Discrete ordinates method-like transport computation with equivalent group condensation and angle-collapsing for local/global iteration

Research highlights: → Angle-dependent total cross section is generated during fine-to-few group condensation, and implemented/demonstrated its efficacy in neutron transport computation. → Angle-collapsing concept is introduced to further reduce calculational burden. → A local/global iteration framework is also proposed based on half-overlapped nodes. → The iteration converges within one or two iterations (for the test problem), reproducing the fine-group reference solution. - Abstract: The group condensation of the transport equation is studied in this paper so that the computational burden can be reduced. The group condensation procedure leads to equivalent total cross section that becomes angle dependent. The difficulty of angle dependency has been traditionally treated by consistent P or extended transport approximation in multigroup transport computation. However, in this study, the angle dependency of the total cross section is applied directly to the discrete ordinates equation, and the solution procedure is validated numerically on a test problem. In addition, an angle-collapsing concept is proposed for the purpose of further simplifying the group condensed problem. A local/global iteration framework is also described, in which fine-group discrete ordinates calculation is used in local problems while few-group angle collapsed transport calculation is used in the global problem, with excellent test results in the keff and flux estimation.