Initiation and propagation of nuclear burning wave in fast reactor

The regime of the nuclear burning wave (NBW) in a fast reactor (FR) is described using the non-stationary diffusion equation for neutron transport and equation of the fuel component burn-up and of nuclear kinetics for precursor nuclei of delayed neutrons. A critical two-zone fast reactor of cylindrical form with metal fuel of the U-Pu cycle is considered. The initiation of nuclear burning in an enriched ignition zone by means of an external neutron flux that is turned off at an early stage of FR operation has been simulated. The possibility of creating a self-organizing regime of a running NBW in the breeding zone along the reactor axis has been demonstrated. The neutron leakage in a transverse direction was taken into account using the concept of radial buckling. The calculation results of the space-time evolution of neutron flux in this system using the effective multi-group approximation are presented. The average fuel burn-up is about 50%. The velocity of NBW propagation strongly depends on the transverse size of FR. For example, in the reactor of 110 cm radius and 500 cm length the NBW velocity is about 22 cm/year. (author)