Long-term simulation of Cs behavior in the ocean around Fukushima considering multiphase interaction processes

Ikenoue, Tsubasa; Nakanishi, Takahiro; Kawamura, Hideyuki

Marine Pollution Bulletin, 232, p.120110_1 - 120110_9, 2026/11

https://doi.org/10.1016/j.marpolbul.2026.120110

The accident at the Fukushima Daiichi Nuclear Power Plant caused a large-scale migration of radionuclides, including cesium-137 (Cs), into the marine environment. Cesium-137 in the ocean exists in four phases (dissolved, suspended, seabed sediment, and biota), and the interactions between these phases have a great impact on its long-term behavior. Therefore, this study developed an oceanic dispersion model considering multiphase behavior and evaluated the impact of interphase interactions on the long-term behavior of Cs during the decade after the accident. The model sufficiently reproduced the oceanographic conditions and the behavior of planktons, suspended particles, and Cs. The results were consistent with previous studies, suggesting that the dissolved phase and seabed sediment phase played a central role in the Cs behavior within the first three months after the accident and thereafter, respectively. Within 10 years after the accident, the concentrations of all phases in offshore waters (deeper than 25 m) returned to pre-accident levels, but those in coastal waters (shallower than 25 m) were still at high levels due to the long-term source from seabed sediment to other phases, which is attributed to the retention of high concentrations in the seabed sediment phase. The quantitative analysis of interphase interactions made it possible to confirm that this retention was caused by a large proportion of fine-grained particles (bay area), riverine inputs (northern Fukushima), and high accumulation in the surface layers in the early stage of the accident and vigorous vertical mixing (southern Fukushima).

Removal and storage of asbestos-containing materials used in radiation controlled areas

Ishida, Reiya; Aoki, Emi; Sonobe, Hiroshi; Oto, Tsutomu; Kimura, Akihiro

JAEA-Review 2026-019, 50 Pages, 2026/07

JAEA-Review-2026-019.pdf:5.3MB

Subsequent to a leakage incident in October 2012 involving the SFC waste liquid transfer piping in the C Trench, additional leakage incidents occurred in the No. 4 drainage system piping and the SFC waste resin transfer piping. Furthermore, leakage incidents occurred in the tank yard, including seepage at welded joints in the waste liquid piping, as well as leakage from the waste liquid tanks. Since these incidents, the transfer of liquid waste from the hot laboratory facility to the JMTR tank yard has been suspended. Currently, as the waste liquid piping in the JMTR tank yard and the waste liquid tanks receiving liquid waste from the hot laboratory have been replaced and in sound condition, a plans is being developed to resume liquid waste transfer. To confirm the integrity of the waste liquid piping system, which runs from the hot laboratory through the C Trench to the tank yard, radiographic testing (hereafter referred to as "RT") of the pipe welds will be conducted. As it has been confirmed that the waste liquid piping is wrapped with asbestos-containing thermal insulation materials, these materials will be removed from the piping prior to RT. During this removal work, it is essential to comply with applicable laws and regulations and to ensure worker safety. This report summarizes the plan for removal of asbestos-containing thermal insulation materials in radiation controlled areas in order to minimize asbestos-related risks, as well as the procedures for the removal work and the methods for storage management.

Investigation of differences in the mean time between beam trips between normal-conducting and superconducting acceleration cavities

Takei, Hayanori

JPS Conference Proceedings (Internet), 45, p.011175_1 - 011175_7, 2026/06

https://doi.org/10.7566/JPSCP.45.011175

The Japan Atomic Energy Agency is working on the research and development of an accelerator-driven nuclear transmutation system (ADS) for transmuting minor actinides. This system is a combination of a subcritical nuclear reactor and a high-power superconducting proton linear accelerator (JADS-linac). One of the challenges in developing the JADS-linac is to reduce the number of beam trips. Until now, the beam trip frequency of the JADS-linac has been estimated from the operation data of the J-PARC linac, which uses the normal-conducting acceleration (NC) cavities. Recently, data on beam trips in the superconducting acceleration (SRF) cavities of the Spallation Neutron Source of the Oak Ridge National Laboratory (SNS) have been published. These data are important for the estimation of the beam trip frequency of the JADS-linac. Rather, the SNS data are more appropriate than the J-PARC data, because the JADS-linac uses the SRF cavities. On the other hand, the calculation methods in the published data for the NC cavities of J-PARC and the SRF cavities of SNS are different, so it is not possible to simply compare the two. In this study, the mean time between beam trips (MTBT) of the J-PARC NC cavity and the SNS SRF cavity are compared using the same condition. Specifically, the MTBT of the acceleration cavities connected to a single klystron system was calculated and compared. As a result, the MTBT of the SNS SRF cavity was 5.0 and 8.8 times longer than that of the J-PARC NC cavity for and h, respectively, where is the beam trip duration.

International benchmark on radionuclide solubility and speciation for the Long-term In-situ Test (LIT) at Grimsel Test Site (GTS, Switzerland)

Noseck, U.*; Schfer, T.*; Alonso, U.*; Hamamoto, Takafumi*; Havlova, V.*; Hibberd, R.*; Ishidera, Takamitsu; Kitamura, Akira; Klajmon, M.*; Missana, T.*; et al.

Applied Geochemistry, 201, p.106762_1 - 106762_23, 2026/04

https://doi.org/10.1016/j.apgeochem.2026.106762

Thermodynamic benchmark calculations have been performed to better understand the behavior of Se(VI), Tc(VII), U(VI), Np(V), Am(III), Th(IV) and Pu(IV)) in the evolving geochemical conditions of the Long-term In-situ Test (LIT) at the Grimsel Test Site (GTS) and corresponding mock-up experiment. It also aims to identify the status of the geochemical speciation models and databases for these elements. The experiments are simulating the near-field conditions in some radioactive waste repository concept including a bentonite engineered barrier emplaced in crystalline rock and the findings are contributing to the long-term safety assessment of these facilities.

Measurement of uranium and fission products in a spent fuel sample using fiber-optic laser-induced breakdown spectroscopy

Batsaikhan, M.; Oba, Hironori*; Karino, Takahiro; Akaoka, Katsuaki; Wakaida, Ikuo*; Iwata, Yoshihiro; Sakamoto, Kan*

Journal of Analytical Atomic Spectrometry, 41(4), p.1324 - 1335, 2026/04

https://doi.org/10.1039/D5JA00451A

Risk communication activity which used "YUME Chisoukan" in the Horonobe Underground Research Center (FY 2024)

Hoshino, Masato; Sasaki, Yoshifumi; Horikoshi, Hidehiko*; Tani, Kosuke*

JAEA-Review 2025-047, 122 Pages, 2026/03

JAEA-Review-2025-047.pdf:3.75MB

Horonobe Underground Research Center managed by Japan Atomic Energy Agency (JAEA) is the Japan's best environment to understand the project of geological disposal of high-level radioactive waste, because there is an Underground Research Laboratory (URL) in the center besides an exhibition facility which explains the content of research conducted in the URL. In the area of the center, there is also an exhibition facility for the full-scale model of engineered barrier system of geological disposal. JAEA takes advantage of this opportunity to conduct public hearing including questionnaire research regarding the questions, anxieties and comments by the visitors for geological disposal project. This report summarizes the result of statistical analysis of 2,830 visitors from April 2024 to January 2025.

Synthesis report on the R&D for the Horonobe Underground Research Laboratory Project carried out between fiscal years 2020-2024

Nakayama, Masashi; Ishii, Eiichi; Aoyagi, Kazuhei; Hayano, Akira; Ono, Hirokazu; Ozaki, Yusuke; Mochizuki, Akihito; Takeda, Masaki; Kimura, Shun

JAEA-Research 2025-016, 141 Pages, 2026/03

JAEA-Research-2025-016.pdf:13.37MB

The Horonobe Underground Research Laboratory (URL) Project is being pursued by the Japan Atomic Energy Agency (JAEA). The main aim of the project is to enhance the reliability of relevant technologies for the geological disposal of high-level radioactive waste by investigating the deep geological environment within the host sedimentary rocks at Horonobe in Hokkaido, northern Japan. These investigations have been conducted in three phases: "Phase 1: Surface-based investigation", "Phase 2: Construction" (investigation during tunnel excavation) and "Phase 3: Operation" (investigation in subsurface facilities). Since the fiscal year 2020, we have been conducting R&D based on the Horonobe Underground Research Plan for the Fiscal Year 2020 Onwards, which was approved by Hokkaido Prefecture and Horonobe Town. In particular, we are working on the following key tasks with the aim of completing JAEA's 3rd and 4th Mid- and Long-Term Plans: "Study on near-field system performance in geological environments", "Demonstration of repository design options" and "Understanding of buffering behaviour of sedimentary rocks to natural perturbations". This report summarizes the R&D activities on the three above-mentioned key tasks, the goals of which were achieved between fiscal years 2020 and 2024. The results obtained from these tasks will be systematically organized as part of the "Systematic integration of technologies towards EBS emplacement" which has been in progress since fiscal year 2024. This task includes concepts related to the layout of galleries and pits, installation methods for engineered barrier materials, and methods for evaluating their containment performance.

Benchmark analyses of criticality calculation on SCALE 6.2.3 code system

Okamoto, Naritoshi; Komeno, Akira; Seya, Atsumasa; Inaba, Hideki*; Terakado, Shinichi*; Higuchi, Masashi*

JAEA-Data/Code 2025-022, 497 Pages, 2026/03

JAEA-Data-Code-2025-022.pdf:18.06MB

The Plutonium Fuel Third Development Laboratory of the Nuclear Fuel Cycle Engineering Laboratories has applied for a change of use permit (hereinafter referred to as "license") for plutonium fuel facilities. For the criticality safety design of gloveboxes and equipment/instruments handling mixed oxide (MOX), various criticality calculation codes are used. The most recent employs the 3D Monte Carlo calculation code KENO-V.a embedded in the SCALE 4.4 code system, along with the 27-group ENDF/B-IV neutron cross-section library. SCALE 4.4 was released by the Oak Ridge National Laboratory (ORNL) in the US in 1998, and has now been in use for 27 years. ORNL has continuously improved its functionality, with SCALE 6.3.2 released in 2024. When designing and constructing new MOX fuel facilities, it is desirable to obtain a license using criticality calculation codes based on the latest knowledge. However, it is necessary to verify that these codes have sufficient reliability. Therefore, in 2018, benchmark calculations were performed using the 252-group ENDF/B-VII.1 neutron cross-section library (v7-252n) for two versions of the criticality calculation sequences KENO-V.a and KENO-VI from SCALE 6.2.3, based on past criticality experimental setups. The estimated critical-limiting multiplication factor was calculated. The results indicate that these codes can be used with sufficient confidence for criticality safety design of MOX fuel facilities.

Effect of coaxial HPGe detector structure on -ray beam measurements

Omer, M.; Shizuma, Toshiyuki*; Koizumi, Mitsuo; Taira, Yoshitaka*; Zen, H.*; Ogaki, Hideaki*; Hajima, Ryoichi*

Radiation Physics and Chemistry, 240, p.113467_1 - 113467_8, 2026/03

https://doi.org/10.1016/j.radphyschem.2025.113467

Experimental study of AESOP code for aerosol removal behavior from a rising gas bubble in water pool and parametric study for application to sodium pool system

Miyahara, Shinya*; Koie, Ryusuke*; Uno, Masayoshi*; Kawaguchi, Munemichi*; Sato, Rika; Seino, Hiroshi

Nuclear Engineering and Design, 446(Part A), p.114523_1 - 114523_14, 2026/01

https://doi.org/10.1016/j.nucengdes.2025.114523