Method and system for heating a body of semiconductor material

Abstract

Heating method and heating system for heating a body made of semiconductor material (1) the method comprising: - applying a polarization to the body made of semiconductor material via polarization electrodes (2), - applying induction heating to the body made of semiconductor material via electrical windings (3) arranged near the body made of semiconductor material, the electrical windings being traversed by an alternating current, application in particular to silicon carbide (SiC), and application in particular to the melting of molten salts in the context of a fourth generation nuclear reactor.

Description

[0001] The present invention relates to a method and system for heating a body made of semiconductor material.

[0002] Induction heating has long been used in industry to deliver very large amounts of heat to a container. For example, in the steel industry, a container of metallic products that one wishes to melt and then pour is heated by induction.

[0003] Induction heating is also used in a domestic context thanks to suitable cooktops and cooking appliances.

[0004] In many known configurations, a high-frequency alternating electromagnetic field is applied to a container, usually metallic, which generates induced currents in the metallic material, the metallic container then being heated to the core and not just on the outer surface.

[0005] Furthermore, the present inventors are developing new solutions for so-called 4th generation nuclear reactors based on molten salts.

[0006] In the nuclear industry, it is common practice to use high-performance steel tanks, pipes and containers to contain fluids, whether liquid or two-phase e.g. liquid and gaseous.

[0007] Such steel containers and tanks may be suitable for induction heating where appropriate.

[0008] However, it turns out that in a configuration where the primary fluid of the reactor core is based on molten salt, for example lithium chloride or lithium fluoride, the corrosion of the metal vessel makes it impossible to expect a reasonable, or even desirable, service life. It is therefore advisable to manufacture the vessels, pipes, and containers from a material other than steel or any type of steel alloy.

[0009] Silicon carbide, with the chemical molecular symbol C₂H₅, is a particularly interesting candidate for manufacturing the tanks and pipes in question. SiC (and from the Anglo-Saxon name 'silicon carbide').

[0010] Furthermore, it turns out that the salts intended to become the molten salts of the reactor or its downstream auxiliaries must be heated with a very substantial heat input.

[0011] However, silicon carbide is not electrically conductive and is therefore unsuitable for induction heating. Silicon carbide belongs to the family of semiconductor materials.

[0012] It is in this context that the inventors came to propose the particularly ingenious solution described below.

[0013] To this end, a method for heating a body made of semiconductor material (1) is proposed, comprising: apply a polarization to the semiconductor material body via polarization electrodes (2), apply induction heating to the semiconductor material body via electrical windings (3) arranged near the semiconductor material body, the electrical windings being traversed by an alternating current.

[0014] Thanks to these arrangements, the electrical polarization of the semiconductor material advantageously allows it to acquire electrical conductivity properties and consequently to accept the circulation of induced currents resulting from the presence of alternating current on the windings. This is particularly beneficial when the semiconductor material is near the body to be heated.

[0015] Put another way, despite the fact that the body made of semiconductor material is not generally intrinsically conductive, the trick of polarizing the body made of semiconductor material is used to make induction heating work efficiently.

[0016] According to one embodiment, the effective activation of induction heating is selectively controlled by means of controlling a bias voltage delivered to the bias electrodes.

[0017] As a result, we avoid having to control the strong alternating currents on the induction windings, because instead we control the bias voltage, which is in practice much easier and much less expensive.

[0018] It is thus possible to control a bias voltage in an analog manner or to control an average voltage via a pulse width modulation control ('PWM' in the jargon of the trade).

[0019] According to one embodiment, the body made of semiconductor material is a silicon carbide body.

[0020] Silicon carbide is a material with very high mechanical properties and a very interesting chemical passivity; its chemical molecular symbol is SiC and its Anglo-Saxon name is 'silicon carbide'.

[0021] Silicon carbide is particularly interesting as a molten salt receiving material in the context of the development of 4th generation molten salt nuclear reactors.

[0022] However, the present invention can also be applied to other semiconductor materials such as Boron Nitride BN, Gallium Nitride GaN or Gallium Arsenide GaAs, without this list being exhaustive.

[0023] According to a particular embodiment, the polarization of the body in semiconductor material is a selective polarization of one or more predetermined regions of the body in semiconductor material.

[0024] It is therefore possible to perform one or more selective local heatings and, for example, localized welding zones.

[0025] The present invention also relates to a heating system for a body made of semiconductor material comprising: polarization electrodes configured to contact the semiconductor body at at least two locations on the semiconductor body, and deliver a polarization voltage there; electrical windings arranged near the semiconductor body, configured to apply induction heating to the semiconductor body when the windings are traversed by an alternating current and a polarization voltage is applied.

[0026] The electrical polarization of the semiconductor material allows it to have electrical conductivity properties and therefore to advantageously accept the circulation of induced currents resulting from the presence of alternating currents on the electrical windings near the body of semiconductor material to be heated.

[0027] According to one design, the semiconductor material body is silicon carbide. Silicon carbide is a good candidate for forming vessels and pipes in a Generation IV nuclear reactor.

[0028] It is noted that the present invention can also be applied to other semiconductor materials as already mentioned above.

[0029] According to one embodiment, the body made of semiconductor material is a crucible for receiving a product to be heated. This crucible can receive salts used as the primary fluid for a 4th generation nuclear reactor.

[0030] In other applications, the crucible in question can generally receive a material to be melted, such as a metallurgical product that one wants to pour after melting it in the crucible.

[0031] In one example, the product to be heated is a salt, such as a chlorinated or fluorinated salt. A fourth-generation nuclear reactor, known as a molten salt reactor, uses this type of salt. This type of salt has a melting point between 500°C and 800°C. This type of salt is aggressive in terms of corrosion, which eliminates the conventional choices made for earlier-generation reactors when designing the vessels and piping in a fourth-generation nuclear reactor.

[0032] In an alternative embodiment, the semiconductor material body acts as a conduit for carrying a product to be heated. The product to be heated can thus be melted in the conduit on the fly, in a supply line leading from the product to a container or another conduit.

[0033] In one embodiment, the electrical windings (3) surround the body made of semiconductor material. In this configuration, the electromagnetic field, resulting from the alternating current in the electrical windings, effectively covers the entire volume of the semiconductor body.

[0034] In an alternative embodiment, the electrical windings (3) can be close to the semiconductor body without surrounding it. In practice, induction heating is only required if the semiconductor body is immersed in the electromagnetic field lines generated by the electrical windings.

[0035] In one embodiment, the semiconductor material body is typically rotated around a reference axis, and the electrical windings are generally circular with one axis aligned with the reference axis. In this configuration, the effect of the electromagnetic field can be optimized and reach all areas of the semiconductor material body. Calculations or models established for cylindrical electrical windings can be used.

[0036] According to one embodiment, the system may further include a control unit (4) configured to control the bias voltage applied to the bias electrodes.

[0037] It is therefore possible to adjust the heating power by adjusting the bias voltage applied to the terminals of the semiconductor material body, without needing to adjust the power delivered by the alternating current on the electrical windings.

[0038] The control can be on / off or modulated. Furthermore, the control can be real-time based on a temperature reading from one or more temperature sensors.

[0039] According to one embodiment, the polarizing electrodes are interposed between the semiconductor material body and the electrical windings.

[0040] Advantageously, the presence of the polarization electrodes does not significantly disturb the electromagnetic field of the inductive heater and conversely, the alternating electromagnetic field prevailing at the polarization electrodes does not prevent the polarization function from working correctly.

[0041] According to one embodiment, the body made of semiconductor material is capable of withstanding temperatures between 500°C and 1200°C. This makes it possible to heat a contained product which has a high melting point, i.e. in practice above 500°C.

[0042] The present invention also relates to a nuclear reactor using as its primary fluid a molten salt-type fluid contained in a semiconductor material body and comprising at least one heating system as described above. The reactor in question is a fast neutron nuclear fission reactor with a fuel fluid including components such as uranium, plutonium, or even thorium.

[0043] The invention allows the reactor to be started simply and efficiently with a new charge of fissile products mixed with molten salts which have a high melting point.

[0044] The invention will be further detailed by the description of non-limiting embodiments, and on the basis of the attached figures illustrating variants of the invention.

[0045] There figure 1 schematically illustrates the principle of an example of an induction heating system capable of heating a body made of semiconductor material.

[0046] There figure 2 shows in perspective an example of the application of induction heating to a cylindrical bar made of semiconductor material.

[0047] There figure 3 shows in perspective another example of the application of induction heating to a pipe made of semiconductor material.

[0048] There figure 4 shows in perspective another example of the application of induction heating to a crucible made of semiconductor material.

[0049] There figure 5 shows a schematic diagram of an example control system configured to control induction heating.

[0050] There figure 6 shows in cross-section another example of the application of induction heating to selective welds in relation to a semiconductor material.

[0051] In the various figures, the same references designate identical or similar elements. For the sake of clarity, some elements are not necessarily shown to scale.

[0052] With reference to the figures, we will now describe a heating system for heating a body by induction. The body in question is labeled 1. The body in question is made of a semiconductor material. Its electrical resistivity is high in its normal resting state.

[0053] In the illustrated example, the semiconductor material in question is silicon carbide (SiC).

[0054] The semiconductor material can also be chosen from other semiconductor materials, such as Boron Nitride (BN), Gallium Nitride (GaN), or Gallium Arsenide (GaAs). This list is not exhaustive.

[0055] The shape of the body made of semiconductor material can be any shape.

[0056] The shape of the body made of semiconductor material 1 It can be of revolution or prismatic. Of course, any other form factor is not excluded. The dimensions of the body made of semiconductor material 1 can range from a few millimeters to several meters.

[0057] We illustrated at the figure 2 the case of a solid bar with a vertical axis in the figure. Generally speaking, a reference axis can often be defined, denoted A for the body made of semiconductor material. This was illustrated at the figure 3 the case of a vertical axis pipe. For example, the pipe can be cylindrical in revolution.

[0058] We illustrated at the figure 4 the case of a container with an upward-facing mouth. In the relevant trades, this type of container is often called a 'crucible' or a 'vat'.

[0059] Electrical windings are installed near the body made of semiconductor material. 3. These electrical windings, when traversed by an alternating current, generate an electromagnetic field all around the area adjacent to the electrical windings and in particular at least partly in the body made of semiconductor material which is located near the electrical windings. The phrase "nearby" here typically refers to a distance of a few centimeters.

[0060] These electrical windings 3They are therefore used to apply induction heating within the semiconductor material body, provided that induced currents can exist within the semiconductor material body. 1.

[0061] Ingeniously, the inventors proposed a body polarization system made of semiconductor material. Polarization electrodes are used, generally identified by the reference number. 2, in contact with the body made of semiconductor material.

[0062] At least one positive electrode is planned 21 and a negative electrode 22. In the examples illustrated in figures 1 à 5 Only two electrodes are used, but of course it is possible to use several positive voltage electrodes and several negative voltage electrodes as will be seen in the detailed commentary of the figure 6 .

[0063] As schematically illustrated on the figure 1 a source of voltage 61 rated EP is used to apply polarization to a body made of semiconductor material 1.

[0064] We note that the bias voltage denoted V is not alternative. However, the bias voltage noted V may vary and / or is controlled.

[0065] A power generator is also planned. 62 note G, to generate heating power in the form of alternating current intended to be injected into the electrical windings 3.

[0066] Alternating current excitation can be achieved in single-phase or three-phase systems. Electrical windings 3 can be in the form of a winding C.The number of winding turns is adapted according to the current that will flow in the conductors and the desired electromagnetic field strength in the target areas of the semiconductor material body to be heated.

[0067] As illustrated in the figure 5 , the bias voltage V can be controlled by a control unit 4. This control or command can be done in on / off mode or by modulation, for example to regulate the temperature of a semiconductor body. 1 relative to a desired setpoint temperature.

[0068] Depending on the spatial configuration and volume of the body made of semiconductor material, the bias voltage V It could be a few volts or a few tens of volts.

[0069] For this purpose, the system may include one or more temperature sensors 42.The temperature sensor(s) provide temperature information to the control unit. 4. Temperature sensors 42 These can typically be thermocouples.

[0070] Regarding the power circuit for the heating power, a power switch or relay is planned. 51 and a transformer and / or frequency converter 52, known in itself in the field of induction heating and therefore not described in detail here.

[0071] Electrical power is generally delivered in three-phase and the frequency converter can deliver output power in single-phase or three-phase in accordance with the power transformer scheme.

[0072] It is noted that the frequency of the alternating current flowing through the electrical windings is high, typically at least 10 kHz. In some implementations, the frequency of the alternating current flowing through the electrical windings is at least 50 kHz. This frequency can be chosen to minimize the skin effect in the semiconductor material body. 1

[0073] The transformer output is connected via at least two conductors respectively, labeled 31 And 32, to power the electrical windings 3.

[0074] On the figure 6 We have represented areas to be heated selectively, marked with the reference 15, in order to solder a component identified 8 on still made of semiconductor material, for example silicon carbide. The polarization electrodes can be formed by test points.

[0075] This forms several pairs of positive and negative electrodes, each pair being designed to polarize an area of ​​the body made of semiconductor material close to the component to be welded.

[0076] It is observed that the application of polarization is localized. At a distance from the areas located near the electrodes, the polarization of the semiconductor material is insufficient to make it conductive, and consequently the effects of induction heating are zero or negligible in these areas.

Claims

1. Method for heating a body made of semiconductor material (1) comprising: - applying a polarization to the body made of semiconductor material via polarization electrodes (2), - applying induction heating to the body made of semiconductor material via electrical windings (3) arranged near the body made of semiconductor material, the electrical windings being traversed by an alternating current.

2. Heating method according to claim 1, wherein the effective activation of induction heating is selectively controlled by means of controlling a bias voltage delivered to the bias electrodes.

3. Heating method according to claim 1 to 2, wherein the body made of semiconductor material is a silicon carbide (SiC) body.

4. Heating method according to claim 1 to 3, wherein the polarization of the body in semiconductor material is a selective polarization of one or more predetermined regions (15) of the body in semiconductor material.

5. A heating system for a body made of semiconductor material comprising: - polarizing electrodes (2) configured to contact the body made of semiconductor material at at least two locations on the body made of semiconductor material, and to deliver a polarizing voltage thereon, - electrical windings (3) arranged near the body made of semiconductor material, configured to apply induction heating to the body made of semiconductor material, when the windings are traversed by an alternating current and a polarizing voltage is applied.

6. Heating system according to claim 5, wherein the body made of semiconductor material is a silicon carbide body.

7. Heating system according to claim 5 to 6, wherein the body made of semiconductor material is a crucible for receiving a product to be heated.

8. Heating system according to claim 7, wherein the semiconductor material to be heated is a salt, for example a chlorinated or fluorinated salt.

9. Heating system according to claim 5 to 8, wherein the body made of semiconductor material is a conduit suitable for conducting a product to be heated.

10. Heating system according to claim 5 to 9, in which the electrical windings (3) surround the body made of semiconductor material.

11. Heating system according to claim 5 to 10, wherein the body made of semiconductor material is generally of revolution about a reference axis (A) and the electrical windings are generally circular with an axis aligned with the reference axis.

12. Heating system according to claim 5 to 11, further comprising a control unit (4) configured to control the bias voltage applied to the bias electrodes.

13. Heating system according to claim 5 to 12, wherein the polarization electrodes (21,22) are interposed between the body made of semiconductor material (1) and the electrical windings (3).

14. Heating system according to claim 5 to 13, wherein the body made of semiconductor material (1) is capable of withstanding temperatures between 500°C and 750°C.

15. Nuclear reactor using as primary fluid a molten salt type fluid contained in a body of semiconductor material (1) and comprising at least one heating system according to any one of claims 5 to 14.

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