US3603415A - Thulium oxide heat source and method for forming same - Google Patents

Thulium oxide heat source and method for forming same Download PDF

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Publication number
US3603415A
US3603415A US751454A US3603415DA US3603415A US 3603415 A US3603415 A US 3603415A US 751454 A US751454 A US 751454A US 3603415D A US3603415D A US 3603415DA US 3603415 A US3603415 A US 3603415A
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sheath
rods
fuel
connecting member
diameter
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US751454A
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English (en)
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Charles H Allen
Charles E Leach
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US Atomic Energy Commission (AEC)
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US Atomic Energy Commission (AEC)
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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
    • G21H3/00—Arrangements for direct conversion of radiation energy from radioactive sources into forms of energy other than electric energy, e.g. into light or mechanic energy
    • 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

  • This invention relates to a radioisotopic heat source and more particularly to an internally shielded heat source with fuel rods of thulium oxide.
  • Radioisotopes as a heat source is not new, but the proximity of extended manned space and undersea missions has spurred development of a reliable, portable, easily serviced, isotopic heat source.
  • Some isotopes available for and applicable as heat sources are Ru, Co, "Sr, Ce, “Cs and ""Tm. Each has characteristics which make it use advantageous depending upon the required design parameters. Watts per gram, density, power density, availability, type of irradiation, amount of required shielding, half life and cost are important characteristics.
  • Tm upon absorption of a neutron becomes ""Tm which is a radioisotope that decays to or Tm O has superior characteristics to the metal for many purposes and is the preferred form.
  • Tm O with a half life of about four months, a density of 8.5 gms/cm, a power density of 1.2 watts per gram of 90 weight percent "Tm.,,0;,l weight percent Tm- 0 and with only moderate shielding requirements seems .a good .compromise for manned missions of about 3 to 6 months.
  • Thulium has a very large thermal-neutron cross section, hence a very small thickness of thulium absorbs large numbers of neutrons.
  • the invention comprises the irradiation of Im O in the form of encapsulated rod in a properly balanced thermalepithermal flux .to produce a'suitable Im O fuel element for use as a heat source in which the fuel elements are separated .from the coolant by a heat-exchange medium that also acts as an internal radiation shield.
  • a backup coolant system separate from the primary coolant system ensures overall system integrity.
  • the rod shaped fuel element is more reliable than an assembly of wafers because only two welds are required per rod whereas welds are required for each wafer in the assembly. If the assembly contains 10 to wafers there is 10 to 20 times greater a chance of a bad weld with the wafers than with the rod. One bad weld may result in an entire heat source becoming inoperable or in .an entire piece of equipment becoming contaminated. Also, rods are not as delicate as wafers and not as likely to be damaged by handling. For a system which is to serve manned space or undersea missions removed from sophisticated repair facilities, a
  • Rods may be reirradiated as complete fuel elements exactly as they are removed from the heat source because their geometry as fuel elements is the same with respect to Tm O thickness as when they were initially irradiated.
  • wafers In contrast, wafers must be disassembled from their fuel element and reirradiated as wafers then reassembled before they are reusable as fuel elements. The necessary time, labor and shielding requirements make wafer reirradiation expensive compared to rod reirradiation.
  • FIG. 1 is a partial section view of the heat source of this invention.
  • FIG. 2 is an enlarged partial section view of a fuel element.
  • FIG. 3 is a section view taken on line 3--3 in FIG. 1.
  • FIG. 4 is a section view taken on line 4-4 in FIG. 1.
  • FIG. 5 is a graph showing the decrease in average activation for rods of increasing diameter in in a flux of thermal and epithermal neutrons.
  • FIG. 6 is a graph of the relationship between activation and depth in a Tm O, rod for different flux spectra.
  • a heat block 10 consists of fuel elements 11 arranged in clusters manifolds surrounded by a heat exchange medium 13.
  • the fuel elements 11 and heatcxchange medium 13 are housed within a tubular body 14 closed at the bottom end between an upper head 15 and a lower head 16.
  • Coolant tubes 17 are U-shaped and mate at both ends with manifolds 18 in lower head 16. Intermediate their ends, the coolant tubes 17 follow an upward path through the heat-exchange medium 13 proximate the fuel element clusters 12 to a point near the upper head 15 where they become parallel to the upper head for a distance and turn downward to the manifolds 18.
  • Upper head 15 has an annular channel 19 in its lower edge which houses an inlet header 20.
  • Backup coolant tubes 21 are connected to inlet head 20 and to an outlet header 22 located at the bottom of the tubular body 14.
  • the paths of backup coolant tubes 21 between the inlet header 20 and the outlet header 22 closely approximate and are predominantly parallel to the paths of coolant tubes 17.
  • Backup coolant enters inlet header 20 through backup coolant inlet 23 via a valve 24 located outside heat block 10 intermediate inlet header 20 and backup coolant inlet 23.
  • a fusible plug 25 In parallel arrangement to valve 24 and in thermal contact with body 14 or heat-exchange medium 13 is a fusible plug 25.
  • Upper head 15 and lower head 16 are connected to flanges 26 of body 14 by a plurality of screws 27 around the body circumference and by a nut 28 and bolt 29 assembly extending through the center of the body.
  • Tubular insulating material 30 surrounds bolt 29.
  • each manifold 18 in lower head 16 consists of an aperture 31 through the lower head and three grooves 32 connected to the aperture. Each groove 32 receives a coolant tube 17, and each aperture 31 leads to one of a series of collector rings 33.
  • each fuel element cluster 12 rests on plate 34 which is attached to the bottom of body 14; the plates 34 are elliptical and each receives 10 fuel elements 11.
  • FIG. 3 shows the spa tial relationship between fuel element clusters 12, coolant tubes 17 and backup coolant tubes 21. Fuel elements 11 extend through upper head 15 to plugs 35 which are easily removed from the upper head by means of bolts 36.
  • fuel elements 11 are housed within fuel tubes 37 and rest on plates 34.
  • Each fuel element 11 has an encapsulated fuel rod 38 and a smaller diameter shaft 39 connected to the top of the fuel rod.
  • Shaft 39 has a slot 40 and fits inside and is slidable with respect to a sheath 41 which is the same diameter as the fuel rod 38.
  • Sheath 41 has an internal roll pin 42 which fits inside of and is slidable with slot 40.
  • Roll pin 42 connects sheath 41 to shaft 39 and fuel rod 38.
  • a gripping portion or knob 43 is formed at the top of sheath 41 and abuts plug 35 when fuel element 11 is in operating position.
  • a spring 44 between fuel rod 38 and sheath 41 urges the sheath away from the fuel rod.
  • Heat block 10 may be assembled as follows, but the order of the steps is not critical and may be varied. Either "fm O pellets are encapsulated in a cladding material or Tm O powder is vibratorily compacted in a tube of cladding material to form each fuel rod 38 of fuel element 11.
  • the cladding material may be selected from any of a number of artrecog nized materials, such as titanium, beryllium or zirconium, de pending upon factors like operating temperature and the amount of shielding required. Titanium is preferred over zirconium where less shielding is desired because zirconium becomes more radioactive than the titanium.
  • Fuel rods 38 are inserted into a nuclear reactor in an area of suitably balanced thermal-epithermal flux.
  • the amount of time fuel rods 38 are irradiated depend upon the flux field, the rod diameter and density as well as the desired activation level. Elongated rods 0.171 inches in diameter and up to 1.75 inches in length have been substantially uniformly irradiated.
  • Fuel tubes 37 are placed within body 14 at their proper places on plates 34 in the desired cluster configuration 12.
  • the exact geometry of clusters 12 is not critical, it depends upon the number of fuel elements 11 to be used and the number of coolant tubes 17. After clusters 12 are positioned,
  • the heat-exchange medium 13 can be selected from a variety of materials depending upon operating temperature, required heat transfer coefficients, component compatibility and shielding requirements. Various metals in solid, liquid or powdered form are applicable as the heat-exchange medium 13 with powdered tungsten the preferred material. Tungsten is sufficiently dense to provide an adequate internal shield for manned missions while at the same time it has good heat transfer and compatibility characteristics. Mo, Na, Hg or Cu are alternatives provided the accompanying increased radiation intensity and/or shielding requirements are acceptable. The heat-exchange medium 13 of powdered tungsten is vibratorily compacted in body 14 to form a solid mass around the aforementioned components.
  • the inlet header 20 is connected to backup coolant tubes 21 then upper head 15 and lower head 16 are added to complete heat block 10 except for fuel elements 11.
  • An external backup coolant supply (not shown) is connected to backup coolant inlet 23 and may consists of water under pressure in any kind of convenient container.
  • decay of the Tm O in fuel elements 11 produces heat which is transmitted from the fuel elements through the fuel tubes 37 and heat-exchange medium 13 to coolant flowing through the coolant tubes 17.
  • Coolant flows through tubes 17 to one of the collector rings 33 and thence to a heat-exchanger (not shown) where heat is extracted from the coolant.
  • the coolant is returned to another of the collector rings and then into the coolant tubes for recirculation. If heat block 10 is used in combination with a power source based on the Stirling Cycle, then a gas coolant is preferred.
  • Valve 24 exter' nal to heat block 10 provides a nonemergency means for activation of the system; for instance, during startup, or shutdown or leak testing, etc.
  • Fusible plug 25 in thermal contact with body 14 or heat-exchange medium 13 provides for cooling if extra programmed temperatures occur. Choice of the material for fusible plug 25 depends, of course, on the programmed temperature and the leeway provided for temperature excursions. The parallel arrangement of valve 24 and plug 25 enable the use of the backup coolant without destruction of the plug.
  • FIG. 5 shows the relationship between average neutron activation and radius for thulium oxide rods irradiated in a flux field comprised of 1 l0 neutrons/cm sec thermal neutrons and 5.6 10" neutrons/cm sec epithermal neutrons.
  • a fuel rod 0.17l inches in diameter corresponds to a 0.218 cm radius and as shown in the Figure results in only slightly more than a 2 percent loss in average activation.
  • FIG. 6 shows the relationship between activation in a Tm O rod as a function of neutron penetration depth and the neutron energy levels.
  • the normalized activation is the ratio of localized, or incremental, activation to total activation.
  • the ratio of activation at the rod skin, a theoretical depth of zero, to total activation is set equal to one. If the activation at any point in the rod was equal to that at the skin, then the normalized activation would always be one, but as previously explained, the large thermal neutron cross section prevents absolute uniform activation.
  • curve A shows that the fraction of total rod activation due to epithermal neutrons is essentially constant from skin to core.
  • Curve B shows that the fraction of total rod activation due to thermal neutrons decreases with increasing TM O thickness.
  • Curve D is the sum of curves A and B and shows the total activation due to irradiation with the above defined flux spectrum while curve C shows the total activation resulting from irradiation with only thermal neutrons.
  • Curve D shows the value of using a suitably balanced flux spectrum. As shown by curve A, a substantially pure epithermal flux would be most desirable from the standpoint of uniformity.
  • thulium-169 reacts to a minor extent with epithermal neutrons according to the reaction "'Im(n,2n)*Tm.
  • the thulium-168 emits gamma radiation, which increases the shielding requirements. Accordingly, we usually prefer to use a flux approximating curve D. In some cases, uniformity may be sacrificed to obtain a lower gamma radiation and a flux containing less than this proportion of epithermal flux may be used.
  • the heat source of this invention may be used in any attitude without adverse affect on its performance.
  • the fuel elements 11 may be repeatedly reirradiated because only about 10 percent to 20 percent of the 'lm O is converted during each irradiation. During each irradiation some '"Tm o is produced but it is a minor amount and has been discounted in the explanation of this invention.
  • a heating device comprising:
  • a housing having solid upper and lower heads connected by a hollow body, said lower head having therein a plurality of manifolds;
  • each coolant tube being perpendicular to the upper and lower heads and a portion of each coolant tube being parallel to the upper and lower heads;
  • a heat-exchange medium filling the space between the coolant tubes and the fuel tubes; and a backup cooling system separate from said coolant tubes for introducing coolant into the body at a predetermined time.
  • the fuel elements comprise a gripping portion at the top thereof, an encapsulated fuel portion shorter than the distance between the upper and lower heads an means for projecting the gripping portion at least part way through the upper head upon removal of the mating plug therefrom.
  • the fuel elements have a slotted connecting member of smaller diameter than the encapsulating material connected to the end of the encapsulating material closest to the upper head; a sheath of the same diameter as the encapsulating material positioned over said connecting member and slidable in relation thereto, said sheath having an internal roll pin positioned within the slot in the connecting member and slidable therewith; and a spring positioned about the connecting member between the encapsulating material and the sheath urging the sheath away from the encapsulating material, whereby removal of the mating plug from the upper head results in movement of the sheath and gripping portion through the upper head until the roll pin contacts one end of the slot preventing further movement of the sheath.
  • thermoelectric medium is tungsten and the encapsulating material is selected from the class consisting of titanium, beryllium and zirconium.
  • a fuel element comprising a cladding material encapsulating a rod greater than 0.04 inch in diameter containing a radioisotope of thulium oxide substantially uniformly distributed throughout the rod and further comprising a slotted connecting member of smaller diameter than the cladding material connected to one end of the cladding material; a sheath of the same diameter as the cladding material positioned over said connecting member and slidable in relation thereto, said sheath having an internal roll pin positioned within the slot in the connecting member and slidable therewith; and a spring positioned about the connecting member between the cladding material and the sheath luring the sheath away from the cladding material until the roll pin contacts one end of the slot preventing further movement of the sheath.
  • a method of utilizing thulium for heating comprising:
US751454A 1968-08-09 1968-08-09 Thulium oxide heat source and method for forming same Expired - Lifetime US3603415A (en)

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3836781A (en) * 1972-08-01 1974-09-17 Water Purification Corp Irradiator for water purification
US5082617A (en) * 1990-09-06 1992-01-21 The United States Of America As Represented By The United States Department Of Energy Thulium-170 heat source
US20130299713A1 (en) * 2010-11-15 2013-11-14 Schlumberger Technology Corporation Multiplier Tube Neutron Detector

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DD89554B1 (de) * 1971-05-05 1986-03-12 Nagema Veb K Vorrichtung zur uebergabe von kronenverschluessen an verschliessorgane

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3306045A (en) * 1963-12-19 1967-02-28 Marquardt Corp Radioisotope rocket
US3350231A (en) * 1963-05-14 1967-10-31 Mobil Oil Corp Fuel cell electrode and method of using same
US3353354A (en) * 1963-04-08 1967-11-21 Trw Inc Radioisotope attitude control engine
US3378449A (en) * 1967-07-27 1968-04-16 Atomic Energy Commission Usa Nuclear reactor adapted for use in space
US3378455A (en) * 1963-02-20 1968-04-16 Nasa Usa Reactor fuel element for a nuclear rocket motor
US3421001A (en) * 1964-03-16 1969-01-07 Iso Serve Inc Radioisotopic heat source and method of production

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3378455A (en) * 1963-02-20 1968-04-16 Nasa Usa Reactor fuel element for a nuclear rocket motor
US3353354A (en) * 1963-04-08 1967-11-21 Trw Inc Radioisotope attitude control engine
US3350231A (en) * 1963-05-14 1967-10-31 Mobil Oil Corp Fuel cell electrode and method of using same
US3306045A (en) * 1963-12-19 1967-02-28 Marquardt Corp Radioisotope rocket
US3421001A (en) * 1964-03-16 1969-01-07 Iso Serve Inc Radioisotopic heat source and method of production
US3378449A (en) * 1967-07-27 1968-04-16 Atomic Energy Commission Usa Nuclear reactor adapted for use in space

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
S. Untermger, May 1954 Nucleonles (Vol. 12 No. 5) pp. 35. 36. *

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3836781A (en) * 1972-08-01 1974-09-17 Water Purification Corp Irradiator for water purification
US5082617A (en) * 1990-09-06 1992-01-21 The United States Of America As Represented By The United States Department Of Energy Thulium-170 heat source
US20130299713A1 (en) * 2010-11-15 2013-11-14 Schlumberger Technology Corporation Multiplier Tube Neutron Detector

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DE1939945A1 (de) 1970-02-12
FR2015364A1 (de) 1970-04-24
GB1204300A (en) 1970-09-03

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