Flux expansion nodal method for solving static and transient neutron diffusion equations, in hexagonal-z geometry

An intra-nodal flux expansion nodal method (FENM) for solving static and transient neutron diffusion equations in hexagonal-z geometry has been developed, in which the flux distributions are expanded into a set of analytic basis functions and orthogonal second-order polynomials. In order to improve the nodal coupling relations, a new type of nodal boundary conditions is proposed, which requires the continuity of both the zero- and first-order moments of partial currents across the nodal surfaces. The numerical results for a series of benchmark problems demonstrate that FENM exhibits good accuracy and convergence. (authors)