Neutron Balance — Energy

The basic framework of the neutron balance equation has been derived and presented in the previous chapters. However, before we can proceed to realistic neutronic calculations, the various neutron-nuclei interaction rates must be considered in more detail. Of the various interactions that occur (e.g. capture, fission, scattering) the scattering interactions are by far the most prelevant. For example, in all types of reactors neutrons are produced as ‘fast’ neutrons which have an average energy of ~ 2.0 MeV. However, in ‘thermal’ reactors most of these neutrons are absorbed only after they have reached quite low, ‘thermal’ kinetic energy levels (well below 1 eV). They approach these low levels by loosing energy in repeated scattering interactions. A neutron is absorbed only once, but before it does so, it can experience up to a hundred or even more scattering events (this depends upon the type of the reactor). Thus looking at neutron interactions from the total interaction rate point of view, the scattering interaction is indeed the dominant interaction type.