US3909617A - Radioisotopic heat source - Google Patents

Radioisotopic heat source Download PDF

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Publication number
US3909617A
US3909617A US474548A US47454874A US3909617A US 3909617 A US3909617 A US 3909617A US 474548 A US474548 A US 474548A US 47454874 A US47454874 A US 47454874A US 3909617 A US3909617 A US 3909617A
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United States
Prior art keywords
container
heat source
alloy
mixture
plutonium
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US474548A
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English (en)
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Gary J Jones
James E Selle
Paul E Teaney
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US Department of Energy
Energy Research and Development Administration ERDA
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US Department of Energy
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Priority to US474548A priority Critical patent/US3909617A/en
Priority to DE19752523863 priority patent/DE2523863A1/de
Priority to JP50064432A priority patent/JPS512900A/ja
Priority to FR7516893A priority patent/FR2275856A1/fr
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    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21H—OBTAINING ENERGY FROM RADIOACTIVE SOURCES; APPLICATIONS OF RADIATION FROM RADIOACTIVE SOURCES, NOT OTHERWISE PROVIDED FOR; UTILISING COSMIC RADIATION
    • G21H1/00—Arrangements for obtaining electrical energy from radioactive sources, e.g. from radioactive isotopes, nuclear or atomic batteries
    • G21H1/10—Cells in which radiation heats a thermoelectric junction or a thermionic converter
    • G21H1/103—Cells provided with thermo-electric generators
    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21G—CONVERSION OF CHEMICAL ELEMENTS; RADIOACTIVE SOURCES
    • G21G4/00—Radioactive sources
    • G21G4/04—Radioactive sources other than neutron sources
    • G21G4/06—Radioactive sources other than neutron sources characterised by constructional features

Definitions

  • Radioisotopic heat sources are used in many applications which require a relatively long life. These uses include providing thermal energy for thermoelectric energy conversion generators, heaters, and the like
  • Plutonium radioisotopes and particularly plutonium- 238, are attractive as long life radioisotope heat sources due to the long half-life of the isotope and its being predominantly an alpha emitter and only a limited emitter of more penetrating radiations.
  • Plutonium is extremely toxic to humans when inhaled at even low quantities and any heat source utilizing same must be designed to withstand the internal temperatures or pressures produced by the raidioisotope itself without adverse reaction therewith, as well as any potential impact or other loads and temperatures which may be provided externally of the heat source.
  • Radioisotope powered thermoelectric generators are presently being utilized in various space and the like applications.
  • a typical generator such as that described in U.S. Pat. No. 3,388,008 to R. J. Campana et al. for Thermoelectric Generator and issued June 1 l, 1968, may produce about one milliwatt of electrical power output using wire-type thermocouples.
  • These generators may be limited in their electrical energy output, in the thermal energy which is produced by their heat source, and/or in their lifetimes. ⁇ Nhen attempts are made to increase electrical or thermal energies, generator lifetimes are generally decreased due to the more difficult environmental conditions to which the materials which contain the radioisotope are subjected.
  • thermoelectric generator It is a further object of this invention to provide such a heat source which may be utilized in a thermoelectric generator.
  • the invention relates to a radioisotope heat source and method of making same in which plutonium dioxide shards are mixed with yttrium particles inside a sealed tantalum alloy layer or layers and heat treated at a temperature of from about 1570K to about l72OK for at least about 1 hour and then encased in an outer nickel alloy clad body.
  • FIG. 1 is a crosssectional side view of a thermoelectric generator incorporating the heat source of this invention
  • FIG. 2 is a cross-sectional view of the radioisotope heat source utilized in the generator of FIG. 1;
  • FIG. 3 is a graph showing the hardness of the tantalum alloy liner walls without the treatment prescribed by the present invention.
  • FIG. 4 is a graph showing the hardness of the tantalum alloy liner across its cross section after the heat source has been subjected to certain heat treatments and operations.
  • Radioisotope thermoelectric generator having a lifetime of up to about 15 to 16 years with an electrical output of about 25 milliwatts or more in a radiologically safe configuration.
  • generator 10 may include a radioisotope heat source 12, which will be described more fully with respect to FIG. 2, suitably supported within a cavity in a cylindrical insulator block 14 and an outer cladding 16.
  • Heat source 12 may be maintained under pressure against a suitable planar thermocouple arrangement or thermopile 18 by a spring biasing member 20 through an insulating plug 22 which is supported in a bore of insulator block 14 at one end of the generator 10.
  • a transition member 24 is positioned intermediate the heat source 12 and thermopile 18 to provide good thermal contact therebetween whileelectrically insulating the thermopile from the heat source.
  • the thermopile 18 is supported by an end wall 26, mounting block 28 and transition member 30, with the end wall 26 suitably attached to the cladding 16 to provide a rigid support for the mounting block 28 and transition member 30.
  • Transition member 30, like transition member 24, provides good thermal conductivity to mounting block 28 while electrically insulating the thermopile from the mounting block.
  • Electrical connection may be made to the thermocouples in the thermopile 18 by a suitable electrical connector 32 and leads or circuit board 33.
  • the interior of generator may be suitably evacuated or pumped down and then back filled with an inert gas like Xenon to stabilize thermal conductivities through pinch-off tube 35.
  • thermocouples utilized in the thermopile 18 may require an extreme aspect ratio (that is cross-sectional area to length ratio) as determined by resistivity, Seebeck coefficients, temperature differential, load voltage, and electrical power requirements.
  • a typical thermopile l8 arrangement is shown in US. Pat. application Ser. No. 290,685 to Paul Wilcox for Thermocouple and Method of Making Same, filed Sept. 20, 1972, now U.S. Pat. No. 3,821,053.
  • the thermocouples are high resistivity silicon-germanium alloys formed into wafers about .18 millimeters (mm) thick and 2.5 by 3.8 mm in size.
  • the wafers are bonded together in a stack by suitable glass material using appropriate interconnections at opposite ends of the wafers to form the desired number of thermocouples.
  • suitable glass material such as aluminum, copper, magnesium, magnesium, and zinc.
  • the heat source 12 is pressed into firm contact with the thermopile 18 through transition member 24 by the spring biasing member 20.
  • the spring biasing member 20 should be designed to maintain a relatively constant spring pressure even if the insulator plug 22 should be dimensionally unstable to some degree.
  • Other biasing arrangements can be utilized including such as a tension rod or combination of tension rods which are positioned about the heat source 12 and mechanically coupled thereto and to the base plate 26 to provide the desired compressive forces which are constant over generator lifetime.
  • the transition members 24 and 30 may be discs of boron nitride, glass, or ceramics which provide the desired thermal conductivity and electrical insulation. Boron nitride may be utilized as a block or by being vapor deposited on a suitable substrate, such as thin wafers of gold, copper or alloys of such as nickel or the like, and similar arrangements.
  • thermopile 18 and the connector 32 may be made with suitable wire leads of materials such as gold or gold-plated alloys or may be provided by use of a printed-circuit type of interconnection and conductor system using such as alumina substrates with chrome-gold or plati-
  • the heat source 12 as shown in greater detail in FIG.
  • a radioisotope containing heat source material or fuel mixture 34 which may be enclosed within a sealed liner or container 36 with or without an additional strength member 38.
  • the liner 36 and strength member 38 may in turn be enclosed and nested within a sealed outer cladding 40 to provide a complete heat surce 12 which is capable of containing the radioactive material for extended periods of time, for example up to 16 years or more, without release of radioactive material due to degradation of the container for normal operating conditions or from any accident conditions which may possibly be incurred.
  • the liner 36, strength member 38 and cladding 40 may be formed of the same general configuration and shape with a generally hollow cylindrical body portion 42 which is closed at one end by an arcuate or hemispherical shaped end portion 44, which may be somewhat flattened if desired, and at the other end by a planar end cap suitably welded to the cylindrical body portion 42.
  • the configuration shown minimizes the number of welds which have to be provided and permits the cylindrical portion 42 and arcuate or hemispherical portions 44 to be formed by relatively simple and low cost hydroforming or deep drawing techniques with limited machining operations.
  • Such a configuration and the proper forming thereof may also minimize the working and mechanical stress points with may normallyoccur in machined and otherwise formed members and which may often act as a failure point under long term usage in high temperature environments with materials which may tend to oxidize, reduce or otherwise attack the container materials.
  • an alpha-emitting isotope such as plutonium-238
  • plutonium-238 is preferred due to its low or nonexistent emission of beta and gamma radiation and because of its relatively high power density and long half-life.
  • Plutonium-238 has a half-life of about 88.4 years and in the dioxide form may have a specific power of about 0.4 watts/gram.
  • the isotope be in a cermet or ceramic form.
  • a high power density may be achieved using plutonium oxides, principally, at least initially, in the form of plutonium dioxides, though carbides and nitrides may provide similar power densities under some operating conditions.
  • the isotope material 34 be in a form which minimizes the production of fines (that is particles less than about 3.4 micrometers in size) which are particularly hazardous to people because of the potential for accidental inhalation.
  • the plutonium oxide fuel in material 34 may be formed as a solid, pressed pellet or as irregular shaped particles referred to as shards having random sizes (as determined by sieving) of from about 50 to 500 micrometers. The shards may be produced with much less handling and consequently far less cost than other plutonium fuel forms.
  • Plutonium oxide fuel which is 80% enriched in the plutonium-238 isotope, may typically emit about 14,000 neutrons/gram-second and gamma at a peak of about 6 rads/year.
  • the neutron flux may be reduced to about 3,500 to 4,000 neutrons/gram-second by sintering the plutonium oxide shards in a flow of oxygen-16.
  • a gettering material such as yttrium or hafnium metal parti cles which are the most stable oxide forming agents compatible with the materials used for liner 36 and strength member 38, may be mixed therewith.
  • the plutonium oxides may be from about 96.8 to 92.9 weight percent as plutonium dioxide with from about 3.2 to 7.1 weight percent of the gettering material.
  • Yttrium is preferred as the getter material as it is easy to handle in air and is more effective as a getter for hydrogen, carbon, and nitrogen which may be present in small quantities as organic impurities in the fuel material 34.
  • the gettering material should preferably be in a particle or chip form, and with dimensions of about 3.0 by 3.0 by .25 mm or smaller. Larger pieces or metal foils of the gettering material may not provide sufficient reduction of the plutonium oxide fuel.
  • Materials for liner 36, strength member 38 and cladding 40 must take into consideration the corrosion and oxidation resistance of the materials in the particular environments to which they may be subjected, as well as mechanical properties such as tensile strength at temperatures (above 1200K) and impact resistance, fabricability and weldability.
  • the liner 36 and strength member 38 must be resistant to corrosion and oxidation which may be caused by heat source material 3 4 and impurities enclosed therein while the cladding 40 should be resistant to corrosion or other attack from materials or environment to which the outside of heat source 12 may be subjected, such as from fresh and sea water, air, and the like.
  • the container materials should be capable of functioning for the lifetime of the heat source at its operating temperatures as well as at excessive temperatures caused by fire, reentry from space and the like and still provide high impact resistance should the heat source 12 strike an object at high speed even after being utilized over its lifetime at normal operating conditions and in addition being subjected to abnormal or accident conditions.
  • the liner 36 may act as a sacrificial layer which is of sufficient thickness to react with whatever impurities or other materials may be enclosed within the heat source in the radioisotope fuel material 34 over the lifetime of the heat source 12 so that whatever deleterious effects which may occur from such reactions will adversely effect only the liner 36.
  • the liner 36 is preferably made of the same material as the strength member 38 to simplify compatibility or may be incorporated into a single container. It has been found that a material which will provide the long life characteristics desired for the heat source is tantalum base solid solution alloys, and particularly the tantalum-tungsten-hafnium alloy of about 90 w/o tantalum, 8 w/o tungsten and 2 w/o hafnium.
  • the liner 36 of this material is typically deep drawn to a thickness of about 0.5 mm in the configuration shown and is provided with a cover 36;: of similar thickness and same material which is welded thereto.
  • the strength member 38 may be comparably formed into a similar shape in which the liner 36 may be nested but with a thickness of from about 1 to about 1.5 mm which in turn is closed by an end cap 38a of similar thickness and same material welded thereto.
  • the cladding material for cladding 40 may be a high temperature corrosion resistant material or alloy, such as certain nickel base alloys, having the desired formability and weldability. It has been found that a suitable alloy having these desired characteristics may include about l4.5l6.5% chromium, l5-l7% molybdenum, 3-4.5% tungsten, 47% iron, 2.5% cobalt with small amounts of Mn, Si, V, C, P and S and the balance of about 55% being nickel.
  • the cladding can be deep drawn into the generally hollow cylindrical and an arcuate or hemispherical end closed shape into which the strength member 38 may be :nested and the open end closed and sealed by a similar cladding end cap 40a.
  • the cladding thickness may typically be from about 0.5 to 1.5 mm thick.
  • the three-layer capsule or heat source arrangement described is desired, not only for safety reasons, but for fabrication and handling reasons as well.
  • a threelayer heat source there are two layers between the exterior environment and the decontaminable outer surface of the liner 36.
  • Such may be preferred even though the materials recited exhibit a high degree of resistance to contamination or attack by the other materials and the environment to which the heat source 12 may be subjected when the heat source is treated as described below. If the materials are attacked even at a reduced or low rate over the lifetime of the heat source, it may be compensated for by providing a sufficient thickness of container materials to survive all potential environments to which they may be subjected.
  • the thicknesses noted above provide more than an adeuqate amount of containment material to provide this operation over a 16 year lifetime of the heat source.
  • the desired mixture of getter material chips or particles and plutonium oxide shards are mixed together in the amounts and form recited above.
  • the fuel mixture 34 is then poured or otherwise loaded into the liner 36 and a shim or disc 48 of the same material as liner 36 used to cover the fuel mixture 34 during welding.
  • the insertion of the shim 48 into the liner 36 body tends to wipe clean a portion of the inner surface of the liner 36 of residual fuel material aiding in weld integrity and leaves a space or void 50 at the open end of liner 36.
  • the end cap 36a may then be welded in place over the open end of liner 36.
  • Space 50 provides an area into which helium from radioactive decay of the plutonium fuel or other gases may be collected over the lifetime of the heat source. This volume, for
  • a heat source having about 12 grams of plutonium should be about 2.7 cubic centimeters.
  • the liner'36 and its end cap 36a may then be cleaned by appropriate means to thoroughly decontaminate its outer surface of any of the fuel material 34 or other contaminants. Thereafter, the sealed liner 36 may be placed and nested within the strength member 38 and sealed therein by end cap 38a and the cladding 40 and end cap 404; appropriately positioned thereabout.
  • the various end caps may be gas tungsten arc welded in place in an appropriate manner to provide a gas tight seal.
  • the liner 36 at the liner-fuel interface begins to absorb oxygen into the liner material and increases in hardness as indicated by curves 52 and 54 in FIG. 3.
  • the absorption of oxygen into the liner material progresses through the liner, progressively decreasing its ductility. This oxygen is released from the fuel material 34 and from any contaminants that may have remained therein.
  • this oxygen absorption and container material ductility reduction may be drastically reduced by a pretreatment which includes heating the assembled fuel material 34 with liner 36 and/or strength member 38 at a temperature of from about 1570K to about 1720K for about 1 hour.
  • the desirable effects of this pretreatment begin to decrease at temperatures below about 1570K and above about 1720K.
  • Pretreatment below 1570K requires excessive periods of time which may result in excessive and undesirable grain growth in the container materials. Above 1720K temperature fluctuation could lead to melting of the getter.
  • FIG. 4 shows the hardness of the liner material across its cross section after the heat source has been heat treated at 1670K for 1 hour.
  • Curve 58 illustrates the hardness of a similar liner which was heat treated at 1720K for one hour and then operated for 60 days at 1 170K.
  • Curve 60 illustrates another liner which was heat treated at 1570K for 1 hour and then operated for 60 days at 1170K while curve 62 shows a liner treated at 1670K for 1 hour and then operated for 60 days at 1 170K.
  • this pretreatment effectively reduces the oxygen reactivity within the capsule before oxygen has time to diffuse into the liner 36 and other container materials.
  • curve 56 illustrates that little or no oxygen absorption results from the pretreatment itself.
  • a heat source having thermal power of about 6 watts from 10.4 grams of plutonium-238 may produce about 25 electrical milliwatts per channel or milliwatts total output over a 16 year service life with the heat source operating at a nominal temperature of about 700K.
  • the heat source 12 may be about 2.3 centimeters in diameter and about 2.3 centimeters long and have a weight of about 70 grams.
  • the plutonium-238 isotope fuel is initially PuO in the form of irregular ceramic shards having a size range of from about 50 to 500 micrometers. Using the recited liner 36 and strength member 38 materials, operating temperatures of even 900K may be utilized for similar lifetimes with some modification of other generator materials and configurations.
  • Heat sources as described above have been impacted against a hardened tool-steel surface at angles of 45 or more and at velocities of from 100 meters per second to 300 meters per second without release of fuel from their interiors.
  • heat source strength members have been exposed to a 1270K fire for 1 hour without any rupturing thereofleven when the interior is pressurized with helium at end-of-life concentrations.
  • Method for producing a radioisotopic heat source comprising mixing from about 96.8 to 92.9 w/o plutonium dioxide shards of from about 50 to 500 micrometers in size with from about 3.2 to 7.1 w/o of yttrium getter material; sealingly enclosing said mixture in a first container comprising about w/o Ta, 8 w/o W, 2 w/o Hf alloy; heating said first sealed container and mixture to a temperature of from about 1570K to about 1720K for about one hour; and thereafter ne sting and sealingly enclosing said first container in a second container comprising about 55% Ni, 16% Cr, 16% Mo, 4% W, 5% Fe, 2.5% Co alloy.
  • a radioisotope heat source comprising an outer sealed container of about 55% Ni, 16% Cr, 16% Mo, 4% W, 5% Fe, 2.5% Co alloy; an inner sealed container of about 90 w/o Ta, 8 w/o Hf alloy nested inside said outer container; and a mixture of from about 96.8 to 92.9 w/o plutonium dioxide shards with a yttrium getter material at least partially filling said inner container, inner walls of said inner container embodying the enhanced characteristics resulting from subjection of said inner container and said mixture to heating to temperature of from about 1570K to about 1720K for a period of about 1 hour.
  • the heat source of claim 5 including an additional container of about 90 w/o Ta, 8 w/o W, 2 w/o Hf alloy nested inside said outer container intermediate said inner and outer containers.
  • thermoelectric generator for use in a thermoelectric generator having a lifetime of about 16 years wherein said mixture includes about 12 grams of plutonium, said outer container has a wall thickness of about .5 mm, said intermediate container has a wall thickness of about 1.0 mm, and said inner container has a wall thickness of about .5 mm.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • General Engineering & Computer Science (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Inorganic Compounds Of Heavy Metals (AREA)
US474548A 1974-05-30 1974-05-30 Radioisotopic heat source Expired - Lifetime US3909617A (en)

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US474548A US3909617A (en) 1974-05-30 1974-05-30 Radioisotopic heat source
DE19752523863 DE2523863A1 (de) 1974-05-30 1975-05-30 Radioisotop-waermequelle sowie verfahren zu deren herstellung
JP50064432A JPS512900A (enrdf_load_stackoverflow) 1974-05-30 1975-05-30
FR7516893A FR2275856A1 (fr) 1974-05-30 1975-05-30 Source de chaleur a radio-isotope et procede pour la former

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FR (1) FR2275856A1 (enrdf_load_stackoverflow)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4881979A (en) * 1984-08-29 1989-11-21 Varian Associates, Inc. Junctions for monolithic cascade solar cells and methods
US20040055292A1 (en) * 2002-09-20 2004-03-25 Claudio Filipppone AlphaCor alpha powered miniaturized power plant
WO2007121994A1 (de) * 2006-04-25 2007-11-01 Georg-August-Universität Göttingen Stiftung Des Öffentlichen Rechts (Ohne Bereich Humanmedizin) Verfahren zum nachweis von gasförmigen verunreinigungen in werkstoffen
WO2022099279A1 (en) * 2020-11-04 2022-05-12 Westinghouse Electric Company Llc Nuclear battery
US12080435B2 (en) 2020-12-17 2024-09-03 Westinghouse Electric Company Llc Methods of manufacture for nuclear batteries

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS54132439A (en) * 1978-04-05 1979-10-15 Furukawa Electric Co Ltd:The Electroplating method
JPS5893898A (ja) * 1981-11-30 1983-06-03 Sumitomo Metal Ind Ltd 電気メッキ浴室のｐＨ管理方法
JPS5893888A (ja) * 1981-11-30 1983-06-03 Sumitomo Metal Ind Ltd 電気メツキにおける金属イオンの供給方法
JPS58199890A (ja) * 1982-05-19 1983-11-21 Tokuyama Soda Co Ltd 電気メツキ方法
JPS59189199U (ja) * 1983-06-03 1984-12-15 アースニクス株式会社 Ｒｉ密封カプセル

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3533913A (en) * 1967-02-06 1970-10-13 North American Rockwell Radioisotope heat source
US3600585A (en) * 1967-02-03 1971-08-17 Atomic Energy Commission Plutonium heat source
US3697329A (en) * 1971-06-04 1972-10-10 Atomic Energy Commission Radioisotope heat source system
US3767930A (en) * 1972-06-21 1973-10-23 Atomic Energy Commission Radioisotopic heat source

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3600585A (en) * 1967-02-03 1971-08-17 Atomic Energy Commission Plutonium heat source
US3533913A (en) * 1967-02-06 1970-10-13 North American Rockwell Radioisotope heat source
US3697329A (en) * 1971-06-04 1972-10-10 Atomic Energy Commission Radioisotope heat source system
US3767930A (en) * 1972-06-21 1973-10-23 Atomic Energy Commission Radioisotopic heat source

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4881979A (en) * 1984-08-29 1989-11-21 Varian Associates, Inc. Junctions for monolithic cascade solar cells and methods
US20040055292A1 (en) * 2002-09-20 2004-03-25 Claudio Filipppone AlphaCor alpha powered miniaturized power plant
WO2007121994A1 (de) * 2006-04-25 2007-11-01 Georg-August-Universität Göttingen Stiftung Des Öffentlichen Rechts (Ohne Bereich Humanmedizin) Verfahren zum nachweis von gasförmigen verunreinigungen in werkstoffen
US20090241639A1 (en) * 2006-04-25 2009-10-01 Reiner Kirchheim Method for the Detection of Gaseous Impurities in Materials
US8113035B2 (en) * 2006-04-25 2012-02-14 Reiner Kirchheim Method for the detection of gaseous impurities in materials
WO2022099279A1 (en) * 2020-11-04 2022-05-12 Westinghouse Electric Company Llc Nuclear battery
US12198826B2 (en) 2020-11-04 2025-01-14 Westinghouse Electric Company Llc Nuclear battery
US12080435B2 (en) 2020-12-17 2024-09-03 Westinghouse Electric Company Llc Methods of manufacture for nuclear batteries

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FR2275856A1 (fr) 1976-01-16
JPS512900A (enrdf_load_stackoverflow) 1976-01-10
DE2523863A1 (de) 1975-12-18

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