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

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

Improvements in neutron and gamma measurements for material testing reactors

International audienceIn order to ensure the quality and the relevance of irradiation programs in the future Jules Horowitz Reactor (JHR), the French Alternative Energies and Atomic Energy Commission (CEA) has significantly increased its RandD effort in the field of in-pile instrumentation during the last decade. Major progresses have thus been achieved in the capability to perform accurate in-pile measurements using reliable and updated techniques. Benefits of this enhanced measurement potential, illustrated with some improvements achieved in neutron and gamma flux detection, are described in this paper.This paper also discusses the needs for irradiation capabilities within the coming years, in order to complete the in-pile qualification of newly developed sensors and the extensive validation of their corresponding simulation model

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