Applicability of the Diffusion and Simplified P3 Theories for Pin-by-Pin Geometry of BWR

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In this paper, the neutron current interpolation (NCI) method is proposed to treat the staggered mesh on the basis of the Simplified P3 (SP3) theory code. In the NCI method, the response matrix formulation is applied to the SP3 theory code, and neutron partial currents at assembly boundary are interpolated using low-order polynomial functions, i.e., flat, linear or quadratic function. The pin-by-pin fine-mesh core analysis method is considered as a candidate next-generation core calculation method for BWR. Since the number of fuel rods in BWR assembly is increased with the higher burn-up, the different types of assembly may be adjacent in a BWR core. Therefore, when the cell-homogenized pin-by-pin analysis method is applied to the BWR core analysis, it must have a capability to treat the staggered mesh. Our previous study indicates that the SP3 theory is appropriate for pin-by-pin BWR calculations. However, the SP3 theory code that can treat the staggered mesh has not been developed so far. For these reasons, the treatment method of the staggered mesh is investigated to develop such SP3 theory code. The performances of the NCI method are evaluated through comparison with the cell-heterogeneous detailed transport calculations by the method of characteristics (MOC). Two-dimensional, 2 Â 2 multi-assembly geometries are used to compare the prediction accuracy of the NCI method. The 2 Â 2 multi-assembly geometries consist of 9 Â 9 UO 2 and 10 Â 10 MOX fuel assemblies. The calculation results indicate that the prediction accuracy of the NCI method is similar to that of the detailed transport calculation method.

Section: Calculation Resultssupporting

confidence: 76%

Section: Calculation Resultsmentioning

confidence: 73%

Treatment of Staggered Mesh for BWR Pin-by-Pin Core Analysis

Tada

Yamamoto

Yamane

2009

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“…Recently, as a next generation core analysis method, the pin-by-pin fine mesh core calculation method for BWR core analysis has been studied [7,8]. The previous study indicates that the pin-by-pin approach for BWR core analysis has good accuracy to evaluate important parameters for highly heterogeneous cores (e.g., mixed-oxide (MOX) or high-burnup fuel loaded core).…”

Section: Introductionmentioning

confidence: 99%

“…In order to capture significant variation on energetic distribution of neutron spectrum in BWR fuel assemblies or in highly heterogeneous cores and to obtain higher prediction accuracy, utilization of finer energy group structure in core calculations is desirable. For example, eight-or nine-group structure is used in the previous study of the pin-by-pin approach for light water reactor core analysis [7][8][9]. However, even if we utilize such finer energy group structure, the spectral interference effect on the energy collapsing should be still taken into account and several correction techniques considering this effect are necessary.…”

Section: Introductionmentioning

confidence: 99%

A new technique for spectral interference correction on pin-by-pin BWR core analysis

Fujita

Endo

Yamamoto

2014

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A new correction technique to capture the spectral interference effect on collapsed cross sections, which focuses on application to the pin-by-pin boiling water reactor (BWR) core analysis, is proposed. The spectral interference effect, which is caused by adjacent loadings of different types of fuel assemblies, has relationship with variations of neutron leakage in each pin-cell from the viewpoint of neutron balance. Variation of neutron leakage affects neutron spectrum and thus the neutron leakage is considered to be important to correct coarse-group cross sections used in core calculations. We focus on the neutron leakage in each pin-cell and use it as a correction index (i.e., a leakage index (LI)), which is defined as the volume-averaged neutron leakage in a pin-cell. By utilizing the leakage index, we represent the variations of coarse-group cross sections as the linear combination of LIs. In order to verify and discuss the applicability of the present correction technique, two-dimensional benchmark calculations considering typical characteristics of BWR cores are carried out. From the calculation results, the present correction technique well reproduces the reference coarse-group cross sections and improves the calculation accuracies.

“…Recently, a pin-by-pin approach is studied and is applied for BWR core calculations as a candidate of the next generation core analysis methods [5][6][7][8]. However, the number and the structure of energy groups, which are suitable for the pin-by-pin core analysis, have not been extensively investigated yet.…”

Section: Introductionmentioning

confidence: 99%

An optimization approach to establish an appropriate energy group structure for BWR pin-by-pin core analysis

Fujita

Tada

Endo

et al. 2012

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An optimization approach to establish an appropriate multi-group energy structure for boiling water reactor (BWR) pin-by-pin fine mesh core analysis is proposed. In the present approach, the number of energy groups of cross sections is successively reduced or increased. In order to select an energy group boundary that is removed or added, performances of all possible candidates of energy group structures are tested in multi-assembly geometries. Then, the energy group boundary, which provides the minimum difference of the k-infinity or the pin-by-pin fission rate distribution, is finally removed or added. This procedure is repeated until the number of energy groups reaches to the target value. In order to confirm the applicability of the present approach, the accuracies of the k-infinity and the pin-by-pin fission rate distribution are investigated in various 2 6 2 multi-assembly geometries with the established energy group structure. From the verification results, the differences of the k-infinity and the pin-by-pin fission rate distribution between the reference (fine) and the established (coarse) energy group structure are small in the various 2 6 2 multiassembly geometries. Therefore, we can conclude that the present approach is efficient to establish an appropriate energy group structure for BWR pin-by-pin fine mesh core analysis.