Radiological characterization of nuclear waste drums is an important task for the nuclear industry. The amount of actinides, such as or , contained in a package can be determined using ...non-destructive active methods based on the fission process. One of these techniques, known as neutron interrogation, uses a neutron beam to induce fission reactions on the actinides. Optimization of the neutron flux is an important step towards improving this technique. Electron accelerators enable to achieve higher neutron flux intensities than the ones delivered by deuterium-tritium generators traditionally used on neutron interrogation industrial facilities. In this paper, we design a neutron interrogation cell based on an electron accelerator by MCNPX simulation. We carry out photoneutron interrogation measurements on uranium samples placed at the center of 220 liter nuclear waste drums containing different types of matrices. We quantify impact of the matrix on the prompt neutron signal, on the ratio between the prompt and delayed neutron signals, and on the interrogative neutron half-life time. We also show that characteristics of the conversion target of the electron accelerator enable to improve significantly measurement performances.
Radiological characterization of nuclear waste packages is an industrial issue in order to select the best mode of storage. The characterization becomes particularly crucial for waste packages ...produced at the beginning of the French nuclear industry. For the latter, available information is often incomplete and some key parameters are sometimes missing (content of the package, alpha-activity, fissile mass...) In this case, the use of non-destructive methods, both passive and active, is an appropriate solution to characterize nuclear waste packages and to obtain all the information of interest. In this article, we present the results of a complete characterization carried out on the TE 1060 block, which is a nuclear waste package produced during the 1960's in Saclay. This characterization is part of the DEMSAC (Dismantling of Saclay's facilities) project (ICPE part). It has been carried out in the SAPHIR facility, located in Saclay and housing a linear electron accelerator. This work demonstrates the utility of active methods (photon activation analysis and high-energy imaging) compared to conventional passive detection methods.
In the frame of a partnership between CEA and VINCI, various measurement techniques are applied to soil analysis and tested in different laboratories located at CEA Saclay (France). This paper deals ...with two nuclear measurement techniques assessed in this project. More specifically, this paper presents the feasibility study carried out for two non-destructive active methods: photon activation and neutron activation. First, some atomic nuclides are activated either by photons or neutrons. Secondly, gamma-rays of specific energies are emitted by activated nuclides and gamma-ray spectrometry enables to identify these activated nuclides. Calibration of the full measurement system with reference samples would enable to quantify the mass of activated nuclides. Irradiations performed for photon activation measurements were conducted using a linear electron accelerator (linac) as the latter enables to generate high-energy photons by
Bremsstrahlung
thanks to its conversion target. Furthermore, irradiations performed for neutron activation measurements were also conducted with a linac. Indeed, photons may be converted to neutrons by photonuclear reactions using a secondary target. In the frame of this project, experiments were carried out at the SAPHIR platform (CEA Saclay) with a Linatron-M9 VARIAN linac. The electron energy was either 6 or 9 MeV. For neutron activation measurements, a secondary target made of heavy water has been used as neutron source and a polyethylene cell enabled to thermalize neutrons and increase the number of reactions of interest. In this paper, we present the different experimental setups and the measurement protocols established for this feasibility study. We show experimental results obtained with raw material samples coming from three construction sites.
Cet article éclaire les pratiques de recrutement en s’appuyant sur une enquête réalisée par Pôle emploi sur les compétences attendues par les employeurs. Les attentes vis-à-vis du diplôme et de ...l’expérience professionnelle sont analysées en mettant en évidence leurs déterminants (mode de représentation de l’acquisition de la compétence, spécificités du poste à pourvoir, compétences attendues). Une typologie réalisée par métiers montre que le diplôme et l’expérience professionnelle sont à la fois des signaux et des éléments de régulation du marché du travail des métiers. Enfin, dans les critères de sélection du candidat retenu in fine , l’expérience professionnelle et les compétences comportementales ont une large place, au détriment du diplôme, mais dépendent aussi des attentes initiales des recruteurs et des difficultés de recrutement.
La prise en compte des épisodes de chômage et de leur durée permet de décrire le fonctionnement des différents segments du marché du travail français au regard des trajectoires professionnelles. ...Ainsi la durée du chômage est positivement corrélée avec la probabilité de changer de métier, de basculer dans un contrat précaire ou dans un emploi à temps partiel, ou encore de connaître une mobilité sociale descendante. Cependant un scoring des situations professionnelles à cinq ans d’intervalle met en évidence le fait qu’une partie des personnes passées par le chômage peut bénéficier de « ports d’entrée » conduisant à des mobilités ascendantes ou à un accès à des emplois stables. Les parcours professionnels des personnes touchées par le chômage apparaissent ainsi très hétérogènes. Ce papier prolonge ainsi les enseignements de précédentes études portant sur la mobilité professionnelle.
Abstract-The Alpha-activity resulting from the presence of actinides inside nuclear waste packages must be characterized, in order to select the most appropriate means of storage. Non-destructive ...active methods, based on the fission process, allow the global mass of actinides to be quantified. However, in most cases, these measurements provide no information on the nature of the isotopes. We are currently developing a method dedicated to the identification of the actinides ( 235 U, 238 U, 239 Pu) contained inside nuclear waste packages. This technique is based on the detection of delayed gammas emitted by fission products, the latter being created by irradiation with a neutron or photon beam. The delayed gamma spectrum can be thought of as a "fingerprint" of the irradiated sample. Qualitative and quantitative analysis of the peaks allows the actinides to be identified. In this paper, we firstly explain the theoretical principle of our method. We then present experimental results obtained on sample mixtures for both types of interrogation ( 236 U/ 239 Pu in fission, 235 U/ 238 U in photofission). Finally, we describe the experiments carried out on different mock-up packages, dedicated to the assessment of the performance and limitations of our technique.
Nuclear decommissioning takes places after dismantling, and consists of studying the possible presence of any residual contamination. To do so, every surface inside the facility must be ...radiologically characterized, and every contamination removed. In the case of an alpha contamination linked with a low gamma activity, using a High-Purity Germanium detector (HPGe) combined with hypothesis tests on the count statistics can be helpful to assess said contamination. Gamma-ray activity enables to determine the total contamination activity provided both are related, like in the case of an uranium-based contamination. Hypothesis tests determine the statistical power of the measurement, allowing decision making when dealing with countings below the detection limit. A representation of the tests results using Receiver Operating Characteristics (ROC) curves allow the user to select an appropriate time of measurement, true detection and false alarm rates, in accordance to the required specifications. This paper presents the feasibility study of such a method, applied to the detection of a low-activity gamma surface contamination of uranium on concrete, with varying enrichment levels.
Under given temperature and bias voltage conditions, partial discharges can create pulses in fission chambers. Based on experimental results, this phenomenon is in-depth investigated and discussed. A ...pulse-shape-analysis technique is proposed to discriminate neutron-induced pulses from partial-discharge-induced ones.
Active neutron interrogation is a nondestructive active method that consists in inducing fission reactions on actinides (e.g., 235 U and 239 Pu) and then in detecting prompt and delayed particles ...emitted further to these reactions. This method is required in various application fields such as radiological characterization of nuclear waste packages and homeland security. Neutron sources traditionally used in neutron interrogation facilities are deuterium-tritium neutron generators. However, a linear electron accelerator (LINAC) can also be used as a photoneutron generator. When accelerating electrons with energy lower than 10 MeV, the use of a secondary target such as heavy water is of interest to convert bremsstrahlung photons to neutrons and to improve neutron production. In this paper, we characterize the photoneutron flux emitted by a Linatron-M9 VARIAN LINAC and the photoneutron flux emitted by a secondary target made of heavy water. We show that operating the LINAC at 9 MeV, the average emission intensity reaches 1.08 × 10 10 neutrons per second, which is on the order of 10× higher than the maximum average emission intensity delivered by a traditional deuterium-tritium neutron generator. Then, we carry out neutron interrogation measurements on uranium samples using the Linatron-M9 LINAC and a secondary target made of different volumes of heavy water. We show that prompt neutron signals were enhanced when using 16 kg of heavy water and operating the LINAC at 9 MeV. Performances of the setup were then assessed by carrying out measurements on a mockup of nuclear waste drum containing different types of matrices. Considering a 0.22-g/cm 3 iron matrix and a uranium sample at the center of the drum, 44 mg of 235 U can be detected in 5 min of irradiation time using a single detection block housing five 150NH100 3 He detectors.
Metrological non-destructive characterization of intense (α, n) neutron sources (emission rate between 107 and 3×108 s−1 into 4π sr solid angle) is a challenge for nuclear applications. In this ...article, we will present the design, development and in situ validation of two measurement cells especially dedicated to this characterization. The main goal consists in determining the absolute neutron emission rate of this type of neutron sources with relative uncertainties less than 5% (k=1). Another purpose is related to the qualitative and quantitative analysis of fission products present in irradiated neutron sources. Because of experimental constraints, acquisitions were carried out underwater which required a full remote control of the measurement cells. Neutron emission rate is assessed using three different non-destructive techniques: (i) global neutron counting, (ii) neutron activation using gold dosimeters and (iii) gamma-ray spectrometry. We will successively present the design step and associated constraints, main characteristics of measurement cells and associated laboratory characterization as well as experimental results obtained during the final in situ measurement campaign. The latter shows an excellent agreement regarding the neutron emission rate values provided by the three different non-destructive techniques and a relative combined standard uncertainty less than 5% (k=1) for the investigated neutron sources.
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