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[en] In this paper, we propose a numerical methodology for the development of a method of the spectral nodal class that generates numerical solutions free from spatial truncation errors. This method, denominated Spectral Deterministic Method (SDM), is tested as a study of the solutions (spectral analysis) of neutron transport equations in the discrete ordinates (SN) formulation, in slab geometry, multigroup approximation, with linearly anisotropic scattering, considering a heterogeneous domain with fixed-source. The unknowns in the methodology are the cell-edge, and cell average angular fluxes, the numerical values calculated for these quantities coincide with the analytic solution of the equations. These numerical results are shown and compared with the traditional fine-mesh Diamond Difference (DD) method and the coarse-mesh spectral Green's function (SGF) method to illustrate the method's accuracy and stability. The solution algorithms problem is implemented in a computer simulator made in C++ language, the same that was used to generate the results of the reference work. (author)
[en] In this work the latest developments a Monte Carlo simulator with continuous energy is reported. This simulator makes use of a sum of three probability distributions to represent the neutron spectrum. Two distributions have known shape, but have varying population of neutrons in time, and these are the fission neutron spectrum and the Maxwell-Boltzmann distribution. The third distribution has an a priori unknown and possibly variable shape with time and is determined from parametrizations of Monte Carlo simulation. In this work the possible neutron-matter interactions are simulated with exception of the up-scattering of neutrons. In order to preserve the thermal spectrum, neutrons are selected stochastically as being part of the thermal population and have an energy attributed to them taken from a Maxwellian distribution, such an approximation is valid due to the fact that for fast neutrons up-scattering occurrence is irrelevant, being only appreciable at low energies. It is then shown how this procedure can emulate the up-scattering effect by the increase in the kinetic energy of the neutron population. Since the simulator uses tags to identify the reactions it is possible not only to plot the distributions by neutron energy, but also by the type of interaction with matter and with the identification of the target nuclei involved in the process. (author)
[en] Described in this paper is an analytic methodology for the solution of the neutron transport equation in slab geometry using PN method. The first part of the present methodology consists of obtaining a local general solution for the PN equations with arbitrary order 𝑵 L ≤ Nand degree 𝑳 ≤ 𝑵 of scattering anisotropy. In the second part, the local general solution for the PN equations was replaced in the scattering source of a simplified version of the linear Boltzmann transport equation, i. e., stationary, slab-geometry, monoenergetic, azimuthally symmetric, for non-multiplying media and isotropic internal source. This methodology has been implemented in a computer code developed on the MatLab® platform for Windows. As a result, in addition to generating numerical results for the scalar flux through the PN method, the computer code generates numerical results for the angular flux at any position in the domain and for any direction not perpendicular to the domain. To evaluate the applicability of the PN method and the analytic methodology, as described in this paper, numerical results for a model problem are presented. (author)
[en] We describe in this work the application of the modified power method for solving the multigroup neutron diffusion eigenvalue problem in slab geometry considering two-dimensions for criticality global calculations. In order to solve this problem a modified power method is used to obtain the dominant eigenvalue (effective multiplication factor) and its corresponding eigenfunction (scalar neutron flux). The innovation of this work is solving the neutron diffusion equation in analytical form for each new iteration of the power method. For solve this problem we propose to apply the Finite Fourier Sine Transform on one of the variables obtaining a transformed problem which is resolved by well-established methods for ordinary differential equations. The inverse Fourier Transform is used to reconstruct the solution for the original problem. In order to maintain the analytical character for the solution in each new iteration of the power method the neutron flux is reconstructed through a polynomial interpolation. The methodology is implemented to solve a homogeneous and heterogeneous problems and the results are compared with works presents in the literature. (author)
[en] This article presents nuclide-specific organ dose rate coefficients for environmental external exposures due to soil contamination assumed as a planar source at a depth of 0.5 g cm in the soil and submersion to contaminated air, for a pregnant female and its fetus at the 24th week of gestation. Furthermore, air kerma free-in-air coefficient rates are listed. The coefficients relate the organ equivalent dose rates (Sv s) to the activity concentration of environmental sources, in Bq m or Bq m, allowing to time-integrate over a particular exposure period. The environmental radiation fields were simulated with the Monte Carlo radiation transport codes PHITS and YURI. Monoenergetic organ dose rate coefficients were calculated employing the Monte Carlo code EGSnrc simulating the photon transport in the voxel phantom of a pregnant female and fetus. Photons of initial energies of 0.015–10 MeV were considered including bremsstrahlung. By folding the monoenergetic dose coefficients with the nuclide decay data, nuclide-specific organ doses were obtained. The results of this work can be employed for estimating the doses from external exposures to pregnant women and their fetus, until more precise data are available which include coefficients obtained for phantoms at different stages of pregnancy.
[en] This white paper aims at proposing answers to some questions regarding the situation in Fukushima and the consequences of the accident, notably the situation regarding dismantling, the remaining radioactive substances, lessons learned, and other issues. Thus, a first article presents the radio-ecology discipline and describes how this technique allowed the control and reduction of radionuclide transfers in Fukushima (interview of an IRSN expert). A second article addresses the transport of radioactive substances, more particularly in France where nearly hundred significant events are noticed every year. Classification (in terms of hazard) and regulation (technical requirements and others related to radioactive products and to their transport) aspects are overviewed. The third article addresses the evolution of the dismantling of the Fukushima Daiichi nuclear plant (interview of an IRSN expert). The last article discusses the action plan implemented by France to improve the safety of its nuclear installations, with the installation of back-up Diesel units, the installation of ultimate water sources to cool reactors, and the construction of local crisis centres able to withstand extreme aggressions. Five articles are also proposed. They address the French challenge of management of nuclear wastes, the development of small nuclear reactors everywhere in the world, the necessary adaptation of nuclear plants to extreme air temperatures, the safety of French nuclear installations which is globally good but still to be improved, and the causes and consequences of the Fukushima accident.
[en] In this paper, translated from an article published by Nuclear Engineering International (NEI), the author presents his views on the future of civil nuclear propulsion: nuclear powered container ships have returned after a decade in the doldrums, nuclear energy already present at sea with more than 200 naval reactors, the development of Floating nuclear power plants, the question of docking of nuclear-powered ships, the possible resistance from incumbent interests at sea in future.
[en] The research was focused on the level and distribution of 90Sr in various parts of the terrestrial environment of Spitsbergen. The mean activity concentrations were noted lower in peats and soils than in cryoconite. Analysis of vertical variation of 90Sr for soils and peats as well as isotopic ratios of 137Cs/90Sr and 239+240Pu/90Sr for cryoconite clearly showed substantial migration or depletion of the considered radionuclide. Due to the large dispersion of isotopic signatures, the 90Sr provenance was difficult to identify in the examined region. However, observed high mobility of the 90Sr might indicate the global fallout origin. (author)
[en] Subterranean radioiodine contamination at the Hanford Site in Washington State is believed to be present as iodide, iodate, and organo-I species, with iodate being the predominant form. Because these species have different sediment-sorption characteristics, understanding their distribution is important for developing an accurate understanding of iodine migration in the subsurface. Herein, we report a novel, rapid technique for simultaneous iodine speciation (iodide/iodate) and isotopic ratio (129I/127I) measurements using ion chromatography (IC) joined with collision/reaction cell inductively coupled plasma mass spectrometry (ICP-MS), collectively referred to as IC-ICP-MS. This approach employs online dynamically regenerated eluent suppression post chromatographic separation of the samples and collision cell technology, with pure oxygen as a collision gas for the active suppression of 129Xe (which naturally exists in the argon supplied to the ICP source) to rapidly (< 15 min) achieve precise and reproducible results. Speciated standard reference materials yielded detection limits for 127I of approximately 23.8 ng/L for iodate and 24.3 ng/L for iodide, and for 129I of approximately 1.81 ng/L for iodate and 2.62 ng/L for iodide. The method was demonstrated by analyzing groundwater samples from six wells from 129I-contaminated regions of the Hanford Site; iodate was the primary species for both 127I and 129I. Small quantities of 127I-iodide were also detected in most of the samples, but all 129I-iodide results were below the detection limit. An interference from molybdenum prevented the estimation of organo-iodine concentrations but did not affect the iodate and iodide results. This new analytical capability will enable rapid, simultaneous characterization of speciated inorganic iodine in vadose zone sediments and groundwater samples at levels below the US federal drinking water standard for 129I of 1 pCi/L (∼ 5.6 ng/L). (author)