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Concept

Détection de neutrons

Résumé

vignette|Structure des quarks neutroniques (forme annulaire) La détection de neutrons est la détection effective de neutrons entrant dans un détecteur. Il existe deux aspects de la détection effective de neutrons : l'aspect matériel (hardware) et l'aspect logiciel (software). Le matériel de détection désigne le genre de détecteur utilisé (le plus souvent, un détecteur à scintillation) et l'électronique qui y est liée. D'autre part, le montage du matériel définit aussi les paramètres expérimentaux, tels que la distance entre source et détecteur ou l'angle solide du détecteur. Les logiciels de détection sont des outils analytiques qui performent des tâches telles que l'analyse graphique pour mesurer le nombre et l'énergie des neutrons arrivant dans le détecteur. Bases physiques de la détection de neutrons Signatures des neutrons Les particules atomiques et subatomiques sont détectées par la signature qu'elles produisent par interaction avec leur environnement. Ces

Source officielle

https://fr.wikipedia.org/wiki/D%C3%A9tection_de_neutrons

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The course presents the detection of ionizing radiation in the keV and MeV energy ranges. Physical processes of radiation/matter interaction are introduced. All steps of detection are covered, as well as detectors, instrumentations and measurements methods commonly used in the nuclear field.

This course is intended to understand the engineering design of nuclear power plants using the basic principles of reactor physics, fluid flow and heat transfer. This course includes the following: Reactor designs, Thermal analysis of nuclear fuel, Nuclear safety and Reactor dynamics

Ce cours d'introduction à la microscopie a pour but de donner un apperçu des différentes techniques d'analyse de la microstructure et de la composition des matériaux, en particulier celles liées aux microscopies électronique et optique. Le cours comprend des cours ainsi que des démonstrations.

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Miniature and Minimalistic Neutron Detectors for Online High-Resolution Experiments in the Zero-Power Reactor CROCUS

Fanny Vitullo

The continuous strive for more efficient and reliable nuclear power plants is leading to increasing complexity in the design and operations of reactors. As a consequence, comprehensive analyses are required to assess the reactor's safety during normal and accidental conditions. Validated simulation tools with high-fidelity capabilities, i.e., at the pin or sub-pin scale, are necessary to predict local neutronics effects in the core. However, the scarcity of high-resolution in-core experimental data imposes limitations to the validation of such high-fidelity pin-resolved neutronics codes. The challenges in performing online high-resolution in-core experiments are numerous: from the accessibility of in-core locations to the availability of neutron detection technologies with adequate dimensions and online capabilities. In the present thesis, the development of a novel miniature and minimalistic (MiMi) neutron detection technology is presented, allowing unprecedented spatial resolution for the online study of the neutron flux in zero-power research reactors. The MiMi neutron detectors are tested in the EPFL zero-power reactor CROCUS and used to build a data set of high-resolution neutronics experiments in CROCUS, including measurements of local gradients and directionality of neutron flux, and the local impact of a fuel rod displacement. As the next level of development, a three-dimensional (3D) full-core mapping system named SAFFRON, consisting of 149 MiMi neutron detectors distributed in-core, is designed and installed in CROCUS. Static thermal neutron flux maps are measured in absolute terms and between different core configurations, e.g., water level vs. control rod operation at criticality. The obtained results open up the investigation of a variety of space-dependent neutronics phenomena in CROCUS.

EPFL2022

Chargement

Noise analysis applied to nuclear reactor physics is a powerful tool to investigate a reactor's kinetic parameters, and more generally underlying physical processes determining core behavior. The kinetic parameters are the coefficients of simplified time-dependent neutron population equations, the so-called point kinetics equations. Experimentally determined kinetic parameters aid to validate codes and to potentially evaluate nuclear data. This thesis focuses on improvements to the kinetic parameter and uncertainty quantification, the experimental techniques, and the direct simulation of noise experiments. In particular, the notion of spatial effects, i.e. effects that render point kinetics assumptions inaccurate for noise measurements, was investigated. This was achieved by drawing on experiments conducted in the zero power reactor CROCUS. New detection instrumentation for noise experiments was developed for CROCUS, namely current mode amplifiers for neutron detectors to allow for higher detection efficiency and thus precision; and a scintillation-based gamma detection array, called LEAF, to enable the study of gamma noise. A set of reference neutron and gamma noise experiments were conducted to exemplify an improved method of parameter and uncertainty estimation based on bootstrapping. It lead to a full uncertainty budget showing a relative uncertainty of 3.6% and 1.3% on the prompt decay constant with neutron and gamma noise, respectively. Moreover, reporting of full distributions of kinetic parameters was shown to be required in order to provide an accurate representation of the experimental results. Gamma noise was shown to be superior in terms of precision by a factor of at least two compared to neutron noise when determining the prompt decay constant. To study spatial effects and the spatial extent of the noise field of CROCUS, a set of experiments with varying detector locations, reactivity, and particle type were conducted. The neutron noise field study showed that measurements are limited to the immediate proximity of the core, and that CROCUS is reliably modeled as a point kinetic reactor for static configurations. Nonetheless, a systematic trend was shown when comparing to code predictions, pointing to a weak spatial effect biasing neutron noise measurements at a distance. The observable gamma noise field using high efficiency detectors was shown to extend beyond neutron noise limits, enabling ex-vessel measurements. The prompt decay constant was determined at about 0.9 meters to the core center with comparable accuracy to that of gamma in-core reference experiments using less-efficient detectors. Gamma correlations were be observed outside of the reactor cavity in front of an experimental channel, enabling a prompt decay constant determination at 7 meters to the core center. To complement the experimental investigation and to study the underlying physics, a simulation methodology to estimate noise responses was developed. Specifically, the explicit simulation of noise experiments using analog Monte Carlo transport coupled to a fission model was studied. An established code with an existing fission library coupling, TRIPOLI-4, was used as reference. In addition, a newly developed coupling of a fission library to Serpent 2 allowed for code-to-code comparison. The full methodology, verification, and validation to the aforementioned CROCUS experiments is presented.

EPFL2020

Chargement

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

Chargement

EPFL2020

Détection de neutrons

les s

Miniature and Minimalistic Neutron Detectors for Online High-Resolution Experiments in the Zero-Power Reactor CROCUS

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

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

Miniature and Minimalistic Neutron Detectors for Online High-Resolution Experiments in the Zero-Power Reactor CROCUS