US3454797A - Thermionic converter - Google Patents

Thermionic converter Download PDF

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Publication number
US3454797A
US3454797A US481318A US3454797DA US3454797A US 3454797 A US3454797 A US 3454797A US 481318 A US481318 A US 481318A US 3454797D A US3454797D A US 3454797DA US 3454797 A US3454797 A US 3454797A
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United States
Prior art keywords
reservoir
cesium
alkali metal
compound
temperature
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Expired - Lifetime
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US481318A
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English (en)
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Bernard Devin
Robert Lesueur
Ralph Setton
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J45/00—Discharge tubes functioning as thermionic generators
    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21C—NUCLEAR REACTORS
    • G21C3/00—Reactor fuel elements and their assemblies; Selection of substances for use as reactor fuel elements
    • G21C3/40—Structural combination of fuel element with thermoelectric element for direct production of electric energy from fission heat or with another arrangement for direct production of electric energy, e.g. a thermionic device
    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21C—NUCLEAR REACTORS
    • G21C7/00—Control of nuclear reaction
    • G21C7/02—Control of nuclear reaction by using self-regulating properties of reactor materials, e.g. Doppler effect
    • G21C7/04—Control of nuclear reaction by using self-regulating properties of reactor materials, e.g. Doppler effect of burnable poisons
    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21D—NUCLEAR POWER PLANT
    • G21D7/00—Arrangements for direct production of electric energy from fusion or fission reactions
    • G21D7/04—Arrangements for direct production of electric energy from fusion or fission reactions using thermoelectric elements or thermoionic converters
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E30/00—Energy generation of nuclear origin
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E30/00—Energy generation of nuclear origin
    • Y02E30/30—Nuclear fission reactors

Definitions

  • the diode comprises an evacuated envelope in which are disposed a heated cathode and an anode kept at a temperature lower than that of said cathode.
  • Reservoir means are provided, in free communication with the inside of this envelope, containing: (l) a compound of insertion in graphite of an alkali metal selected from the group of rubidiurn, potassium and especially cesium, and (2) a metal having a low work function and not forming a compound of insertion in graphite.
  • This last-mentioned metal which can advantageously be an alkaline-earth metal, is volatile or incorporated in a volatile compound, so as to be able, during operation of the diode, to be volatilized and a cover, at least partly, the surface of the cathode and/or anode, thus lowering the work function thereof.
  • the present invention relates to plasma diodes and it is more especially concerned with diodes intended to transform into electrical energy the thermal energy generated in a nuclear reactor.
  • the chief object of the present invention is to provide an improved diode of this type which makes it possible, on the one hand, independently to adjust both the ionized atmosphere or plasma, to neutralize the space charge inside the diode, and the Work function of the electrodes, and, on the other hand, to locate the plasma source in a zone at predetermined high temperature (ranging for instance from 500 to l000 C.).
  • the diode according to the present invention comprises an evacuated envelope in which are disposed at least one heated cathode and at least one anode kept at a temperature lower than that of the cathode and this diode is characterized by the fact that it comprises at least one reservoir in free communication with the inside of said envelope and containing, on the one hand, at least one compound containing an alkali metal, this compound advantageously consisting of a compound of insertion of an alkali metal, such in particular as cesium, in graphite and, on the other hand, at least one metal, either volatile or belonging to a volatile product, having a low work function value (in particular an alkaline-earth metal) capable, during the operation of the diode, of volatilizing and of covering at least partly the surface of said cathode and/or of said anode, in order to reduce the work function value thereof.
  • a low work function value in particular an alkaline-earth metal
  • the invention is more especially intended for systems including several plasma diodes incorporated in nuclear reactors and working at anode temperatures higher than approximately 500 C.
  • FIG. 1 is a sectional view of a plasma diode according to the present invention and belonging to a system of several plasma diodes housed in the core of a nuclear reactor, said diode including a single reservolr for the 3,454,797 Patented July 8, 1969 alkali metal compound and for the metal of low work function; and
  • FIG. 2 is a view similar to FIG. 1 but corresponding to the case where are two distinct reservoirs, for the alkali metal compound and for the low work function metal, respectively,
  • Said prior plasma diodes comprised, in an evacuated gastight envelope, at least one cathode and at least one anode located at a distance from each other of some millimeters or of a fraction of a millimeter.
  • the cathode was heated to a temperature corresponding to an abundant electron emission (through thermionic eifect) and the anode was kept at a temperature substantially lower than that of the cathode for collecting the electrons emitted by the cathode without in turn emitting a substantial number of electrodes.
  • the temperature of the rescrvoir was generally chosen such that the alkali metal pressure (in particular the cesium vapor pressure in the envelope and reservoir system) was of the order of 2 mm. of mercury (a higher pressure producing too high a electrical resistivity between the cathode and the anode) which required a relatively low reservoir temperature, 300 C. in the case of cesium.
  • the alkali metal (cesium for instance) served two purposes, to wit, on the one hand, to lower the work function value of the electrodes, partly coated with cesium during the operation, due to the fact that the work function valve of the alkali metal is lower than that of the electrode itself (that of cesium is of 1.8 elec tron volts), and, on the other hand, to produce positive ions which neutralize the (negative) space charge resulting from the emission of electrons by the cathode, this production of positive ions taking place according to the Langmuir eifect, the alkali metal of low ionization potential (3.9 volts in the case of cesium) getting ionized by contact with electrodes made of a material having a work function valuel higher than this ionizing potential.
  • this alkaline metal (cesium) served both of these two purposes, the relative importance of which depended upon the temperature of the electrodes (immediate re-evaporation of the alkali metal on one electrode and complete ionization of this metal taking place when the temperature of the electrode exceeds a critical value proportional to the temperature of the cesium reservoir), it was not possible to adjust the two functions of the alkali metal separately;
  • the object of the present invention is to obviate the above mentioned drawbacks by permitting on the one hand, an independent adjustment of the lowering of the work function value and of the production of positive ions neutralizing the space charge and, on the other hand, of bringing the alkali metal reservoir at a relatively high temperature ranging from 500 to 1000 C.
  • a diode 14 comprising an evacuated envelope 1 (closed by packing members 1a) wherein are provided at least one cathode 2 (advantageously charged with issionable material, in which case system 3 constitutes a nuclear reactor slug) heated to be brought to a ltemperature of abundant electron emission (advantageously through nuclear iissions) and at least one anode 4 kept at a temperature lower than that of the cathode (advantageously by circulation of a cooling fluid in the channel 5 provided between a tube 6 in thermal contact with anode 4 through a weld 6a, and an external tube 7), packing members 1a being made of a material ensuring thermal insulation;
  • At least one reservoir (for instance a single reservoir 8 in the embodiment of FIG. 1 or two reservoirs 8a, 8b in the embodiment of FIG. 2) in free communication with said enevlope 1 (through channels 9 in the case of FIG. 1 or 9a, 9b in the case of FIG. 2) and containing:
  • At least one compound 101 con-taining an alkali metal in the bound or combined state housed in reservoir 8 in the case of FIG. 1 and in reservoir 8a in the case of FIG. 2), this compound advantageously being a compound of insertion of cesium in graphite, and
  • At least one metal 11 either volatile or belonging to a volatile compound, having a low work function value, in particular an alkaline-earth metal housed in reservoir 8 in the case of FIG. l or in reservoir 8b in the case of FIG. 2, this metal 11 being capable, during the operation of diode 14, of volatilizing and coming to coat, at least partly, the surface of said cathode and/ or anode in order to reduce the work function value thereof.
  • envelope 1 a saturated vapor pressure of the alkali metal of compound 10 and of metal 11.
  • the reservoir 8 or 8a containing ceslum or another alkali metal may be housed, as illustrated, inside a slug 3, hence at relatively high temperature, to with substantially that of anode 4, a little higher than that of the cooling fluid circulating in channel 5.
  • the temperature of reservoir 8 or 8a may be adjusted to the desired value by suitably choosing the cross section of the connecting conducting pieces constituted by the walls 12 and 13 of channel 9 and reservoir 8, respectively.
  • diodes 14 disposed end t0 end, as illustrated, in the same slug 3 (limited by a tube 6), the connection between two successive diodes 14 and 14a being ensured by connectors 15 the cross section and the thermal conductivity of which are chosen in such manner as to adjust, in combination with the cross sections of walls 12 and 13 (which may be different for every diode 14, 14a), the desired reservoir temperature which is a function of the neutron flux received by every diode. It will be noted that the reservoir is no longer, as in the prior plasma diodes above referred to, necessarily the coldest point of the system.
  • the element 16 of FIGS. 1 and 2 constitutes the pumping nipple through which it is possible to evacuate the whole of envelope 1 and either reservoir 8 (in the case of'FIG. 1) or reservoirs 8a and 8b (in the case of FIG. 2).
  • Cathode 2 may be made of uranium carbide, possibly with the addition of other carbides, partly covered with the alkali metal (cesium) during the operation;
  • Anode 4 may be made either of niobium or of rhenium, partly covered with the alkali metal (cesium) during the operation;
  • the cooling tiuid may be a molten alloy of sodium and potassium
  • Tubes 6 and 7 and connectors 15 may be made of stainless steel
  • Packing means 1a may be made of alumina with an addition of yttrium oxide.
  • the alkali compound may be constituted by a chemical compound, an amalgam or, preferably, a compound of insertion into graphite (either natural or pyrolytic) of an alkali metal or an alloy of alkali metals (potassium and cesium, potassium and rubidium), in particular by a compound of insertion of cesium in graphite.
  • a chemical compound an amalgam or, preferably, a compound of insertion into graphite (either natural or pyrolytic) of an alkali metal or an alloy of alkali metals (potassium and cesium, potassium and rubidium), in particular by a compound of insertion of cesium in graphite.
  • the compounds of insertion in graphite, and in particular CsCs may be prepared in the following manner:
  • the alkali compound that is brought into play constitutes a reversible association of an alkali metal maintaining in its vicinity an alkali vapor pressure in equilibrium with an alkali metal bound in the compound.
  • 10g facesse-$5- wherein P is the pressure in millimeters of mercury, or torrs, and T is the temperature in Kelvin degrees.
  • the pressure of equilibrium P is 2 mm. of mercury, which is suitable.
  • the metal or product serving to lower the work function value for the electrodes either consists of an alkali or alkaline-earth metal (beryllium, magnesium, calcium, strontium, barium, sodium, lithium) in the free state or the bound state, or consists of a volatile element or compound the work function value of which is lower than 3.5 electron volts approximately, such as polonium, lanthanum, uranium, beryllium, cerium, samarium, thorium, zinc, BaO, LaB6.
  • an alkali or alkaline-earth metal beryllium, magnesium, calcium, strontium, barium, sodium, lithium
  • a volatile element or compound the work function value of which is lower than 3.5 electron volts approximately, such as polonium, lanthanum, uranium, beryllium, cerium, samarium, thorium, zinc, BaO, LaB6.
  • the ionizable alkali compound and the alkaline-earth compound or the like having a low work function value are either contained, both at the same temperature, in a .common reservoir 8 (FIG. 1), or at diiferent respective temperatures into reservoirs 8a and 8b (FIG. 2). But in both cases it is possible independently to adjust the saturating pressures in envelope 1, of the ionizable gas, such as cesium and of the body used for lowering the work function value, such as barium.
  • the pressure of equilibrium of barium is 0.05 mm. of mercury and that of cesium 0.1 mm. of mercury, which pressure is sufficient for producing cesium ions upon a surface covered with a thin layer of barium.
  • the lowering of the pressure of the gases contained in the diode increases the free mean path of travel of the electrons in the diodes, which permits Avof providing a relatively large distance between the electrodes (averaging one half millimeter) so that the construction is made easier.
  • the distance between electrodes is easy to obtain.
  • the eiciency is high.
  • a diode which comprises, in combination, an evacuated envelope
  • a tirst electrode in said envelope consisting of a heated cathode
  • a second electrode in said envelope consisting of an anode kept at a temperature lower than that of said cathode
  • reservoir means in free communication with the inside of said envelope
  • said reservoir means on the one hand, at least one compound of insertion in graphite of an alkali metal selected from the group consisting of cesium, rubidium and potassium, and, on the other hand, at least one volatile product consisting, at least partly, of a metal having a low work function value and which does not form a compound of insertion in graphite, said volatile product being capable of volatilizing during the operation of the diode and of covering, at least partly, the surface of at least one said electrodes, thus lowering the work function thereof.
  • a diode according to claim 1 wherein said second mentioned metal is an alkaline-earth metal.
  • a diode according to claim 1 wherein said second mentioned metal is a metal of the group consisting of polonium, lanthanum, uranium, beryllium, cerium, sa marium, thorium and zinc.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • General Engineering & Computer Science (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Plasma Technology (AREA)
  • Manufacture And Refinement Of Metals (AREA)
  • Battery Electrode And Active Subsutance (AREA)
  • Luminescent Compositions (AREA)
US481318A 1964-08-25 1965-08-20 Thermionic converter Expired - Lifetime US3454797A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
FR986133A FR1480112A (fr) 1964-08-25 1964-08-25 Perfectionnements aux diodes à plasma

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US3454797A true US3454797A (en) 1969-07-08

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US481318A Expired - Lifetime US3454797A (en) 1964-08-25 1965-08-20 Thermionic converter

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US (1) US3454797A (fr)
BE (1) BE668624A (fr)
CH (1) CH445588A (fr)
DE (1) DE1489262B2 (fr)
ES (1) ES316698A1 (fr)
FR (1) FR1480112A (fr)
GB (1) GB1044459A (fr)
IL (1) IL23941A (fr)
LU (1) LU49376A1 (fr)
NL (1) NL6511120A (fr)
SE (1) SE317120B (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3793542A (en) * 1972-09-08 1974-02-19 Thomson Csf Thermoionic converter

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2666864A (en) * 1950-01-20 1954-01-19 Westinghouse Electric Corp Image intensifier tube
US3157802A (en) * 1960-09-21 1964-11-17 Fox Raymond Thermionic energy converter
US3215868A (en) * 1961-10-20 1965-11-02 Gen Dynamics Corp Tiiermionic converter
US3353037A (en) * 1964-05-11 1967-11-14 Bbc Brown Boveri & Cie Apparatus for separately adjusting the vapor pressures of two or more substances in a common vapor chamber

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2666864A (en) * 1950-01-20 1954-01-19 Westinghouse Electric Corp Image intensifier tube
US3157802A (en) * 1960-09-21 1964-11-17 Fox Raymond Thermionic energy converter
US3215868A (en) * 1961-10-20 1965-11-02 Gen Dynamics Corp Tiiermionic converter
US3353037A (en) * 1964-05-11 1967-11-14 Bbc Brown Boveri & Cie Apparatus for separately adjusting the vapor pressures of two or more substances in a common vapor chamber

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3793542A (en) * 1972-09-08 1974-02-19 Thomson Csf Thermoionic converter

Also Published As

Publication number Publication date
NL6511120A (fr) 1966-02-28
LU49376A1 (fr) 1965-10-25
DE1489262B2 (de) 1970-09-10
ES316698A1 (es) 1967-06-16
BE668624A (fr) 1965-12-16
FR1480112A (fr) 1967-05-12
DE1489262A1 (de) 1969-01-30
CH445588A (fr) 1967-10-31
IL23941A (en) 1969-03-27
SE317120B (fr) 1969-11-10
GB1044459A (en) 1966-09-28

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