Faculty Profiles - ENDO Tomohiro

MISC - ENDO Tomohiro

Division display 1 - 20 of about 197 ／ All the affair displays >>

Subcriticality: from basics to applications; (3) The ABC's of Subcriticality Measurements Reviewed

T. Endo, S. Atsushi

ATOMOΣ: Journal of the Atomic Energy Society of Japan Vol. 61 ( 12 ) page： 857 - 862 2019.12

Effects of Self-shielding and Scattering Matrix Treatments in Detailed Burnup Calculation Reviewed International journal

Akio Yamamoto, Tomohiro Endo, Tomoaki Watanabe

Transactions of the American Nuclear Society Vol. 133 ( 1 ) page： 698 - 701 2025.11

Theoretical Formula for Probability Generating Function of Neutron Counts in a Non-Multiplication System Reviewed International journal

Tomohiro Endo, Ryonosuke Ohashi, Ryoga Hirota, Akio Yamamoto

Transactions of the American Nuclear Society Vol. 133 ( 1 ) page： 426 - 429 2025.11

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

This study derived the theoretical formula for the probability generating function (PGF) of neutron counts measured in a non-multiplication system driven by a multiple emission source such as Cf252. To rigorously obtain the theoretical formula of the PGF, the theoretical derivation is achieved by taking into account higher-order mode components based on the α-eigenfunction expansion.

Study on Neutron Diffusion Calculation based on Particle Method for Multiphysics Simulation of Fuel Debris Retrieval Reviewed International journal

Shogo Kumita, Endo Tomohiro, Akio Yamamoto

Transactions of the American Nuclear Society Vol. 133 ( 1 ) page： 760 - 763 2025.11

Language：English Publishing type：Article, review, commentary, editorial, etc. (international conference proceedings) Publisher：American Nuclear Society

This study investigates a neutron diffusion calculation method that can be effectively utilized for multiphysics simulation of fuel debris retrieval. For this purpose, we apply the particle method to the neutron diffusion calculation method. Thereby, we aim to reuse the calculation geometry of the fluid analysis using the particle method for the neutron diffusion calculation without converting the calculation geometry between the coupling calculations.

Study on Core Analysis Models for HTGRs: VHTRC Analysis using MVP3 Reviewed International journal

Yusuke Kuroki, Akio Yamamoto, Tomohiro Endo

Transactions of the American Nuclear Society Vol. 133 ( 1 ) page： 632 - 635 2025.11

Nonlinear Diffusion Acceleration with Local Discontinuous Galerkin Method Reviewed International journal

Rikuto Kasama, Akio Yamamo, Tomohiro Endo

Transactions of the American Nuclear Society Vol. 133 ( 1 ) page： 678 - 681 2025.11

Subcriticality Estimation without Point Kinetics Parameters Based on Autocovariance of Reactor Noise Using Delayed Neutron Components Reviewed International journal

Tomohiro Endo, Ryoga Hirota, Akio Yamamoto, Kenichi Watanabe, Genichiro Wakabayashi, Kengo Oda, Junichi H. Kaneko

Proc. M&C2025 page： 2028 - 2037 2025.4

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

The reactor noise analysis method is useful as a passive measurement technique for a steady-state target subcritical system. When detailed information is not available in the target system, there are large uncertainties in the point kinetics parameters, such as the effective delayed neutron fraction and the neutron generation time. In this case, if the subcriticality measurement techniques using the point kinetics parameters (e.g., indirect conversion method from the measured prompt neutron decay constant to the subcriticality) are applied, the measured subcriticality will inevitably have a large uncertainty. To address this problem, the present study aims to investigate the absolute measurement of subcriticality without the point kinetics parameters by focusing on the delayed neutron components in the zero-power reactor noise. For this purpose, an analytical formula for the lag-1 autocovariance of the reactor noise is derived via the pair detection probability based on the fundamental mode approximation using the forward and adjoint eff-eigenfunctions. The proposed method utilizes the nonlinear least squares fitting method for the measured autocovariance to determine the following three fitting parameters: the subcriticality in the dollar units; the ratio of eff ⁄Λ; and a proportional factor related to the Diven factor, the detection efficiency, and so on. Preliminary experimental analysis using the proposed method is demonstrated through the reactor noise measurement at UTR-KINKI (University Teaching and Research Reactor of Kindai University) under a shutdown state.

DOI： 10.13182/MC25-46579

A Simple Resonance Calculation Method for Flexible Geometry Using Equivalence Relation and Point-wise Cross Sections (ERPX) Reviewed International journal

Akio Yamamoto, Tomohiro Endo

Proc. M&C2025 page： 544 - 553 2025.4

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

ERPX, a simple resonance calculation method that can incorporate space-dependent shelf-shielding is proposed. ERPX calculates space-dependent escape cross sections using the ultra-fine group (UFG) calculation in heterogeneous and homogeneous geometries with the narrow resonance (NR) approximation. Then the space-dependent escape cross sections and the explicit slowing down calculation in homogeneous geometry are then used to estimate the space-dependent effective cross section to mitigate the error caused by the NR approximation. The reduce-order model is developed and used in the UFG calculation in heterogeneous geometry to achieve short computation time. Verification calculation is carried out in 3x3 pin-cell geometry containing a large water region. The fuel pellet in focus is azimuthally and annularly divided. The calculation results indicated that the ERPX method can provide reasonable accuracy with practical computation time that can be used for the design calculations.

DOI： 10.13182/MC25-47330

Correction Method of Few-Group Cross Sections for Core Analysis of High-Temperature Gas-Cooled Reactors Reviewed International journal

Amane Haga, Tomohiro Endo, Akio Yamamoto, Go Chiba

Proc. M&C2025 page： 472 - 481 2025.4

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

To reduce the discretization error associated with the energy group collapsing, a correction method for few-group cross sections used in a core calculation of High-Temperature Gas-cooled Reactors (HTGRs) was investigated. It was confirmed that the correction of the removal scattering cross section as a function of the spectral index, which is the ratio of the fast and thermal group neutron fluxes, improves the calculation accuracy of the k-effective and the fuel compact-wise relative power distribution in the two-dimensional heterogeneous full core model of the High Temperature engineering Test Reactor (HTTR). The method of correcting the total scattering cross section, including the self-group scattering cross section, did not improve the accuracy. The method using the removal scattering cross section may be a candidate for a core design method of HTGRs.

DOI： 10.13182/MC25-47343

Reactivity Estimation in Dollar Units Based on Bayesian Monte Carlo Using Autocovariance of Reactor Noise Measurement Reviewed International journal

Ryoga Hirota, Tomohiro Endo, Akio Yamamoto, Kenichi Watanabe, Genichiro Wakabayash, Kengo Oda, Junichi H. Kaneko

Proc. M&C2025 page： 2038 - 2047 2025.4

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

The reactor noise analysis method can measure the prompt neutron decay constant using only time series data of neutron counts measured in a steady-state subcritical system. However, the point kinetics parameters such as the neutron generation time Λ and the effective delayed neutron fraction eff are needed to estimate the reactivity in dollar units by conversion from the measured value. To address the above-mentioned problem, this study aims to develop the estimation technique of the reactivity in dollar units eff , by utilizing the delayed neutron component of reactor noise. To extract the delayed neutron components, this study focused on the lag-1 autocovariance for reactor noise. In addition, the Bayesian Monte Carlo (BMC) with merging particle filter (MPF) was applied as the data assimilation technique to estimate eff from the measured variation of the autocovariance with respect to the counting gate width. As a result, the proposed method was validated through the reactor noise measurement at UTR-KINKI (University Teaching and Research Reactor of Kindai University).

2D Cylindrical SP3 Transport Calculation Using Finite Volume Method with Cross-Diffusion Treatment for Unstructured Meshes Reviewed International journal

Tomohiro Endo, Akio Yamamoto

Transactions of the American Nuclear Society Vol. 131 ( 1 ) page： 1053 - 1056 2024.11

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

This study presents a prototype of an in-house code to numerically solve the simplified P3 (SP3) neutron transport equation for a 2D cylindrical (r-z) geometry using unstructured meshes for spatial discretization. In the developed SP3 calculation code, the cross-diffusion effect due to the unstructured meshes can be treated by a variant of the Green-Gauss reconstruction technique.

DOI： 10.13182/T131-46095

Study on Fusion Safety Concept Based on Nuclear Safety (2) Defense in Depth in Fusion Safety Reviewed International journal

Yoshiki Yamashita, Tomohiro Endo, Akio Yamamoto, Takashi Ino

Transactions of the American Nuclear Society Vol. 131 ( 1 ) page： 299 - 302 2024.11

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

The concept of fusion safety is studied with reference to nuclear safety. Risk profiles of fusion reactor facilities are reviewed and organized and implementation of defense in
depth (DID) in fusion safety is developed based on the risk profiles.

DOI： 10.13182/T131-46140

Study on Fusion Safety Concept Based on Nuclear Safety (1) Fusion Safety Objective and Principles Reviewed International journal

Yoshiki Yamashita, Tomohiro Endo, Akio Yamamoto, Takashi Ino

Transactions of the American Nuclear Society Vol. 131 ( 1 ) page： 292 - 295 2024.11

A Simple Resonance Calculation Approach for Space-Dependent Self-Shielding Reviewed International journal

Akio Yamamoto, Tomohiro Endo

Transactions of the American Nuclear Society Vol. 131 ( 1 ) page： 1038 - 1041 2024.11

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

A simple resonance calculation method for space-dependent self-shielding treatment is proposed. The present method is based on three calculations: 1) ultra-fine group (UFG) calculation with the narrow resonance (NR) approximation in a homogeneous medium, 2) UFG calculation with explicit slowing down (SLD) calculation in a homogeneous medium, and 3) UFG calculation with the NR approximation in a heterogeneous system. The space-dependent effective cross sections are generated by the synthesis of these three calculations.

DOI： 10.13182/T131-45885

Implementation of track length estimator for flux distribution tallies using proper orthogonal decomposition in one-dimensional geometry Reviewed International journal

Ryoichi Kondo, Tomohiro Endo, Akio Yamamoto

EPJ Web of Conferences Vol. 302 page： 04002 2024.10

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

In a recent study, we have developed an efficient flux distribution tallying method in the Monte Carlo calculation toward the high-fidelity, large scale multi-physics simulation. In this method, the proper orthogonal decomposition is applied to the flux distribution tallies. While the tallying method was implemented with the collision estimator in the previous study, the track length estimator is implemented in the present study to obtain the tally with lower statistical error. The implementation of the flux distribution tally with the track length estimator is compared with that of the collision estimator and the normal track length estimator in a one-dimensional problem. The numerical results reveal that the distribution tally using the proper orthogonal decomposition with the track length estimator can obtain a more precise solution compared with that with the collision estimator. Therefore, in terms of the statistical error, the relationship between the distribution tally with track length and collision estimators is similar to that between the conventional track length and collision estimators.

DOI： 10.1051/epjconf/202430204002

Data Assimilation Using Deterministic Sampling Method to Selectively Reduce Uncertainty due to Thermal Neutron Scattering Law for Light Water Reviewed International journal

Yoshinari Harada, Hibiki Yamaguchi, Tomohiro Endo, Akio Yamamoto, Kenichi Tada

Transactions of the American Nuclear Society Vol. 130 ( 1 ) page： 758 - 762 2024.6

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

This study presents data assimilation using the prompt neutron decay constant α of the water tank system to selectively reduce the uncertainties due to the thermal neutron scattering law of light water. For efficient uncertainty quantification and data assimilation, the deterministic sampling method was applied in this study. Furthermore, in the data assimilation, the α measurement of the water tank system was utilized to improve the prediction accuracy of keff calculations in a critical experiment involving light water.

DOI： 10.13182/T130-44516

Loading Pattern Optimization with Deep Learning and Monte-Carlo Tree Search Reviewed International journal

Rikuto Kasama, Akio Yamamoto, Tomohiro Endo

Transactions of the American Nuclear Society Vol. 130 ( 1 ) page： 1044 - 1047 2024.6

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

We have developed a new optimization method based on Deep Learning (DL) and Monte-Carlo Tree Search (MCTS) for fuel loading pattern optimization. The fuel loading pattern optimization is redefined as a sequence of fuel loadings to an empty core, and the sequence is optimized by the DL and MCTS approach, which is used in AI for board games such as Go, Chess, and Shogi (Japanese Chess).

DOI： 10.13182/T130-44319

Statistical Error Estimation of Autocorrelation Method Using Circular Block Bootstrap Method Reviewed International journal

Ryoga Hirota, Tomohiro Endo, Akio Yamamoto, Kenichi Watanabe, Junichi H. Kaneko

Proc. PHYSOR2024 page： 78 - 86 2024.4

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

The autocorrelation method is a subcriticality measurement technique based on the reactor noise analysis method. In this method, the prompt neutron decay constant can be obtained from the exponential decay of the autocorrelation of successively detected neutron counts in a target subcritical system. To simply estimate the statistical error of the prompt neutron decay constant, several measurements of the reactor noise are required, although the total measurement time is inevitably long for typical systems where the reactor noise analysis method is applied. Therefore, the purpose of this study is to investigate the applicability of the circular block bootstrap method in order to estimate the statistical error of the prompt neutron decay constant obtained by the autocorrelation method using a single reactor noise measurement. The bootstrap-based statistical error estimation method is validated using the time series data of reactor noise measurements at UTR-KINKI in a shutdown state with the inherent neutron source in the uranium-aluminum fuel. Consequently, this study demonstrates that the circular block bootstrap method can be also utilized for the autocorrelation method, to estimate the confidence interval of the prompt neutron decay constant as the statistical error. Namely, a single reactor noise measurement can be effectively reused for error estimation instead of multiple measurements.

Other Link： https://www.ans.org/meetings/physor2024/sessions/attachment/paper-9424/

Investigation of Subcriticality Monitoring Method Using Improved Simplest Reactivity Estimator with Bilateral Filter Reviewed International journal

Taiyo Moribe, Tomohiro Endo, Akio Yamamoto, Junichi H. Kaneko

Proc. PHYSOR2024 page： 97 - 106 2024.4

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

In the retrieval of fuel debris from the Fukushima Daiichi nuclear power plant, there are the following issues: lack of information needed to inversely estimate the subcriticality; and the limitation of neutron detector size. In order to address these issues, we propose a reactivity estimation method that combines the improved simplest reactivity estimator (SRE) and the least squares inverse kinetics method. This study aims to estimate the reactivity in dollar units in a data driven manner only from the measured neutron count rate without point kinetics parameters. Furthermore, the usefulness of the bilateral filter in combination with the median for the count rate is also investigated to mitigate statistical errors in the reactivity estimation results due to the statistical fluctuation and outlier in the measured count rate data. To verify our proposed method, point kinetics calculation is performed to simulate the time series data of the neutron count rate during a stepwise transient from a deep subcritical state to the shallower state. Here, the magnitude of the count rate at the initial state is parametrically varied to investigate the effect of the statistical count rate fluctuation on the estimated reactivity. As a result, it is observed that the estimated reactivity tends to be overestimated (i.e., closer to critical) as lower count rate data are used in our proposed method. Thus, our proposed method is considered practical from the perspective of criticality control. Moreover, it is clarified that the combinational use of the bilateral filter and the median can effectively reduce the error of the estimated reactivity due to the statistical fluctuation of the count rate. Consequently, this feasibility study demonstrates our proposed method for monitoring the reactivity change even under the low neutron count rate condition.

DOI： 10.13182/PHYSOR24-43487

Loading Pattern Optimization for LWRs Using Monte Carlo Tree Search Reviewed International journal

Rikuto Kasama, Akio Yamamoto, Tomohiro Endo

Proc. PHYSOR2024 page： 2490 - 2499 2024.4

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

Inspired by recent breakthroughs in AI for games, we transform the fuel loading pattern
optimization problem into a game tree search problem and adopt Monte Carlo Tree Search (MCTS) to solve it. The performance of MCTS is compared with the conventional optimization methods, such as the random search and simulated annealing (SA), for the loading pattern optimization of a typical pressurized water reactor. The results demonstrate the superior efficiency of MCTS over the conventional methods. MCTS consistently produces high-quality patterns and effectively avoids the common problem of falling into local minima. By using techniques rooted in AI, we are
opening up a new way of solving complex problems in nuclear engineering, offering the prospect of more reliable and efficient core designs. This innovative approach will not only benefit the nuclear field, but also serve as a bridge between optimization and artificial intelligence.

DOI： 10.13182/PHYSOR24-43466

　 PREV - NEXT 　

<ENDO Tomohiro>

MISC - ENDO Tomohiro