Aegis: An Advanced Lattice Physics Code for Light Water Reactor Analyses

Self Cite

When the transport correction is applied to the total cross-section, the self-scattering cross-section could have a negative value in order to preserve the balance of partial cross-sections. The negative self-scattering cross-section may lead to a negative impact on the convergence behavior for the method of characteristics (MOC), especially in a problem with large moderator regions containing hydrogen. In order to address this issue, the spectral radius of the inner iteration of MOC is theoretically estimated for various self-scattering cross-sections. It is found that the spectral radius of the inner iteration of MOC could exceed unity for a large negative self-scattering cross-section, which results in numerical divergence. A countermeasure for the divergence using the successive over relaxation method is also discussed in this paper.

Section: Estimation Of the Spectral Radiusmentioning

confidence: 99%

Convergence analysis of MOC inner iterations with large negative self-scattering cross-section

Tabuchi

Yamamoto

Endo

et al. 2013

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“…JENDL-4.0 [1,2] and ENDF/B-VII.1 [3]), numerical analysis methods (e.g. MOC assembly calculation [4] followed by the pin-by-pin core analysis [5]), and computer performance contributes to more accurate and precise prediction. Nevertheless, numerical results of core analysis have biases and uncertainties due to various factors: one of the factors is the analytical modeling error (e.g.…”

Section: Introductionmentioning

confidence: 99%

Bias factor method using random sampling technique

Endo

Yamamoto

Watanabe

2016

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Toward the practical use of the bias factor method for actual light water reactor core analyses, the bias factor method using the random sampling technique is newly proposed. The bias factor method is one of the correction methods using information of E/C values in existing measurable systems, to reduce biases and uncertainties of predicted core characteristics parameters. By the aid of the random sampling technique, our proposed bias factor method can be carried out using only forward calculations without any adjoint calculations, and can easily take into account burnup and thermal-hydraulic feedback effects, which are difficult points in the practical application to actual core analyses. Although the statistical error due to the random sampling technique is inevitable in the proposed method, the statistical error can be simply quantified by the resampling technique such as the bootstrap method. As one of the feasibility studies, effectiveness of the proposed method is verified through a numerical experiment which virtually simulates a typical equilibrium pressurized water reactor core. In this verification problem, it is clarified that E/C values of control rod worth at the beginning of cycle under the hot zero power condition are useful information to reduce biases and uncertainties of predicted assembly-wise power distributions during operation of hot full power.

“…The lattice codes treat these low lying resonances by adopting dozens of fine energy groups, which is not sufficient for high accuracy [6,8]. In order to treat the resonances directly by fine energy groups, an ultra-fine-group structure of typically more than 10,000 groups is required [9]. In this work, a new approach has been adopted to accurately treat the low lying resonances below 4 eV, i.e., the resonance integral table has been extended down to 0.3 eV and the background XSs are evaluated for that energy range to compute more accurate effective XSs.…”

Section: Introductionmentioning

confidence: 99%

Resonance self-shielding methodology of new neutron transport code STREAM

Choi

Lee

2015

This paper reports on the development and verification of three new resonance self-shielding methods. The verifications were performed using the new neutron transport code, STREAM. The new methodologies encompass the extension of energy range for resonance treatment, the development of optimum rational approximation, and the application of resonance treatment to isotopes in the cladding region. (1) The extended resonance energy range treatment has been developed to treat the resonances below 4 eV of three resonance isotopes and shows significant improvements in the accuracy of effective cross sections (XSs) in that energy range. (2) The optimum rational approximation can eliminate the geometric limitations of the conventional approach of equivalence theory and can also improve the accuracy of fuel escape probability. (3) The cladding resonance treatment method makes it possible to treat resonances in cladding material which have not been treated explicitly in the conventional methods. These three new methods have been implemented in the new lattice physics code STREAM and the improvement in the accuracy of effective XSs is demonstrated through detailed verification calculations.