Improving fuel cycle design and safety characteristics of a gas cooled fast reactor

This research concerns the fuel cycle and safety aspects of a Gas Cooled Fast Reactor, one of the so-called "Generation IV" nuclear reactor designs. The Generation IV Gas Cooled Fast Reactor uses helium as coolant at high temperature. The goal of the GCFR is to obtain a "closed nuclear fuel cycle", where only natural uranium is used as raw material, and only fission products are discharged to a repository. Uranium and heavier isotopes (plutonium, americium, etc) are recycled in the reactor and are eventually fissioned. Since the heavy isotopes determine the long-term radiotoxicity of the nuclear waste, application of a closed fuel cycle maximizes the energy output of the fuel material, and can significantly reduce the lifetime of nuclear waste. It is shown that it is possible to obtain a closed fuel cycle with the GCFR. Coated particle fuel and ceramic plate fuel are discussed as fuel candidates for GCFR. A theoretical framework is derived using a combination of eigenvalue perturbation theory and nuclide perturbation theory to estimate the Breeding Gain of the reactor, and the change of Breeding Gain due to changes of the initial fuel composition. It is shown that the GCFR has some potential as an actinide transmutation reactor. To increase the safety of the GCFR, passive elements have been designed to automatically shut down the reactor in case of incidents. These elements use liquid Li-6, which is introduced into special assemblies if necessary. It has been shown that with these elements the reactor can withstand transients without damage to the fuel. The research has been performed in a European framework