The change in the fusion power of a tokamak reactor due to distortions in the reaction component distribution functions has been studied. A numerical solution of the two-dimensional kinetic equation is used to determine the distribution of deuterium, tritium and alpha particles. Neoclassical ripple-plateau radial diffusion of deuterium and tritium components and stochastic transport of alpha particles as well as Coulomb collisions between these components and electrons are taken into account. It is shown that neoclassical transport of fast ions has a weak effect on the power generation. The most important process is ripple diffusion. For a reasonable ripple value, diffusion can reduce the energy input of the D-T reaction to the plasma by 15-30%.