A self-consistent method for evaluating the neutron diffusion coefficient

The problem of the determination of the diffusion coefficient to be used in neutron physics evaluations is given a coherent solution within the framework of space asymptotic transport theory. Some formulae are then derived for the application in multigroup theory and the implications and possibility of utilization in group constants averaging techniques are briefly discussed. Some calculations regarding critical dimension values are finally performed for materials typical of fast assemblies and some comparisons are presented with the results obtained using some standard definitions of the diffusion coefficient, widely employed in reactor calculations. The improved attitude in reproducing transport results shows the remarkable superiority of the definition herewith proposed and utilised. (orig.)