Multigroup Calculations of the Fast Spectrum and Fast Fission Effect

A multigroup procedure for the calculation of the fast fission phenomena in thermal uranium-water reactors has been developed. The method essentially consists of applying the single-flight collision concept in a manner analogous to the calculation of resonance capture in thermal reactor lattices. The collision and escape probabilities are calculated by numerical integration over the actual neutron paths encountered in a reactor lattice. The multigroup equations are solved by an iterative procedure which converges rapidly. The fast neutron spectrum, &dgr;₂₈ and &hexadecimal; can be obtained. Results of calculations are presented in which the value of &dgr;₂₈ homogeneous uranium-water mixtures and for slightly-enriched uranium-water lattices are compared with Monte Carlo calculations and experiment. Very satisfactory agreement has been obtained. Fast neutron spectra in the core of a pool type reactor and in the fuel and moderator regions of a uranium-water lattice, calculated by the present method, are also shown.