Artigos de revistas: "Stochastic neutronics"

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Liu, Shichang, Guanbo Wang, Gaochen Wu e Kan Wang. "Neutronics comparative analysis of plate-type research reactor using deterministic and stochastic methods". Annals of Nuclear Energy 79 (maio de 2015): 133–42. http://dx.doi.org/10.1016/j.anucene.2015.01.027.

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Liu, Shichang, Guanbo Wang, Jingang Liang, Gaochen Wu e Kan Wang. "Burnup-dependent core neutronics analysis of plate-type research reactor using deterministic and stochastic methods". Annals of Nuclear Energy 85 (novembro de 2015): 830–36. http://dx.doi.org/10.1016/j.anucene.2015.06.041.

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Lebrat, J. F., G. Aliberti, A. D’Angelo, A. Billebaud, R. Brissot, H. Brockmann, M. Carta et al. "Global Results from Deterministic and Stochastic Analysis of the MUSE-4 Experiments on the Neutronics of Accelerator-Driven Systems". Nuclear Science and Engineering 158, n.º 1 (janeiro de 2008): 49–67. http://dx.doi.org/10.13182/nse05-100.

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Santanoceto, Mario, Marco Tiberga, Zoltán Perkó, Sandra Dulla e Danny Lathouwers. "UNCERTAINTY QUANTIFICATION IN STEADY STATE SIMULATIONS OF A MOLTEN SALT SYSTEM USING POLYNOMIAL CHAOS EXPANSION ANALYSIS". EPJ Web of Conferences 247 (2021): 15008. http://dx.doi.org/10.1051/epjconf/202124715008.

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Uncertainty Quantification (UQ) of numerical simulations is highly relevant in the study and design of complex systems. Among the various approaches available, Polynomial Chaos Expansion (PCE) analysis has recently attracted great interest. It belongs to nonintrusive spectral projection methods and consists of constructing system responses as polynomial functions of the stochastic inputs. The limited number of required model evaluations and the possibility to apply it to codes without any modification make this technique extremely attractive. In this work, we propose the use of PCE to perform UQ of complex, multi-physics models for liquid fueled reactors, addressing key design aspects of neutronics and thermal fluid dynamics. Our PCE approach uses Smolyak sparse grids designed to estimate the PCE coefficients. To test its potential, the PCE method was applied to a 2D problem representative of the Molten Salt Fast Reactor physics. An in-house multi-physics tool constitutes the reference model. The studied responses are the maximum temperature and the effective multiplication factor. Results, validated by comparison with the reference model on 103 Monte-Carlo sampled points, prove the effectiveness of our PCE approach in assessing uncertainties of complex coupled models.

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Muñoz-Cobo, J. L., e G. Verdú. "Neutron stochastic transport theory with delayed neutrons". Annals of Nuclear Energy 14, n.º 7 (janeiro de 1987): 327–50. http://dx.doi.org/10.1016/0306-4549(87)90114-9.

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KHRENNIKOV, ANDREI. "QUANTUM PROBABILITIES FROM DETECTION THEORY FOR CLASSICAL RANDOM FIELD". Fluctuation and Noise Letters 08, n.º 03n04 (dezembro de 2008): L393—L400. http://dx.doi.org/10.1142/s0219477508005148.

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We present a model of detectors operating with classical random fields and producing probabilities described by the formalism of quantum mechanics. The basic assumption of this measurement theory is that the probability of detection of field (= signal) is proportional to the power of this field. (Therefore we call this approach "power signal-field detection theory" – PFSDT.) Our approach has some similarities with stochastic electrodynamics. However, formalisms describing random fields – "quantum fluctuations" – are different. Moreover, our approach all particles are represented by random fields, e.g., electronic or neutronic field. Thus we have various types of "quantum fluctuations".

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Xenofontos, T., G. K. Delipei, P. Savva, M. Varvayanni, J. Maillard, J. Silva e N. Catsaros. "Testing the new stochastic neutronic code ANET in simulating safety important parameters". Annals of Nuclear Energy 103 (maio de 2017): 85–96. http://dx.doi.org/10.1016/j.anucene.2017.01.012.

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YARMUKHAMEDOV, R., e M. K. UBAYDULLAEVA. "ON ASYMPTOTICS OF THREE-BODY BOUND STATE RADIAL WAVE FUNCTIONS OF HALO NUCLEI NEAR THE HYPERANGLE φ~0 AND φ~π/2 IN THE CONFIGURATION SPACE AND THREE-BODY ASYMPTOTIC NORMALIZATION FACTORS FOR 6He NUCLEUS IN THE (n+n+α)-CHANNEL". International Journal of Modern Physics E 18, n.º 07 (agosto de 2009): 1561–85. http://dx.doi.org/10.1142/s0218301309013701.

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Asymptotic expressions for the bound state radial partial wave functions of three-body (nnc) halo nuclei with two loosely bound valence neutrons (n) are obtained in explicit form, when the relative distance between two neutrons (r) tends to infinity and the relative distance between the center of mass of core (c) and two neutrons (ρ) is too small or vice versa. These asymptotic expressions contain a factor that can strongly influence the asymptotic values of the three-body radial wave function in the vicinity of the hyperangle of φ~0 except 0 (r→∞ and ρ is too small except 0) or φ~π/2 except π/2 (ρ→∞ and r is too small except 0) in the configuration space. The derived asymptotic forms are applied to the analysis of the asymptotic behavior of the three-body (nnα) wave function for 6He nucleus obtained by other authors on the basis of multicluster stochastic variational method using the two forms of the αN-potential. The ranges of r (or ρ) from the asymptotical regions are determined for which the agreement between the calculated wave function and the asymptotics formulae is reached. Information about the values of the three-body asymptotic normalization factors is extracted.

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TAMAGNO, Pierre, e Elias VANDERMEERSCH. "Comprehensive stochastic sensitivities to resonance parameters". EPJ Web of Conferences 239 (2020): 13008. http://dx.doi.org/10.1051/epjconf/202023913008.

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Integral experiments in reactors or critical configurations claim to have very small experimental and technological uncertainties. Therefore these latter can be considered valuable experimental information in nuclear data evaluation. Because in the evaluation process the information is carried by model parameters, to perform a rigorous feedback on a nuclear model parameters p - for instance using a measured reactivity ρ-sensitivities S =∂ρ/ρ⁄∂p/p are needed. In usual integral feedbacks, sensitivity to multi-group cross sections are first obtained with deterministic code using perturbation theory. Then these multi-group cross section sensitivities are “convoluted” with parameter sensitivities in order to provide the sensitivity on nuclear model parameter. Recently stochastic approaches have been elaborated in order to obtain continuous cross-section sensitivities thus avoiding the multi-group discretization. In the present work we used the recent Iterated Fission Probability method of the TRIPOLI4 code [1] in order to obtain directly the sensitivity to nuclear physics parameters. We focus here on the sensitivity on resonance parameters and exemplified the method on the computation of sensitivities for 239Pu and 16O resonance parameters one the ICSBEP benchmark PST001. The underlying nuclear model describing resonant cross sections are based in the R-matrix formalism [2] that provides not only the interaction cross sections but also the angular distribution of the scattered neutrons i.e. differential cross sections. The method has thus been updated in order to compute parameter sensitives that include both contributions: cross section and angular distributions. This extension of the method was tested with exact perturbation of angular distribution and fission spectrum.

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Pál, Lénard, e Imre Pázsit. "Stochastic Theory of the Fission Chamber Current Generated by Non-Poissonian Neutrons". Nuclear Science and Engineering 184, n.º 4 (dezembro de 2016): 537–50. http://dx.doi.org/10.13182/nse16-18.

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Semenov, A. A., e C. H. Woo. "Stochastic fluctuations and microstructural evolution during irradiation by neutrons and heavy ions". Journal of Nuclear Materials 205 (outubro de 1993): 74–83. http://dx.doi.org/10.1016/0022-3115(93)90073-8.

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Getmanov, Victor, Vladislav Chinkin, Roman Sidorov, Alexei Gvishiani, Mikhail Dobrovolsky, Anatoly Soloviev, Anna Dmitrieva, Anna Kovylyaeva, Nataliya Osetrova e Igor Yashin. "Low-Pass Filtering Method for Poisson Data Time Series". Applied Sciences 11, n.º 10 (15 de maio de 2021): 4524. http://dx.doi.org/10.3390/app11104524.

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Problems of digital processing of Poisson-distributed data time series from various counters of radiation particles, photons, slow neutrons etc. are relevant for experimental physics and measuring technology. A low-pass filtering method for normalized Poisson-distributed data time series is proposed. A digital quasi-Gaussian filter is designed, with a finite impulse response and non-negative weights. The quasi-Gaussian filter synthesis is implemented using the technology of stochastic global minimization and modification of the annealing simulation algorithm. The results of testing the filtering method and the quasi-Gaussian filter on model and experimental normalized Poisson data from the URAGAN muon hodoscope, that have confirmed their effectiveness, are presented.

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Lamberti, P. W., e C. A. Condat. "Stochastic resonance effects in the scattering of neutrons by modulated two-state systems". Physica A: Statistical Mechanics and its Applications 283, n.º 1-2 (agosto de 2000): 151–55. http://dx.doi.org/10.1016/s0378-4371(00)00143-6.

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Gualdrini, G., R. J. Tanner, S. Agosteo, A. Pola, R. Bedogni, P. Ferrari, V. Lacoste et al. "Analysis of the CONRAD computational problems expressing only stochastic uncertainties: neutrons and protons". Radiation Protection Dosimetry 131, n.º 1 (7 de agosto de 2008): 7–14. http://dx.doi.org/10.1093/rpd/ncn241.

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Mickus, Ignas, Jeremy A. Roberts e Jan Dufek. "APPLICATION OF RESPONSE MATRIX METHOD TO TRANSIENT SIMULATIONS OF NUCLEAR SYSTEMS". EPJ Web of Conferences 247 (2021): 04014. http://dx.doi.org/10.1051/epjconf/202124704014.

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Until recently, reactor transient problems were exclusively solved by approximate deterministic methods. The increase in available computing power made it feasible to approach the transient analyses with time-dependent Monte Carlo methods. These methods offer the first-principle solution to the space-time evolution of reactor power by explicitly tracking prompt neutrons, precursors of delayed neutrons and delayed neutrons in time and space. Nevertheless, a very significant computing cost is associated with such methods. The general benefits of the Monte Carlo approach may be retained at a reduced computing cost by applying a hybrid stochastic-deterministic computing scheme. Among such schemes are those based on the fission matrix and the response matrix formalisms. These schemes aim at estimating a variant of the Greens function during a Monte Carlo transport calculation, which is later used to formulate a deterministic approach to solving a space-time dependent problem. In this contribution, we provide an overview of the time-dependent response matrix method, which describes a system by a set of response functions. We have recently suggested an approach where the functions are determined during a Monte Carlo criticality calculation and are then used to deterministically solve the space-time behaviour of the system. Here, we compare the time-dependent response matrix solution with the transient fission matrix and the time-dependent Monte Carlo solutions for a control rod movement problem in a mini-core reactor geometry. The response matrix formalism results in a set of loosely connected equations which offers favourable scaling properties compared to the methods based on the fission matrix formalism.

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Matijević, Mario, Dubravko Pevec e Krešimir Trontl. "PWR Containment Shielding Calculations with SCALE6.1 Using Hybrid Deterministic-Stochastic Methodology". Science and Technology of Nuclear Installations 2016 (2016): 1–30. http://dx.doi.org/10.1155/2016/7328131.

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The capabilities of the SCALE6.1/MAVRIC hybrid shielding methodology (CADIS and FW-CADIS) were demonstrated when applied to a realistic deep penetration Monte Carlo (MC) shielding problem of a full-scale PWR containment model. Automatic preparation of variance reduction (VR) parameters is based on deterministic transport theory (SNmethod) providing the space-energy importance function. The aim of this paper was to determine the neutron-gamma dose rate distributions over large portions of PWR containment with uniformly small MC uncertainties. The sources of ionizing radiation included fission neutrons and photons from the reactor and photons from the activated primary coolant. We investigated benefits and differences of FW-CADIS over CADIS methodology for the objective of the uniform MC particle density in the desired tally regions. Memory intense deterministic module was used with broad group library “v7_27n19g” opposed to the fine group library “v7_200n47g” used for final MC simulation. Compared with CADIS and with the analog MC, FW-CADIS drastically improved MC dose rate distributions. Modern shielding problems with large spatial domains require not only extensive computational resources but also understanding of the underlying physics and numerical interdependence betweenSN-MC modules. The results of the dose rates throughout the containment are presented and discussed for different volumetric adjoint sources.

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Pierre, Sciora, Garcia Elias, Rimpault Gerald, Droin Jean-Baptiste e Pascal Vincent. "ANALYSIS OF THE SUPERPHENIX START-UP TESTS WITH APOLLO-3: FROM ZERO POWER ISOTHERMAL CONDITIONS TO DYNAMIC POWER TRANSIENT ANALYSIS". EPJ Web of Conferences 247 (2021): 06044. http://dx.doi.org/10.1051/epjconf/202124706044.

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Sodium-cooled Fast Reactors (SFRs) remain a potential candidate to meet future energy needs. In addition, the SFRs experimental feedback is considerable, for instance, the French research program has considered experimental facilities including the Superphénix which has emerged as a transition to commercial deployment. In this paper a set of tests from the Superphénix start-up are reanalyzed with new tools, considering APOLLO-3 and TRIPOLI-4 (respectively deterministic and stochastic codes) for neutron physics evaluation, GERMINAL-V2 for the fuel irradiation behavior and CATHARE-3 for the thermal-hydraulics modelling. Neutron physics evaluations are performed for the main control rod worth and the Doppler Effect, both measured under isothermal conditions at Superphénix start-up. A good agreement is obtained for these tests, which were purely neutronic tests. Next, the core temperature distribution is evaluated at nominal conditions, where larger discrepancies are observed. However, these deviations are related to the measurement of the fuel assemblies, which have a larger than expected uncertainty. Finally a transient, consisting of a negative reactivity insertion, is analyzed to assess the dynamic core behavior. A good agreement is obtained during the reactivity insertion, however the thermal-hydraulic model has to be improved, namely the vessel model, which is considered as a 0-D volume.

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de Camargo, Dayana Q., Bardo E. J. Bodmann, Marco T. de Vilhena, Sergio de Queiroz Bogado Leite e Antonio Carlos Marques Alvim. "A stochastic model for neutrons simulation considering the spectrum and nuclear properties with continuous dependence of energy". Progress in Nuclear Energy 69 (novembro de 2013): 59–63. http://dx.doi.org/10.1016/j.pnucene.2013.05.007.

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Difilippo, F. C. "Correlation between fission neutrons and the calculation of stochastics descriptors application to the 252Cf ratio method". Annals of Nuclear Energy 18, n.º 9 (janeiro de 1991): 503–10. http://dx.doi.org/10.1016/0306-4549(91)90095-f.

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Gommes, Cedric J. "Three-dimensional reconstruction of liquid phases in disordered mesopores usingin situsmall-angle scattering". Journal of Applied Crystallography 46, n.º 2 (14 de março de 2013): 493–504. http://dx.doi.org/10.1107/s0021889813003816.

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Small-angle scattering of X-rays (SAXS) or neutrons is one of the few experimental methods currently available for thein situanalysis of phenomena in mesoporous materials at the mesoscopic scale. In the case of disordered mesoporous materials, however, the main difficulty of the method lies in the data analysis. A stochastic model is presented, which enables one to reconstruct the three-dimensional nanostructure of liquids confined in disordered mesopores starting from small-angle scattering data. This so-called plurigaussian model is a multi-phase generalization of clipped Gaussian random field models. Its potential is illustrated through the synchrotron SAXS analysis of a gel permeated with a critical nitrobenzene/hexane solution that is progressively cooled below its consolute temperature. The reconstruction brings to light a wetting transition whereby the nanostructure of the pore-filling liquids passes from wetting layers that uniformly cover the solid phase of the gel to plugs that locally occlude the pores. Using the plurigaussian model, the dewetting phenomenon is analyzed quantitatively at the nanometre scale in terms of changing specific interface areas, contact angle and specific length of the triple line.

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Brovchenko, Mariya, e Julien Taforeau. "PIN POWER CALCULATION SCHEME FOR REACTOR PRESSURE VESSEL FAST NEUTRON FLUENCE ESTIMATION". EPJ Web of Conferences 247 (2021): 02029. http://dx.doi.org/10.1051/epjconf/202124702029.

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The estimation of the neutron fluence at the Reactor Pressure Vessel (RPV) is classically carried out by a two-step approach. The first step is to estimate the full core neutron source term whether the second step of the calculation consists in the transport of neutrons from the core (source term) to the RPV using the neutron fission distribution determined in the previous step. For this purpose, the neutron fission distribution is to be accurately determined at the fuel pin level for the assemblies on the border of the core. To achieve this goal, two methods are evaluated in this study. The first method considered is a full core 2D Monte Carlo calculation using the MNCP6 code. The second method is based on a deterministic approach using the CASMO5 multi-segment option, allowing a full 2D transport calculation at the pin level with an expected accuracy similar to a stochastic method. The comparison of the two methods shows an overall good agreement with differences within the statistical uncertainty for different cores: homogeneous UOX core, mixed UOX-MOX loading and the effect of the hafnium rods used in the assemblies in the periphery of the core. The modelling limitation and the associated calculational time are discussed for the comparison of the two approaches.

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Mansur, L. K. "Defect reactions and clustering in irradiated solids". Canadian Journal of Physics 68, n.º 9 (1 de setembro de 1990): 887–905. http://dx.doi.org/10.1139/p90-126.

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Irradiation of solid materials with energetic neutrons or charged particles can lead to profound changes in defect structure, microcomposition, and macroscopic properties. Such changes occur by atomic and microstructural mechanisms, some of which are familiar in "classical" physical metallurgy and materials science. However, other cases appear to be unique to irradiation. Irradiation has considerably broadened and indeed provided an entirely new dimension in materials science, since the energetic displacement of atoms potentially reaches to every property or process. The initial damaging events leading to the creation of point defects are generally complete in times of order 10−11 s. Subsequent changes in structure, composition, and properties take place in a span of much longer time scales corresponding to interstitial and vacancy diffusion, clustering, solute segregation, and precipitation. An extensive theoretical framework has been developed to understand the kinetics of these processes. Emphasis has been placed on both steady cumulative processes and on fluctuations, and on the appropriate application of stochastic and deterministic descriptions. Parallel and interactive experimental activities for both applied and basic programs over the past two decades have increased the level of phenomenological knowledge enormously. Much of the work has emphasized either high-dose phenomena such as irradiation-induced swelling, creep, embrittlement, phase instability, and solute segregation relevant to materials applications, or the properties, structures, and interactions of defects, which underlie more fundamental issues.

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N, Yuliana Dian, Soeparmi Soeparmi e Yohannes Sardjono. "Analysis of Safety and Health of Radiation Officer at Pilot Plant BNCT". Indonesian Journal of Physics and Nuclear Applications 2, n.º 1 (28 de fevereiro de 2017): 42. http://dx.doi.org/10.24246/ijpna.v2i1.42-46.

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Radiation is emission energy which derived from the process of transformation of atoms or nuclei unstable. The emission energy was emitted by a hoarse radiation, can cause changes in physical, chemical and biological material in its path so that the radiation worker should give special attention to health and safety during operate the installation using radiation. Limits opportunities for stochastic effects occur, or the risk resulting from the use of radiation that can be accepted by the public, and workers and prevent the occurrence of deterministic result of radiation harm to the individual. Equivalent dose of radiation received by workers or the public should not be beyond Dose Limit Value (NBD). This also applies to the radiation workers who operate tools for cancer therapy method using boron or Boron Neutron Capture Therapy (BNCT). BNCT is a method of new cancer therapies that are being developed, which combines methods of chemotherapy and radiotherapy. BNCT method utilizing <sup>10</sup>B or boron compounds are likely to capture neutrons in thermal energy, which is produced by high - Linear Energy Transfer (LET). Medical examinations for radiation workers should be done regularly and follow the general principles of treatment work, namely the examination before work and after work. Threshold limit radiation exposure was 0.2 to 0.5 Sv. When a person is exposed to radiation overdose, the investigation dosage needs to be done specifically include biological dosimetry.

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Munoz-Cobo, J. L., J. Peña e E. González. "Rossi-α and Feynmann Y functions for non-Poissonian pulsed sources of neutrons in the stochastic pulsing method: Application to subcriticality monitoring in ADS and comparison with the results of Poissonian pulsed neutron sources". Annals of Nuclear Energy 35, n.º 12 (dezembro de 2008): 2375–86. http://dx.doi.org/10.1016/j.anucene.2008.07.012.

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Behringer, K. "Concerning the neutron level and the neutron RMS value in a linear feedback model of point reactor kinetics with one group of delayed neutrons and driven by random reactivity noise: Application of the runge-kutta method to solve a system of stochastic ordinary differential equations". Annals of Nuclear Energy 25, n.º 11 (julho de 1998): 801–20. http://dx.doi.org/10.1016/s0306-4549(97)00087-x.

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Sarotto, Massimo, Gabriele Firpo, Anatoly Kochetkov, Antonin Krása, Emil Fridman, Jerzy Cetnar e Grazyna Domanska. "Neutronic Analyses of the FREYA Experiments in Support of the ALFRED Lead-Cooled Fast Reactor Core Design and Licensing". Journal of Nuclear Engineering and Radiation Science 6, n.º 1 (29 de novembro de 2019). http://dx.doi.org/10.1115/1.4044000.

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Abstract During the EURATOM FP7 project FREYA, a number of experiments were performed in a critical core assembled in the VENUS-F zero-power reactor able to reproduce the ALFRED lead-cooled fast reactor spectrum in a dedicated island. The experiments dealt with the measurements of integral and local neutronic parameters, such as the core criticality, the control rod and the lead void reactivity worth, the axial distributions of fission rates for the nuclides of major interest in a fast spectrum, the spectral indices of important actinides (238U, 239Pu, 237 Np) with respect to 235U. With the main aim to validate the neutronic codes adopted for the ALFRED core design, the VENUS-F core and its characterization measurements were simulated with both deterministic (ERANOS) and stochastic (MCNP, SERPENT) codes, by adopting different nuclear data libraries (JEFF, ENDF/B, JENDL, TENDL). This paper summarizes the main results obtained by highlighting a general agreement between measurements and simulations, with few discrepancies for some parameters that are discussed here. Additionally, a sensitivity and uncertainty analysis was performed with deterministic methods for the core reactivity: it clearly indicates that the small over-criticality estimated by the different codes/libraries resulted to be lower than the uncertainties due to nuclear data.

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Braga, Viviane Vitória Bento, e Tarcísio Passos Ribeiro de Campos. "Dosimetric effectiveness in implants with distinct ho166-seed distributions in a prostate model". Brazilian Journal of Radiation Sciences 7, n.º 2A (19 de fevereiro de 2019). http://dx.doi.org/10.15392/bjrs.v7i2a.603.

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Currently, there is a need to produce new therapeutic techniques for the treatment of prostate tumors, considering the high incidence of the disease and significant morbidity rates associated with surgery and radiotherapy. Simulations in brachytherapy produce essential information about the efficiency and dosimetric efficacy compared to other techniques. This study estimated the efficiency of dosimetry by parameters of merit generated from volumetric distributions of absorbed doses simulating two spatial distributions of Ho-166 seeds in a prostate model. A computer voxel model was developed, using the SISCODES (Computational System for Dosimetry by Neutrons and Photons by Stochastic Methods applied to radiology and radiotherapy) code. The virtual model reproduced a cubic box, filled with muscle equivalent tissue (TE), in which a 5-cm diameter sphere with TE-prostate was positioned 2-cm from the air-interface. Two Ho-166 seed distributions were employed with distinct pitches: 9 and 10 mm, with same distance between seed of 8mm in a fillet (needle). The MCNP5 code generated the energy deposited per unit mass in each voxel .The spatial dose distributions were obtained for each of the seed distributions. The following parameters-of-merit were evaluated: maximum dose values and histograms. The parameters were compared between the two simulated groups. It was possible to evaluate the most appropriate distribution to the prostate brachytherapy, which has been shown to be a function of the injected seed activity.

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Artigos de revistas sobre o tema "Stochastic neutronics"

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