Patent Number: 044951469
Section: summary

BACKGROUND OF THE INVENTION The present invention relates to the loading of fuel rods with spherical nuclear fuel. In recent years it has been discovered that conventional nuclear reaction fuel composed of fuel pellets encased in cladding tubes may lead to the splitting of the cladding tubes thereby releasing radioactive material to the adjacent cooling water. This splitting is due to an interaction between the pellet and cladding. One way of avoiding this problem is to limit the surface interaction between the fuel and cladding. This may be achieved by loading the fuel cladding tubes with nuclear fuel in the shape of spheres. If three different sizes of spheres are used, then appropriate packing of the spheres into the rods will result in a sufficient density of nuclear fuel to be properly used in a nuclear reactor. One method for loading a fuel rod is to simply drop the spheres into a vertical cladding tube while vibrating the rod to assist in packing. However, this method is not satisfactory for several reasons. The distribution of the particles sizes freely falling from a height of 6 to 12 feet into a cladding tube does not lead to uniform distribution. This method also leads to the trapping of air which requires a longer time to evacuate at the sealing of the tube. In addition, the vibrating packing is extended because of the random loading of the spheres. SUMMARY OF THE INVENTION The invention is a system and method for the loading of spherical nuclear fuel into a fuel rod. The system includes a main housing having an inert atmosphere and having an opening to receive fuel spheres having three different diameters for loading into fuel rods; a weighing station system for receiving the spheres and separating the spheres into three predetermined quantities, the weighing system including a balance means for weighing the nuclear fuel spheres; a means for transferring the fuel spheres after entering the housing to the weighing station within the housing; a fuel rod support system for supporting the fuel rod in an upright position; a feeding probe for loading the predetermined quantities of the fuel spheres in a controlled manner into the fuel rod; and a means for transferring each of the predetermined quantity of the fuel spheres to a corresponding hopper of the feeding probe for subsequent loading into the fuel rod. In addition, a method if disclosed for loading a nuclear fuel rod with spherical nuclear fuel. The method includes the steps of transferring nuclear fuel spheres having three different diameters into a glove box having an inert atmosphere; transferring the fuel spheres to weighing stations, a different weighing station corresponding to each diameter of the nuclear fuel spheres; weighing out a predetermined quantity of fuel spheres for each diameter; transferring the fuel spheres to hoppers on a fuel probe, one hopper corresponding to each of the diameters of the nuclear fuel sphere; lowering the fuel probe into the fuel rod so that the lower end of the probe is just above the bottom of the fuel rod; discharging the nuclear fuel spheres from the fuel probe discharge tube opening at a controlled rate into the fuel rod; and removing the fuel probe from the fuel rod at a rate such that the lower end of the fuel probe remains just above the top of the ascending fuel column.