Patent Number: 046630937
Section: description

DETAILED DESCRIPTION OF THE INVENTION All parts, percentages ratios and proportions are on a weight basis unless otherwise stated herein or obvious herefrom to one ordinarily skilled in the art. FIG. 1 illustrates apparatus 100 for forming the invention aged gel spheres of nuclear fuel. According to the invention, apparatus 100 includes trough-shaped vessel 102, which is connected on its exit end to horizontal ager column 104. The entrance end of troughshaped vessel 102 contains two horizontally-positioned pipes, namely, entrances pipe 106 and overflow pipe 108. Hot perchloroethylene, which is normally at about 85.degree. C., enters into vessel 102 via entrance pipe 106 below the top surface of the perchloroethylene flowing in vessel 102. Near the entrance of pipe 16 into vessel 102 is located vertical baffle 100, which extends above the top surface of the perchlorethylene flowing in vessel 102. Baffle 110 does not extend all the way down to the bottom of vessel 102, so as to provide a passageway thereunder for the entering hot perchloroethylene from entrance pipe 106. A short distance down stream from vertical baffle 110 is located vertical baffle 112. Vertical baffle 112 extends all the way down to the bottom of vessel 102 and has a height which is slightly higher than the top surface of the perchloroethylene down stream portion of the flow in trough-shaped vessel 102. In this manner, there are two top surfaces of the perchloroethylene flow in vessel 102, that is, main flow portion 114 and entrance portion 116. The hot perchloroethylene entering into vessel 102 flows under baffle 110 and then seeps outwardly onto curved top portion 118 of second baffle 112. The use of baffles 110 and 112 helps to provide a smooth down stream flow of perchloroethylene without any turbulence caused by the entering of hot perchlorethylene via pipe 106. Exit pipe 108 is positioned such that its bottom rim is slightly above the normal height of upper perchloroethylene portion 116, so as to provide an overflow means when too much hot perchloroethylene enters via pipe 106. Device 120 injects metal solution droplets into the hot perchloroethylene flow 114 in vessel 102, which includes vertical tube 122, which is attached to short back nozzle 124 of cross pipe 126. As shown in FIG. 1, a U-Pu gelation broth is fed into pipes 122 and subsequently dispersed across the entire length of cross pipe 126. At that point, six streams 128 of the feed broth exit from six orifices 130, which are positioned on the float side of crossed pipe 126. The six short streams 130 are set at an angle of approximately 45.degree. C. to the horizontal. The angle of pipes 130 plus the use of slightly pressurized feed broth in pipes 122 and cross pipe 126 cause droplets 128, which form from the exiting short jets 120, to be forced outwardly at a slight angle and then into perchloroethylene flow 114. Droplets 128 rise back to the surface of perchloroethylene flow 114 because the droplets of nuclear feed float on perchlorethylene. The slight flow of hot perchloroethylene in vessel 112 carries the floating droplets toward its exit end. As the droplets are carried along, the drops solidify into gelled spheres. The holding time from the entrance of the droplets into the perchloroethylene flow until the exit from the vessel of the gelled spheres is approximately 20 minutes. This time span allows the spheres to age. Also the baffle arrangement helps prevent the backward movement of the droplets of gelled spheres toward overflow pipe 108. At this point, droplets 128 are designated in FIG. 1 as aged gelled spheres 132. Vertical column 104 interfaces with vessel 102 to form vertical wall 134. The top rim of vertical wall 134 is complete and establishes the maximum height of perchloroethylene flow 114 in vessel 102. The amount of perchloroethylene flow in vessel 102 is adjusted by the amount of perchloroethylene entering pipe 106 entrance as modified by exit pipe 108. Aged gelled spheres 132 approach the wall over the top edge of vertical pipe sections 136 and 138. Vertical column 104 contains perchloroethylene to a height below the top rim of vertical wall 134. The aged gelled spheres 132, which have fallen into vertical chamber 104 float on the top of the perchloroethylene in column 104 and exit via pipe 139 in the bottom of column 104. The fully aged gelled spheres are indicated in FIG. 1 by the numeral 140. Some perchloroethylene also falls over the top of vertical wall 134 to constantly replenish the perchloroethylene in vertical chamber 104. Spheres 140 in the bottom of chamber 104 are also entrained in perchloroethylene. Referring to FIG. 2, gelled spheres 140 in order to be drained of perchloroethylene, are deposited on moving conveyor 142 where the perchloroethylene is separated from aged gelled spheres 140. Moving conveyor 142 is a flexible screen which in effect allows the perchloroethylene to flow therethrough to funnel 160. The separated perchloroethylene passes down pipe 162 to holding tank 144 and then by means of pump 146 to heater 148 where it is heated to about 85.degree. C.; and subsequently the heated perchloroethylene is recycled into gellation trough 102 via entrance pipe 106. Gelled spheres 140 which were separated from the perchloroethylene are deposited in aqueous wash column 150. After being washed and drained for approximately 5 minutes on the moving conveyor 142, gelled spehres 140 and chamber 150 are subjected to an ammonium hydroxide solution wash. The aqueous wash utilizes wash water from wash tank 152 is deposited in chamber 150 by means of pump 154. The wash water can also be used by intermixing with ammonium solution and the injected into chamber 150. After the aqueous solution and ammonium hydroxide-treated gel spheres 140 are removed, they are sent through belt dryer 150. The wash water is first drained off and recycled to wash tank 152. Drained gelled spheres 140 are subjected to moist air and belt drier 156. The result is dried gelled spheres 158. The simpified apparatus provided by this invention comprises trough 102 and column 104--See FIG. 1. Gelation is accomplished by directing a stream of U-Pu broth droplets 128 from conventional nozzle 126 into a moving volume of hot (about 85.degree. C.) perchloroethylene in trough-shaped vessel 12. The velocity of droplets 128 carries them into the perchloroethylene momentarily, after which, they rise to float on the surface until gelation is complete. Gelled spheres 132 are transported by the perchloroethylene stream into connecting aging column 104 in which a 20 minute holdup allows the spheres to age in the perchloroethylene. From ager 104 the spheres are transported onto moving screen 142 (See FIG. 2) where the perchloroethylene is removed from them, and they are deposited in an aqueous wash column 150. The invention continuous gelation system using perchloroethylene (FIG. 2) is greatly simplified as compared to the prior art system using silicone oil (FIG. 3). A single flow of perchloroethylene replaces nine flows of silicone oil and trichloroethylene. The complex equipment and procedures for a trichloroethylene wash and for the organic recovery have been eliminated. Two difficult solid-liquid detection and control systems are replaced by a simple floating bed of spheres in the ager without any need for detection and control of a solids level. The perchloroethylene provides a nearly ideal combination of gelation temperature, easy removal from the gel, and nonflammability for the preparation of (UPu)O.sub.2. The drops easily enter the PERC and the controlled jet-catcher stream used for silicone oil is not needed. EXAMPLE In this typical microsphere forming experiment, 31.5 ml of a metal feed solution, that was 0.64 M in Pu(NO.sub.3).sub.4 and 2.00 M in A.D. UO.sub.2 (NO.sub.3).sub.2 [(Pu/(U+Pu)=0.236)], was added to a feed pot and cooled to -3.degree. C. A.D. UO.sub.2 (NO.sub.3).sub.2 means acid deficient uranyl nitrate equivalent to UO.sub.2 (OH).sub.x (NO.sub.3).sub.2-x, where x may be between 0 and 0.6. The uranyl is partly hydrolyzed, but remains in solution. [During preparation, the metal feed solution was made acid deficient by the addition of NH.sub.4 OH to provide an unneutralized nitrate/metal mol ratio of 1.90.] A solution, that was 3.2 M in hexamethylenetetramine and 3.2 M in urea, was then slowly added to the feed pot (42.2 ml). The temperature was not allowed to increase above 0.degree. C. during this addition. This solution was dispensed by air pressurization of the feed pot to a vibrated nozzle that introduced 1 mm diameter droplets into the sphere forming trough that contained a flowing stream of perchlorethylene maintained at 85.degree. C. The droplets gelled in about 10 seconds. The residence time in the trough was about 30 seconds. The gelled spheres flowed into a screen collector and were aged for 20 minutes in perchlorethylene at 85.degree. C. After aging, the spheres were allowed to drain for 5 minutes and were then batch washed four times in 3 M NH.sub.4 OH. The spheres were then dried at 110.degree. C. in moist air. Good quality microspheres were obtained in high yield (greater than 98%), and the tap density was 1.27 gm/cc which is in excellent agreement with the density obtained for spheres formed at 90.degree. C. in silicone oil (1.25.+-.0.02 gm/cc). By way of summary, the invention involves a process for preparing gel spheres of (UPu)O.sub.x and other nuclear fuels. The process includes releasing droplets of U-Pu solution into a moving stream of hot perchoroethylene. The droplets form gel spheres which float on the surface of the moving perchloroethylene stream. The spheres are then dropped through a vertical column of perchloroethylene and are allowed to age. Finally, the spheres are subjected to an aqueous wash step and are allowed to dry. The invention also involves an apparatus in which hot, sphere-carrying perchloroethylene is transported, and a vertical column through which the gel spheres descend during the aging process. The foregoing description of preferred embodiments of the invention has been presented for purposes of illustrated and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teachings. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable one skilled in the art to best utilize the invention in various embodiments and with various mdofications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.