Results 1 - 10 of 48
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[en] Neutron moderation properties from the cold mesitylene moderator have been studied. The Kyoto University Accelerator driven Neutron Source (KUANS) has been used for these experiments. In KUANS neutrons are produced by 9Be(p,n)9B reaction using a pulsed 3.5 MeV proton beam. The neutrons are moderated by the polyethylene. The container of the mesitylene moderator is situated in front of the polyethylene moderator and the change of the time of flight spectrum has been recorded as a function of the temperature of the mesitylene moderator. By fitting the Maxwell distribution to the obtained TOF spectra, the neutron temperature corresponding to the mesitylene temperature (from room temperature to 28 K) has been estimated. Measured neutron spectra have changed corresponding to the mesitylene temperature. As the mesitylene temperature decreases, the peak of the neutron spectrum shifts to longer wavelength side
[en] Investigation of the unexplained changes of neutron flux fluctuation magnitudes observed in KWU-built PWRs has drawn attention to long known but still incompletely understood spatial correlation patterns of the neutron flux fluctuations in the frequency range 0-2 Hz. These patterns, namely an out-of-phase behavior of signals from oppositely located core quadrants and an in-phase behavior of signals from axially aligned locations, are the dominant fluctuation phenomena because the range 0-2 Hz carries more than 95 % of the power of the signal fluctuations and the coherence functions of respective signal pairings have values between 0.5 and 1.0 in this frequency range. Therefore, finding the mechanism effecting the measured fluctuation patterns is believed to be key to explain the changes of the fluctuation amplitudes.
[en] The effect for different types of scattering on the critical half thickness in slab geometry for one speed neutron transport equation is studied for isotropic, linearly anisotropic and quadratic anisotropic scatterings. An extensive numerical survey is carried out for the critical thickness in order to provide the effect of the different scattering types. The numerical results are obtained by P, T and U methods. The P method is the Legendre polynomial solution that is accepted as the exact result for the neutron transport theory calculations and the U and T methods are the types of Chebyshev polynomials. Critical thickness values are calculated by using Mark boundary condition. Results are compared with the literature.
[en] The ODETTA calculation code and a comparative analysis of the program simulation with using of MPI principles as well as the possibility of applying MPI technology to speed up the calculation code are considered in the paper. The development of the ODETTA program algorithmic part with MPI using is described. Features and specifics of this program parallelizing are presented. The modification of the calculation code is given
[ru]В работе рассматриваются программа ODETTA и сравнительный анализ работы программы с применением принципов MPI, а также возможности применения этой технологии для ускорения расчетного кода. Описана разработка алгоритмической части программы ODETTA с использованием MPI. Представлены особенности и специфика распараллеливания данной программы, приведена модификация расчетного кода, рассмотрены соответствующие программные алгоритмы
[en] The problem of unfolding measured Bonner sphere data to derive a neutron spectrum is outlined and the use of a priori information, derived either from neutron transport calculations or measurements with other instruments, is discussed. Examples are given of cases where this a priori information greatly increases the confidence in the final spectrum. Neutron transport calculations can also help in understanding Bonner sphere measurements in particular if unexpected features are seen. (author)
[en] Presented here is an extension of the spectral Green’s function-constant nodal (SGF-CN) method for the numerical solution of energy multigroup, fixed-source, discrete ordinates (SN) problems in X, Y geometry with arbitrary L'th-order of scattering anisotropy, provided L
[en] The telegrapher's theory was used to develop a new formulation for the neutron noise equation. Telegrapher's equation is supposed to demonstrate a more realistic approximation for neutron transport phenomena, especially in comparison to the diffusion theory. The physics behind such equation implies that the signal propagation speed is finite, instead of the infinite as in the case of ordinary diffusion. This paper presents the theory and results of the development of a new method for calculation of the neutron noise using the telegrapher's equation as its basis. In order to investigate the differences and strengths of the new method against the diffusion based neutron noise, a comparison was done between the behaviors of two methods. The neutron noise based on SN transport considered as a precision measuring point. The Green's function technique was used to calculate the neutron noise based on telegrapher's and diffusion methods as well as the transport. The amplitude and phase of Green's function associated with the properties of the medium and frequency of the noise source were obtained and their behavior was compared to the results of the transport. It was observed, the differences in some cases might be considerable. The effective speed of propagation for the noise perturbations were evaluated accordingly, resulting in considerable deviations in some cases.
[en] A new approach for the application of the coarse-mesh Modified Spectral Deterministic method to numerically solve the two-dimensional neutron transport equation in the discrete ordinates (𝑺𝑵) formulation is presented in this work. The method is based on within node general solution of the conventional one-dimensional 𝑺𝑵 transverse integrated equations considering constant approximations for the transverse leakage terms and obtaining the 𝑺𝑵 spatial balance equations. The discretized equations are solved by using a modified Source Iteration scheme without additional approximations since the average angular fluxes are computed analytically in each iteration. The numerical algorithm of the method presented here is algebraically simpler than other spectral nodal methods in the literature for the type of problems we have considered. Numerical results to two typical model problems are presented to test the accuracy of the offered method. (author)
[en] In this paper, we propose a new deterministic numerical methodology to solve the one-dimensional linearized Boltzmann equation applied to neutron shielding problems (fixed-source), using the transport equation in the discrete ordinates formulation (SN) considering the multigroup theory. This is a hybrid methodology, entitled Modified Spectral Deterministic Method (SDM-M), that derives from the Spectral Deterministic Method (SDM) and Diamond Difference (DD) methods. This modification in the SDM method aims to calculate neutron scalar fluxes with lower computational cost. Two model-problems are solved using the SDM-M, and the results are compared to the coarse-mesh methods SDM, Spectral Green's Function (SGF) and Response Matrix (RM), and the fine-mesh method DD. The numerical results were obtained in the programming language JAVA version 1.8.091. (author)