N. Authier

Cea Leti, Grenoble, Rhône-Alpes, France

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Publications (11)6.43 Total impact

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    ABSTRACT: We provide in this article, experimental data of initiation of persistent fission chains obtained at different supercritical states, using the Fast Burst Reactor CALIBAN. In many past papers, theory has been compared mostly to initiation experiments at various super-prompt critical states, whereas very few experimental data has been published in delayed supercritical states. To fill the lack of data, we have conducted three campaigns on the reactor at reactivities far below 0.7$ which was one of the rare lowest state ever published on a similar assembly [2][1]. We give a justification of the use of the gamma function to fit experimental results of the temporal distributions of waiting times and compare experiments with numerical simulations obtained with a zero-D punctual Monte Carlo code. (authors)
    07/2012;
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    ABSTRACT: The domain of evaluated nuclear data involves at the same time, a close interaction between the field of nuclear applications and that of nuclear physics, and a close interaction between experiments and theory. The final product, the evaluated data file, synthesises vast amounts of information stemming from all of the above fields. In CEA DAM, all these aspects of nuclear data are investigated in a consistent way, making full use of experimental facilities and high-performance computing as well as numerous national and international collaborations, for the measurement, calculation, evaluation, and validation of nuclear data.
    European Physical Journal A 01/2012; 48(8). · 2.04 Impact Factor
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    ABSTRACT: In the 1970's and early 1980's, an experimental program was performed on the facilities of the CEA Valduc Research Center to measure several actinide-fission product yields. Experiments were, in particular, completed on the Caliban and Prospero metallic core reactors to study fission-neutron-induced reactions on {sup 233}U, {sup 235}U, and {sup 239}Pu. Thick actinide samples were irradiated and the number of nuclei of each fission product was determined by gamma spectrometry. Fission chambers were irradiated simultaneously to measure the numbers of fissions in thin deposits of the same actinides. The masses of the thick samples and the thin deposits were determined by mass spectrometry and alpha spectrometry. The results of these experiments will be fully presented in this paper for the first time. A description of the Caliban and Prospero reactors, their characteristics and performances, and explanations about the experimental approach will also be given in the article. A recent work has been completed to analyze and reinterpret these measurements and particularly to evaluate the associated uncertainties. In this context, calculations have also been carried out with the Monte Carlo transport code Tripoli-4, using the published benchmarked Caliban description and a three-dimensional model of Prospero, to determine the average neutron energy causing fission. Simulation results will be discussed in this paper. Finally, new fission yield measurements will be proposed on Caliban and Prospero reactors to strengthen the results of the first experiments. (authors)
    07/2011;
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    ABSTRACT: We investigated the feasibility of using phosphorus-doped optical fibers to monitor the levels of deposited dose during an irradiation. For this, we characterized their spectral and time dependence of the steady state 10keV X-ray radiation-induced attenuation in the ultraviolet and visible range of wavelengths (200nm–900nm). Their radiation sensitivity is very high with losses exceeding 10dBm−1 for doses larger than 10Gy and wavelengths shorter than 550nm. Our results reveal a sub linear dose dependence of the induced losses that also depends on the dose rate (1Gys−1–50Gys−1) between 350nm and 900nm. For this spectral domain, excess of attenuation is due to the phosphorus oxygen-hole centers. P2 defects are responsible for the induced losses around 300nm that linearly increase with the dose at least until 1kGy and without dose rate effect. We measured no noticeable influence of the temperature (5°C–50°C) on the radiation-induced attenuation in the studied spectral domain. Our study shows that dosimetry with phosphorus-doped fibers seems possible in the ultraviolet (around 300nm) with a sensitivity enhanced by a factor >100 compared to the one observed in the infrared region (>900nm).
    Journal of Non-Crystalline Solids 01/2011; 357(8):1871-1874. · 1.72 Impact Factor
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    ABSTRACT: The yields of more than fifteen fission products have been carefully measured using radiochemical techniques, for {sup 235}U(n,f), {sup 239}Pu(n,f) in a thermal spectrum, for {sup 233}U(n,f), {sup 235}U(n,f), and {sup 239}Pu(n,f) reactions in a fission neutron spectrum, and for {sup 233}U(n,f), {sup 235}U(n,f), {sup 238}U(n,f), and {sup 239}Pu(n,f) for 14.7 MeV monoenergetic neutrons. Irradiations were performed at the EL3 reactor, at the Caliban and Prospero critical assemblies, and at the Lancelot electrostatic accelerator in CEA-Valduc. Fissions were counted in thin deposits using fission ionization chambers. The number of fission products of each species were measured by gamma spectrometry of co-located thick deposits.
    Nuclear Data Sheets 12/2010; 111(12). · 2.67 Impact Factor
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    ABSTRACT: We will present the integral measurement of the neutron inelastic cross section of ^235U leading to the 26-minute, E*=76.5 eV isomer state. Small samples (5-20 microgm) of isotope-enriched ^235U were activated in the central cavity of the CALIBAN pulsed reactor at Valduc where a nearly pure fission neutron spectrum is produced with a typical fluence of 3x10^14 n/cm^2. After 30 minutes the samples were removed from the reactor and counted in an electrostatic-deflecting electron spectrometer that was optimized for the detection of ^235mU conversion electrons. From the decay curve analysis of the data, the 26-minute ^235mU component was extracted. Preliminary results will be given and compared to gamma-cascade calculations assuming complete K-mixing or with no K-mixing.
    10/2009;
  • P. Casoli, N. Authier, J. Baud
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    ABSTRACT: Several experimental devices are operated by the Criticality and Neutron Science Research Department of the CEA Valduc Laboratory. One of these is the metallic core reactor Caliban. Knowing the fundamental kinetic parameters of the reactor is very useful, indeed necessary, to the operator. The purpose of this study was to develop and perform experiments allowing to determinate some of these parameters. The prompt neutron decay constant and particularly its value at criticality can be measured with reactor noise techniques such as the interval-distribution, the Feynman variance-to-mean, and the Rossi-α methods. By introducing the Nelson number, the effective delayed neutron fraction and the average neutron lifetime can also be calculated with the Rossi-α method. Subcritical, critical, and even supercritical experiments were performed. With the Rossi-α technique, it was found that the prompt neutron decay constant at criticality was 6.02 × 10<sup>5</sup> ± 9%. Experiments also brought out the limitations of the used experimental parameters.
    Advancements in Nuclear Instrumentation Measurement Methods and their Applications (ANIMMA), 2009 First International Conference on; 07/2009
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    ABSTRACT: The PROSPERO reactor is located at CEA Valduc Center in France. The reactor is composed of an internal core made of High Enriched Uranium metal alloy surrounded by a reflector of depleted uranium. The size of the assembled core is 352 mm length and 314 mm in diameter. The reactor is used as a fast neutron spectrum source and is operated in delayed critical state with a continuous and steady power for several hours, which can vary from 3 mW to 3 kW, which is the nominal power. The core of the PROSPERO reactor is made critical by driving depleted uranium control rods through the length of the reflector. The PROSPERO reactor is operated in a cell 10 m × 8 m × 6 m high, with 1.4-meter-thick concrete walls. This large cell offers a wide range of irradiation sites from the reflector surface to 6 meter away from the reactor central axis. The flux at nominal power varies from 5.10+10 n.cm-2/s at the reflector surface to 10+7 n.cm-2/s at 5 meters from reactor axis. Due to scattering events in the assembly, the mean energy of the leakage neutron spectrum is 0.8 MeV. This experimental tool is devoted to mixed neutron and gamma fluxes production. The neutron over gamma fluences ratio near the reflector surface is approximately equal to 10. Within the framework of a diversified use of the irradiation tools and in accordance with a request of the scientific community to offers new opportunities, our laboratory, the "Criticality and Neutronics Research Laboratory", decided to build a neutron energy converter allowing the production of a neutron thermal spectrum using PROSPERO. As the core produces fast neutrons spectrum, we built a hollow cubic box of 50 cm × 50 cm × 50 cm with 10-cm-thick polyethylene bricks and placed one meter away from central reactor axis to moderate as much as possible neutrons to lower energies (E
    01/2009;
  • P. Casoli, N. Authier
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    ABSTRACT: Reactivity worth measurements of material samples put in the central cavities of nuclear reactors allow to test cross section nuclear databases or to extract information about the critical masses of fissile elements. Such experiments have already been completed on the Caliban and Silene experimental reactors operated by the Criticality and Neutronics Research Laboratory of Valduc (CEA, France), using the perturbation measurement technique. Calculations have been performed to prepare future experiments on new materials.
    http://dx.doi.org/10.1051/ndata:07271. 01/2008;
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    ABSTRACT: The 'service of research on neutronics and criticality' of Valduc CEA research center, proposes several experimental facilities for neutron and gamma irradiation: two metallic reactors, a solution reactor, two accelerators.
    Radiation and Its Effects on Components and Systems, 2005. RADECS 2005. 8th European Conference on; 10/2005
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    ABSTRACT: Measurements of the creation and destruction cross sections for actinide nuclei constitute an important experimental effort in support of Stockpile Stewardship. In this talk I will give a progress report on the effort to measure the production cross section of the ^235mU isomer integrated over a fission neutron spectrum. This ongoing experiment is fielded at CEA in Valduc, France, taking advantage of the CALIBAN critical assembly. This effort is performed in collaboration with LANL, LLNL, Bruyeres le Chatel, and Valduc staff. This experiment utilizes a technique to measure internal conversion electrons from the ^235mU isomer with the French BIII detector (Bruyeres le Chatel), and involves a substantial chemistry effort (LANL) to prepare targets for irradiation and counting, as well as to remove fission fragments after irradiation. Experimental techniques will be discussed and preliminary data presented. *Work performed under the auspices of the U.S. Department of Energy by Los Alamos National Laboratory (W-7405-ENG-36) and Lawrence Livermore National Laboratory (W-7405-ENG-48), and CEA-DAM under CEA-DAM NNSA-DOE agreement.