Neutron wave propagation in multiplying assemblies with and without control rods

In this work the dispersion law is expanded in a power series of the frequency up to the third order; for this, two-group diffusion theory is used. In this manner the nuclear parameters of this approximation can be related with the experimental observables in a closed and definite form. Also a model is developed that predicts the existance of an asymptotic progagation mode even in the presence of control rods; this model permits one to calculate the wave front and the dispersion law. The models are compared with experiments done in a highly compact system with 90% ²³⁵U enriched uranium fuel and H₂O moderator.