Propagation of a nuclear chain reaction in the diffusion approximation

A nuclear chain reaction has been studied in the diffusion approximation. A breeder medium in the form of a long cylinder has been considered. Both su per- and subcritical regimes have been studied. The finiteness of the neutr on-moderation length has been taken into account. It has been found that, i n the supercritical regime, the velocity of propagation of the nuclear chai n reaction is described by a formula similar to that for slow burning and i s proportional, in the simplest case, to the square root of the product of the neutron diffusion coefficient and the neutron multiplication factor.