Acceleration of a 2-Dimensional, 2-Energy Group Neutron Noise Solver Based on a Discrete Ordinates Method in the Frequency Domain

Abstract

The acceleration of the convergence rate is studied for a neutron transport solver to simulate 2-D, 2-energy-group neutron noise problems in the frequency domain. The Coarse Mesh Finite Difference (CMFD) method is compared to the Diffusion Synthetic Acceleration (DSA) method. Numerical tests are performed using heterogeneous system configurations with different boundary conditions. The CMFD scheme leads to a better convergence rate. The results also show that CMFD can accelerate neutron noise problems in a wide range of perturbation frequencies with almost equal efficiency. An unstable convergence behavior is nevertheless observed in problems with purely reflective boundary conditions. Stabilization techniques such as performing multiple transport sweeps, underrelaxing the flux update, and using the lpCMFD method are investigated and improvements can be obtained.

Characterization of High Harmonic Frequencies in Reactor Noise Experiments Within the CORTEX Project

“…The aim of the EU H2020 CORTEX project [6] is to develop tools and techniques for the localization and identification of noise sources by neutron flux measurements using multiple detectors. This is performed by analyzing the measured data by machine learning algorithms [7], [8], which have been previously trained using validated neutron noise propagation simulation computer codes [9]- [15]. The code validation is also performed within the scope of this project by performing experiments at zero power reactor facilities capable of inducing neutron noise: the Techniche Universität Dresden (TUD) Ausbildungskernreactor 2 (AKR-2) [16] equipped with a rotating and oscillating neutron absorber, entering the core from the side through its experimental channels (Figure 1) and the École Polytechnique Fédérale de Lausanne (EPFL) CROCUS reactor [17] with CROCUS Oscillator for Lateral Increase Between U -metal Rods and Inner zone (COLIBRI) experiment [18] located inside the reactor pool on the west side, oscillating up to 18 fuel rods and Pile Oscillator for Localized and Low Effect Noise (POLLEN) oscillating neutron absorber [19] usually installed at the core center.…”