Faculty Profiles - YAMAMOTO, Akio

Papers - YAMAMOTO, Akio

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Estimation of sensitivity coefficient based on lasso-type penalized linear regression

Katano Ryota, Endo Tomohiro, Yamamoto Akio, Tsujimoto Kazufumi

JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY Vol. 55 ( 10 ) page： 1099 - 1109 2018

Radially and azimuthally dependent resonance self-shielding treatment for general multi-region geometry based on a unified theory

Koike Hiroki, Kirimura Kazuki, Yamaji Kazuya, Kosaka Shinya, Yamamoto Akio

JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY Vol. 55 ( 1 ) page： 41 - 65 2018

Dimension-reduced cross-section adjustment method based on minimum variance unbiased estimation

Yokoyama Kenji, Yamamoto Akio, Kitada Takanori

JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY Vol. 55 ( 3 ) page： 319 - 334 2018

Estimation of Sensitivity Coefficient based on Lasso-type Penalized Linear Regression Reviewed

R. Katano, T. Endo, A. Yamamoto, K. Tsujimoto

JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY Vol. 55 page： 1099-1109 2018

Utilization of Region-wise Even-Parity Discontinuity Factor to Reduce Discretization Error of MOC Reviewed

A. Yamamoto, A. Giho, T. Endo

Nuclear Science and Engineering Vol. 193 page： 253-268 2018

Flux Region Assignment Method using Ray Trace Information for the Method of Characteristics to Improve Cache Efficiency

A. Yamamoto, A. Giho, T. Endo

Nuclear Science and Engineering Vol. 192 page： 243-250 2018

Flux Region Assignment Method Using Ray Trace Information for the Method of Characteristics to Improve Cache Efficiency

Yamamoto Akio, Giho Akinori, Endo Tomohiro

NUCLEAR SCIENCE AND ENGINEERING Vol. 192 ( 3 ) page： 240 - 253 2018

Symposium Report on ASRAM2017

Yamaguchi Akira, Yamamoto Akio, Narumiya Yoshiyuki

Journal of the Atomic Energy Society of Japan Vol. 60 ( 6 ) page： 362 - 363 2018

Research and development roadmap for reactor physics 2017:future of reactor physics projected by next generations

Yamamoto Akio, Chiba Go, Kirimura Kazuki, Miki Yosuke, Yokoyama Kenji

Journal of the Atomic Energy Society of Japan Vol. 60 ( 4 ) page： 241-245 2018

Surrogate model of severe accident analysis code for SBO aiming probabilistic safety margin analysis

Matsushita M., Endo T., Yamamoto A.

Transactions of the American Nuclear Society Vol. 119 page： 900 - 903 2018

Cache efficient flux region assignment for the method of characteristics

Yamamoto A., Giho A., Endo T.

International Conference on Physics of Reactors, PHYSOR 2018: Reactor Physics Paving the Way Towards More Efficient Systems Vol. Part F168384-2 page： 788 - 799 2018

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：International Conference on Physics of Reactors, PHYSOR 2018: Reactor Physics Paving the Way Towards More Efficient Systems

A flux region assignment algorithm to increase cache efficiency for the method of characteristics is proposed. In order to minimize the stride of memory access, flux region IDs are assigned based on the ray trace sequence during the method of characteristics calculation. The present method is implemented in the three-dimensional transport code GENESIS and its performance is confirmed through verification calculations ranging from single PWR fuel assembly to PWR full core benchmark problems. The present method can reduce computational time by improving cache efficiency while suppressing memory requirement.

Scopus

Development of reduced order model of severe accident analysis code for probabilistic safety margin analysis

Matsushita M., Endo T., Yamamoto A., Kitao T.

International Conference on Physics of Reactors, PHYSOR 2018: Reactor Physics Paving the Way Towards More Efficient Systems Vol. Part F168384-5 page： 3042 - 3053 2018

For probabilistic safety margin analysis, we developed a reduced order model (ROM) that reconstruct calculation results of typical severe accident progressions obtained by the severe accident analysis code, MAAP. The ROM is applied for fast reconstruction of time series plant parameters (e.g., pressure and temperature) obtained by the MAAP code. The ROM is applied to two severe accident scenarios, i.e., the station black out (SBO) with loss of all feed water capabilities and the large break loss of coolant accident (large break LOCA) without the emergency core cooling system (ECCS) capability. Verification results indicate that the ROM reasonably reproduces temporal variation of plant parameters with a few bases obtained by the ROM, which enables very fast reconstruction of complicated accident progression of a severe accident.

Scopus

Development of the uncertainty quantification method of activation in reactor structures using reduced-order modeling

Yokoi K., Endo T., Yamamoto A., Hayashi K., Mizuno R., Kimura Y.

International Conference on Physics of Reactors, PHYSOR 2018: Reactor Physics Paving the Way Towards More Efficient Systems Vol. Part F168384-3 page： 1793 - 1804 2018

Uncertainty quantification of activation in structure materials around a nuclear reactor is important for efficient planning of decommissioning. In order to quantify the uncertainty of activation in reactor structures, neutron shielding calculations are necessary. Since the neutron shielding calculation is performed for spatially large regions around a reactor, it requires a lot of computation time especially in the case of multi-dimensional geometry. In this study, the reduced-order modeling (ROM) is applied to the sensitivity and uncertainty analysis of activation in reactor structures to reduce computation time. The ROM can reduce calculation cost for evaluation of sensitivity coefficients by identifying important or sensitive subspace (active subspace, AS) in input data. In this study, an AS is constructed by the several sensitivity coefficients in reactor structures which are evaluated by the perturbation theory (PT). Sensitivity coefficients of activation throughout reactor structures are estimated using the AS and the uncertainty of activation is evaluated by the "sandwich formula." The calculation results indicate that the uncertainty of the activation in reactor structures can be reproduced with low calculation cost (approximately 30 neutron transport calculations) using the ROM in one-dimensional geometry of a 500 MWe class BWR.

Scopus

Estimation of region-wise even-parity discontinuity factor for MOC through iterative procedure

Yamamoto A., Giho A., Endo T.

International Conference on Physics of Reactors, PHYSOR 2018: Reactor Physics Paving the Way Towards More Efficient Systems Vol. Part F168384-3 page： 1892 - 1903 2018

To reduce angular and spatial discretization error of MOC with a coarse calculation condition, region-wise even-parity discontinuity factor (EPDF) for transport calculations is evaluated through an iterative procedure using only region-wise scalar flux, i.e., without odd parity angular flux, partial-, or net-current at region boundary. Region-wise EPDF is evaluated in a single assembly geometry with reflective boundary condition. The evaluated EPDFs are applied to a 2x2 colorset assembly configuration and its performance is compared to the conventional superhomogenization (SPH) method. The calculation results indicate that 1) no convergence issue is observed during the iteration process to estimate EPDF, 2) performance of the region-wise EPDF is better than that of the conventional SPH method.

Scopus

Estimation of subcriticality in dollar units based on integral method for arbitrary state-change in subcritical system

Nonaka A., Endo T., Yamamoto A.

Transactions of the American Nuclear Society Vol. 119 page： 1112 - 1115 2018

Estimation of subcriticality in dollar units using integral method for subcritical system

Nonaka A., Endo T., Yamamoto A.

International Conference on Physics of Reactors, PHYSOR 2018: Reactor Physics Paving the Way Towards More Efficient Systems Vol. Part F168384-5 page： 3271 - 3282 2018

A subcriticality measurement method using the integral method is developed for any stepwise transient. The integral method usually applied to a negative reactivity insertion using the rod-drop and the source-jerk methods. In this study, it is clarified that the integral method can be applied to measure positive reactivity insertion. During refueling of a reactor, not only reactivity but also neutron source intensity and neutron generation time simultaneously change. In order to accurately monitor the subcriticality under these conditions, variations of these parameters must be taken into consideration. Therefore, a subcriticality measurement method is developed, which is applicable to not only variation of reactivity but also simultaneous variations of neutron source intensity and neutron generation time. Furthermore, the present method utilizes only measurement value of neutron count rate, thus the proposed method is practical. Verification calculations are carried out for a step-wise change of reactivity, neutron source intensity, and neutron generation time. The results indicate that reactivity is accurately predicted for the change of the neutron source intensity, which is difficult to achieve by the neutron source multiplication method. On the other hand, although the change of the neutron generation time has considerable impacts on the estimated result of subcriticality, the predicted error is less than 10% for very large variation of neutron generation time.

Scopus

Estimation of subcriticality using particle filter method

Ikeda T., Kimura T., Endo T., Yamamoto A.

Transactions of the American Nuclear Society Vol. 118 page： 851 - 854 2018

Estimation of subcriticality using particle filter method

Ikeda T., Kimura T., Endo T., Yamamoto A.

AISTech - Iron and Steel Technology Conference Proceedings Vol. 2018-May page： 851 - 854 2018

Inverse estimation methods of unknown radioactive source for fuel debris search

Sugaya S., Endo T., Yamamoto A.

International Conference on Physics of Reactors, PHYSOR 2018: Reactor Physics Paving the Way Towards More Efficient Systems Vol. Part F168384-4 page： 2632 - 2643 2018

To identify distribution of fuel debris remaining in the reactor vessel and/or the containment vessel of Fukushima Daiichi NPS, we focused on the inverse estimation of radioactive source distribution using measured values of radiation counts. The Maximum Likelihood-Expectation Maximization (ML-EM) method and the Moore-Penrose Matrix Inverse (MPMI) method are examined. The ML-EM method has been used for image reconstruction of computed tomography, and the MPMI method is one of the solution methods for simultaneous linear equations. A simple calculation model simulating the containment vessel were constructed including detectors and radiation sources. In actual situation, sufficient number of radiation measurement positions would not be available owing to the complexity of structures inside the containment vessel. Thus, the number of radiation measurement points (number of constraints) are smaller than positions of radiation source. It means that an underdetermined inverse problem should be solved. The detection probability of radiation (neutron or photon) is calculated by the adjoint transport calculation since the detection probability is used as the coupling coefficient between a radiation count at a detector and a radioactive source. Result of estimation using the ML-EM or the MPMI method indicates that the accuracy of estimation depends on the distance between a radiation source and a detector, and radiation count measurement positions. The ML-EM and the MPMI methods show different prediction accuracy depending on the calculation condition. It is found that the detectors should be placed at vicinity of radiation sources of interest and that the applicability of the inverse estimation does not strongly depend on the radioactivity distribution.

Scopus

Quantification of modeling approximation error of pin-cell calculation using kriging and principal component analysis

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

Transactions of the American Nuclear Society Vol. 118 page： 875 - 878 2018

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Papers - YAMAMOTO, Akio