Patent Number: 040000397
Section: description

EXAMPLE 1 Manufacturing of the Fuel Elements For the fabrication of the cylindrical fuel inserts (11 mm diameter, 40 mm high) overcoated particles are utilized. For this coated particles are used which contain 5.1% of Uranium and 47.4 weight percent of Thorium as mixed oxide and are coated with a duplex layer of pyrolytic carbon. The overcoated particles contain 59 weight percent of coated particles and 41% of graphite matrix powder layed on by a dragee type process. The graphite matrix powder contains 96% natural graphite and 4% phenolic resin binder. For the fabrication of one fuel insert of the dimensions described above 11.5 g overcoated particles are filled in a steel die and pressed at 150.degree. C (pressure 80 kg/cm.sup.2) After pressing the green inserts are filled in the bores of the structural graphite and then heat treated to 800.degree. C for coking the phenolic resin binder. After heat treatment the inserts have such dimensions fitting in the boreholes of the structural graphite block. The binder coke content relative to the matrix is 1.2 weight percent. The matrix density is about 1.2 g/cm.sup.3, the particle volume is about 40% of the insert volume. Measurements of the binding strength of such fuel inserts show values of about 10 kg/cm.sup.2. The binding strength of the structural graphite however is 250 kg/cm.sup.2. EXAMPLE 2 Reutilization of the Structural Graphite after Irradiation First there was unscrewed the screw cap consisting of structural graphite of the fuel element block coming from the reactor (or the tight fitting stopper consisting of matrix graphite was bored out with a crown borer). Then the fuel zone can be disintegrated with the same crown borer or with a spiral borer or an end-milling cutter. This operation takes place from below so that the disintegrated fuel particles and matrix graphite crumbs fall freely from the bore-holes of the graphite block. In using a spiral borer it is advantageous to pneumatically assist the disintegrated particles from the block by a channel in the inside of the spiral borer in order to avoid a blocking by poor conveying of material. It is also possible to use pneumatic conveying of the fuel in working with crown borers. In both of these cases using spiral and crown borers with pneumatic conveying it is also possible to bore from above downwardly. According to the present invention, there is saved in a second insertion of the structural graphite block filled with new fuel and breeder material, produced like described in example 1, into the reactor both the cost of the machined graphite block and also the burning or storage of this block. This means in two insertions of a structural graphite block a reduction in cost of about 15%, in a three time insertion of about 20 to 25%. Finally, it is established that an especial advantage of the process of the invention is that by reducing the burning of graphite in half or to one-third, brings nearer the solution of a significant problem in regard to protecting the environment.