Evaluation of 1D Models for Particle Transport with Wall Migration in Ducts of Rectangular Cross Section

Approximate 1D models of particle transport in ducts that make use of an exponential displacement kernel to describe the effect of wall migration are evaluated for ducts of rectangular cross section. The studied models are based on the use of either one or two basis functions to approximate the transverse and azimuthal dependencies of the angular flux in the duct. Thermal-neutron reflection and transmission probabilities resulting from Monte Carlo simulations carried out with the MCNP and PHITS codes for iron, concrete and graphite ducts are used as reference solutions. It is concluded that the model built on two basis functions performs well (deviations typically < 10% in magnitude) for iron, the material for which absorption is most important, but less so for the scattering-dominated materials concrete and graphite. It is also concluded that changes in the energy distribution of the incident source have their strongest influence on the results for iron ducts.