Investigation of self-organization of the non-linear nuclear burning regime in fast neutron reactors

The possibility of creating a self-organizing non-linear regime in the form of a running wave of nuclear burning in a critical fast neutron reactor is studied. The description of this regime is based on solving the non-stationary neutron diffusion equation together with the fuel burn-up equations and the equations of nuclear kinetics for the delayed neutron precursor nuclei in the one-group approximation. The calculations are carried out in the plane one-dimensional model for a two-zone homogeneous reactor with metal fuel of the U–Pu cycle, the Na coolant and constructional material Fe. The temperature effects and heat sink are not taken into account. The requirements for wave initiation and evolution in space and time are discussed. The mechanism of the reactivity feedback in the reactor and the stability of the nuclear burning wave regime relative to distortions of the neutron flux are analyzed. The results obtained show that under certain conditions the reactor can go into the mentioned regime. At this regime, the reactor remains in the state close to the critical one without any control during a long time. A high burn-up level of fuel (up to 30%) can be attained.