Deterministic Multigroup Modeling of Thermal Effect on Neutron Scattering by Heavy Nuclides (original) (raw)

The principal physical phenomenon underlying the computation of neutron spectra is the nuclear reaction in which neutrons lose or gain energy, i.e., the neutron scattering process. As long as neutrons only lose energy they are “slowing down”. The loss of energy by the neutrons is the dominant energy exchange mechanism for very fast (and hence very energetic) neutrons. In the past this fact led to the use of approximations in which the gain of energy by the neutron in collisions with the fuel lattice atoms or other materials, such as surrounding moderator, was assumed negligible in the energy range above thermal. This assumption was demonstrated to be inaccurate and unacceptable when scattering resonances are present at intermediate energies (the lower energy domain within the slowing down range). The purpose of this thesis is to contribute a method that allows the relaxation of the incorrect assumption. Namely, a method is developed that accounts for up-scattering by heavy nuclides ...