Faculty Profiles - YAMAMOTO, Akio

Papers - YAMAMOTO, Akio

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Recent Research Activities on Nuclear Reactor Physics Using the Computational Science

YAMAMOTO Akio

The Proceedings of Mechanical Engineering Congress, Japan Vol. 2020 ( 0 ) page： K08101 2020

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers

<p>Outline of the nuclear reactor core analysis and computational methods used in this analysis are described. Various techniques and approximations are used to perform core analysis with practical computational resources. Recent progress on computer hardware and numerical algorithms enabled us to use more precise and accurate analysis methods.</p>

DOI： 10.1299/jsmemecj.2020.k08101

CiNii Research

A resonance calculation method using energy expansion based on a reduced order model: Use of ultra-fine group spectrum calculation and application to heterogeneous geometry

Kondo R., Endo T., Yamamoto A., Takeda S., Koike H., Yamaji K., Ieyama K., Sato D.

International Conference on Physics of Reactors: Transition to a Scalable Nuclear Future, PHYSOR 2020 Vol. 2020-March page： 152 - 161 2020

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：International Conference on Physics of Reactors: Transition to a Scalable Nuclear Future, PHYSOR 2020

A Resonance calculation using energy Spectral Expansion (RSE) method has been recently proposed in order to efficiently treat complicated heterogeneous geometry and resonance interference effect. In the RSE method, ultra-fine group spectra are generated from ultra-fine group calculations in homogeneous geometry, and the spectra are expanded by the orthogonal basis on energy based on the singular value decomposition. Then the transport calculation for expansion coefficients is numerically performed, and the ultra-fine group spectra in the target heterogeneous regions are reconstructed by the expansion coefficients and the orthogonal basis. In this study, the RSE method is applied to multi-cell geometries including UO2, MOX and water cells, in which the resonance interference effect between UO2 and MOX fuel cells appears. The validity of the RSE method is confirmed through comparison with the reference effective multi-group cross sections obtained from the direct ultra-fine group calculation in the target heterogeneous geometry.

DOI： 10.1051/epjconf/202124702006

Scopus

Experiment of unique combination number due to the third-order neutron-correlation

Endo T., Imai S., Watanabe K., Yamamoto A., Sakon A., Hashimoto K., Yamanaka M., Pyeon C.H.

International Conference on Physics of Reactors: Transition to a Scalable Nuclear Future, PHYSOR 2020 Vol. 2020-March page： 1736 - 1744 2020

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：International Conference on Physics of Reactors: Transition to a Scalable Nuclear Future, PHYSOR 2020

From zero-power reactor noise measurement, the second- and third-order neutron correlation factors Y and y3 can be evaluated by analyzing mean, variance, the third-order central moment of neutron count data. Theoretically, it is expected that the neutron-correlation ratio Y3/Y2 converges to the unique combination number “3” at a near-critical state in an arbitrary system without depending on the fissile material and the neutron-energy spectrum of core, as the neutron counting gate width T increases sufficiently. Thus, the information about the difference between y3/Y2 and “3” has the potential to judge whether a target unknown system is critical or not and to roughly guess the absolute value of subcriticality. In this study, the detector dead-time effect on y3/Y2 is theoretically investigated based on the heuristic method using the single-, pair-, and trio-detection probabilities with the fundamental mode approximation. As a result, it is clarified that the saturation value of y3/Y2 converges to “3” independent of the dead time, when a target system is a critical state. For validation, actual experimental results are presented for a non-multiplication system driven by 252Cf spontaneous source, and shallow and deep subcritical systems at Japanese experimental facilities (UTR-KINKI and KUCA) under the shutdown state. Consequently, it is demonstrated that y3/Y2 shows a significant difference from “3” in the non-multiplication system. In the case of subcritical systems driven by inherent neutron sources, it is confirmed that the ratios y3/Y2 are close to the unique combination number “3,” and the slight difference from “3” is measurable by the long-time reactor noise measurement for the deep subcritical system.

DOI： 10.1051/epjconf/202124709004

Scopus

Estimated criticality lower-limit multiplication factor of low-enriched uranium dioxide-concrete system using the bootstrap method

Hayashi T., Nishioka F., Endo T., Yamamoto A.

International Conference on Physics of Reactors: Transition to a Scalable Nuclear Future, PHYSOR 2020 Vol. 2020-March page： 2690 - 2697 2020

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：International Conference on Physics of Reactors: Transition to a Scalable Nuclear Future, PHYSOR 2020

The present paper aims to evaluate the estimated criticality lower-limit multiplication factor of fuel debris in a form of uranium dioxide-concrete mixture for a study of criticality control on the fuel debris generated through the molten core concrete interaction in a severe accident of a light water reactor. The estimated criticality lower-limit multiplication factor is evaluated using the bootstrap method where the assumption of the normal distribution is not necessary. In addition, it is calculated taking into account correlation coefficients that represent the degrees of neutronic similarity between the target system and benchmark critical experiment systems, experimental uncertainties of benchmark data, and statistical uncertainties of calculated effective multiplication factor by a continuous energy Monte Carlo code. This paper shows that the estimated criticality lower-limit multiplication factor using the bootstrap method can be comparable with a baseline upper-subcritical-limit which is evaluated by Whisper-1.1 without margins of subcriticality for uncertainties from nuclear covariance data and undetected errors in software.

DOI： 10.1051/epjconf/202124717001

Scopus

Development of FRENDY nuclear data processing code: Generation capability of multi-group cross sections from ace file

Yamamoto A., Endo T., Tada K.

Transactions of the American Nuclear Society Vol. 122 page： 714 - 717 2020

Application of bootstrap method to estimated criticality lower-limit multiplication factor considering nuclear data-induced uncertainty

Hayashi T., Endo T., Yamamoto A.

Transactions of the American Nuclear Society Vol. 122 page： 458 - 461 2020

Loading pattern optimization for a PWR using Multi-Swarm Moth Flame Optimization Method with Predator Reviewed

Ishiguro Satomi, Endo Tomohiro, Yamamoto Akio

JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY 2019.12

Development of a reduced order model for severe accident analysis codes by singular value decomposition aiming probabilistic safety margin analysis Reviewed

Matsushita Masaki, Endo Tomohiro, Yamamoto Akio

JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY 2019.12

Track 1: Severe Accident Phenomena, Fukushima Accident Analysis

Journal of the Society of Mechanical Engineers Vol. 122 ( 1211 ) page： 10 - 12 2019.10

APPLICATION OF THE FOREST SHIELDING FACTOR TO THE MAXIMUM-LIKELIHOOD EXPECTATION MAXIMIZATION METHOD FOR AIRBORNE RADIATION MONITORING Reviewed

Sasaki M., Sanada Y., Yamamoto A.

RADIATION PROTECTION DOSIMETRY Vol. 184 ( 3-4 ) page： 400-404 2019.10

Transport consistent diffusion coefficient for CMFD acceleration and comparison of convergence properties

Yamamoto Akio, Endo Tomohiro, Giho Akinori

JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY Vol. 56 ( 8 ) page： 716 - 723 2019.8

A simple treatment of increased gap due to fuel assembly bowing through correction of cross sections

Yamamoto Akio, Endo Tomohiro, Nagano Hiroaki, Ohoka Yasunori, Yamamoto Kento

JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY Vol. 56 ( 6 ) page： 471 - 478 2019.6

Development of assembly bowing model for pin-by-pin core calculations

Yamamoto K., Ohoka Y., Nagano H., Yamamoto A., Endo T.

International Conference on Nuclear Engineering, Proceedings, ICONE Vol. 2019-May 2019.5

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：International Conference on Nuclear Engineering, Proceedings, ICONE

Calculation capability of the pin-power distribution considering the variation of the assembly gap size due to assembly bowing was implemented in the pin-by-pin core calculation code SCOPE2. The previous studies show that the perturbation of geometry can be treated by the perturbation of macroscopic cross-section or atomic number density of the region instead of explicit consideration of geometry deformation. This methodology was applied to the assembly gap region: the variation of the gap size was treated by the correction on the macroscopic cross-section of the gap water. The correction model for the cross-section of gap water was implemented in SCOPE2 since it treats pin-by-pin cross-sections in a transport calculation. The correction was made according to the variation in the gap size. This implemented model has an advantage that the modification of the cross-section tables used in the core calculation is not necessary to consider the variation of gap size. For single assembly and multi-assemblies geometries, the assembly bowing model implemented in SCOPE2 was verified by comparing with the reference results using the assembly calculation code AEGIS, where the gap size perturbation was explicitly considered by varying the geometry of the gap region. It was confirmed that the variation of pin-power distribution due to the assembly bowing can be appropriately treated by SCOPE2 with the assembly bowing model.

Scopus

Experimental validation of unique combination numbers for third- and fourth-order neutron correlation factors of zero-power reactor noise Open Access

Endo Tomohiro, Yamamoto Akio, Yamanaka Masao, Pyeon Cheol Ho

JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY Vol. 56 ( 4 ) page： 322 - 336 2019.4