Faculty Profiles - ENDO Tomohiro

MISC - ENDO Tomohiro

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Fast Reproduction of Time-dependent MOC Calculations using the Reduced Order Model based on the Proper Orthogonal and Singular Value Decompositions Reviewed International journal

Kosuke Tsujita, Tomohiro Endo, Akio Yamamoto

Transactions of the American Nuclear Society Vol. 123 page： 1349 - 1353 2020.11

Development of FRENDY Nuclear Data Processing Code: Generation Capability of Multi-group Cross Sections from ACE File Reviewed International journal

Akio Yamamoto, Tomohiro Endo, Kenichi Tada

Transactions of the American Nuclear Society Vol. 122 page： 714 - 717 2020.6

Application of Bootstrap Method to Estimated Criticality Lower-Limit Multiplication Factor Considering Nuclear Data-Induced Uncertainty Reviewed International journal

Takuto Hayashi, Tomohiro Endo, Akio Yamamoto

Transactions of the American Nuclear Society Vol. 122 page： 458 - 461 2020.6

Impact of Diffusion Coefficient and Correction Term on the Convergence of CMFD Acceleration for MOC Reviewed International journal

Y. Oshima, T. Endo, A. Yamamoto

Proceedings of Reactor Physics Asia 2019 page： 62 - 65 2019.12

Application of Singular Value Decomposition and Low Rank Approximation for Compression of Macroscopic and Microscopic Cross Section Table for Core Calculations Reviewed International journal

M. Yamamoto, T. Endo, A. Yamamoto

Proceedings of Reactor Physics Asia 2019 page： 166 - 169 2019.12

Uncertainty Quantification of Neutronics Characteristics in Thermal Systems Using Random Sampling and Continuous Energy Monte-Carlo Methods Reviewed International journal

H. Oike, R. Kondo, T. Endo, A. Yamamoto

Proceedings of Reactor Physics Asia 2019 page： 14 - 17 2019.12

Performance of the RSE (Resonance calculation using energy Spectral Expansion) Method for Heterogeneous Pin-cell Geometry Reviewed International journal

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

Proceedings of Reactor Physics Asia 2019 page： 162 - 165 2019.12

Estimated Criticality Lower-Limit Multiplication Factor Considering Neutronic Similarity and Uncertainties of Effective Multiplication Factor Using the Bootstrap Method (2) Application Reviewed International journal

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

Proceedings of Reactor Physics Asia 2019 page： 254 - 257 2019.12

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

Proceedings of Reactor Physics Asia 2019 page： 250 - 253 2019.12

Effectiveness of Subcritical Measurement at Solid Moderated KUCA Core for Reducing Nuclear Data-Induced Uncertainties in Other Light Water Reactor Analysis Reviewed International journal

T. Endo, A. Yamamoto

Proceedings of Reactor Physics Asia 2019 page： 262 - 265 2019.12

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper, summary (international conference)

This paper aims to clarify that the subcritical measurement at the solid moderated KUCA core is useful to reduce nuclide data-induced uncertainties of the effective neutron multiplication factors keff in other light water moderated systems. For this purpose, we pay attention to the prompt neutron decay constant α, which was measured by the Feynman-α method with the moving block bootstrap method for the deep subcritical KUCA core under the shutdown state without any external neutron source. The sensitivity analyses of α for the subcritical KUCA core and of keff for various light water moderated critical cores were carried out based on the first-order perturbation theory. Consequently, it is demonstrated that the nuclear data-induced uncertainties of keff can be reduced by the bias factor method using the measurement value of α, if the target keff value has a strong correlation with the measured α value in the subcritical KUCA core.

Discontinuity Factor; A Discontinuity Condition for Angular Flux? Reviewed International journal

A. Yamamoto, T. Endo

Proceedings of Reactor Physics Asia 2019 page： 155 - 157 2019.12

C5G7-TD Benchmark Analysis using Multigrid Amplitude Function Method Reviewed International journal

K. Tsujita, T. Endo, A. Yamamoto

Proceedings of Reactor Physics Asia 2019 page： 201 - 204 2019.12

Application of Surrogate Modeling with Singular Value Decomposition for Design Basis Accident Aiming Statistical Safety Analysis Reviewed International journal

M. Matsushita, T. Endo, A. Yamamoto

Proceedings of Reactor Physics Asia 2019 page： 282 - 285 2019.12

Development of Efficient Data Sampling Method to Construct Surrogate Model of Severe Accident Analysis Code for SBO Aiming Probabilistic Safety Margin Analysis Reviewed International journal

M. Matsushita, T. Endo, A. Yamamoto

Trans. Am. Nucl. Soc. Vol. 121 page： 979 - 982 2019.11

Language：English Publishing type：Research paper, summary (international conference) Publisher：American Nuclear Society

An efficient data sampling method is developed in order to construct a ROM, which accurately reproduces the results of a severe accident code, with the small number of the training data. The proposed sampling method is categorized as the adaptive sampling and this study newly applies the concept of the gravity field to its sampling method in order to make efficient sampling. The proposed sampling method can choose the input training data which have significant new information for ROM construction. The proposed sampling method is applied to PCT obtained by RELAP5/SCDAPSIM calculations for the SBO accident scenario. ROM is improved by adding the new training data to satisfy MPCT=1200°C on the core intact/damage boundary. The core intact/damage boundary predicted by ROM improved as the number of iterations increases. In other words, the input training data are heavily sampled near the core intact/damage boundary. This sampling makes the proposed method more efficient than the conventional random sampling method. As future problems, applications of the present method to calculate CDF considering the uncertainty of the ROM and to the other accident scenarios will be considered.

DOI： 10.13182/T30744

Resonance Calculation Using Energy Spectral Expansion Based on Reduced Order Model: Application to Heterogeneous Geometry Reviewed International journal

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

Trans. Am. Nucl. Soc. Vol. 121 page： 1316 - 1320 2019.11

Language：English Publishing type：Research paper, summary (international conference) Publisher：American Nuclear Society

The Resonance calculation based on energy Spectral Expansion (RSE) is applied to a pin cell geometry and its accuracy is verified through comparison with the results by the ultra-fine group MOC and the MCNP calculations. Impact of the generation method of the orthogonal bases and the neutron source treatment is quantified through the benchmark calculation. The numerical results are promising; the RSE method accurately reproduces the reference results obtained by the ultra-fine group calculation by MOC or MCNP. There are several issues to be addressed; performance of the present method in more complicated and practical geometries/material arrangements, treatment of scattering source term, numerical solution method, extension of the present concept to the unresolved resonance energy range.

DOI： 10.13182/T30993

Reduction of Macroscopic and Microscopic Cross Section Table Size for Heterogeneous Core Calculation using Dimensionality Reduction Reviewed International journal

M. Yamamoto, T. Endo, A. Yamamoto

Trans. Am. Nucl. Soc. Vol. 121 page： 1309 - 1312 2019.11

Language：English Publishing type：Research paper, summary (international conference) Publisher：American Nuclear Society

Reduction of cross section table size including macroscopic and microscopic cross sections is tried by applying the dimensionality reduction technique with the singular value decomposition and the low-rank approximation. Among the material-wise cross sections obtained by a lattice physics calculation, those of fuel region are considered in this study. The impact of dimensionality reduction is investigated with a comparison of the assembly calculations using the reconstructed and original cross sections. In this study, approximately 99% reduction in cross section table size is possible while suppressing the error of keff and flux below 0.1%. As a future study, development of the tabulation method using dimensionality reduced cross sections is considered to verify the applicability of the present method for core calculations.

DOI： 10.13182/T30783

Subcriticality: from basics to applications; (1) Revisiting subcriticality Reviewed

T. Endo, K. Tsujimoto, A. Yamamoto

ATOMOΣ: Journal of the Atomic Energy Society of Japan Vol. 61 ( 10 ) page： 734 - 738 2019.10

Conversion from prompt neutron decay constant to subcriticality using point kinetics parameters based on α- and keff-eigenfunctions Reviewed International journal

T. Endo, A. Yamamoto

Proc. ICNC2019 2019.9

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper, summary (international conference)

The conversion from the measurement value of prompt neutron decay constant α to the subcriticality –ρ is investigated, using special point kinetics parameters which are defined by mixing forward α- and adjoint keff-eigenfunctions. The mixing α-k weighted point kinetics parameters are very useful to reduce the conversion bias of neutron multiplication factor in a deeper subcritical system. In the same manner as the k-ratio method, the mixing α-k weighted point kinetics parameters can be well approximated by three eigenvalues of α, keff, and prompt keff,p to be simply estimated by the forward eigenvalue calculations without any adjoint calculations.

Measurement of subcriticality in dollar units using time-domain decomposition based integral method Reviewed International journal

A. Nonaka, T. Endo, A. Yamamoto, M. Yamanaka, T. Sano, C.H. Pyeon

Proc. ICNC2019 2019.9

Language：English Publishing type：Research paper, summary (international conference)

This paper presents an estimation method of subcriticality in dollar units developed on the basis of an integral method for arbitrary state changes in a subcritical system. In a general transient in a subcritical system, reactivity, neutron source intensity, and point kinetics parameters (and) can vary simultaneously. To address this problem, the "time-domain decomposition based integral method (TDDI)" has been proposed. The TDDI method can estimate the subcriticality only using the time variation of the neutron count rate. Therefore, the proposed method is useful to estimate the subcriticality in the reactor where the detailed conditions are unknown. To investigate the applicability of the TDDI method to actual subcritical measurement, a transient experiment in a source-driven subcritical system is conducted at the Kyoto University Critical Assembly. As a result, it is concluded that the TDDI method can approximately estimate the order of magnitude for the subcriticality in dollar units. Meanwhile, the estimation is difficult owing to the statistical errors when the neutron count rate is low.

Application of Various Superhomogenization (SPH) methods for the Method of Characteristics Reviewed International journal

K. Sawada, T. Endo, A. Yamamoto

Proc. M&C2019 page： 1534 - 1543 2019.8

Language：English Publishing type：Research paper, summary (international conference) Publisher：American Nuclear Society

To reduce the error due to the difference between the fine and the coarse calculation conditions in a transport calculation using method of characteristics (MOC), the superhomogenization (SPH) method has been widely used. However, the conventional SPH method has a problem with numerical stability in the iterative calculations for the estimation of SPH factors, especially when local strong absorbers exist in a calculation geometry. To address this problem, improvements of the SPH methods were tested to reduce the angular and spatial discretization error of the MOC. The performances of the various SPH methods were confirmed in pressurized water reactor (PWR) 2 × 2 fuel assembly geometries and in a PWR core geometry. The results of verification indicate that in a core geometry the improved SPH methods provide better accuracy than that of the conventional SPH.

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