Patent Number: 041636899
Section: summary

This invention relates to nuclear reactors and in particular to fuel for, and fission gas venting of a thermionic or similar fuel element. In thermionic nuclear reactors, the generation of gases upon the fission of the fissile fuel presents at least a two-fold problem; first, particular fission product gases such as xenon and krypton have such large neutron absorption cross sections so that if they remain in the reactor core in the neutron flux an appreciable number of neutrons are lost from the fission process effectively reducing the reactor efficiency and possibly reducing reactivity to below critical; and second, fission product gases or other volatile products may be sufficient in amount to create excessive pressure to cause the fuel container to bulge and deform. Since, in a thermionic reactor or any other high temperature reactor the fuel container forms the emitter portion of the thermionic cell, and since the spacing between the emitter and collector portions of the cell are very small, being of the order of hundredths to thousandths of an inch and very critical, any bulging or changing of shape of the emitter may be highly detrimetal to reactor operation and/or thermionic performance of the fuel cell or element. The device of the present invention eliminates these problems by taking advantage of phenomena associated with high temperature operation of nuclear fuels to remove and conduct away from the fuel cell or rod the various gases and volatile products generated during the fission process. Where other venting methods merely permit the gaseous and volatile products permeate the fissile fuel, the present invention provides an arrangement promoting gas and vapor migration to form an accumulated pocket of gas and to remove it from the fuel soon after it is generated. It is, therefore, an object of this invention to provide a venting device for a thermionic nuclear fuel cell or a high temperature fuel element whereby deformation of the cell cladding caused by fission gas pressure is eliminated. It is a further object of this invention to provide a venting device for a nuclear reactor fuel element whereby fission product gases having a high neutron absorption cross section are readily removed from the fuel element. It is another object of this invention to provide a venting device for a nuclear fuel element providing for the directional migration of fission product gases to be accumulated and removed from the reactor.