[en] Today, nuclear energy represents a non-negligible part of the global energy market, most likely a rolling wheel to grow in the coming decades. Reactors of the future must face the criteria including additional economic but also safety, non-proliferation, optimized fuel management and responsible management of nuclear waste. In the framework of this thesis, studies on non-proliferation of nuclear weapons are discussed in the context of research and development of a new potential tool for monitoring nuclear reactors, the detection of reactor antineutrinos, because the properties of these particles may be of interest for the International Agency of Atomic Energy (IAEA), in charge of the verification of the compliance by States with their safeguards obligations as well as on matters relating to international peace and security. The IAEA encouraged its member states to carry on a feasibility study. A first study of non-proliferation is performed with a simulation, using a proliferating scenario with a CANDU reactor and the associated antineutrinos emission. We derive a prediction of the sensitivity of an antineutrino detector of modest size for the purpose of the diversion of a significant amount of plutonium. A second study was realized as part of the Nucifer project, an antineutrino detector placed nearby the OSIRIS research reactor. The Nucifer antineutrino detector is dedicated to non-proliferation with an optimized efficiency, designed to be a demonstrator for the IAEA. The simulation of the OSIRIS reactor is developed here for calculating the emission of antineutrinos which will be compared with the data measured by the detector and also for characterizing the level of background noises emitted by the reactor detected in Nucifer. In general, the reactor antineutrinos are emitted during radioactive decay of fission products. These radioactive decays are also the cause of the decay heat emitted after the shutdown of a nuclear reactor of which the estimation is an issue of nuclear safety. In this thesis, we present an experimental work which aims to measure the properties of beta decay of fission products important to the non-proliferation and reactor decay heat. First steps using the technique of Total Absorption Gamma-ray Spectroscopy (TAGS) were carried on at the radioactive beam facility of the University of Jyvaskyla. We will present the technique used, the experimental setup and part of the analysis of this experiment. (author)

[en] Neutrinos are the most abundant matter particles in the Universe. Thoroughly investigated in basic science, the neutrino field is now delivering first applications to the monitoring of nuclear reactors. The neutrinos are emitted in the decay chain of the fission products; therefore measuring their flux provides real-time information, directly related to the fission process occurring in the reactor core. Because of the very weak interaction of neutrinos with matter a neutrino detector can stand outside the core containment vessel and provide a non-intrusive and inherently tamper resistant measurement. After a brief review of the existing data and worldwide projects, we present the NUCIFER experiment. The active part of the detector is a tank filled up with one ton of Gadolinium-doped liquid scintillator. Sixteen photomultiplier tubes, isolated from the liquid by an acrylic buffer, read out the light produced by the interaction of a neutrino with the protons of the liquid. The tank is surrounded by plastic scintillator plates to veto the cosmic rays. Then polyethylene and lead shielding suppress the background coming from external neutrons and gamma rays respectively. The NUCIFER detector has been designed for an optimal compromise between the detection performances and the specifications of operation in a safeguards regime. Its global footprint is 2.8 m x 2.8 m and it can monitor remotely the nuclear power plant thermal power and Plutonium content with very little maintenance on years scale. The experiment is currently installed near the OSIRIS research reactor (70 MWth) at CEA, in Saclay, France. First data are expected by May 2012. This work is done in contact with the IAEA/SGTN division that is currently investigating the potentiality of neutrinos as a novel safeguards tool. A dedicated working group has been created in 2010 to coordinate the simulation effort of various reactor types as well as the development of dedicated detectors and define and eventually test the end product to be used by the agency.

[en] Nuclear power plants produce large quantities of antineutrinos due to the beta decays of the fission products. Antineutrino measurements could comprise a unique means of providing information on the isotopic composition of the core, non-intrusively and in near real-time. To this aim we have started to study PBRs (Pebble Bed Reactors) with our simulation tools. We use a package called MCNP Utility for Reactor Evolution (MURE), initially developed by CNRS/IN2P3 labs to study Generation IV reactors. The MURE package has been coupled to fission product beta decay nuclear databases for studying reactor antineutrino emission. As a first step, the simulation of a pebble surrounded by He coolant which design is taken from an OECD/NEA benchmark has been performed. Simulations of the evolution of a single-cell for 3 kinds of prospect fuel: uranium, uranium/thorium or PuO_x, are compared with the results of the OECD/NEA benchmark. Various diversion scenarios assuming a 200 MWth reactor are discussed, deduced from our cell calculation, as a first estimate of the antineutrino emission characteristics. The emitted antineutrino characteristics depend on the fuel type, the mixing of regular fuel and proliferation-prone fuel, the pebble residency time. The first gross scenario presented in this paper prove that the usefulness of a neutrino detector is very sensitive to the power of the reactor and the reactor type itself. For the UO_x fuel, we have first focused on the reactor at steady state, which is the most relevant for a first sight, and found that an antineutrino detector of 2m³ placed at 25 m from a reactor of 200 MWth would be sensitive to the diversion of 1 SQ (Significant Quantity) within 3 months, even without taking into account the physics of detection which would enhance the discrepancy between the fissions of uranium and plutonium

[en] During the last decades, tremendous progresses have been achieved on the fundamental knowledge and detection of neutrinos which give new opportunities of applied neutrino physics. Among them, antineutrinos could be exploited for two nuclear reactor monitoring applications: the thermal power measurement and the control of the isotopic composition of the reactor fuel. This application arouses the International Atomic Energy Agency (IAEA) interest as a potential new safeguard tool. Large quantities of antineutrinos, about 10²⁰ electronic antineutrinos per second in a 1 GWe reactor core, are produced by β decays of the fission products. Since the distribution of fission fragments depends on the fissile and fertile isotopes (²³⁵U, ²³⁸U, ²³⁹Pu and ²⁴¹Pu), the average number of emitted antineutrinos and their mean energy are sensitive to the isotopic composition of the core. Recently, thanks to a cubic meter sized antineutrino detector with Gd-doped liquid scintillator installed at the San Onofre power plant, SONGS1, Bowden et al. have confirmed that it is possible to monitor precisely the thermal power over hour to month-time scales in a non intrusive and unattended mode but also to have information on the plutonium content of the reactor core. The Nucifer detector, under development in France, will be dedicated to non-proliferation and thermal power applications. The design of the detector takes advantage of the technical improvements performed for fundamental neutrino experiments such as Double Chooz. Nucifer, encouraged by the results of SONGS1 and based on the same detection techniques, aims at increasing the overall neutrino rate by a factor 8, using a larger and one-piece target volume and better shielding without increasing the complexity, and keeping a footprint compatible with the restricted place near a power reactor. Nucifer will be tested within the next two years at the OSIRIS (Saclay-France) and the ILL (Grenoble-France) research reactors. Its improved design should allow reaching a 1% statistical accuracy on the antineutrino flux on less than a week scale when placing Nucifer at 25 m of a 1 GWe reactor core. After a brief overview on the worldwide effort in the field of reactor monitoring with antineutrinos, the Nucifer experiment will be presented. (authors)

[en] After many years of fundamental research, physicists have a good understanding of the neutrinos detection techniques. It is now possible to apply neutrino physics as a new tool to monitor nuclear power plants. We already know that modest size detectors are achievable to fulfill that task such as the SONGS 1 and the future Nucifer detectors. In parallel, sophisticated simulations of reactors and their associated antineutrino flux and energy spectrum have been developed to predict the neutrino signature of the fuel burnup and of a diversion. Taking advantage of the tremendous quantity of information available nowadays in nuclear databases, the total β spectrum of a reactor is built by adding the contributions of all the β branches involved in the decay of all fission products (FP). A package called MCNP Utility for Reactor Evolution (MURE) computes the fuel and FP inventories by simulating the neutronics and time evolution of a reactor core. MURE, initially developed by CNRS/IN2P3/LPSC Grenoble and IPN Orsay to study Generation IV reactors, is a precision code written in C++ which automates the preparation and computation of successive MCNP calculations either for precision burnup or thermal-hydraulics purpose. MURE will be soon available at NEA. The only user-defined inputs driving the time evolution of the isotopic composition of the core are the initial fuel composition, the refueling scheme, and the thermal power. The evolution of the antineutrino flux and energy spectrum with the fuel burnup, as well as the effect of neutron capture on various nuclei are taken into account. Nonproliferation scenarios and burnup monitoring with antineutrinos have been studied using these tools for PWR and Candu reactors. A full core simulation of an N4-PWR will be presented in a first part. Gross unveiling diversion scenarios using a PWR have been simulated in order to test the ability of the antineutrino probe. A channel of a Heavy Water Reactor (Candu 600) loaded with natural Uranium, has been simulated also in order to provide a first hint of what antineutrino detection would bring to the monitoring of such on-line refueled reactor which are maintained in a steady state through quasi-continuous refueling. Very simple proliferation scenario studies with Candu reactors, based on several channel calculations, made at various fuel dwell-times, will be shown in a second part. In both cases, the response of a Nucifer-like detector placed at 25 m from the core to these scenarios has been studied. (authors)

[en] Neutrinos are the most abundant matter particles in the Universe. Thoroughly investigated in basic science, the neutrino field is now delivering first applications for nuclear reactor monitoring. We present here the NUCIFER neutrino experiment to automatically and non-intrusively monitor nuclear power plant thermal power and Plutonium content. The core of the detector is a one ton Gadolinium-doped liquid scintillator tank to be installed in a basement room less than 30 m from a reactor core. The Division of Technical Support (SGTS) within the IAEA Department of Safeguards is currently investigating the potentiality of neutrinos as a novel safeguards tool. (author)

[en] The major advances achieved over the last decades in the understanding of fundamental neutrino physics allow us to apply the detection of reactor antineutrino signals to automatic and non intrusive nuclear power plant surveys. Here, we present the NUCIFER experiment, a 1-ton Gd-doped liquid scintillator detector to be installed a few 10 m from a reactor core for measurements of its thermal power and plutonium (Pu) content. The design of such a small volume detector has been focused on high detection efficiency (similar to 50% and good background rejection. Detailed simulations of reactor-emitted antineutrino spectrum and detector response have been developed and used to calculate the NUCIFER sensitivity to illicit retrieval of Pu from the core. These results have been presented in October 2008 to the International Atomic Energy Agency (IAEA), which has expressed its interest in the potentialities of this detector as a new safeguard tool. (authors)

[en] An overview is given of our activities related to the study of the beta decay of neutron rich nuclei relevant for nuclear applications. Recent results of the study of the beta decay of "8"7","8"8Br using a new segmented total absorption spectrometer are presented. The measurements were performed at the IGISOL facility using trap-assisted total absorption spectroscopy

[en] β-decay properties are usually determined by measuring, with high resolution Ge crystals, the intensity and energy of γ-rays emitted after the beta decay. In the case of large Q_β, or complex de-excitation pattern, it happens that some transitions are missed due to the low efficiency of Germanium detectors for high energy gammas or high multiplicity decay cascades. This leads to an overestimation of the high energy part of the β spectra and the anti-neutrino ones. This is called the Pandemonium effect. Some of the data present in nuclear databases suffer from the distortion caused by this effect. A way to avoid the Pandemonium effect is to use a Total Absorption Spectrometer (TAS), this detector is a 4π calorimeter constituted of one large or segmented crystals and with the particularity of having a cascade detection efficiency close to 100%. A TAS device has been built and calibrated with "1"3"7Cs, "6"0Co and "2"2"-"2"4Na sources. A test performed on "9"2Rb shows that we have a good agreement between the simulated spectrum and the experimental one. The use of TAS for β-decay properties will help to assess the decay heat (or residual power) of reactors

[en] The aim of this work is to study the impact of the inclusion of the recently measured β decay properties of the "1"0"2","1"0"4","1"0"5","1"0"6","1"0"7Tc, "1"0"5Mo, and "1"0"1Nb nuclei in the calculation of the antineutrino (anti-ν) energy spectra arising after the fissions of the four main fissile isotopes "2"3"5","2"3"8U, and "2"3"9","2"4"1Pu in PWRs. These β feeding probabilities, measured using the Total Absorption Technique (TAS) at the JYFL facility of Jyväskylä, have been found to play a major role in the γ component of the decay heat for "2"3"9Pu in the 4-3000 s range. Following the fission product summation method, the calculation was performed using the MCNP Utility Reactor Evolution code (MURE) coupled to the experimental spectra built from β decay properties of the fission products taken from evaluated databases. These latest TAS data are found to have a significant effect on the Pu isotope energy spectra and on the spectrum of "2"3"8U showing the importance of their measurement for a better assessment of the reactor anti-ν energy spectrum, as well as importance for fundamental neutrino physics experiments and neutrino applied physics