Coupled scalar and vector PN methods for solving multigroup transport problems in multislab geometry

A spherical-harmonics (PN) method that incorporates and couples existent scalar and vector versions of the method is developed. The scalar (group-by-group) version of method is applied to the slowing-down energy range and the vector version to the thermal energy range. The link of coupling between these methods is the slowing-down source to the thermal groups which becomes available once the problems for all of the slowing-down groups are solved with the scalar method. The advantage of using the coupled PN method over the vector method when solving transport problems defined in extended energy range is demonstarted in this work.