Extension of nodal diffusion solver of Ants to hexagonal geometry

The development of a new computational framework for core multi-physics problems, called Kraken, has been started at VTT Technical Research Centre of Finland Ltd. The framework consists of modular neutronics, thermal hydraulics and thermal mechanics solvers, and is based on the use of continuous-energy Monte Carlo reactor physics program Serpent. Ants is a new reduced order nodal neutronics program developed as a part of Kraken. The published methodology and first results of Ants has previously been limited to rectangular geometry steady state multigroup diffusion solutions. This work describes the solution methodology of Ants extended to hexagonal geometry steady state diffusion solutions. The first results using various two-dimensional and three-dimensional hexagonal geometry numerical benchmarks are presented. These benchmarks include the AER-FCM-001 and AER-FCM-101 three-dimensional VVER- 440 and VVER-1000 mathematical benchmarks. The obtained effective multiplication factors of all considered benchmarks are within 18 pcm and the RMS relative assembly power relative differences are within 0.4% of the reference solutions.