Three-dimensional high order nodal code, ACNECH, for the neutronic modeling of hexagonal-z geometry

• A 3D high order nodal expansion code, ACNECH, is developed for hexagonal-z geometries.
• An adopted iterative scheme is implemented in ACNECH for the neutron balance equation solution.
• Numerical results indicate the adequate accuracy of ACNECH consuming appropriate run time.
• Results show the higher accuracy of Moments weighting than Galerkin scheme in obtaining high order coefficients.

In this work, we developed a new high order nodal code for the neutronic analysis of hexagonal-z geometry using the first order accuracy of Average Current Nodal Expansion Method (ACNEM) for radial direction and the second order solution of ACNEM for axial direction. For this purpose, we prepared Average Current Nodal Expansion Code for three-dimensional Hexagonal geometries (ACNECH) in which it calculates with coarse meshes i.e. one node per hexagon assembly. In this code, we performed an adopted iterative approach for the solution of neutron diffusion equation in order to overbear some divergence situations. The results of ACNECH are validated against some well-known benchmark problems. Results show the accuracy of high order ACNEM calculation consuming relatively suitable computational time. In addition, for obtaining high order expansion coefficients, the computations are done using Galerkin and Moments weightings for the radial direction in which results confirm the higher accuracy of Moments weighting. At last, we can conclude that ACNECH can be used in the neutronic analysis of problems where the run time is important such as loading pattern optimization.