What does one-group diffusion theory assume about neutron energy in a reactor?

The one-group diffusion theory simplifies the analysis of neutron behavior in a nuclear reactor by assuming that all neutrons are at a single constant energy. This is a crucial assumption because it allows for the modeling of neutron distribution and movement without the complexities that arise from accounting for variations in neutron energies.

In a reactor, neutrons can possess a range of energies, but by treating them as a homogeneous group, the one-group theory enables the application of simpler mathematical models to predict neutron flux and ensure system stability. This means that the interactions and reactions occurring in the reactor can be approached with more straightforward calculations, ultimately aiding in reactor design and safety analyses.

This assumption is particularly useful when focusing on thermal reactors, where neutrons are primarily at low energies, and helps streamline computations needed for reactor kinetics and dynamics. The focus on a single energy group allows engineers and scientists to predict critical parameters such as multiplication factors and reaction rates without the need for cumbersome energy spectra considerations.