Development and first results of a new rectangular nodal diffusion solver of Ants

Studies on producing homogenized group constants for nodal diffusion programs at VTT Technical Research Centre of Finland Ltd have been focused on the calculation chain with the continuous-energy Monte Carlo reactor physics program Serpent and the in-house reactor simulator program ARES. The results of the Serpent–ARES calculations together with the recent publication of detailed methods of nodal diffusion calculations led to re-evalution of the status of the currently used nodal methods at VTT. The development of an entirely new Serpent-based computational framework for coupled core physics problems, Kraken, was started. The Kraken framework consists of modular neutronics, thermal hydraulics and thermal mechanics solvers. This paper introduces a new reduced-order nodal neutronics module Ants which is developed as a part of Kraken. The solution method of the steady state rectangular geometry diffusion solver of Ants is introduced and its first results are presented. The IAEA 3D PWR benchmark is solved using several different spatial discretizations with Ants to analyze the convergence of the solution as the nodalization is refined. In addition, the Ants results for the benchmark are compared to DYN3D, PARCS and VENTURE results. In the examined case, the effective multiplication factors of Ants results converge to within 1pcm from the established diffusion solvers of DYN3D and PARCS.