RU2223571C2 - Multiple-element thermoionic electrogenerating assembly - Google Patents

Abstract

FIELD: direct conversion of thermal energy to electric one, applicable in production of a thermionic reactor-converter, first of all of space designation. SUBSTANCE: the thermionic electrogenerating assembly has a carrying tube accommodating at least three series-connected electrogenerating elements with a fuel-emitter unit and a collector and a collector insulation common for all electrogenerating elements, made in the form of two layers insulated from the carrying tube by a protective electrode. The protective electrode is electrically connected to the collector of one of the central electrogenerating elements. The electrical connection of the collector to the protective electrode may be may be made of the same metal as the protective electrode. EFFECT: enhanced reliability and service life capacity of the thermionic electrogenerating assembly. 2 cl, 1 dwg

Description

 The invention relates to a thermionic method of converting thermal energy into electrical energy and can be used to create multi-element power generating assemblies of a thermionic converter reactor, primarily for space purposes.

 The most common design of power generating assemblies (EHS) with series-connected electrical generating elements (EGE) of a coaxial circuit with cylindrical electrodes (emitter and collector) [1]. The emitter shell, the cylindrical part of which is an emitter of a thermionic converter (TEC), is filled with fissile material, forming a fuel-emitter unit (CHP). The emitter is installed with a gap of 0.3-0.5 mm relative to the cylindrical collector. EGE are connected to each other in series using switching jumpers. The collectors of individual EHEs are separated from the body (carrier tube, cover) by common collector electrical insulation for all EHEs. Collectors, electrical insulation and carrier tube are made together and form the so-called collector package (KP), in this case three-layer.

 The main problem of creating such EHS is to ensure a long service life, which requires ensuring the geometrical stability of the emitter, i.e., preventing deformation of the emitter shell of the TEU due to swelling of the fuel core during operation, and ensuring the electrical strength of the electrical insulation.

 However, in a three-layer KP, the electrical insulation is in contact with a pair and cesium plasma - the TEC working fluid - and does not allow high voltage due to the possibility of breakdown of collector insulation. Therefore, the EHS under consideration can only be used in TRP with a low operating voltage.

 Known EHS based on thermionic EGE with a sealed emitter shell [2]. EGEs contain a fuel-emitter assembly with a sealed emitter shell inside which a fissile material is placed, usually uranium dioxide. Part of the outer surface of the emitter shell serves as the emitter of the TEC. EGE also contains a switching jumper, with the help of which EGE are connected in EHS, which contains collector insulation common to all EGE and the outer casing.

 However, in this EHS with a three-layer KP, the electrical insulation contacts the vapor and cesium plasma and does not allow high voltage due to the possibility of breakdown of collector insulation. Therefore, the EHS under consideration can only be used in TRP with a low operating voltage.

 Known multi-element thermionic EHS proposed in [3]. It consists of series-connected EGEs, each of which contains a ventilated TEU in the form of a cylinder with a fuel core and an emitter shell with two end caps, the first of which has a gas outlet device (GOU), and the second end cap is connected to a switching jumper that electrically commutates the emitter a shell with a collector of neighboring EGE. The long life of such an EHS in the process of swelling of the fuel core is ensured by the removal of gaseous fission products (GPA) from the fuel core in the form of GOU. GPA are removed through this tube from the core to the MEZ, as a result of which gas swelling of the fuel, and, accordingly, deformation of the emitter shell, does not occur.

 However, in the considered EHS, a three-layer KP is also used, which does not allow high voltage between the carrier tube and the EGE collectors. Therefore, such an EHS cannot be used to create a high-voltage TRP.

 Closest to the invention in technical essence is a multi-element thermionic emission EHS described in [4].

 Thermionic EHS contains a carrier tube (case, cover), inside of which are placed no less than three in series EGEs with a fuel-emitter unit and a collector and collector insulation common for all EGEs, made in the form of two layers separated by a guard electrode isolated from the carrier tube.

 In the EHS under consideration, the exclusion of electrical breakdown between the EGE collectors and the carrier tube is solved by introducing an intermediate conductive shell (guard electrode) between the collectors and the carrier tube, dividing the insulation into two layers. The layer adjacent to the carrier tube is protected from cesium vapor (the so-called “dry” insulation layer) and can withstand significant voltages (at least 100-150 V) at the operating temperature. The second insulation layer works in pairs and cesium plasma (the so-called “wet” insulation layer) and, like a three-layer CP, the voltage on it should not be high to exclude electrical breakdown of collector insulation. However, in total, two layers of insulation can withstand significantly higher voltage than a three-layer KP with "wet" insulation. On the basis of such five-layer gearboxes, EHS for TRP with a relatively high operating voltage (more than 100 V) can be created.

 The introduction of two layers of insulation separated by a guard electrode (electrically conductive sheath) reduces the likelihood of electrical breakdown of “wet” insulation. However, for this, the voltage on it should not significantly exceed the voltage of the EHS. However, the introduction of a guard electrode with a floating potential does not guarantee that the main voltage drop between the collector and the EHS carrier tube will be on "dry" insulation. Cases are possible, for example, in the presence of defects in the “wet” insulation layer, when the voltage on the “wet” insulation exceeds the breakdown voltage, a breakdown occurs or a so-called thermal breakdown in the “wet” insulation occurs, which can then cause thermal breakdown and “dry” isolation, resulting in a type of “short circuit” or “open circuit” failure.

 The objective of the invention is to enable the exclusion of electrical breakdown of the insulation layer in contact with steam and cesium plasma in a multi-cell EHS with a guard electrode and, therefore, increasing the reliability and serviceability of a thermionic EHS for TRP with a high operating voltage.

 The indicated task is realized in a multi-element thermionic EHS containing a carrier tube, inside of which at least three series-connected EGEs with a fuel-emitter assembly and a collector are placed, and collector insulation common to all EGEs made in the form of two layers separated by a protective layer isolated from the carrier tube an electrode in which the guard electrode is electrically connected to the collector of one of the central EGE. The electrical connection of the collector to the guard electrode is made of the same metal as the guard electrode.

 The drawing shows a structural diagram of a multi-element thermionic EHS.

 EHS is drawn from successively electrically commutated at least three EGEs (the drawing shows a five-element EHS). Each EGE contains a cylindrical fuel-emitter unit 1 installed with an interelectrode gap 2 in the collector 3, and a jumper 4. The fuel-emitter unit consists of a fuel core 5 and an emitter shell including a side cylindrical part 6, the outer surface of which serves as an emitter of a thermionic converter , and two end parts: the first 7 and second 8, which is electrically connected to the switching jumper 4, which provides electrical switching of the emitter shell with the collector 3 of one o from neighboring EGE during electrical switching of EGE to EHS. The gap 2 between the emitter (the outer surface of the side portion 6 of the emitter shell) and the collector 3 is the interelectrode gap (MEZ) of the thermionic converter and is filled with steam and cesium plasma under operating conditions.

 Common to all EHEs are a carrier tube (case or cover) 9, which is cooled externally by a coolant (not shown), and two collector insulation layers 10 and 11 separated by a guard electrode 12. The first collector insulation layer 10 is in contact with steam and plasma cesium in the MEZ 2, i.e. is the so-called wet insulation. The second layer 11 of collector insulation due to the guard electrode 12 is separated from the vapor and cesium plasma, i.e. is the so-called "dry" insulation. The guard electrode 12 using the connector 13 is electrically closed to the collector 3 of the Central EGE. If the number of EGE in the EHS is even, then the guard electrode 12 can be closed on either of the two central EGE. The extreme EGEs have current outputs, one of which 14 is an emitter current output, and the other 15 is a collector current output made in the form of a tube through which cesium vapor is supplied to MEZ 2. The current leads 14 and 15 are electrically insulated from the housing by the hermetic leads 16. With the help of the current leads 14 and 15, electrical switching of the EHS in the TRP (not shown) is provided.

 The collectors 3, layers 10 and 11 of the collector insulation, the guard electrode 12 and the carrier tube 9 are made as a whole, as a rule, by gas-static pressing and form the so-called collector package (KP). The main requirements for the scheme, materials and method of manufacturing KP is to ensure low thermal resistance and high electrical strength. The first is achieved by the choice of materials KP and the manufacturing method. High temperature metal and ceramics with almost the same linear expansion coefficients were selected as KP materials, namely, collector 3, guard electrode 12 and support tube 9 are made of a niobium alloy, for example, NbTsU (niobium-zirconium-carbon), and layers of electrical insulation 10 and 11 are made from aluminum oxide. The connector 13 is also made of the same material as the guard electrode 12, for example a niobium alloy, which ensures compatibility of the connector 13 with the collector insulation layer 10. The production of KP as a whole is carried out by the method of gas-static pressing, which provides diffusion welding of dissimilar materials without thermal resistance in the contacts between the layers of dissimilar materials. A high value of KP dielectric strength is achieved by introducing a guard electrode 12, usually in the form of a thin niobium foil, which separates collector insulation into two layers: a wet insulation layer 10 in contact with vapor and cesium plasma and, as a result, having a low electric strength value, and layer 11 “dry” insulation, which, thanks to the guard electrode 12, is protected from contact with steam and cesium plasma and, as a result, has a high value of electric strength, as a rule, in operating conditions of at least 100 ... 150 V.

 Multi-element thermionic EHS works as follows (as part of TRP).

 The manufactured EHSs are assembled in the active zone, which is surrounded by a reflector with TRP controls (not shown). EHS with the help of insulated grommets 16 current leads 14 and 15 are switched in series - in parallel to obtain the required voltage of the TRP, for example 120 V. under operating conditions, in the initial state of the MEZ 2 all the EHS is evacuated. The TRP is launched at a certain intermediate level of neutron power. During operation, due to the fission of uranium nuclei, the fuel core 5 heats up.

 The heat generated during the fission of the uranium nuclei of the core 5 is supplied to the cylindrical part 6 (as well as to the end parts 7 and 8) of the emitter shell, and then through the MEZ 2, which is initially evacuated, is transferred to collector 3 by radiation. From collector 3, heat through the first collector insulation layer 10, the guard electrode 12 and the second collector insulation layer 11 is transferred to the carrier tube (housing) 9, from which heat is removed by the heat carrier (not shown).

 To generate electricity, it is necessary to fill the MEZ 2 with the working fluid of the TEC - cesium vapor. Filling the MEZ with cesium vapor is carried out through the current lead tube 15 with a gradual increase in the cesium vapor pressure to the working one, which is usually from 1 ... 2 to 6 ... 8 mm Hg. depending on the magnitude of the MEZ 2 and the density of the electric power of the TEC formed by the electrodes 6 and 3. After reaching the working value of the cesium vapor pressure (or in the process of increasing), the neutron power of the TRP, and therefore the thermal power of the EHS, is increased to the working nominal value.

 In the nominal mode (as well as in the starting mode), the heat released during fission of the uranium nuclei of core 5 is supplied to the cylindrical part 6 of the emitter shell, which is heated to 1600 ... 2100 K, and then through the MEZ 2, which is filled with cesium vapor during operation pressure, radiation, and with such an electron is transferred to collector 3 with an operating temperature of the order of 1000 K. In the MEZ 2, part of the heat (with an efficiency of about 15% is converted into electricity at a voltage of one EGE of 0.5 ... 1.0 V (most often 0, 5 ... 0.7 V). Unconverted part of the heat from the collector 3 through the first collector layer 10 insulation, the guard electrode 12 and the second collector insulation layer 11 is transferred to the carrier tube 9, with which heat is removed by the heat carrier (not shown). It is possible to remove heat from the carrier tube 9 through a special heat transfer system, for example, during thermal reactor tests of such EHS (not shown )

 The series connection of 4 separate EEGs using the jumper wires leads to the addition of the voltages of all EGEs in the EHS, as a result of which the total voltage of the EHS between current outputs 14 and 15 is approximately equal to the product of the voltage of one EGE by the number of EGEs in the EHS.

 Due to the fabrication of KP by the method of gas-static pressing, which provides diffusion welding of dissimilar materials without thermal resistance in the contacts between layers of dissimilar materials, under operating conditions, the temperature drop across the KP is the minimum possible and usually does not exceed 50. . 100K. Thus, the discharge of untransformed heat into space is made by radiation at high temperatures.

 Since a multi-element EHS is designed to operate as part of a TRP with an operating voltage of the order of 100 ... 150 V, in the TRP in operating modes there can be an EHS in which the potential difference between the collector 3 and the carrier tube 9 will be at least half of the operating voltage TRP, and with some EGS switching schemes in TRP and in emergency situations - the same order. Therefore, KP EHS must have an electric strength of not less than the operating voltage of the TRP, i.e. not less than 100 ... 150 V. In the proposed EHS, this is ensured by two-layer collector insulation with a guard electrode electrically closed to the collector of one of the central EGE. Due to the fact that the guard electrode 12 is electrically closed via the connector 13 to the collector 3 of one of the central EGEs, the guard electrode 12 will not have a floating potential, which in principle can be any, but have the potential of a secondary EGE collector. As a result, the maximum potential difference between the collectors 3 of the extreme EGE and the guard electrode 12 will be, firstly, predictable, and, secondly, equal to approximately half the operating voltage of the EHS (half the potential difference between the current leads 14 and 15). The predicted and relatively low value of the potential difference on the wet insulation layer 10 allows us to design the EHS in such a way that, in any EHS operation modes, the maximum potential difference on the collector insulation layer 10 will be less than the breakdown voltage of the insulation in the cesium vapor and plasma. Especially dangerous is the cesium vapor filling mode of the MEZ EHS, when the cesium vapor pressure gradually rises from zero to the operating value. In this mode, any values of the product pd are possible, where p is the cesium vapor pressure and d is the distance, including those corresponding to the minimum of the Paschen curve, when electrical breakdown is possible at relatively low potential differences.

 However, due to the fact that in the EHS under consideration, the potential difference on the "wet" insulation is small and known, its breakdown will be excluded. And the required high breakdown voltage is provided by a layer of 11 “dry” collector insulation that is not in contact with steam and cesium plasma due to the presence of a guard electrode 12 and whose electric strength can be several hundred volts, i.e. significantly higher operating voltage TRP.

 Thus, the electrical connection of the guard electrode to the collector of one of the central EGE allows eliminating the electrical breakdown of the insulation layer in contact with steam, both in the nominal and starting modes of operation, and, therefore, to increase the reliability and serviceability of the multi-element thermionic power generation assembly and create a thermionic reactor with increased operating voltage.

 1. Design and testing of thermionic fuel elements / V.V. Sinyavsky and others // M .: Atomizdat, 1981, p. 15-20.

 2. Patent RU 2095881 C1, H 01 J 45/50. Thermionic power generation assembly.

 3. Patent RU 2151440 C1, H 01 J 45/50. Thermionic power generation assembly. 06/20/2000. Bull. 17.

 4. Sinyavsky V.V. Methods and means of experimental research and reactor testing of thermionic assemblies. M .: Energoatomizdat, 2000, p. 35-39, fig. 1.13.

Claims (2)

1. A multi-element thermionic power generation assembly containing a carrier tube, inside of which at least three series-connected power-generating elements with a fuel-emitter assembly and a collector are placed, and common to all power-generating elements collector insulation made in the form of two layers separated from the carrier tube a guard electrode, characterized in that the guard electrode is electrically connected to the collector of one of the central power generating elements. 2. The multi-element thermionic power generation assembly according to claim 1, characterized in that the electrical connection of the collector with the guard electrode is made of the same metal as the guard electrode.