Computation of anisotropic flux escape and transmission probabilities for cylindrical annular regions

In the interface current method of solving the integral transport equation, most of the time is spent in the computation of various escape and transmission probabilities. The numerical integration of these probabilities is time consuming. Bonalumi's Pseudo-linear (P-L) approximation is found to be a good approximation for transmission probabilities from the outer to inner (POI) region and not for the outer to outer (POO) region. Effort was made in the past, by us, and a combination of a polynomial and P-L approximation was found to give good results for POO as well. For isotropic incident flux we computed POO as POO = POO1 - POO2. Here POO1 is related with the escape probability for a homogeneous solid cylinder, which can be expressed as a polynomial of its average chord length, and POO2 was expressed very well by the P-L approximation. In this paper, this approach has been extended to compute probabilities corresponding to anisotropic terms of the angular flux expansion at region interfaces for cylindrical annular geometry. (Author)