Functional Expansion Tallies in Monte Carlo High Fidelity LWR Analysis

Abstract

Functional expansion tallies (FETs) are implemented in the Monte Carlo code MCS to improve the fidelity of multi-physics (MP) solution of light water reactor (LWR) problems. Neutronics (N) parameters (spatial flux or power) are expanded in a set of orthogonal basis functions (Legendre and/or Zernike polynomials) and the coefficients of the functional expansions are etermined from the Monte Carlo (MC) simulations. With the coefficients, the required distribution is reconstructed continuously in space. Moreover, thermal-hydraulic (TH) quantities (fuel temperature, coolant density) obtained from the TH calculations of MCS are integrated into polynomial functions and their coefficients are calculated. Coupled MP simulation results are presented in this paper using a three-dimensional (3D) PWR fuel pin. FETs coefficients of power are transferred to the TH solver. Then the power distribution is reconstructed for the TH calculations. Subsequently, the coefficients of fuel temperature/coolant density are returned as feedback, and the fuel temperature/coolant density profiles are reconstructed for the next neutronic cycle. The results obtained with the coefficients demonstrates promise of the FETs for high fidelity MP coupled calculations.