An Improvement of the PALLAS Discrete-Ordinates Transport Code

An improvement in the approximation of the spatial distribution of the source term in the PALLAS discrete-ordinates code by a combination of linear and exponential functions results in a reduction of numerical errors compared with those due to the use of only a linear approximation based on a direct integration method. The results obtained by the improved approximation for one-dimensional radiation transport calculations are compared with those by the PALLAS code with the original linear approximation and by the S_N code ANISN. For further verification, this improved approximation is applied to two-dimensional neutron transport calculations, in which numerical errors due to the spatial mesh sizes used in the calculations are studied. As a result, it is found that the use of the improved approximation gives reasonable solutions with small numerical errors, irrespective of the spatial mesh size in both one- and two-dimensional PALLAS calculations of radiation transport.