Kraftwerk Union Aktiengesellschaft

Reaktor-brennelement Union Gmbh

Siemens Aktiengesellschaft

Kernforschungsanlage Julich

Martin Peehs

Wolfgang Dorr

Gerhard Gradel

Georg Maier

Helmut Assmann

Gerhard Dichtjar

Manfred Hunner

Peter Rau

Werner Petri

Erhard Ortlieb

Thomas Sondermann

Richard A Perkins

Alfons Roppelt

Wilfried Jung

Harald Cura

Wolfgang Krug

Viktor Mathieu

Reinhard Schafer

Sieghard Hellmann

Horst Stechemesser

Heinrich Bayer

Ulrich Jenczio

Jurgen Laucht

A uranium-containing nuclear-fuel sintered pellet containing UO.sub.2, (U, Pu)O.sub.2, (U, Th)O.sub.2, (U, RE)O.sub.2, (U, Pu, Th)O.sub.2, (U, Pu, RE)O.sub.2, (U, Th, RE)O.sub.2 or (U, Pu, Th, RE)O.sub.2, wherein RE=rare earth, has a sintered-pellet surface layer being formed of at least 80% by volume of a chemical boron compound UB.sub.x or (U, . . . )B.sub.x, wherein x=2;4;6 or 12, and a remainder of the sintered pellet containing at most 5% by volume of the chemical boron compound. A nuclear-reactor fuel assembly has a fuel rod containing such a uranium-containing nuclear-fuel sintered pellet in a cladding tube with the boron as a burnable absorber for thermal neutrons. The surface layer having the chemical boron compound is obtained by treating the nuclear-fuel sintered pellet with boron or a boron-containing chemical compound at an appropriately high treatment temperature.

Uranium-containing nuclear-fuel sintered pellet

Method for manufacturing sintered oxidic nuclear fuel bodies by molding uranium oxide starting powder, a mixture of uranium oxide and plutonium oxide starting powder or of uranium-plutonium oxide mixed-crystal starting powder to form blanks and by a heat treatment of these blanks with a U.sub.4 O.sub.9 or (U, Pu).sub.4 O.sub.9 crystal phase developed in them to a degree which can be crystallographically detected at a sintering temperature in the range of 1000.degree. to 1400.degree. C. in an oxidizing and subsequently in a reducing gas atmosphere. The starting powder and/or the blanks are preroasted at a roasting temperature below the sintering temperature in a roasting gas atmosphere with oxidizing action and with an oxygen potential in which the U.sub.4 O.sub.9 (U, Pu).sub.4 O.sub.9 crystal phase is developed and cooled down subsequently to a starting temperature below the roasting temperature in an inert or oxidizing cooling-down gas atmosphere. Starting from this starting temperature, the blanks are heated to the sintering temperature in an inert or oxidizing heating gas atmosphere while maintaining the U.sub.4 O.sub.9 or the (U, Pu).sub.4 O.sub.9 crystal phase.

Method for the manufacture of oxide sintered nuclear fuel bodies

Method for sintering blanks into fuel pellets, in which the blanks are moved through the muffle of a tunnel furnace by pushing the blanks through the muffle on a guiding device which goes through the muffle and protrudes therefrom at least on the input side, in the form of a single-layer column of abutting blanks.

Method and tunnel furnace for sintering blanks

A sintered nuclear fuel compact of UO.sub.2 or the mixed oxides (U, Pu)O.sub.2 and (U, Th)O.sub.2, with which reactivity losses in a nuclear reactor having relatively long fuel element cycles are avoided, has in its sintered matrix neutron poison in the chemical compound form UB.sub.x with x=2; 4 and/or 12 and/or B.sub.4 C. A sintered nuclear fuel compact of this kind is produced by sintering from a compact comprising a mixture of at least one of the mixture components UO.sub.2, PuO.sub.2, (U, Pu)O.sub.2 and (U, Th)O.sub.2 powder with UB.sub.x powder, where x=2; 4 and/or 12 and/or B.sub.4 C powder.

Sintered nuclear fuel compact and method for its production

UO.sub.2 base powder exhibiting any specific surface and crystallite diameter properties is mixed with rare earth (SE) oxide-containing powder, the particles of which exhibit at least in one surface layer, a crystal lattice of the fluorite type, with the stoichiometric composition (SE.sub.0.5, U.sub.0.5) 0.sub.2.00 and/or form it in sintering; and is compacted to form compacts which are sintered in a gas atmosphere with reducing action at 1500.degree. C. to 1750.degree. C. to form high-density sintered bodies.

Method for producing oxidic sintered nuclear fuel bodies

Method for the manufacture of oxidic nuclear fuel bodies by a heat treatment of blanks obtained from UO.sub.2 starting power or a mixture of UO.sub.2 and PuO.sub.2 starting powder at a treatment temperature in the range of 1000.degree. C. to 1400.degree. initially in a gas atmosphere with oxidizing action and subsequently in a gas atmosphere with reducing action. The oxygen potential of the gas atmosphere with oxidizing action is kept in a range in which a crystallographically demonstrable U.sub.4 O.sub.9 or (U, Pu).sub.4 O.sub.9 crystal phase is generated in the blanks during the heating to the treatment temperature in this gas atmosphere with oxidizing action.

Method for the manufacture of oxidic sintered nuclear fuel bodies

Method for the manufacture of oxidic sintered nuclear fuel bodies by compacting UO.sub.2 -starting powder or a mixture of UO.sub.2 -and PuO.sub.2 starting powder which contains up to 10% by weight rare-earth oxide, especially Gd.sub.2 O.sub.3, as an additive into blanks and subsequent densification of these blanks by a heat treatment in a sintering atomsphere with reducing action. The UO.sub.2 -starting powder used for compacting has a specific surface in the range of 2 to 4.5 m.sup.2 /g and/or a mean crystallite diameter in the range of 80 nm to 250 nm, and the heat treatment in the sintering atmosphere with reducing action is carried out at a temperature in the range of 1,500.degree. C. to 1,750.degree. C.

Method for manufacturing oxidic sintered nuclear fuel bodies

Manufacture of very dense oxidic fuel bodies of UO.sub.2 with rare earth oxides in which pressed blanks are subjected to sintering in an oxidizing atmosphere at relatively low temperature and are sintered in a reducing atmosphere at a higher temperature. This avoids sintering-inhibiting phases and permits very dense bodies with greater content of rare earth oxides to be produced.

Method for the manufacture of very dense oxidic nuclear fuel bodies

Fuel assembly storage capsule for storing spent fuel assemblies in water-filled fuel pits, the capsule being formed of a sleeve sealed at the bottom thereof, having an upper opening closable by a cover and having a cross section matching that of a fuel assembly to be received therein, includes a rim formed on the cover and laterally embracing the sleeve in installed condition of the cover, the cover being retained on the sleeve of its own weight exclusively, the inner surface of the sleeve and the cover rim, in installed condition of the cover, under water, defining an annular space filled with air.

Fuel assembly storage capsule for storing spent fuel assemblies

Fuel assemblies forming cores of gas-cooled reactors, operate at temperatures too high to permit the use of resilient contact elements for holding the fuel rods centered in the openings of the spacer grids of the fuel assemblies, solid and rigid contact elements not relying on resilience, being required. In such cases intercontacting surfaces of the fuel rod metal claddings and the spacer grid contact elements, are capable of sticking together, preventing relative sliding by these surfaces to accommodate thermally induced movements, resulting in the claddings being highly stressed. To prevent this, one or both of the intercontacting surfaces are roughened or otherwise processed to have peaks and valleys or depressions so that abrasion products are carried off between the peaks, permitting the intercontacting surfaces to remain relatively slidable with the result that the previously referred to stressing of the claddings is substantially reduced as compared to that resulting when there is surface sticking together.

Fuel assembly for gas-cooled nuclear reactors

A gas-cooled nuclear reactor, having a tight connection with an intentionally provided leak site between a fission-gas discharge channel formed in a reactor core carrying plate as well as in a head portion of encased fuel elements that are suspended in receiving bores formed in the core carrying plate, the tight connection being formed by an annular member having a sealing surface engaging the core carrying plate at a region thereof in which an opening to the fission-gas discharge channel formed in the core carrying plate is located, a gas-tight, elastic and substantially cylindrical member, variable in length, connecting the annular member to the fission-gas discharge channel formed in the head portion of the fuel element, compression spring means biasing the annular member in a direction away from the fission gas discharge channel formed in the fuel-element head portion, and a sealing abutment plate secured to a central pin and limiting clearance for play of the annular member with respect to an annular zone thereof disposed within the sealing surface of the annular member, the leak site including a radial bore formed in and extending through the annular member between the annular zone and the sealing surface of the annular member.

Tight connection between fission gas discharge channels

The individual fuel rods of a fuel assembly are connected to a fission gas exhaust system via perforated end caps. For this purpose, the perforated end caps are provided with external threads and screwed into a rod holding plate of the fuel assembly. In addition to the attachment thus provided, a tight connection to the canals of the fission gas exhaust system, which are built into the rod holding plate, is accomplished thereby at the same time.

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Bubenreuth, Germany

Martin Peehs