Development and validation of a time-dependent deterministic model for neutron noise on CROCUS experimental measurements

Abstract

In the framework of the European project CORTEX, included in the H2020 program, the experimental campaign carried out with the CROCUS reactor, at the École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland, aims at setting up methodologies and tools for the analysis and the interpretation of neutron noise in view of their industrial applications. An important part of the CORTEX project deals with code development and validation. In this paper, a new methodology for the simulation of neutron noise has been formulated and implemented in the APOLLO3 code. In the first part of this paper, the experimental setup and the methodology for the experimental data analysis developed by CEA are presented. The experimental outcomes are reported in terms of Cross-Power Spectral Densities (CPSD) of detector responses. The results produced with CEA analysis are compared to those obtained by EPFL. The second part of the work presents the noise simulator based on an improved point-kinetics model employed in a fully heterogeneous 2D transport calculation including its theoretical derivation. The computed results, i.e. the temporal signals of the detector responses, are treated to recover the CPSDs to be compared to the experimental ones. In the third part of the work, the paper presents a series of interpretive exercises performed with the IPK noise model aiming at showing its simulation capabilities and at trying to address some of the discrepancies observed in the direct comparison. Beside the promising outcomes of the simulations, some work is still being done from the experimental and computational side for a better comprehension of the problem before the extension of the model to full 3D problems and industrial application.