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US 4,056,584 AGranted
Method of making a graphite fuel element having carbonaceous fuel bodies
AssigneeGeneral Atomic Company
InventorsGary N. Miertschin, David F. Leary
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AssigneeGeneral Atomic Company
InventorsGary N. Miertschin, David F. Leary
Estimating the term…
Particulate nuclear fuel material, particulate carbon and pitch are combined with an additive which is effective to reduce the coke yield upon carbonization to mold a green fuel body. The additive may be polystyrene, a styrene-butadiene copolymer, an aromatic hydrocarbon having a molecular weight between about 75 and 300 or a saturated hydrocarbon polymer. The green fuel body is inserted in a complementary cavity within a porous nuclear fuel element body and heated in situ to decompose the pitch and additive, leaving a relatively close-fitting fuel body in the cavity.
A method of making a nuclear fuel element comprising the steps of providing a porous rigid fuel element block of graphite having a cavity of precise dimension formed therein, combining particulate nuclear fuel material having fission-product retentive coatings, particulate carbon, pitch, and a carbonizable coke-reducing additive which is effective to reduce the coke yield upon carbonization, said additive being selected from the group consisting of (1) polystyrene and styrene-butadiene copolymers having a molecular weight between about 500 and 1,000,000, (2) aromatic hydrocarbons having a molecular weight between about 75 and 300, and (3) saturated hydrocarbon polymers having a molecular weight between about 5,000 and 1,000,000, said pitch and said additive being heated to a temperature of at least 100.degree. C., molding a green fuel body from said combination of materials under pressure, inserting said molded green fuel body into said cavity within said fuel element block and heating said molded green body in situ in said fuel element cavity to decompose the pitch and said additive leaving a relatively close-fitting fuel body in said cavity, which fuel body comprises coated nuclear fuel particles plus particulate carbon in a coke matrix formed from said carbonized pitch and additive, wherein said coke constitutes an amount not more than 25 weight percent of the original weight of pitch plus said additive.
A method of making a nuclear fuel element which method comprises the steps of providing a porous rigid fuel element block of graphite having a cavity of precise dimension formed therein, combining particulate carbon, pitch, a release agent, and a carbonizable coke-reducing additive which is effective to reduce the coke yield upon carbonization, said additive being selected from the group consisting of (1) polystyrene and styrene-butadiene copolymers having a molecular weight between about 500 and 1,000,000, (2) aromatic hydrocarbons having a molecular weight between about 75 and 300, and (3) saturated hydrocarbon polymers having a molecular weight between about 5,000 and 1,000,000, molding a green fuel body by loading a mold cavity with a desired amount of coated nuclear fuel particles, heating said combination of materials to a temperature of at least 100.degree. C., injecting said heated materials into the mold cavity under pressure, and cooling the mold cavity and removing the green fuel body, inserting said molded green fuel body into said cavity within said porous graphite nuclear fuel element block, and heating said molded green body in situ with said graphite block to decompose said pitch and said additive leaving a relatively close-fitting fuel body in the cavity, which fuel body comprises coated nuclear fuel particles plus particulate carbon in a coke matrix formed from said carbonized pitch and additive, wherein said coke constitutes an amount not more than 25 weight percent of the original weight of pitch plus said additive.
Dependencies are inferred from the claim text.
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No related US applications are recorded in the indexed filing history.
Apparatus or processes specially adapted to the manufacture of reactors or parts thereof: manufacture of fuel elements or breeder elements…
Obtained from carbonaceous particles with or without other non-organic components: containing a carbonisable binder
Ceramic fuel: ceramic dispersion fuel, e.g. cermet
Energy generation of nuclear origin: nuclear fission reactors
Term ended 1 Nov 1994 (estimated)
USPTO file history isn’t available for this patent, so only indexed dates are shown.
This invention relates to carbonaceous nuclear fuel bodies and more particularly to methods of making nuclear fuel elements containing a plurality of discrete nuclear fuel bodies, particularly fuel elements designed for use in a high-temperature gas-cooled nuclear reactor.
U.S. Pat. Nos. 3,274,068 (issued Sept. 20, 1967) and 3,413,196 (issued to Nov. 26, 1968) disclose different designs of fuel elements suitable for use in high-temperature gas-cooled nuclear reactors that employ fuel elements formed from a block of refractory material, usually dense graphite, wherein there are a plurality of fuel chambers containing fissile and/or fertile nuclear fuel material. The later patent discloses a fuel element in the form of a large hexagonal block measuring, for example, 15 to 16 inches high and about 14 inches across the flats. Each of these hexagonal fuel elements may contain, for example, about 90 coolant holes and 240 fuel chambers, with the diameters of the fuel chambers being between one-half and three-quarters of an inch.
Such fuel chambers may be filled with packed beds of coated nuclear fuel particles, with a paste made of a mixture of coated fuel particles plus a carbonaeous matrix material, for example, coal tar pitch, or with individual fuel compacts or bodies proportioned to fit therewithin. One method for making nuclear fuel bodies of this general type is disclosed in U.S. Pat. No. 3,558,750 (issued Jan. 26, 1971) wherein mold cavities are filled with coated particles of nuclear fuel and then a molding mixture of carbonaceous binder material is injected under pressure into the mold cavity. The molding mixture may include a suitable organic polymeric resin, for example, a phenolformaldehyde resin, together with a filler, such as graphite or charcoal powder.
A 600 gram batch of a molding mixture is prepared from coal tar pitch (Ashland Oil No. A240), 45 weight percent; graphite flour, 30 weight percent; octadeconal, as a release agent, 5 weight percent; and camphor, as a coke-reducer, 20 weight percent. The graphite flour has a particle size between about 0.4 micron and about 40 microns. The mixture is blended for about thirty minutes in a sigma blade mixer at a temperature of 200.degree. C. and at a mixing rate of about 100 r.p.m.
After blending, the batch is cooled and then ground and sized to provide particles between about 4.7 mm. and 0.7 mm. Molds made of stainless steel having cavities of right cylindrical shape and a diameter of 0.620 inch (1.57cm.) are filled with particles of nuclear fuel. The nuclear fuel particles contain kernals of uranium-thorium carbide coated with a first layer of porous, spongy pyrolytic carbon and an outer layer of dense isotropiic pyrolytic carbon. The coated fuel particles range in size from between about 1150 microns and about 350 microns.
Each of the molds is then filled with about 20 grams of the coated nuclear fuel particles which is a depth of about 21/2 inches. The graphite-filled molding mixture is heated to a temperature to between about 175.degree. C. and 200.degree. C. to fluidize the pitch and is injected into the particle-filled mold cavities using a pressure of about 1,200 p.s.i. Upon completion of injection, the molds are cooled to room temperature to solidify the matrix material, and the green rods are then ejected from the mold.