Formulation and verification of a channel-wise axial homogenization method for Ants steady state nodal calculations

A channel-wise axial homogenization method for steady state problems has been developed for the nodal neutronics program Ants. Each axially heterogeneous channel is separately solved with a one-dimensional formulation of the Ants nodal method combining the function expansion nodal method (FENM) and the analytic function expansion nodal method (AFEN). In the common methodology, an eigenvalue formulation of the nodal diffusion equation is used for fissionable channels, whereas a fixed source formulation is used for channels without a fission source. The one- and three-dimensional nodal solutions are coupled by modeling the threedimensional nodal solution radial leakages in the one-dimensional nodal solvers, whose results are used to produce axially homogenized group constants and axial discontinuity factors for the three-dimensional nodal solver.

The method developed for Ants steady state and burnup calculations is presented in this paper. Its implementation is verified and the performance is shown with a series of calculation cases, beginning with a set of simplified benchmark problems and culminating in an operating cycle simulation of a boron-free small modular reactor.