Patent Number: 044366779
Section: summary

BACKGROUND OF THE INVENTION In the manufacture of recycle pellets for use as nuclear fuel in light water and breeder reactors, it is necessary to process large quantities of highly radioactive powders. These processes typically involve the mixing of fissile material (i.e., material containing elements which can undergo fission) with fertile material (i.e., material containing elements capable of becoming fissile). These powders must be mixed in precise proportions to maintain the proper fissile content of the pellets. After mixing, the pellets are fabricated, sintered, and ground to the proper tolerances. Because pellet manufacture involves such highly radioactive materials, the processing must be done by remote control in a protective canyon, which greatly adds to the difficulty and expense of the manufacturing procedure. In addition, because fine powders are being processed, a dust is produced which clings to and coats the walls and manufacturing equipment. Since some of this dust can contain plutonium, which can be used for making bombs, it is difficult to account for all the plutonium involved in the process in order to insure the nonproliferation of nuclear weapons. Also, because the powder adheres to the processing equipment, it is difficult to produce fuel having different specifications because the powder remaining in the equipment tends to contaminate new powders processed in the equipment. Still another difficulty is the tendency of submicron powders of different chemistries to segregate during blending and during pneumatic transport which results in the production of inhomogeneous pellets. SUMMARY OF THE INVENTION We have discovered a method of making a nuclear fuel pellet which avoids most of the difficulties encountered in previous processes. In our process, the powders are processed in a sealed container, thereby eliminating most of the problems created by powder dust. In addition, the fissile and fertile powders are not mixed together unil they are about to enter the container. This prevents powders of different chemistries from segregating during blending and pneumatic transport. Finally, in our invention the production of pellets of hourglass shape and inhomogeneous density is avoided by pressing the powders isostatically. As a result, it is expected that less grinding will be required to bring the pellets of this invention into the correct tolerances. Another advantage of isostatic pressing is that the pellets can now be made of greater length. Additional advantages include a decrease in the number of manufacturing operations, a smaller floor space requirement, and simpler remote maintenance procedures. Also, because the pellets are enclosed in a plastic container, pellet damage such as chipping, capping, and fracture should be greatly reduced. Another advantage is that pellets of different compositions can be made using the same apparatus without extensive cleaning operations in between, because free-flowing powders are used and the powders are enclosed in a container through much of the manufacturing procedure.