Development and evaluation of a computer code to couple two-dimensional to three-dimensional discrete ordinates calculations

A method has been developed to couple two-dimensional (2-D) to three-dimensional (3-D) discrete ordinates transport calculations. This method is useful for problems in which a 3-D Cartesian (X-Y-Z geometry) region of interest is very far from a point source. A 3-D solution from the source including the region of interest is prohibited due to the large computing cost of such calculations.

The problem is solved by first performing a 2-D discrete ordinates calculation from the source past the region of interest. The results of the 2-D calculations are transformed into a boundary condition on the surface of the 3-D region of interest. This transformation or coupling method is developed and implemented in the DOTTOR computer code. The boundary condition is then used for a subsequent 3-D discrete ordinates calculation in the region of interest.

Simple test problems were used to evaluate the accuracy and speed (i.e., computing cost) of the DOTTOR code. The evaluation indicates that the DOTTOR code produces accurate results with acceptable computing costs. The algorithm, chosen showed a significant speed advantage over others tested when applied to large problems.