Method and system for heating a body made of semiconductor material

Abstract

Disclosed is a heating method and a heating system for heating a body made of semiconductor material (1), the method comprising: - applying 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 close to the body made of semiconductor material, the electrical windings being traversed by an alternating current; use in particular for silicon carbide (SiC); and use in particular for molten salt fusion in the context of a Generation IV nuclear reactor.

Description

[0001] Method and system for heating a body made of semiconductor material

[0002] The present invention relates to a method and system for heating a body made of semiconductor material.

[0003] 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.

[0004] Induction heating is also used in a domestic context thanks to suitable cooktops and cooking appliances.

[0005] 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.

[0006]

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

[0007] 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.

[0008]

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

[0009]

[0008] However, it turns out that in the configuration where the primary fluid of the reactor core is based on molten salt, for example lithium chloride or lithium fluoride, the corrosion phenomenon of the metal vessel does not allow for a reasonable, or at least desirable, service life. It is therefore desirable to manufacture the vessels, pipes, and containers from a material other than steel or any type of steel alloy.

[0010] Silicon carbide, with the chemical molecular symbol SiC (and the English name 'silicon carbide'), is a very interesting candidate for making the tanks and pipes in question.

[0011]

[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.

[0012]

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

[0013]

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

[0014]

[0013] To this end, a method for heating a body made of semiconductor material (1) is proposed, comprising:

[0015] - apply a polarization to the body made of semiconductor material via polarization electrodes (2),

[0016] - applying induction heating to the semiconductor material body via electrical windings (3) arranged near the semiconductor material body, the electrical windings carrying an alternating current.

[0014] Advantageously, thanks to these arrangements, the electrical polarization of the semiconductor material 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 electrical windings near the semiconductor material body to be heated.

[0017]

[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 in order to make induction heating work efficiently.

[0018]

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

[0019]

[0017] By this means, 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.

[0020]

[0018] A bias voltage can thus be controlled in an analog manner or an average voltage can be controlled via a width modulation control (in the jargon of the trade).

[0021] According to one embodiment, the body made of semiconductor material is a silicon carbide body.

[0022] Silicon carbide is a material with very high mechanical properties and a very interesting chemical passivity; its chemical symbol is SiC and its English name is 'silicon carbide'.

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

[0023]

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

[0024]

[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.

[0025]

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

[0026]

[0025] The present invention also relates to a heating system for a body made of semiconductor material comprising:

[0027] - polarization electrodes configured to contact the semiconductor material body at at least two locations on the semiconductor material body, and deliver a polarization voltage there,

[0028] - electrical windings 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 bias voltage is applied.

[0029]

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

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

[0030] It is noted that the present invention can also be applied to other semiconductor materials as already mentioned above.

[0031] 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.

[0032] 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.

[0033]

[0031] According to one embodiment, the product to be heated is a salt, for example, 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 from a corrosion standpoint, which eliminates the conventional choices made for earlier-generation reactors when designing the vessels and piping in a fourth-generation nuclear reactor.

[0034]

[0032] According to an alternative embodiment, the body made of semiconductor material is a conduit suitable for conducting 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.

[0035]

[0033] According to 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, makes it possible to cover the entire volume of the body made of semiconductor material.

[0036]

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

[0037]

[0035] According to one embodiment, the semiconductor body is generally of revolution about a reference axis, and the electrical windings are generally circular with an 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 body. Calculations or models established for cylindrical electrical windings can be used.

[0038]

[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.

[0039]

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

[0040]

[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] In one embodiment, the polarization electrodes are interposed between the semiconductor material body and the electrical windings.

[0041]

[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.

[0042]

[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.

[0043]

[0042] The present invention also relates to a nuclear reactor using as a 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 uranium, plutonium, or even thorium-type components.

[0044]

[0043] The invention makes it possible to start the reactor in a simple and efficient way with a new charge of fissile products mixed with molten salts which have a high melting temperature.

[0045]

[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.

[0046]

[0045] Figure 1 schematically illustrates the principle of an example of an induction heating system suitable for heating a body made of semiconductor material.

[0047] Figure 2 shows in perspective an example of the application of induction heating to a cylindrical bar made of semiconductor material.

[0048] Figure 3 shows in perspective another example of the application of induction heating to a pipe made of semiconductor material.

[0049] Figure 4 shows in perspective another example of the application of induction heating to a crucible made of semiconductor material.

[0050] Figure 5 shows a schematic diagram of an example control system configured to control induction heating.

[0051] Figure 6 shows in cross-section another example of the application of induction heating to selective welds in relation to a semiconductor material.

[0052]

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

[0053]

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

[0054] In the illustrated example, the semiconductor material in question is silicon carbide (SiC).

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

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

[0057]

[0057] Figure 2 illustrates the case of a solid bar with a vertical axis. Generally, a reference axis, denoted A, can often be defined for the body made of semiconductor material. Figure 3 illustrates the case of a pipe with a vertical axis. For example, the pipe could be cylindrical.

[0058] Figure 4 illustrates 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]

[0059] Electrical windings 3 are installed near the body made of semiconductor material. These electrical windings make it possible to generate, when traversed by an alternating current, 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.

[0060]

[0060] The expression "nearby" here typically refers to a distance of a few centimeters

[0061]

[0061] These electrical windings 3 are therefore used to apply induction heating in the body made of semiconductor material, provided that induced currents can exist inside the material of the body made of semiconductor material 1.

[0062] Ingeniously, the inventors proposed a system for polarizing the body made of semiconductor material. Polarizing electrodes, usually identified by the reference 2, are placed in contact with the body made of semiconductor material.

[0063]

[0063] At least one positive electrode 21 and one negative electrode 22 are provided. In the examples illustrated in figures 1 to 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 figure 6.

[0064]

[0064] As schematically illustrated in Figure 1, a voltage source 61, denoted EP, is used to apply a bias to a body made of semiconductor material 1.

[0065]

[0065] It is noted that the bias voltage denoted V is not alternating. However, the bias voltage denoted V can vary and / or is controlled.

[0066] A current generator 62, labeled G, is also planned to generate heating power in the form of alternating current intended to be injected onto the electrical windings 3.

[0067] Alternating excitation can be achieved in single-phase or three-phase configurations. The three electrical windings can be in the form of a C-shaped winding. The number of turns of the windings is adapted according to the current that will flow in the conductors and the desired strength of the electromagnetic field in the target areas of the semiconductor material to be heated.

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

[0068]

[0069] Depending on the spatial configuration and volume of the body made of semiconductor material, the bias voltage V can be a few volts or a few tens of volts.

[0069]

[0070] For this purpose, the system may include one or more temperature sensors 42. The temperature sensor(s) deliver temperature information to the control unit 4. The temperature sensors 42 can typically be thermocouples.

[0070]

[0071] Regarding the power circuit for the heating power, a power switch or relay 51 and a transformer and / or frequency converter 52 are provided, which is known in itself in the field of induction heating and therefore not described in detail here.

[0071]

[0072] 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]

[0073] 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.

[0073]

[0074] The transformer output is connected via at least two conductors respectively, marked 31 and 32, to supply the electrical windings 3.

[0074]

[0075] Figure 6 shows areas to be selectively heated, labeled with the reference numeral 15, for the purpose of soldering a component marked 8 onto a semiconductor material, for example, silicon carbide. The polarization electrodes can be formed by probe tips.

[0075]

[0076] 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]

[0077] 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 detrimental or negligible in these areas.

Claims

DEMANDS 1. A method for heating a body made of semiconductor material (1) comprising: - apply a polarization to the body made of semiconductor material via polarization electrodes (2), - apply 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 the 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. Heating system for a body made of semiconductor material comprising: - at least one body made of semiconductor material (1), - polarization electrodes (2) configured to contact the semiconductor material body at at least two locations on the semiconductor material body, and to deliver a polarization voltage there, - electrical windings (3) arranged near the body of semiconductor material, configured to apply induction heating to the body of semiconductor material, when the windings are traversed by an alternating current and a bias voltage is applied.

6. Heating system according to claim 5, wherein the body made of semiconductor material (1) is a silicon carbide body.

7. Heating system according to claim 5 to 6, wherein the body made of semiconductor material (1) is a crucible for receiving a product to be heated.

8. Heating system according to claim 7, wherein the product 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 one or more bodies of semiconductor material (1) and comprising at least one heating system according to any one of claims 5 to 14.

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