Pin power reconstruction method for rectangular geometry in nodal neutronics program Ants

VTT Technical Research Centre of Finland Ltd (VTT) is developing a new computational framework, called Kraken, for reactor core multi-physics problems. The framework consists of modular neutronics, thermal hydraulics and thermal mechanics solvers coupled together via a central multi-physics driver module. Ants is a novel reduced order nodal neutronics program developed as a part of Kraken. The published methodology and first results of Ants have previously been limited to steady state multigroup nodal diffusion solutions in both rectangular and hexagonal geometries. Ants solves the multigroup nodal neutronics using a hybrid of analytic function expansion nodal (AFEN) and flux expansion nodal (FENM) methods using a set of analytic basis functions for each mode flux. The pin powers are reconstructed by modulating the homogeneous pin cell fluxes obtained with direct integration of the homogeneous nodal fluxes over the pin cells with the heterogeneous group-dependent pin power form functions. The form functions are obtained from single assembly calculations using the continuous-energy Monte Carlo particle transport code Serpent 2. This work describes the Ants pin power reconstruction methodology for rectangular geometry. Initial comparisons with the heterogeneous solutions of Serpent are presented in simple configurations