Patent Number: 059784326
Section: description

* Captions for the major parts of this drawing ______________________________________ (1) Crucible (2) High-frequency generator (3) Chamber (4) Vacuum pump system (5) Gas supply valve (6) Check valve (7) Rotating disk (8) Recovery container (9) Cyclone (10) Cooling gas (11) Orifice (13) Stopper (31) Gas injection nozzle (32) Chamber wall (71) Electric motor (100) Centrifugal atomizer ______________________________________ DETAILED DESCRIPTION OF THIS INVENTION This invention comprises high-density dispersion fuels containing atomized spherical particles, and fuel fabrication processer related thereto. Comparing with the conventional method, the invention has many advantages for the direct formation of meta-stable .gamma.-U phase, process simplification, the minimization of fabrication space, improvements of production yield, fuel productivity, powder purity and fuel formability, a higher thermal conductivity in real heat flow direction, the decrease of as-fabricated porosity, and a smaller thermal swelling. A preferred manufacturing method is as follows. Uranium and alloying metals are charged in a heat-resistant crucible having a stopper and a small orifice. The atomizer chamber is evacuated up to the vacuum degree of above 10.sup.-3 torr using vacuum pumps. Uranium and alloying metals charged in the crucible are melted by vacuum induction or arc heating. The alloy melt is fed through a nozzle onto a rotating disk. Then melt droplets are formed and spread by the centrifugal force of rotating disk. The flying fine droplets are cooled rapidly (above 10.sup.4 .degree. C./sec in cooling rate) in an inert atmosphere of argon or helium gas due to the large specific surface area. The particles may thereafter be dispersed in a nonfissionable matrix (for example, an aluminum (Al) matrix), is desired. FIG. 1. shows a schematic diagram of the centrifugal atomizer, and FIG. 2 shows a block diagram of this invention. The equipment of this invention is composed of the heat-resistant crucible (1) having a stopper and an orifice (11), the high-frequency generator (2) for heating the crucible, the vacuum pump system (4) evacuating the chamber (3) to a proper vacuum degree, the gas supply valve (5) providing with the cooling gas (10) in the chamber (3), the check valve (6) discharging the over-pressurized gas outside the chamber, the rotating disk (7), the container (8) collecting the produced powder, and the cyclone (9) collecting the very fine powder. The crucible (1) is located in the chamber and surrounded by induction coil. Alloying metals are charged in the crucible. The chamber is evacuated up to about 10.sup.-3 torr by a vacuum pump system. The crucible is heated by an induction method. High frequency electric power is supplied to the coil from a generator. The melt is discharged by lifting the stopper and fed through the orifice onto the rotating disk. At the same time the cooling gas of Ar or He is supplied in a downward direction from the nozzles at the middle chamber. The flow rate of the cooling gas is controlled by adjusting valves. The melt is spread with forming droplets by the centrifugal force of the rotating disk. The flying melt droplets are rapidly solidified by cooling gas due to a large specific surface area. The solidified particles slide along the inclined wall of the chamber (3) into the powder container (8) at the bottom of the chamber (3). The check valve (6) located between the cyclone and the chamber discharges the used cooling gas (10) by the over-pressure of the chamber. This invention is explained as the following example (I). In the case of preparing an alloy powder containing uranium and 8 wt. % Mo, uranium and Mo metal are weighed in proportion to the alloy composition and charged into a crucible. The crucible (1) and insulation are assembled properly. The atomizer chamber is evacuated up to about 10.sup.-3 torr using a vacuum system. Then the crucible is heated by switching on the generator. When the crucible temperature reaches 200.degree. C. higher than the melting point, the disk (7) is rotated to about 30,000 rpm using an electric motor (71). By lifting the stopper the melt is poured on rotating disk though an orifice. The melt is spread by the centrifugal force of the rotating disk, and forms fine droplets, which fly through the downward injecting cooling gas toward the wall of the chamber. The fine droplets are rapidly solidified into the meta-stable .gamma.-U phase at a cooling rate of about 10.sup.4 .degree. C./sec. The atomized powder is collected in the container (8) at the bottom of the chamber (3). The median particle size is about 65 .mu.m, and the portion of powder below 125 .mu.m in size is about 95%. Then the atomized powder is blended with aluminum powder and compacted into pellets. The pellets are preheated at 420.degree. C. and extruded into fuel meats in an inert atmosphere. Another example (II) is as follows, where spherical particles of uranium, about 4-9 wt % Q and about 0.1-4 wt % X are made (wherein Q is selected from Mo, Nb and Zr; X is selected from Mo, Nb, Zr, Ru, Pt, Si, Ir, Pd, W and Ta, with the proviso that Q.noteq.X.) Other alloys such as uranium and about 4-9 wt % Q can also be made using the process described herein. In the case of preparing an alloy powder containing uranium, 5 wt % Mo and 2 wt % Ir, U, Mo and Ir element are weighed in proportion to the alloy composition and charged in a ceramic crucible. Thereafter the atomizer chamber is evacuated up to above 10.sup.-3 torr using a vacuum pump system in the same way as the atomization process described previously. After the alloy melt is superheated to about 200.degree. C. higher than the melting point, the rotation of disk is started and increased to about 30,000 rpm. The fuel particles are produced with rapid solidification effect (a cooling rate of above 10.sup.4 .degree. C./sec in an inert atmosphere (10). Spherical alloy powder of 30.about.55% in volume percentage is blended with aluminum powder, and then compacted into billets. The billets are preheated at 370.degree. C., and extruded in an inert atmosphere into a fuel meat. In this invention, uranium alloy powders are obtained directly from the melt. The followings are the merits obtained by this technology. First, the powder fabrication by atomization method is excellent in yield and productivity. The fabrication processes such as mechanical comminution of ingots, rinsing and drying chips for the removal of cutting fluid components, and magnetic separation can be eliminated. Second, the gamma phase of uranium alloy is formed directly from the melt by the rapid cooling effect. Third, atomized particles have a spherical shape, which gives many kinds of beneficial effects on fuel performance such as: a smaller interaction swelling between fuel particles and matrix, a better thermal conductivity in the real heat flow direction, and improving the formability of fuel meat. Fourth, the powder quality is pure because there are no chances for contamination from the cutting fluid and grinding tools.