Numerical method for the solution of three-dimensional neutron-transport problems

A low-order discrete ordinates model for the solution of a certain class of three-dimensional neutron-transport problems is described. The method can be applied to cuboidal configurations with a region structure that allows the use of constant mesh spacings in each of the three coordinate directions. The angular flux distribution in a unit mesh cell is described in terms of discrete directions connecting the midpoints of 14 neighbor cells. A three-dimensional multigroup discrete ordinates code 3DT has been written for x, y, z-geometry which allows calculation of various configurations for small critical assemblies with computing speed far surpassing Monte Carlo techniques. The computed results for individual fuel-block reactivity worths of the fast thermionic critical experiment of Gulf General Atomic are in most cases in excellent agreement with experiment.