Noirot L.,CEA Cadarache Center
Nuclear Engineering and Design | Year: 2011
The relevant phenomena concerning stable-fission gas behavior in nuclear fuels are combined in a single model: MARGARET. This same tool can be used for base irradiations up to high burnup, ramp tests and annealing tests. The representation of intragranular or intergranular bubbles and fabrication pores is highly mechanistic. The partition of fission gas between these cavities and dissolved in the solid permits determination of swelling of the fuel. The released gas is obtained by difference between the created and retained gas in the fuel. The model has been validated against base irradiations, ramps and annealing tests of UO2 fuel. The article presents the complete equations of the model in the base irradiation condition (Part I), followed by a detailed analysis of the behavior of a fuel irradiated up to 61 GWd/tU, extensively examined after irradiation (Part II). Part III presents the specific additional terms used for the calculation of transient and annealing conditions. © 2011 Elsevier B.V. All rights reserved.
Noguere G.,CEA Cadarache Center
Physical Review C - Nuclear Physics | Year: 2010
This work reports Np237 neutron resonance parameters obtained from the simultaneous analysis of time-of-flight data measured at the GELINA, ORELA, KURRI, and LANSCE facilities. A statistical analysis of these resonances relying on average R-matrix and optical model calculations was used to establish consistent l-dependent average resonance parameters involved in the description of the unresolved resonance range of the Np237 neutron cross sections. For neutron orbital angular momentum l=0, we obtained an average radiation width Γγ=39.3±1.0 meV, a neutron strength function 104S0=1.02±0.14, a mean level spacing D0=0.60±0.03 eV, and a potential scattering length R′=9.8±0.1 fm. © 2010 The American Physical Society.
Kvashnina K.O.,European Synchrotron Radiation Facility |
Butorin S.M.,Uppsala University |
Martin P.,CEA Cadarache Center |
Glatzel P.,European Synchrotron Radiation Facility
Physical Review Letters | Year: 2013
We report here the first direct observation of U(V) in uranium binary oxides and analyze the gradual conversion of the U oxidation state in the mixed uranium systems. Our finding clarifies previous contradicting results and provides important input for the geological disposal of spent fuel, recycling applications, and chemistry of uranium species. © 2013 American Physical Society.
Andre M.J.,CEA Cadarache Center
BioSystems | Year: 2011
The studies of Rubisco characteristics observed during plant evolution show that the variation of the Rubisco specificity factor only improved by two times from cyanobacteria to modern C3 plants. However we note important variations of the ratio between the maximum rates of oxygenation and carboxylation (VO/VC). Modelling in vivo 18O2 data in plant gas exchange shows that the oxygenation reaction of Rubisco plays a regulating role when the photochemical energy exceeds the carboxylation capacity. A protective index 'oxygenation capacity' is postulated, related to the ratio VO/VC of Rubisco, and hence to the sink energy effect of photorespiration. Analysing the trends of Rubisco parameters along the evolutionary scale, we show: (1) the increase of both VC and VO; (2) the enhancement of CO2 affinity; and (3) the rise in oxygenation capacity at the expense of the CO2 specificity. Hence, the factors of evolutionary pressure have not only directed the enzyme towards a more efficient utilisation of CO2, but mainly to positively use the unavoidable great loss of energy and assimilated carbon in the process of photorespiration. These observations reinforce the hypothesis of plant-atmosphere co-evolution and of the complex role of Rubisco, which seems to be selected to develop both better CO2 affinity and oxygenation capacity. The latter increases the capacity of sink of photorespiration, in particular, during water stress or under high irradiance, the two conditions experienced by plants in terrestrial environments. These observations help to explain some handicaps of C4 plants, and the supremacy of CAM and C3 perennial higher plants in arid environments. © 2010 Elsevier Ireland Ltd.
Litaize O.,CEA Cadarache Center |
Serot O.,CEA Cadarache Center
Physical Review C - Nuclear Physics | Year: 2010
A Monte Carlo simulation of the fission fragment deexcitation process was developed in order to analyze and predict postfission-related nuclear data which are of crucial importance for basic and applied nuclear physics. The basic ideas of such a simulation were already developed in the past. In the present work, a refined model is proposed in order to make a reliable description of the distributions related to fission fragments as well as to prompt neutron and γ energies and multiplicities. This refined model is mainly based on a mass-dependent temperature ratio law used for the initial excitation energy partition of the fission fragments and a spin-dependent excitation energy limit for neutron emission. These phenomenological improvements allow us to reproduce with a good agreement the Cf252(sf) experimental data on prompt fission neutron multiplicity ν̄(A), ν̄(TKE), the neutron multiplicity distribution P(ν), as well as their energy spectra N(E), and lastly the energy release in fission. © 2010 The American Physical Society.
Carasco C.,CEA Cadarache Center
Computer Physics Communications | Year: 2010
MCNP Output Data Analysis with ROOT (MODAR) is a tool based on CERN's ROOT software. MODAR has been designed to handle time-energy data issued by MCNP simulations of neutron inspection devices using the associated particle technique. MODAR exploits ROOT's Graphical User Interface and functionalities to visualize and process MCNP simulation results in a fast and user-friendly way. MODAR allows to take into account the detection system time resolution (which is not possible with MCNP) as well as detectors energy response function and counting statistics in a straightforward way. Program summary: Program title: MODAR. Catalogue identifier: AEGA_v1_0. Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEGA_v1_0.html. Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland. Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html. No. of lines in distributed program, including test data, etc.: 155 373. No. of bytes in distributed program, including test data, etc.: 14 815 461. Distribution format: tar.gz. Programming language: C++. Computer: Most Unix workstations and PC. Operating system: Most Unix systems, Linux and windows, provided the ROOT package has been installed. Examples where tested under Suse Linux and Windows XP. RAM: Depends on the size of the MCNP output file. The example presented in the article, which involves three two-dimensional 139 × 740 bins histograms, allocates about 60 MB. These data are running under ROOT and include consumption by ROOT itself. Classification: 17.6. External routines: ROOT version 5.24.00 (http://root.cern.ch/drupal/). Nature of problem: The output of an MCNP simulation is an ASCII file. The data processing is usually performed by copying and pasting the relevant parts of the ASCII file into Microsoft Excel. Such an approach is satisfactory when the quantity of data is small but is not efficient when the size of the simulated data is large, for example when time-energy correlations are studied in detail such as in problems involving the associated particle technique. In addition, since the finite time resolution of the simulated detector cannot be modeled with MCNP, systems in which time-energy correlation is crucial cannot be described in a satisfactory way. Finally, realistic particle energy deposit in detectors is calculated with MCNP in a two-step process involving type-5 then type-8 tallies. In the first step, the photon flux energy spectrum associated to a time region is selected and serves as a source energy distribution for the second step. Thus, several files must be manipulated before getting the result, which can be time consuming if one needs to study several time regions or different detectors performances. In the same way, modeling counting statistics obtained in a limited acquisition time requires several steps and can also be time consuming. Solution method: In order to overcome the previous limitations, the MODAR C++ code has been written to make use of CERN's ROOT data analysis software. MCNP output data are read from the MCNP output file with dedicated routines. Two-dimensional histograms are filled and can be handled efficiently within the ROOT framework. To keep a user friendly analysis tool, all processing and data display can be done by means of ROOT Graphical User Interface. Specific routines have been written to include detectors finite time resolution and energy response function as well as counting statistics in a straightforward way. Additional comments: The possibility of adding tallies has also been incorporated in MODAR in order to describe systems in which the signal from several detectors can be summed. Moreover, MODAR can be adapted to handle other problems involving two-dimensional data. Running time: The CPU time needed to smear a two-dimensional histogram depends on the size of the histogram. In the presented example, the time-energy smearing of one of the 139 × 740 two-dimensional histograms takes 3 minutes with a DELL computer equipped with INTEL Core 2. © 2010 Elsevier B.V. All rights reserved.
Dorado B.,CEA DAM Ile-de-France |
Garcia P.,CEA Cadarache Center
Physical Review B - Condensed Matter and Materials Physics | Year: 2013
We report first-principles DFT+U calculations of the paramagnetic phases of uranium dioxide (UO2) and (U,Pu) mixed oxides (MOX). We use a combination of two techniques, the first of which enables us to treat the presence of metastable states and the other the random distribution of spins (for paramagnetism) and of plutonium atoms (for MOX). The resulting method is first used to determine the ground-state properties of paramagnetic UO 2 and is then applied to MOX with 12.5% and 25% Pu, for which both experimental and theoretical studies are lacking. We find the paramagnetic phase of fluorite UO2 to be more stable than the antiferromagnetic phase as expected from experimentation, with ground-state properties in excellent agreement with experimental data. Results on MOX show that most of the ground-state properties of UO2 are affected by addition of 12.5% Pu and do not seem to be much different when the plutonium content changes, at least for Pu contents below 30%. For both UO2 and MOX, it is found that the true paramagnetic order has a significant effect on the calculated elastic constants, compared to the antiferromagnetic and ferromagnetic orders. By contrast, we find that regarding energetics, the antiferromagnetic order may be used as a very good approximation of the paramagnetic state. © 2013 American Physical Society.
Cahyna P.,EURATOM |
Nardon E.,CEA Cadarache Center
Journal of Nuclear Materials | Year: 2011
This work addresses the question of the relation between strike-point splitting and magnetic stochasticity at the edge of a poloidally diverted tokamak in the presence of externally imposed magnetic perturbations. More specifically, ad-hoc helical current sheets are introduced in order to mimic a hypothetical screening of the external resonant magnetic perturbations by the plasma. These current sheets, which suppress magnetic islands, are found to reduce the amount of splitting expected at the target, which suggests that screening effects should be observable experimentally. Multiple screening current sheets reinforce each other, i.e. less current relative to the case of only one current sheet is required to screen the perturbation. © 2010 Elsevier B.V. All rights reserved.
Swarup R.,University of Nottingham |
Peret B.,CEA Cadarache Center
Frontiers in Plant Science | Year: 2012
Auxin regulates several aspects of plant growth and development. Auxin is unique among plant hormones for exhibiting polar transport. Indole-3-acetic acid (IAA), the major form of auxin in higher plants, is a weak acid and its intercellular movement is facilitated by auxin influx and efflux carriers. Polarity of auxin movement is provided by asymmetric localization of auxin carriers (mainly PIN efflux carriers). PIN-FORMED (PIN) and P-GLYCOPROTEIN (PGP) family of proteins are major auxin efflux carriers whereas AUXIN1/LIKE-AUX1 (AUX/LAX) are major auxin influx carriers. Genetic and biochemical evidence show that each member of the AUX/LAX family is a functional auxin influx carrier and mediate auxin related developmental programmes in different organs and tissues. Of the four AUX/LAX genes, AUX1 regulates root gravitropism, root hair development and leaf phyllotaxy whereas LAX2 regulates vascular development in cotyledons. Both AUX1 and LAX3 have been implicated in lateral root (LR) development as well as apical hook formation whereas both AUX1 and LAX1 and possibly LAX2 are required for leaf phyllotactic patterning. © 2012 Swarupand Péret.
Salvatores M.,CEA Cadarache Center |
Salvatores M.,Idaho National Laboratory |
Palmiotti G.,Idaho National Laboratory
Progress in Particle and Nuclear Physics | Year: 2011
If nuclear power becomes a sustainable source of energy, a safe, robust, and acceptable solution must be pursued for existing and projected inventories of high-activity, long-lived radioactive waste. Remarkable progress in the field of geological disposal has been made in the last two decades. Some countries have reached important milestones, and geological disposal (of spent fuel) is expected to start in 2020 in Finland and in 2022 in Sweden. In fact, the licensing of the geological repositories in both countries is now entering into its final phase. In France, disposal of intermediate-level waste (ILW) and vitrified high-level waste (HLW) is expected to start around 2025, according to the roadmap defined by an Act of Parliament in 2006. In this context, transmutation of part of the waste through use of advanced fuel cycles, probably feasible in the coming decades, can reduce the burden on the geological repository. This article presents the physical principle of transmutation and reviews several strategies of partitioning and transmutation (P&T). Many recent studies have demonstrated that the impact of P&T on geological disposal concepts is not overwhelmingly high. However, by reducing waste heat production, a more efficient utilization of repository space is likely. Moreover, even if radionuclide release from the waste to the environment and related calculated doses to the population are only partially reduced by P&T, it is important to point out that a clear reduction of the actinide inventory in the HLW definitely reduces risks arising from less probable evolutions of a repository (i.e., an increase of actinide mobility in certain geochemical situations and radiological impact by human intrusion). © 2010 Elsevier B.V. All rights reserved.