Fission Source Convergence of Monte Carlo Criticality Calculations in Weakly Coupled Fissile Arrays.

Yamamoto, Toshihiro; Nakamura, T.; Miyoshi, Y.

doi:10.3327/jnst.37.41

Cited by 11 publications

(12 citation statements)

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“…The anomalies in Ref. 5 were reproduced, but results with collision sites as potential source sites were much worse than those using absorption sites. The fourth group is a set of VIM computations modeling a hypothetical large three-dimensional thermal reactor, both in a homogenized form and with a plate structure.…”

Section: Methods and Test Problemsmentioning

confidence: 93%

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Alternative Implementations of the Monte Carlo Power Method

Blomquist

Gelbard

2002

Nuclear Science and Engineering

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We compare nominal efficiencies, i.e. variances in power shapes for equal running time, of different versions of the Monte Carlo eigenvalue computation, as applied to criticality safety analysis calculations. The two main methods considered here are "conventional" Monte Carlo and the superhistory method, and both are used in criticality safety codes. Within each of these major methods, different variants are available for the main steps of the basic Monte Carlo algorithm. Thus, for example, different treatments of the fission process may vary in the extent to which they follow, in analog fashion, the details of real-world fission, or may vary in details of the methods by which they choose next-generation source sites. In general the same options are available in both the superhistory method and conventional Monte Carlo, but there seems not to have been much examination of the special properties of the two major methods and their minor variants. We find, first, that the superhistory method is just as efficient as conventional Monte Carlo and, secondly, that use of different variants of the basic algorithms may, in special cases, have a surprisingly large effect on Monte Carlo computational efficiency. v

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Section: Methods and Test Problemsmentioning

confidence: 93%

“…The problem geometry is depicted in Figure 1 (in our case with T 1 = 35 and T c = 30), and it seems that the simplest way to describe the problem is to quote Ref. 5, as we do below.…”

Section: Jaeri Two-core Criticality Safety Problemmentioning

confidence: 99%

Alternative Implementations of the Monte Carlo Power Method

Blomquist

Gelbard

2002

Nuclear Science and Engineering

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“…8) To obtain the symmetric distribution, the weight adjustment method described by Yamamoto 8) is preferable for an ordinary Monte Carlo calculation. However we did not use this method in our investigation, because the method improves the asymmetry of the distribution of a neutron source, and does not improve the asymmetry of the fission matrix elements expressed by the fractional term of Eq.…”

Section: As Shown Inmentioning

confidence: 99%

Evaluation of Eigenvalue Separation by the Monte Carlo Method

Kitada

Takeda

2002

Journal of Nuclear Science and Technology

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A new technique for evaluating an eigenvalue separation by the Monte Carlo method is proposed. This technique uses a fission matrix evaluated by an ordinary Monte Carlo calculation and enables us to evaluate higher order eigenvalues and eigenvectors that have not been able to be determined by Monte Carlo calculation. To validate it, the proposed technique was applied to the analysis of the modeled BWR core and the coupled-core reactor assembled at the C-core tank of KUCA (Kyoto University Critical Assembly). Consequently, it was found that this new technique gave good results regarding eigenvalue separation, although regional division needs to be noted in a system for evaluating a fission matrix.

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“…There have been a number of studies on fission source convergence by Monte Carlo methods. [1][2][3] These studies revealed difficulties in Monte Carlo criticality calculations in loosely-coupled arrays of fissionable material units in which each unit scarcely interacts with other units. This situation is often encountered in criticality safety analyses for nuclear fuel facilities.…”

Section: Introductionmentioning

confidence: 99%

Reliable Method for Fission Source Convergence of Monte Carlo Criticality Calculation with Wielandt's Method

Yamamoto

Miyoshi

2004

J. Nucl. Sci. Technol.

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A new algorithm of Monte Carlo criticality calculations for implementing Wielandt's method, which is one of acceleration techniques for deterministic source iteration methods, is developed, and the algorithm can be successfully implemented into MCNP code. In this algorithm, part of fission neutrons emitted during random walk processes are tracked within the current cycle, and thus a fission source distribution used in the next cycle spread more widely. Applying this method intensifies a neutron interaction effect even in a loosely-coupled array where conventional Monte Carlo criticality calculation methods have difficulties, and a converged fission source distribution can be obtained with fewer cycles. Computing time spent for one cycle, however, increases because of tracking fission neutrons within the current cycle, which eventually results in an increase of total computing time up to convergence. In addition, statistical fluctuations of a fission source distribution in a cycle are worsened by applying Wielandt's method to Monte Carlo criticality calculations. However, since a fission source convergence is attained with fewer source iterations, a reliable determination of convergence can easily be made even in a system with a slow convergence. This acceleration method is expected to contribute to prevention of incorrect Monte Carlo criticality calculations.

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Fission Source Convergence of Monte Carlo Criticality Calculations in Weakly Coupled Fissile Arrays.

Cited by 11 publications

References 0 publications

Alternative Implementations of the Monte Carlo Power Method

Alternative Implementations of the Monte Carlo Power Method

Evaluation of Eigenvalue Separation by the Monte Carlo Method

Reliable Method for Fission Source Convergence of Monte Carlo Criticality Calculation with Wielandt's Method

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