Mesures neutroniques et photoniques combinées pour la caractérisation précise des canaux expérimentaux du futur réacteur d'irradiation Jules Horowitz (RJH).

Le futur Réacteur d'irradiation Jules Horowitz (RJH) constituera à partir de 2016 sur le site du CEA Cadarache (France) un outil unique dédié aux besoins de l'industrie et de la recherche dans le domaine de l'énergie nucléaire. La qualité des programmes de recherche qui seront conduits dans le RJH dépendra pour une grande part de la bonne connaissance et de la maîtrise des conditions expérimentales dans les canaux d'essais. Dans ce contexte, le CEA et Aix-Marseille Université conduisent conjointement un projet scientifique et technique baptisé IN-CORE. Ce projet a pour but d'améliorer la connaissance des flux neutroniques et photoniques du cœur du réacteur RJH. Un des enjeux est donc d'identifier les détecteurs capables de mesurer de tels flux et de déterminer les méthodes d'interprétation des signaux les plus appropriées. Les travaux de thèse s'inscrivent dans ce programme ambitieux et ont pour objectif d'étudier les potentialités et l'intérêt de la combinaison des mesures des rayonnements dans la perspective d'une meilleure évaluation des niveaux de flux neutroniques, rayonnement gamma et d'échauffement nucléaire dans les emplacements expérimentaux du RJH. Une première étape du projet a consisté à réaliser et exploiter un dispositif de mesure appelé CARMEN-1, adapté à la cartographie des conditions d'irradiation du réacteur OSIRIS (France). Cette expérience a été l'occasion de tester l'ensemble des détecteurs des flux de rayonnement susceptibles de répondre aux besoins du RJH, notamment ceux récemment développés.A new Material Testing Reactor (MTR), the Jules Horowitz Reactor (JHR), is under construction at the CEA Cadarache (French Alternatives Energies and Atomic Energy Commission). From 2016 this new MTR will be a new facility for the nuclear research on materials and fuels. The quality of the experiments to be conducted in this reactor is largely linked to the good knowledge of the irradiation conditions. Since 2009, a new research program called IN-CORE “Instrumentation for Nuclear radiations and Calorimetry Online in Reactor” is under progress between CEA and Aix-Marseille University. This program aims to improve knowledge of the neutron and photon fluxes in the RJH core. One of the challenges is to identify sensors able to measure such fluxes in JHR experimental conditions and to determine how to analyse the signals delivered by these sensors with the most appropriate methods. The thesis is part of this ambitious program and aims to study the potential and the interest of the combination of radiation measurements in the prospect of a better assessment of the levels of neutron flux, gamma radiation and nuclear heating in the JHR experimental locations. The first step of IN-CORE program was to develop and operate an instrumented device called CARMEN-1 adapted to the mapping of the OSIRIS reactor (France). This experiment was the opportunity to test all the radiation sensors which could meet the needs of JHR, including recently developed sensors

Computational support on the development of nuclear heating calorimeter detector design

Heating due to energy deposition of intense ionizing radiation in samples and structural materials of nuclear reactors poses severe limitations in terms of cooling requirements for safe reactor operation, especially in high neutron and gamma flux environments of material testing fission reactors (MTRs) and novel fusion devices. A bilateral CEA-JSI research project was launched in 2018 with the objective to measure the gamma heating rates in standard reactor-related materials (graphite, aluminium, stainless steel and tungsten) as well as fusionrelevant materials (low-activation steel Eurofer-97 and Nb3Sn superconductor) in the JSI TRIGA reactor my means of gamma calorimeters. The calorimeter design will be based on the the CALMOS-2 calorimeter developed at the CEA and used to perform gamma heating measurements in the OSIRIS MTR in Saclay. In order to optimize the detector response inside the JSI TRIGA reactor field and not to perturb the measurement field, a detailed computational analysis was performed in terms of energy deposition assessment and measurement field perturbation using the MCNP v6.1 code, and in terms of heat transfer using the COMSOL Multiphysics code. The abovementioned activities enabled us to finalize the detector design with the experimental campaign planned for the end of year 2019

Computational support on the development of nuclear heating calorimeter detector design

Heating due to energy deposition of intense ionizing radiation in samples and structural materials of nuclear reactors poses severe limitations in terms of cooling requirements for safe reactor operation, especially in high neutron and gamma flux environments of material testing fission reactors (MTRs) and novel fusion devices. A bilateral CEA-JSI research project was launched in 2018 with the objective to measure the gamma heating rates in standard reactor-related materials (graphite, aluminium, stainless steel and tungsten) as well as fusionrelevant materials (low-activation steel Eurofer-97 and Nb3Sn superconductor) in the JSI TRIGA reactor my means of gamma calorimeters. The calorimeter design will be based on the the CALMOS-2 calorimeter developed at the CEA and used to perform gamma heating measurements in the OSIRIS MTR in Saclay. In order to optimize the detector response inside the JSI TRIGA reactor field and not to perturb the measurement field, a detailed computational analysis was performed in terms of energy deposition assessment and measurement field perturbation using the MCNP v6.1 code, and in terms of heat transfer using the COMSOL Multiphysics code. The abovementioned activities enabled us to finalize the detector design with the experimental campaign planned for the end of year 2019

Calculations to Support On-line Neutron Spectrum Adjustment by Measurements with Miniature Fission Chambers in the JSI TRIGA Reactor

Preliminary calculations were performed with the aim to establish optimal experimental conditions for the measurement campaign within the collaboration between the Jožef Stefan Institute (JSI) and Commissariat à l’Énergie Atomique et aux Énergies Alternatives (CEA Cadarache). The goal of the project is to additionally characterize the neutron spectruminside the JSI TRIGA reactor core with focus on the measurement epi-thermal and fast part of the spectrum. Measurements will be performed with fission chambers containing different fissile materials (235U, 237Np and 242Pu) covered with thermal neutron filters (Cd and Gd). The changes in the detected signal and neutron flux spectrum with and without transmission filter were studied. Additional effort was put into evaluation of the effect of the filter geometry (e.g. opening on the top end of the filter) on the detector signal. After the analysis of the scoping calculations it was concluded to position the experiment in the outside core ring inside one of the empty fuel element positions

Evaluation of neutron flux and fission rate distributions inside the JSI TRIGA Mark II reactor using multiple in-core fission chambers

International audienceWithin the bilateral project between the CEA Cadarache and the Jožef Stefan Institute (JSI) a wide variety of measurements using multiple fission chambers simultaneously inside the reactor core were performed. The fission rate axial profiles were measured at different measuring positions and at different control rod configurations. A relative comparison of calculated fission rates using the MCNP code and the measured fission rates was performed. In general the agreement between the measurements and calculations is good, with deviations within the uncertainties. For better observation and understanding of neutron flux redistributions due to the control rod movement, the neutron flux and fission rate had been tallied through the entire reactor core at different control rod configurations. The optimal detector position with minimum signal variations due to the control rod movement was determined

Éléments piézoélectriques sérigraphiés pour Instrumentation Acoustique Haute Température en Réacteur Expérimental de Recherche

International audienceL’équipe Acoustique de l’IES (UMR5214 Université Montpellier - CNRS) travaille sur la mise en place d’une instrumentation acoustique pour le réacteur Jules Horowitz (RJH). Ce dispositif, a pour objectif le suivi et l’étude du relâchement des gaz de fission dans un élément combustible expérimental. La méthode acoustique qui permet le suivi du relâchement des gaz de fission a prouvé son efficacité au cours de l’expérience REMORA 3 en 2010. Cette première génération de capteurs utilisait des éléments acoustiques du commerce à température de Curie inférieure à 250°C. L’équipe acoustique, en collaboration avec le CEA développe des transducteurs permettant de réaliser de telles mesures sous contraintes radiatives et thermiques [1] avec des applications visées dans le futur réacteur RJH [2]. A ce titre, nos recherches menées actuellement consistent à déposer du NBT sous la forme d’encre visqueuse par sérigraphie. L’objectif étant de développer un matériau piézoélectrique avec des performances piézoélectriques similaires aux NBT commerciaux massifs (PZ46 de chez MEGGITT®), déposés directement sur des substrats en alumine. Le choix de ces matériaux et des procédés de fabrication associés devrait nous permettre d’avoir un rapport signal sur bruit suffisant pour réaliser une mesure acoustique du relâchement gazeux. Ces travaux peuvent aussi permettre la réalisation de capteur de composition de gaz performant pour des conditions environnementales moins critiques. [1]JY. Ferrandis et al., « Acoustic instrumentation of the new generation of MTR: effect of nuclear radiation on modified Bismuth Titanate piezoelectric elements », ANIMMA 2019, EPJ Web Conf., vol. 225, p. 04012, 2020, doi: 10.1051/epjconf/202022504012. [2]F. Baudry, E. Rosenkrantz, P. Combette, D. Fourmentel, C. Destouches, et JY. Ferrandis, « Design of an acoustic sensor for fission gas release characterization devoted to JHR environment measurements », ANIMMA 2019, EPJ Web Conf., vol. 253, p. 04028, 2021, doi: 10.1051/epjconf/202125304028

Reaction Rate Benchmark Experiments with Miniature Fission Chambers at the Slovenian TRIGA Mark II Reactor

A series of fission rate profile measurements with miniature fission chambers, developed by the Commisariat á l’énergie atomique et auxénergies alternatives, were performed at the Jožef Stefan Institute’s TRIGA research reactor. Two types of fission chambers with different fissionable coating (235U and 238U) were used to perform axial fission rate profile measurements at various radial positions and several control rod configurations. The experimental campaign was supported by an extensive set of computations, based on a validated Monte Carlo computational model of the TRIGA reactor. The computing effort included neutron transport calculations to support the planning and design of the experiments as well as calculations to aid the evaluation of experimental and computational uncertainties and major biases. The evaluation of uncertainties was performed by employing various types of sensitivity analyses such as experimental parameter perturbation and core reaction rate gradient calculations. It has been found that the experimental uncertainty of the measurements is sufficiently low, i.e. the total relative fission rate uncertainty being approximately 5 %, in order for the experiments to serve as benchmark experiments for validation of fission rate profiles. The effect of the neutron flux redistribution due to the control rod movement was studied by performing measurements and calculations of fission rates and fission chamber responses in different axial and radial positions at different control rod configurations. It was confirmed that the control rod movement affects the position of the maximum in the axial fission rate distribution, as well as the height of the local maxima. The optimal detector position, in which the redistributions would have minimum effect on its signal, was determined

Reaction Rate Benchmark Experiments with Miniature Fission Chambers at the Slovenian TRIGA Mark II Reactor

A series of fission rate profile measurements with miniature fission chambers, developed by the Commisariat á l’énergie atomique et auxénergies alternatives, were performed at the Jožef Stefan Institute’s TRIGA research reactor. Two types of fission chambers with different fissionable coating (235U and 238U) were used to perform axial fission rate profile measurements at various radial positions and several control rod configurations. The experimental campaign was supported by an extensive set of computations, based on a validated Monte Carlo computational model of the TRIGA reactor. The computing effort included neutron transport calculations to support the planning and design of the experiments as well as calculations to aid the evaluation of experimental and computational uncertainties and major biases. The evaluation of uncertainties was performed by employing various types of sensitivity analyses such as experimental parameter perturbation and core reaction rate gradient calculations. It has been found that the experimental uncertainty of the measurements is sufficiently low, i.e. the total relative fission rate uncertainty being approximately 5 %, in order for the experiments to serve as benchmark experiments for validation of fission rate profiles. The effect of the neutron flux redistribution due to the control rod movement was studied by performing measurements and calculations of fission rates and fission chamber responses in different axial and radial positions at different control rod configurations. It was confirmed that the control rod movement affects the position of the maximum in the axial fission rate distribution, as well as the height of the local maxima. The optimal detector position, in which the redistributions would have minimum effect on its signal, was determined