Reactivity in the theory of the stationary nuclear fission wave

We studied axial motion of the stationary nuclear fission wave in the cylindrical core of the traveling wave reactor (known also as CANDLE) using an effective one-dimensional model of the fast spectrum reactor with uranium plutonium fuel. The model includes one-group diffusion equation for the neutron flux and kinetic equations for nuclear densities. The so-called velocity characteristic has been studied in our previous works. It is the dependence of the wave velocity on the effective concentration of the absorber. Due to instability of long-living 241Pu it has two branches, and the solutions of the lower branch are unstable. In this paper, reactivity was introduced into the diffusion equation as an additional parameter of the model, and the generalized equation of the velocity characteristic connecting the wave velocity with the effective concentration of the absorber and reactivity is obtained. Since the equation includes both parameters linearly and additively, their variations are interchangeable, in the appropriate scale. Obtained results open the way to study the velocity characteristic of the reactor with powerful reactor codes (outside one-group diffusion approximation), calculating the effective multiplication factor in the stationary wave mode for a series of fixed values of the reactor power.