Future experimental programmes in the CROCUS reactor

CROCUS is a teaching and research zero-power reactor operated by the Laboratory for Reactor Physics and Systems Behaviour (LRS) at the Swiss Federal Institute of Technology (EPFL). Three new experimental programmes are scheduled for the forthcoming years. The first programme consists in an experimental investigation of mechanical noise induced by fuel rods vibrations. An in-core device has been designed for allowing the displacement of up to 18 uranium metal fuel rods in the core periphery. The vibration amplitude will be 6 mm in the radial direction (±3 mm around the central position), while the frequency can be tuned between 0.1 and 5 Hz. The experiments will be used to validate computational dynamic tools currently under development, which are based on DORT-TD and CASMO/S3K code systems. The second programme concerns the measurement of in-core neutron noise for axial void profile reconstruction. Simulations performed at Chalmers University have shown how the void fraction and velocity profiles can be reconstructed from noise measurements. The motivation of these experiments is to develop an experimental setup to validate in-core the method in partnership with Chalmers University. The third experimental programme aims at continuing the validation effort on the nuclear data required in the calculation of GEN-III PWR reactors with heavy steel reflectors. This is a collaboration with CEA Cadarache that extends the results of the PERLE experiments carried out in the E reactor at CEA. Scattering cross sections at around 1 MeV will be studied separately by replacing successively the water reflector by sheets of stainless steel alloy and pure metals – iron, nickel, and chromium. Data will be extracted from the measured flux attenuation using foils in the metal reflector and from the criticality effects of these reflectors. In parallel to the three reactor experiments, we develop in-core detectors and measurement systems. Following the last development of a neutron noise measurement station in pulse mode, a second neutron noise station in current mode is being designed. In current mode the reactor can be used at higher power without dead time effects. It allows faster measurement time or lower results uncertainties. Finally, a joint development of a full new detection system based on chemical vapour deposited (sCVD) diamond has been started with the CIVIDEC instrumentation start-up company. A first prototype has been tested in November 2015 in CROCUS. One of the main purposes is to work on the discrimination of gammas, thermal and fast neutrons for demonstrating the interest of this detector type in a mixed neutron-gamma field

Modeling noise experiments performed at AKR-2 and CROCUS zero-power reactors

CORTEX is a EU H2020 project (2017-2021) devoted to the analysis of ’reactor neutron noise’ in nuclear reactors, i.e. the small fluctuations occurring around the stationary state due to external or internal disturbances in the core. One important aspect of CORTEX is the development of neutron noise simulation codes capable of modeling the spatial variations of the noise distribution in a reactor. In this paper we illustrate the validation activities concerning the comparison of the simulation results obtained by several noise simulation codes with respect to experimental data produced at the zero-power reactors AKR-2 (operated at TUD, Germany) and CROCUS (operated at EPFL, Switzerland). Both research reactors are modeled in the time and frequency domains, using transport or diffusion theory. Overall, the noise simulators managed to capture the main features of the neutron noise behavior observed in the experimental campaigns carried out in CROCUS and AKR-2, even though computational biases exist close to the region where the noise-inducing mechanical vibration was located (the so-called ”noise source”). In some of the experiments, it was possible to observe the spatial variation of the relative neutron noise, even relatively far from the noise source. This was achieved through reduced uncertainties using long measurements, the installation of numerous, robust and efficient detectors at a variety of positions in the near vicinity or inside the core, as well as new post-processing methods. For the numerical simulation tools, modeling the spatial variations of the neutron noise behavior in zero-power research reactors is an extremely challenging problem, because of the small magnitude of the noise field; and because deviations from a point-kinetics behavior are most visible in portions of the core that are especially difficult to be precisely represented by simulation codes, such as experimental channels. Nonetheless the limitations of the simulation tools reported in the paper were not an issue for the CORTEX project, as most of the computational biases are found close to the noise source

Détermination de sections efficaces pour la production de champs neutroniques monoénergétiques de basse énergie

The response of a neutron detector, defined as the reading of the device per unit of incident fluence or dose, varies with neutron energy. The experimental determination of this variation, i.e. of the response function of this instrument, has to be performed by facilities producing monoenergetic neutron fields. These neutrons are commonly produced by interaction between accelerated ions (proton or deuteron) onto a thin target composed of a reactive layer deposited on a metallic backing. Using the 7Li(p,n), 3H(p,n), 2H(d,n) and 3H(d,n) reactions, monoenergetic neutrons are obtained between 120 keV and 20 MeV in the ion beam direction (0°).To reach lower neutron energies, the angle of the measuring point with respect to the ion beam direction can be increased. However, this method presents several problems of neutron energy and fluence homogeneities over the detector surface, as well as an important increase of the scattered neutron contribution. Another solution is to investigate other nuclear reactions, as 45Sc(p,n) allowing to extend the neutron energy range down to 8 keV at 0°.A complete study of this reaction and its cross section has been undertaken within the framework of a scientific cooperation between the laboratory of neutron metrology and dosimetry (IRSN, France), two European national metrological institutes, the National Physical Laboratory (UK) and the Physikalisch-Technische Bundesanstalt (Germany), and IRMM, the Institute for Reference Materials and Measurements (EC).In parallel, other possible reactions have been investigated: 65Cu(p,n), 51V(p,n), 57Fe(p,n), 49Ti(p,n), 53Cr(p,n) and 37Cl(p,n). They were compared in terms of neutron fluence and minimum energy of the produced neutrons.La réponse d’un détecteur de neutrons varie avec l’énergie du neutron incident. La détermination expérimentale de cette variation se réalise au moyen de champs neutroniques monoénergétiques. Ceux-ci sont produits par l’interaction entre un faisceau d’ions accélérés et une cible fine constituée d’un dépôt réactif sur un support métallique. En utilisant différentes réactions telles que 7Li(p,n), 3H(p,n), 2H(d,n) et 3H(d,n), il est possible de produire des neutrons entre 120 keV et 20 MeV dans la direction du faisceau incident (0°).Pour atteindre des énergies inférieures, il est possible d’augmenter l’angle du point de mesure par rapport à la direction du faisceau d’ions. Cependant, cette méthode présente des problèmes d’homogénéité en énergie et en fluence des neutrons à la surface du détecteur, ainsi qu’une augmentation de la proportion de neutrons diffusés. Une alternative est l’utilisation d’autres réactions nucléaires, notamment la réaction 45Sc(p,n) qui permet de descendre jusqu’à des énergies de 8 keV à 0°.Une étude complète de cette réaction et de sa section efficace a été menée au sein d’une coopération scientifique entre le laboratoire de métrologie et de dosimétrie des neutrons (LMDN) de l’IRSN, deux instituts de métrologie européens, le NPL (National Physical Laboratory, RU) et le PTB (Physikalisch-Technische Bundesanstalt, All), et l’IRMM (Institute for Reference Materials and Measurements, CEE). Parallèlement, d’autres réactions envisageables ont été étudiées : 65Cu(p,n), 51V(p,n), 57Fe(p,n), 49Ti(p,n), 53Cr(p,n) et 37Cl(p,n). Elles ont été comparées en termes d’émission neutronique et d’énergie minimale des neutrons produits

Determination of cross sections for the production of low-energy monoenergetic neutron fields

La réponse d’un détecteur de neutrons varie avec l’énergie du neutron incident. La détermination expérimentale de cette variation se réalise au moyen de champs neutroniques monoénergétiques. Ceux-ci sont produits par l’interaction entre un faisceau d’ions accélérés et une cible fine constituée d’un dépôt réactif sur un support métallique. En utilisant différentes réactions telles que 7Li(p,n), 3H(p,n), 2H(d,n) et 3H(d,n), il est possible de produire des neutrons entre 120 keV et 20 MeV dans la direction du faisceau incident (0°).Pour atteindre des énergies inférieures, il est possible d’augmenter l’angle du point de mesure par rapport à la direction du faisceau d’ions. Cependant, cette méthode présente des problèmes d’homogénéité en énergie et en fluence des neutrons à la surface du détecteur, ainsi qu’une augmentation de la proportion de neutrons diffusés. Une alternative est l’utilisation d’autres réactions nucléaires, notamment la réaction 45Sc(p,n) qui permet de descendre jusqu’à des énergies de 8 keV à 0°.Une étude complète de cette réaction et de sa section efficace a été menée au sein d’une coopération scientifique entre le laboratoire de métrologie et de dosimétrie des neutrons (LMDN) de l’IRSN, deux instituts de métrologie européens, le NPL (National Physical Laboratory, RU) et le PTB (Physikalisch-Technische Bundesanstalt, All), et l’IRMM (Institute for Reference Materials and Measurements, CEE). Parallèlement, d’autres réactions envisageables ont été étudiées : 65Cu(p,n), 51V(p,n), 57Fe(p,n), 49Ti(p,n), 53Cr(p,n) et 37Cl(p,n). Elles ont été comparées en termes d’émission neutronique et d’énergie minimale des neutrons produits.The response of a neutron detector, defined as the reading of the device per unit of incident fluence or dose, varies with neutron energy. The experimental determination of this variation, i.e. of the response function of this instrument, has to be performed by facilities producing monoenergetic neutron fields. These neutrons are commonly produced by interaction between accelerated ions (proton or deuteron) onto a thin target composed of a reactive layer deposited on a metallic backing. Using the 7Li(p,n), 3H(p,n), 2H(d,n) and 3H(d,n) reactions, monoenergetic neutrons are obtained between 120 keV and 20 MeV in the ion beam direction (0°).To reach lower neutron energies, the angle of the measuring point with respect to the ion beam direction can be increased. However, this method presents several problems of neutron energy and fluence homogeneities over the detector surface, as well as an important increase of the scattered neutron contribution. Another solution is to investigate other nuclear reactions, as 45Sc(p,n) allowing to extend the neutron energy range down to 8 keV at 0°.A complete study of this reaction and its cross section has been undertaken within the framework of a scientific cooperation between the laboratory of neutron metrology and dosimetry (IRSN, France), two European national metrological institutes, the National Physical Laboratory (UK) and the Physikalisch-Technische Bundesanstalt (Germany), and IRMM, the Institute for Reference Materials and Measurements (EC).In parallel, other possible reactions have been investigated: 65Cu(p,n), 51V(p,n), 57Fe(p,n), 49Ti(p,n), 53Cr(p,n) and 37Cl(p,n). They were compared in terms of neutron fluence and minimum energy of the produced neutrons

Détermination de sections efficaces pour la production de champs neutroniques monoénergétiques de basse énergie

La réponse d un détecteur de neutrons varie avec l énergie du neutron incident. La détermination expérimentale de cette variation se réalise au moyen de champs neutroniques monoénergétiques. Ceux-ci sont produits par l interaction entre un faisceau d ions accélérés et une cible fine constituée d un dépôt réactif sur un support métallique. En utilisant différentes réactions telles que 7Li(p,n), 3H(p,n), 2H(d,n) et 3H(d,n), il est possible de produire des neutrons entre 120 keV et 20 MeV dans la direction du faisceau incident (0).Pour atteindre des énergies inférieures, il est possible d augmenter l angle du point de mesure par rapport à la direction du faisceau d ions. Cependant, cette méthode présente des problèmes d homogénéité en énergie et en fluence des neutrons à la surface du détecteur, ainsi qu une augmentation de la proportion de neutrons diffusés. Une alternative est l utilisation d autres réactions nucléaires, notamment la réaction 45Sc(p,n) qui permet de descendre jusqu à des énergies de 8 keV à 0.Une étude complète de cette réaction et de sa section efficace a été menée au sein d une coopération scientifique entre le laboratoire de métrologie et de dosimétrie des neutrons (LMDN) de l IRSN, deux instituts de métrologie européens, le NPL (National Physical Laboratory, RU) et le PTB (Physikalisch-Technische Bundesanstalt, All), et l IRMM (Institute for Reference Materials and Measurements, CEE). Parallèlement, d autres réactions envisageables ont été étudiées : 65Cu(p,n), 51V(p,n), 57Fe(p,n), 49Ti(p,n), 53Cr(p,n) et 37Cl(p,n). Elles ont été comparées en termes d émission neutronique et d énergie minimale des neutrons produits.The response of a neutron detector, defined as the reading of the device per unit of incident fluence or dose, varies with neutron energy. The experimental determination of this variation, i.e. of the response function of this instrument, has to be performed by facilities producing monoenergetic neutron fields. These neutrons are commonly produced by interaction between accelerated ions (proton or deuteron) onto a thin target composed of a reactive layer deposited on a metallic backing. Using the 7Li(p,n), 3H(p,n), 2H(d,n) and 3H(d,n) reactions, monoenergetic neutrons are obtained between 120 keV and 20 MeV in the ion beam direction (0).To reach lower neutron energies, the angle of the measuring point with respect to the ion beam direction can be increased. However, this method presents several problems of neutron energy and fluence homogeneities over the detector surface, as well as an important increase of the scattered neutron contribution. Another solution is to investigate other nuclear reactions, as 45Sc(p,n) allowing to extend the neutron energy range down to 8 keV at 0.A complete study of this reaction and its cross section has been undertaken within the framework of a scientific cooperation between the laboratory of neutron metrology and dosimetry (IRSN, France), two European national metrological institutes, the National Physical Laboratory (UK) and the Physikalisch-Technische Bundesanstalt (Germany), and IRMM, the Institute for Reference Materials and Measurements (EC).In parallel, other possible reactions have been investigated: 65Cu(p,n), 51V(p,n), 57Fe(p,n), 49Ti(p,n), 53Cr(p,n) and 37Cl(p,n). They were compared in terms of neutron fluence and minimum energy of the produced neutrons.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF

Comparison of nuclear reactions for the production of monoenergetic neutron fields with energies below 100 keV

NPL, PTB, IRMM and IRSN are involved, within a scientific cooperation, in a comprehensive study aimed at developing reference low-energy monoenergetic neutron fields. This paper will explain the impor- tance of such developments, highlighted by the over response of neutron survey meters in the keV energy range, and also describe the main difficulties encountered. The variation of the neutron yield with ion beam energy from the neutron threshold up to about 50 keV has been measured at IRSN AMANDE facility for the 45Sc(p,n), 65Cu(p,n), 51V(p,n), 57Fe(p,n) and 37Cl(p,n) reactions

Development of a multi-channel gamma-blind fast neutron detector based on wavelength shifting fibers embedded in a ZnS:Ag epoxy mixture

This paper presents a fast neutron detector based on elastic scattering with hydrogen, a silver-activated zinc sulfide scintillator to convert the recoil proton energy to light, and wavelength-shifting fibers (WLSFs) to collect the scintillation light. The detector uses silicon photomultipliers (SiPMs) to recognize individual scintillation photons and a digital filter algorithm based on single photon counting to find clusters of photons belonging to neutron events. The detector presented in this paper features four detection channels, arranged in a 2 × 2 square. The sensitive volume of each detection channel covers a ∼5mm by ∼5mm area from the frontal direction, is 3 cm long, and contains 49 WLSFs. The detector is versatile and performs well under different conditions. Its performance can be tuned to match different applications by simply changing some parameters of the digital filter algorithm. This is illustrated in this paper by extensive measurements in different environments. Using one set of parameters, the detector achieved a gamma-blindness of 10−8 with an intrinsic neutron detection efficiency of ∼1%. With another set of parameters and with lower requirements for gamma blindness, the intrinsic neutron detection efficiency was increased to ∼11%. Yet another set of parameters allows the detector to time incoming fast neutrons with an accuracy of ∼60ns. Additionally, the decay time of the scintillation light created by neutron events was measured, falling to 10% of its peak value in ∼10 μs. Finally, the detector was exposed to strong gamma radiation for a prolonged time to test its radiation resistance. The detection efficiency dropped about linearly with the accumulated gamma fluence, reaching a drop of 40% compared to the initial efficiency at a total gamma fluence of ∼2⋅1013 cm−2.ISSN:0168-9002ISSN:1872-957

Total Monte Carlo acceleration for the PETALE experimental programme in the CROCUS reactor

The Bayesian Monte Carlo technics requires individual evaluations of random cross section files based on a Total Monte Carlo propagation. This article discusses the use of a Correlated Sampling acceleration applied to TMC calculations for experiments where a brute force technics is too expensive. An e_cient estimation of the reaction rate uncertainties in small dosimeters is obtained, together with the inter-dosimeter correlation associated to the cross section uncertainties

Bayesian Monte Carlo assimilation for the PETALE experimental programme using inter-dosimeter correlation

This article presents the methodology developed to generate and use dosimeter covariances and to estimate nuisance parameters for the PETALE experimental programme. In anticipation of the final experimental results, this work investigates the consideration of these experimental correlations in the Bayesian assimilation process on nuclear data. Results show that the assimilation of a given set of dosimeters provides a strong constraint on some of the posterior reaction rate predictions of the other dosimeters. It confirms that, regarding the assimilation process, the different sets of dosimeters are correlated

Total Monte Carlo acceleration for the PETALE experimental programme in the CROCUS reactor

The Bayesian Monte Carlo technics requires individual evaluations of random cross section files based on a Total Monte Carlo propagation. This article discusses the use of a Correlated Sampling acceleration applied to TMC calculations for experiments where a brute force technics is too expensive. An e_cient estimation of the reaction rate uncertainties in small dosimeters is obtained, together with the inter-dosimeter correlation associated to the cross section uncertainties