Vincent Pierre Lamirand | EPFL Graph Search

After a PhD on the measurement of (p,n) reactions cross sections on small accelerators (IRSN, France), I have worked on the development of neutron detectors and measurement methods for reactor physics (CEA, France). I am part of the LRS staff since October 2014.

Analysis of the preliminary campaign for the PETALE program

Vincent Pierre Lamirand, Axel Guy Marie Laureau, Thomas Jean-François Ligonnet, Andreas Pautz

The PETALE program aims to provide new experimental data to constrain the stainless steel nuclear data. In this frame, a preliminary measurement campaign has been performed to characterize the neutron flux in key positions of the CROCUS reactor and to develop analysis tools. During this preliminary campaign detailed in the present paper, an efficiency ratio technique has been developed and tested to speed up HPGe measurements by a factor of 30. A second objective of the campaign concerns the propagation of nuclear data uncertainty from the core neutron cross-sections to the reaction rates in the dosimeters. Uncertainties in the core cross sections, such as the uranium cross section, are nuisance parameters that add uncertainty to the dosimeter reaction rate calculation. This component must be fully characterized with covariances to constrain the metal reflector component for Bayesian assimilation. The experimental results are compared to the calculations with different nuclear databases for the nuclear data uncertainty propagation. A good agreement is obtained with the ENDF/B-VII.1 database and a systematic underestimation of around 5-10% in the fast range is observed with the ENDF/B-VIII.0 and JEFF-3.3 databases.

EDP SCIENCES S A2023

Characterization of high harmonic frequencies in reactor noise experiments within the CORTEX project

Vincent Pierre Lamirand, Andreas Pautz

We present a novel technique of neutron noise detection and experimental data interpretation developed during the EU H2020 project CORTEX aiming to improve the capabilities for identification and localization of neutron noise sources. The experimental data analysis is performed in the frequency domain by extracting the spectral power density and the phase angle using a novel spectral variance reduction technique based on per cycle based bootstrapping with replacement. This technique allows for variance reduction of measured spectral power and phase angle not only at base frequency but at higher harmonic frequency contributions as well. This allows for a more representative treatment of experimental data and validation of codes for neutron noise propagation, some of which have been developed within the project. The detector response is not necessarily linearly dependent on the oscillator movement, and the study of non-linear terms provides additional information which can improve the accuracy of neutron noise source identification and localization. Moreover those terms can be used in a Taylor series to identify a more complex dependence. The process is simplified in the sense, that these contributions are linearized in the frequency domain as higher harmonic frequency contributions and can be easily identified and extracted due to spectral peaks prominence provided by the bootstrapping with replacement method. Combined with the spectral power and phase, we present a preliminary investigation of usability of higher order terms for noise source identification and localization. In this paper, we outline the CORTEX project, the experiments and the measurement analysis methodology based on the bootstrapping with replacement along with the initial developments on the study of non-linear terms in CROCUS reactor, using several different noise source configurations at a set frequency.

2022

High accuracy measurement of the prompt neutron decay constant in CROCUS using Gamma Noise and bootstrapped uncertainties

Pavel Frajtag, Vincent Pierre Lamirand, Tom Mager, Oskari Ville Pakari, Andreas Pautz

We experimentally demonstrate the advantages of gamma detection for noise measurements to deter-mine the prompt neutron decay constant a of a nuclear reactor using the power spectral density (PSD) method, coupled to a new uncertainty estimation scheme based on bootstrapping. We compare the rel-ative precision of gamma noise measurements and neutron noise measurements performed in the CROCUS research reactor. The reference neutron noise experiment employs two large U-235 fission chambers, whereas the new gamma noise experiment is based on two CeBr3 scintillators. The results demonstrate that gamma noise is superior to neutron noise with respect to precision, giving an advantage with regards to measurement time to reach desired uncertainty levels: the uncertainty budget shows a relative uncertainty of 3.6% and 1.3% on the prompt neutron decay constant with neutron and gamma noise, respectively. Moreover, thanks to bootstrapping, the reporting of full distributions - rather than assuming Gaussian spreads - of kinetic parameters is shown to be relevant in order to provide an accurate rep-resentation of the experimental results in some cases. In addition, we notably discuss the lower level discrimination threshold and its effect on the gamma PSDs. Gamma ray cross PSDs exhibit a behaviour contrary to that of a standard neutron acquisition system, and we discuss the implications. Gamma noise could prove to be a cheaper, more precise, and more flexible method to determine reactor kinetics. (C) 2022 The Author(s). Published by Elsevier Ltd.

PERGAMON-ELSEVIER SCIENCE LTD2022

Characterization of high harmonic frequencies in reactor noise experiments within the CORTEX project

Vincent Pierre Lamirand, Andreas Pautz

2022