Multidimensional Discrete Ordinates Nodal and Characteristics Methods for the Apollo2 Code

This paper describes the nodal and characteristics options of the discrete ordinates flux solver of APOLLO2 general purpose transport code. The discrete equations for two and three-dimensional Cartesian geometry are written in the same form for both classes of methods, allowing the use of the same sweeping algorithm. The calculational coefficients are computed using the method specific relations together with balance equation for spatial flux moments. This formulation allows for an easy implementation of the transport synthetic acceleration technique for inner iterations such as boundary projection acceleration. Linear and bilinear approximations of both methods are implemented in the code. (author)