Faculty Profiles - ENDO Tomohiro

MISC - ENDO Tomohiro

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Experiment of Unique Combination Number due to the Third-Order Neutron-Correlation Reviewed International journal

Tomohiro Endo, Sho Imai, Kenichi Watanabe, Akio Yamamoto, Atsushi Sakon, Kengo Hashimoto, Masao Yamanaka, Cheol Ho Pyeon

EPJ Web of Conferences Vol. 247 page： 09004 - 09004 2021.2

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

From zero-power reactor noise measurement, the second- and third-order neutron correlation factors <italic>Y</italic> and <italic>y</italic>3 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 <italic>y</italic>3/<italic>Y</italic>2 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 <italic>T</italic> increases sufficiently. Thus, the information about the difference between <italic>y</italic>3/<italic>Y</italic>2 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 <italic>y</italic>3/<italic>Y</italic>2 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 <italic>y</italic>3/<italic>Y</italic>2 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 <italic>y</italic>3/<italic>Y</italic>2 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 <italic>y</italic>3/<italic>Y</italic>2 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

Estimated Criticality Lower-Limit Multiplication Factor of Low-Enriched Uranium Dioxide-Concrete System Using the Bootstrap Method Reviewed International journal

Takuto Hayashi, Fuga Nishioka, Tomohiro Endo, Akio Yamamoto

EPJ Web of Conferences Vol. 247 page： 17001 - 17001 2021.2

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

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

Basic Study on a Pseudo Trend Phenomenon of The Feynman-α Analysis with Bunching Method Reviewed International journal

Sin-ya Hohara, Atsushi Sakon, Tomohiro Endo, Tadafumi Sano, Kunihiro Nakajima, Kazuki Takahashi, Kengo Hashimoto

EPJ Web of Conferences Vol. 247 page： 09008 - 09008 2021.2

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

In these years, reactor noise analysis methods have been studied to apply for the Debris’ criticality management at the Fukushima Daiichi NPP, Japan. The Feynman-α analysis with bunching method is one of the candidate techniques, however the bunching method itself has never been validated in detail. This synthesis technique is useful to reduce a time required for the experiment, however it is known that a non-physical trend unrelated to the state of a nuclear reactor is generated by the multiple use of time series data, and this phenomenon (we call “pseudo trend phenomenon”) has never been systematically studied in detail. In this study, Poisson events, whose statistical characteristics were clarified, were employed to investigate the pseudo trend phenomenon of the bunching method. The time-sequence count data for various statistical parameters were generated by the Monte Carlo time series simulator. Comparing the two results obtained by applying the conventional bunching method and the moving-bunching method for the same Poisson event time series, and it was found that the same pseudo trend component appears in both results of the bunching method and the moving bunching method. In addition, it was also found that the fluctuation width of the pseudo trend component is smaller than the statistical fluctuation range.

DOI： 10.1051/epjconf/202124709008

Study on Multi-unit PRA Considering Correlation between Multiple Safety Systems Using the Continuous Markov chain Monte Carlo Method Reviewed International journal

Kento Sawada, Tomohiro Endo, Akio Yamamoto, Sunghyon Jang, Daisuke Fujiwara, Chikahiro Sato

Proc. ASRAM2020 page： 1027 2020.11

Language：English Publishing type：Research paper, summary (international conference) Publisher：Atomic Energy Society of Japan

After the accident in Fukushima Dai-ichi Nuclear Power Plants, the necessity for the safety assessment considering multiple nuclear power units is increasing. However, the conventional event tree (ET) method, which is widely used in probabilistic risk assessment (PRA), cannot consider the interdependency among safety systems or events in multiple units as well as time dependency of the accident progressions. Recently, a new approach that couples the Continuous Markov chain Monte Carlo (CMMC) method with a plant safety analysis or a severe accident analysis code is suggested to address these issues. However, applications of the CMMC coupling method to safety assessment for multiple units are still limited. In the present study, the CMMC coupling method is applied to multiple units analysis in order to get practical insights and to clarify the issues of this method. Since the CMMC coupling method requires a large number of executions of an accident analysis code, a meta-model that simplifies the systems and the physical phenomena in accidents is used in this study to avoid the high computational cost of the existing accident analysis codes. In the present study, the numerical investigation of a BWR accident under station blackout (SBO) with loss of RCIC is carried out. The preliminary results suggested that the CMMC coupling method can appropriately treat the interdependency and time dependency among events in multiple units.

Subcriticality Estimation using Unscented Kalman Filter for Reactivity- and Source-Transients Reviewed International journal

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

Transactions of the American Nuclear Society Vol. 123 page： 841 - 844 2020.11

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

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