 0.025 mm to 0.25 mm.

12. 10. The coating of claim 1, wherein the capillary retention structure is positionable in direct exposure to plasma present in a machine utilizing controlled thermonuclear fusion phenomena.

13. The coating of claim 1 , wherein the capillary retention structure is flexible and moldable.

14. 10. The coating of claim 1, wherein the capillary retention structure has an overall thickness of 0.5 mm to 10 mm, and wherein the coating is interposed between the plasma and a containment wall of the machine utilizing the phenomenon of controlled thermonuclear fusion.

15. 2. The coating of claim 1, further comprising a washing and spreading means for the liquid metal, operably engaged with the capillary holding structure and adapted to direct a predetermined flow of liquid metal when the liquid metal is at least partially lost due to sputtering and / or evaporation phenomena.

16. 16. A device utilizing the phenomenon of controlled thermonuclear fusion configured to generate a plasma occupying a working volume, said device comprising a confinement wall in which said plasma resides, characterized in that it comprises at least one coating according to any one of claims 1 to 15 interposed between said confinement wall and said plasma, said coating being configured to cooperate with magnetic confinement means for the thermonuclear plasma active in cooperation with said confinement wall and / or said working volume.

17. 17. The apparatus of claim 16, wherein the apparatus is a tokamak fusion reactor.

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