Results 1 - 10 of 10840
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[en] In the Matrix MOC a linear algebraic equation system can be constructed by sweeping only once, and then solving the linear system takes the place of repeatedly characteristics sweeping. Traditionally, k_e_f_f is computed by power iteration (PI), whose convergence rate depends on the dominance ratio deeply. Large problems of practical interest often have dominance ratios close to 1, leading to slow convergence of PI. Combined with multi-group GMRES coupling all groups directly, Wielandt iteration is studied for accelerating Matrix MOC. Numerical results of several benchmarks demonstrate that Wielandt iteration combined with multi-group GMRES can obtain good accuracy and higher efficiency compared with PI. (authors)
[en] Full core calculations by ordinary transport methods can demand considerable computational time, hardly acceptable in the industrial work frame. However, the trend of next generation nuclear cores goes toward more heterogeneous systems, where transport phenomena of neutrons become very important. On the other hand, using diffusion solvers is more practical allowing faster calculations, but a specific formulation of the diffusion coefficient is requested to reproduce the scalar flux with reliable physical accuracy. In this paper, the Ronen method is used to evaluate numerically the diffusion coefficient in the slab reactor. The new diffusion solution is driven toward the solution of the integral neutron transport equation by non linear iterations. Better estimates of currents are computed and diffusion coefficients are corrected at node interfaces, still assuming Fick's law. This method enables obtaining closer results to the transport solution by a common solver in multigroup diffusion. (author)
[en] Highlights: • Picard iteration with Discrete Generalized Multigroup found to be unstable in general. • Krasnoselskij (relaxation) iteration scheme yields improved stability. • Informed choice of group map improves convergence behavior. • Better performance observed with larger number of groups. - Abstract: This paper investigates the stability of the recondensation procedure of the Discrete Generalized Multigroup method and proposes alternatives to improve stability of the original formulation. Instabilities are shown to happen when employing a simple Picard fixed point iteration and an ill-informed group mapping scheme. This work presents a mapping procedure that improves stability of the original method for fine group calculations. Additionally, a relaxation scheme, Krasnoselskij iteration, is introduced to the fixed point iteration to further improve the stability characteristics and remove the need for fine group flux updates. Both improvements are applied on heterogeneous problems using the SHEM361 and the NG2042 group structures. The results indicate improved stability from a well-informed group mapping and demonstrate the possibility of eliminating the need for fine group flux updates
[en] New method to calculate equi-probability bins from Legendre expansion scattering cross-sections is proposed. The method uses correction of equi-probability bins boundaries to provide conservation of the first angular moment. CRSRD-ST code is developed to reformat cross sections from DTF to ACE format using proposed technique. Numerical results show that the proposed method significantly improves agreement between deterministic and Monte-Carlo calculations. (authors)
[en] The European Electronic Toll Service (EETS) was created in 2004 with the aim of ensuring interoperability among the existing electronic toll collection (ETC) systems in Europe. However, the lack of cooperation between groups of stakeholders has not made possible to achieve this goal ten years later. The purpose of this research is to determine the better way to achieve interoperability among the different ETC systems in Europe. Our study develops a review of the six main ETC systems available worldwide: Automatic Number Plate Recognition (ANPR), Dedicated Short-Range Communications (DSRC), Radio Frequency Identification (RFID), Satellite systems (GNSS), Tachograph, and Mobile communications tolling systems. The research also provides some insight on different emerging technologies. By focusing on different operational and strategic aspects offered by each technology, we identify their main strengths, weaknesses, opportunities and threats and makes different recommendations to improve the current framework. The research concludes that given the diversity of advantages and inconveniences offered by each system, the selection of a certain ETC technology should also take into account its potential to overcome the weaknesses in the current ETC framework. In this line, different policy recommendations are proposed to improve the present ETC strategy at the EU. (Author)
[en] The paper discusses the advantages and shortcomings of alternate double single track (ADST) lines with respect to double track lines for high speed lines. ADST lines consists of sequences of double and single track segments optimally selected in order to reduce the construction and maintenance costs of railway lines and to optimize the timetables used to satisfy a given demand. The single tracks are selected to coincide with expensive segments (tunnels and viaducts) and the double tracks are chosen to coincide with flat areas and only where they are necessary. At the same time, departure times are adjusted for trains to cross at the cheap double track segments. This alternative can be used for new lines and also for existing conventional lines where some new tracks are to be constructed to reduce travel time (increase speed). The ADST proposal is illustrated with some examples of both types (new lines and where conventional lines exist), including the Palencia-Santander, the Santiago-Valparaíso-Viña del Mar and the Dublin-Belfast lines, where very important reductions (90 %) are obtained, especially where a railway infrastructure already exist. (Author)
[en] The 3-D steady-state SN neutron-gamma transport theory code ATES3 developed at BARC can be utilized for external source problems such as shielding analysis. A brief description on the use of ATES3 and its validation for international shielding type benchmarks problems is presented in the paper. (author)
[en] Highlights: •A modified α − k power iteration method is presented for computing the time-eigenvalue. •It is not required to provide the initial values of α for the modified method. •Computational experiences validate the validity and efficiency of the new method. -- Abstract: A modified α − k power iteration method is presented for the prediction of time-eigenvalue(α) of the neutron transport equation. By developing a direct relationship between K-eigenvalue and α-eigenvalue, a new formula is introduced to estimate the value of α. Compared with the conventional method, it is not required to provide the initial values of α for the modified method. Since it is always difficult to guess the suitable initial values, the modified method is more convenient for solving time-eigenvalue problems. Computational experiences show that the accuracy of the modified method is the same as the conventional method.
[en] The NJOY Nuclear Data Processing System, version 2016, is a comprehensive computer code package for producing pointwise and multigroup cross sections and related quantities from evaluated nuclear data in the ENDF-4 through ENDF-6 legacy card-image formats. NJOY works with evaluated files for incident neutrons, photons, and charged particles, producing libraries for a wide variety of particle transport and reactor analysis codes.
[en] SGRD (Spectroscopy, Gamma rays, Rapid Deterministic) code is used to infer the dimensions of a one-dimensional model of a shielded gamma ray source. The method is based on the simulation of the un-collided leakage current of discrete gamma lines that are produced by nuclear decay. Experimentally, the unscattered gamma lines leakage current is obtained by processing high precision gamma spectroscopy measurements. The material thicknesses are computed with SGRD using a fast ray-tracing algorithm embedded in a non-linear multidimensional iterative optimization procedure that minimizes the error metric between calculated and measured signatures. For verification, numerical results on a test problem are presented. The test problem is a spherical natural shell surrounded by polyethylene (CH2) and an aluminium cover. The gamma source is due to uranium radioactive decay and 5 characteristic lines are chosen for the optimization. The comparison between the initial and the optimized gamma line spectra with measurement simulated by direct transport calculation shows that the optimization method works well