Single bunch injection scheme for doubling the beam intensity of J-PARC Main Ring

Tamura, Fumihiko; Okita, Hidefumi; Hotchi, Hideaki*; Saha, P. K.; Sato, Yoichi*; Yoshii, Masahito*; Omori, Chihiro*; Yamamoto, Masanobu; Seiya, Kiyomi*; Sugiyama, Yasuyuki*; et al.

JPS Conference Proceedings (Internet), 45, p.011129_1 - 011129_7, 2026/06

https://doi.org/10.7566/JPSCP.45.011129

The current goal of the J-PARC Main Ring (MR) is an output beam power of 1.3 MW, with a beam intensity is 3.3e14 protons per pulse (ppp) at a repetition period is 1.16 s. The Rapid Cycling Synchrotron (RCS) delivers two bunches to the MR in each injection and eight bunches are accumulated in the MR with four injections. The harmonic number of the RCS is 2 and the maximum nunch intensity of the RCS is 4.2e13 protons per bunch (ppb). If the harmonic number of the RCS is set to 1 and the RCS can accelerate a single bunch with the same intensity of 8.3e13 ppp/ppb, the bunch intensity in the MR can be doubled to 8.3e13 ppb, which corresponds to the accumulated beam intensity of 6.6e14 ppp with eight bunches. In this presentation, the feasibility of single bunch acceleration in the RCS is discussed based on the longitudinal beam simulations.

Development of deterministic core analysis code system ARCANUM for high-temperature gas-cooled reactors

Tada, Kenichi; Katano, Ryota; Kondo, Ryoichi; Nagaya, Yasunobu; Chiba, Go*; Yamamoto, Akio*

Proceedings of International Conference on the Physics of Reactors (PHYSOR 2026) (Internet), 8 Pages, 2026/04

https://doi.org/10.5281/zenodo.20803625

A High-Temperature Gas-cooled Reactor (HTGR) is a type of Generation IV reactor. HTGRs have a good advantage in preventing the core meltdown in the event of a severe accident, such as loss of forced cooling. We are developing a new core analysis code system, ARCANUM, to accurately calculate HTGR cores within a reasonable calculation time. It consists of two parts, i.e., the 2D lattice calculation part and the 3D triangular prism core calculation part. The MOC-based transport solver GENESIS was used for 2D lattice calculations. The other calculations, such as 3D core calculation code, are performed using newly developed codes. This paper shows an overview of the ARCANUM code system and verification results of this system. Two fuel elements, which are obtained from the IRPhE benchmark, were used to verify the lattice calculation part. Takeda-benchmark Model 4 was used to verify the core calculation part. The calculation results showed good agreement with the reference results.

Assessment of caesium-137 detections at CTBTO radionuclide monitoring stations in East Asia and their relationship to Asian dust dispersion

Furuno, Akiko; Omori, Ryuta*; Tateoka, Hisanori*; Minakawa, Yuya*; Kurihara, Toshiyuki; Yamamoto, Yoichi; Tomita, Yutaka

Pure and Applied Geophysics, 182(12), p.5175 - 5188, 2025/12

https://doi.org/10.1007/s00024-024-03620-y

The Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) Okinawa radionuclide monitoring station (JPP37) is located on a hill facing the East China Sea at the center of the main island of Okinawa. It occasionally detects Cs-137, although no nuclear facilities are located on the island. This study focused on the detection of Cs-137 at JPP37 and examined the ratio of simultaneous detections at nearby stations of the International Monitoring System (IMS) of the CTBTO and the relationship with Asian dust from inland East Asia. The detection of Cs-137 in JPP37 from 2020 to 2023, which motivated this study, was high in spring. Among the nine IMS radionuclide stations in East Asia, the detections in Beijing, Lanzhou, and Ulaanbaatar, Mongolia, were also high in spring. This suggested a high association with the detection of Asian dust in East Asia. Thus, we confirmed the detection of Cs-137 at nine nearby IMS stations when Asian dust was observed at any of the sites in Japan. In addition, we observed that the detection rates were high in Takasaki, Beijing, Lanzhou, and Ulaanbaatar. It can be inferred that the Cs-137 observed mainly in spring at the IMS particulate radionuclide stations in the East Asian region around Japan were likely to pick up the effects of global fallout conveyed by Asian dust. Thereafter, we conducted a preliminary source estimation analysis for Asian dust arrival near Japan. Atmospheric dispersion simulations explained the detection of Cs-137 at nearby IMS particulate radionuclide stations, assuming that Cs-137 was emitted from the desert, the source of the Asian dust.

Self-reconstruction of order parameter in spin-triplet superconductor UTe

Tokiwa, Yoshifumi; Opletal, P.; Sakai, Hironori; Kubo, Katsunori; Kambe, Shinsaku; Yamamoto, Etsuji; Kimata, Motoi; Awaji, Satoshi*; Sasaki, Takahiko*; Aoki, Dai*; et al.

Physical Review Letters, 135(13), p.136502_1 - 136502_6, 2025/09

https://doi.org/10.1103/z8yx-yzdh

We investigate the effect of easy-axis metamagnetic crossover on superconductivity in UTe along the -axis through measurements of AC susceptibility, magnetization, and the magnetocaloric effect. In ultra-clean single crystals, we identify a field-induced phase transition within the superconducting state at 5.6 T, driven by metamagnetism. This transition leads to a high-field superconducting state, significantly increasing the upper critical field to 12 T. A sudden increase in entropy at the transition suggests a self-reconstruction of the order parameter, enabling multi-component superconducting states to adapt to external perturbations.

Observation of nonreciprocal diffraction of surface acoustic wave

Nii, Yoichi*; Yamamoto, Kei; Kanno, Masaki*; Maekawa, Sadamichi*; Onose, Yoshinori*

Physical Review Letters, 134(2), p.027001_1 - 027001_5, 2025/01

https://doi.org/10.1103/PhysRevLett.134.027001

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

Kondo, Ryoichi; Endo, Tomohiro*; Yamamoto, Akio*

EPJ Web of Conferences, 302, p.04002_1 - 04002_10, 2024/10

https://doi.org/10.1051/epjconf/202430204002

In the 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 POD 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 estimator is similar to that between the conventional track length and collision estimators.

Development of nuclear data processing code FRENDY version 2

Tada, Kenichi; Yamamoto, Akio*; Kunieda, Satoshi; Konno, Chikara; Kondo, Ryoichi; Endo, Tomohiro*; Chiba, Go*; Ono, Michitaka*; Tojo, Masayuki*

Journal of Nuclear Science and Technology, 61(6), p.830 - 839, 2024/06

https://doi.org/10.1080/00223131.2023.2278600

Nuclear data processing code is important to connect evaluated nuclear data libraries and radiation transport codes. The nuclear data processing code FRENDY version 1 was released in 2019 to generate ACE formatted cross section files with simple input data. After we released FRENDY version 1, many functions were developed, e.g., neutron multi-group cross section generation, explicit consideration of the resonance interference effect among different nuclides in a material, consideration of the resonance upscattering, ACE file perturbation, and modification of ENDF-6 formatted file. FRENDY version 2 was released including these new functions. It generates GENDF and MATXS formatted neutron multi-group cross section files from an ACE formatted cross section file or an evaluated nuclear data file. This paper explains the features of the new functions implemented in FRENDY version 2 and the verification of the neutron multigroup cross section generation function of this code.

Secondary consolidation characteristic of bentonite by long-term consolidation tests of 2.7, 3.7 and 4 years

Takayama, Yusuke; Yamamoto, Yoichi*; Goto, Takahiro*

Jiban Kogaku Janaru (Internet), 18(3), p.317 - 330, 2023/09

https://doi.org/10.3208/jgs.18.317

It has been reported that the deformation greatly increased in the secondary consolidation process in the past long-term consolidation test of 1.8 years on Na-type bentonite/sand mixed soil. Therefore, we analyzed potential contributing factors in this behavior. A long-term consolidation test for about 10 years on bentonite and kaolinite was started using the test equipment with countermeasures against these factors. In this paper, the secondary consolidation behavior of bentonite was investigated based on the long-term consolidation test data for 2.7, 3.7 and 4 years. The results were generally consistent with the conventional findings on soil mechanics that the deformation due to secondary consolidation progresses linearly with respect to logarithm of time. This test will be continued for about 10 years and longer-term secondary consolidation behavior will be investigated.

Semiconductor pulse power supplies for accelerators at J-PARC

Takayanagi, Tomohiro; Ono, Ayato; Fuwa, Yasuhiro; Shinozaki, Shinichi; Horino, Koki*; Ueno, Tomoaki*; Sugita, Moe; Yamamoto, Kazami; Oguri, Hidetomo; Kinsho, Michikazu; et al.

Proceedings of 19th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.242 - 246, 2023/01

At J-PARC, semiconductor short pulse power supplies to replace kicker power supplies and semiconductor long pulse power supplies to replace klystron power supply systems are under construction. We have fabricated a 40kV/2kA/1.2s unit power supply that employs a linear transformer drivers (LTD) system for kickers. Currently, we are working on a high voltage insulating cylinder insulator that suppresses corona discharges using only the insulator structure, without using insulating oil. In addition, the MARX system was adopted for klystron power supply system. A main circuit unit for 8kV/60A/830s rectangular pulse output and an 800V/60A correction circuit unit that improves the flat top droop from 10% to 1% were manufactured. Furthermore, a 2.2kV/2.4kW high voltage SiC inverter charger has been fabricated for this MARX power supply. The presentation will report the evaluation results of each test and prospects for semiconductor pulse power supplies.

Report of summer holiday practical training 2020; Feasibility study on nuclear battery using HTTR core; Feasibility study for nuclear design, 3

Ishitsuka, Etsuo; Mitsui, Wataru*; Yamamoto, Yudai*; Nakagawa, Kyoichi*; Ho, H. Q.; Ishii, Toshiaki; Hamamoto, Shimpei; Nagasumi, Satoru; Takamatsu, Kuniyoshi; Kenzhina, I.*; et al.

JAEA-Technology 2021-016, 16 Pages, 2021/09

JAEA-Technology-2021-016.pdf:1.8MB

As a summer holiday practical training 2020, the feasibility study for nuclear design of a nuclear battery using HTTR core was carried out, and the downsizing of reactor core were studied by the MVP-BURN. As a result, it is clear that a 1.6 m radius reactor core, containing 54 (183 layers) fuel blocks with 20% enrichment of U, and BeO neutron reflector, could operate continuously for 30 years with thermal power of 5 MW. Number of fuel blocks of this compact core is 36% of the HTTR core. As a next step, the further downsizing of core by changing materials of the fuel block will be studied.