A Robust Arbitrarily High-Order Transport Method of the Characteristic Type for Unstructured Grids

A reformulation of the arbitrarily high-order transport method of the characteristic type (AHOT-C) for unstructured grids (AHOT-C-UG) is presented in this work, which resolves the previous difficulties encountered in the original formalism. A general equivalence between the arbitrary-order neutron balance and arbitrary-order characteristic equations is derived, which improves the numerical computation of the spatial moments of the angular flux and allows a series expansion of the characteristic integral kernel in cases where the medium is optically thin. Numerical results are presented, which verify the convergence behavior of AHOT-C-UG for various expansion orders.