Triangular geometry model for Ants nodal neutronics solver

VTT Technical Research Centre of Finland Ltd recently started the development of a new computational framework for core multi-physics problems, called Kraken. The framework is based on the use of the continuous-energy Monte Carlo reactor physics program Serpent, and consists of modular solvers for neutronics, thermal hydraulics and thermal mechanics. Ants is a reduced order nodal neutronics solver, developed as a part of Kraken. Previously, Ants could be applied to solving the steady-state multi-group diffusion equation in rectangular and hexagonal nodal geometries. This work describes the solution methodology of Ants extended to triangular geometry steady-state diffusion solutions.

The triangular extension serves as a radial decomposition method for the hexagonal node, as hexagons decompose to equilateral triangles. The decomposition method can be used to increase the accuracy in the radial direction as the calculation mesh is made finer, and it also enables the use of better group constant description in asymmetric fuel assemblies. The performance is tested in two- and three-dimensional hexagonal geometry numerical benchmarks and the performance is compared to the Ants hexagonal diffusion solver and to the HEXNEM3 solver of DYND3D. The obtained results demonstrate good agreement with the benchmark reference solutions and the Ants triangular diffusion solver outperforms the two considered hexagonal diffusion solvers.