Development of Software for Preparing Documents for IAEA Random Inspections in Safeguards

Shibata, Akira; Sugaya, Naoto; Nishimura, Arashi; Watahiki, Shunsuke

JAEA-Technology 2026-014, 36 Pages, 2026/08

JAEA-Technology-2026-014.pdf:1.23MB

At the 6th Safeguards Committee Meeting of FY2025, deficiencies in documents for IAEA random inspections were discussed, and, to prevent recurrence, the issue was shared with JOYO, DCA, FMF, and JMTR. At JMTR, IAEA random inspections are conducted with two hours advance notice on the inspection morning. This requires accurate preparation of documents shortly after work starts. One required document is a graph of reactor outlet temperature, inlet temperature and main pump output. Previously, this graph was prepared using Argus data collected from Centum. However, Argus became unusable due to malfunctions. During the random inspection on 18 July 2025, one-hour interval data were manually transcribed from Centum into Excel to create the graph. This method uses coarse data, takes time and may cause errors. Therefore, software was developed to generate inspection graphs rapidly and reliably. A data extraction tool was also developed to simplify retrieval of reactor data from Centum.

Proceedings of the 2024 Symposium on Nuclear Data; November 14-15, 2024, Kumatori Community Center "Smiles Rengakan", Kumatori Town, Osaka, Japan

Hori, Junichi*; Kimura, Atsushi; Terada, Kazushi*

JAEA-Conf 2026-001, 165 Pages, 2026/06

JAEA-Conf-2026-001.pdf:13.0MB

The 2024 Symposium on Nuclear Data was held at Kumatori Town Community Center "Smiles Rengakan" in Kumatori Town on November 14-15, 2024. The symposium was organized by the Nuclear Data Division of the Atomic Energy Society of Japan (AESJ) and the Institute for Integrated Radiation and Nuclear Science, Kyoto University in cooperation with the Investigation Committee on Nuclear Data in AESJ, Nuclear Science and Engineering Center of Japan Atomic Energy Agency, and High Energy Accelerator Research Organization. The symposium consisted of six oral presentation sessions and a poster session, with 17 talks and 29 posters presented. The total number of participants was 80. Each oral and poster presentation was followed by an active question and answer session. This report consists of a total of 27 papers including 8 oral and 19 poster presentations.

Implementation of a new function for handling nuclear data of outgoing particles and residual excitation states in PHITS

Furuta, Takuya; Hashimoto, Shintaro; Ogawa, Tatsuhiko; Tanimura, Yoshihiko

Nuclear Instruments and Methods in Physics Research A, 1086, p.171320_1 - 171320_8, 2026/06

https://doi.org/10.1016/j.nima.2026.171320

A new function to incorporate nuclear data libraries with outgoing particles plus residual nuclei in specific excitation states for neutron-induced reactions has been implemented in a Monte Carlo simulation code, Particle and Heavy Ion Transport code System (PHITS). With this function, accurate predictions of outgoing particle spectra and angular distributions according to the nuclear data libraries become possible, while accounting for production of residual nuclei and de-excitation gammas, conserving total energy and momentum in each event. This feature allows users to perform high-precision simulations of detector responses and radiation damage in materials.

Investigations on distribution of radioactive substances owing to the Fukushima Daiichi Nuclear Power Station Accident in the fiscal year 2024 (Contract research)

Group for Fukushima Mapping Project

JAEA-Technology 2025-013, 206 Pages, 2026/03

JAEA-Technology-2025-013.pdf:34.64MB

This report presents results of the investigations on the distribution-mapping project of radioactive substances conducted in FY2024. Car-borne and walk surveys, a measurement using survey meters, and an unmanned helicopter survey were carried out to obtain air dose rate data on land to create their distribution maps, and temporal changes of those air dose rates were analyzed. In order to confirm the applicability of unmanned aircraft to monitoring in mountainous areas, a basic performance of unmanned aircraft was investigated in mountainous areas. Surveys on depth profile of radiocesium and in-situ measurements as for radiocesium deposition were performed. These measurement results were published on the WEB site. Based on these measurement results, effective half-lives of the temporal changes in the air dose rates and the deposition were evaluated. Using the Bayesian hierarchical modeling approach, we obtained maps that integrated air dose rate distribution data acquired through surveys such as car-borne and walk surveys. Radiation monitoring and analysis of environmental samples owing to the comprehensive radiation monitoring plan were carried out. Representative life patterns that can be expected after the return to the evacuation-designated restricted area were set, and the cumulative exposure doses were evaluated for the local governments and residents in the area. Score maps to classify the importance of the measurement points were created, and the temporal changes in the score were analyzed. A system to report the tritium concentration level in seawater to the Nuclear Regulation Authority was operated, and the variation of tritium concentration before and after the discharge of ALPS treated water to the ocean was analyzed. Monitoring data in coastal area performed owing to the comprehensive radiation monitoring plan until FY2024 was analyzed.

Benefits of sensor integration and data fusion in CBRN agents measurements

Woloszczuk, K.*; Maik, P.*; Safronov, A.*; Wieczorek, A.*; Morishita, Yuki; Sanada, Yukihisa; Szklarski, L.*

Zeszyty Naukowe SGSP, 2(96), p.105 - 121, 2025/12

https://doi.org/10.5604/01.3001.0055.5459

Input data preparation for PWR large-break LOCA analysis with RELAP5/MOD3.3 code

Takeda, Takeshi

JAEA-Data/Code 2025-005, 106 Pages, 2025/06

JAEA-Data-Code-2025-005.pdf:2.93MB

JAEA has been creating input data for pressurized water reactor (PWR) analysis with RELAP5/MOD3.3 code, mainly based on design information for the four-loop PWR's Tsuruga Power Station Unit-2 as the reference reactor of the Large Scale Test Facility (LSTF). The cold leg large-break loss-of-coolant accident (LBLOCA) calculation in the flamework of the BEMUSE program is cited as a representative OECD/NEA activity related to the PWR analysis. The new regulatory requirements for PWRs in Japan include the event of loss of recirculation functions from emergency core cooling system (ECCS) in the cold leg LBLOCA. This event should be evaluated the effectiveness of measures against severe core damage. The input data for this study were made preparations to analyze the PWR LBLOCA, which is one of the design basis accidents that should be postulated in the safety design. This report describes the main features of the input data for the PWR LBLOCA analysis. The PWR model comprised a reactor vessel, pressurizer (PZR), hot legs, steam generators (SGs), SG secondary-side system, crossover legs, cold legs, and ECCS. A four-loop PWR was simulated by two loops in the LBLOCA calculation. Specifically, loop-A attached with the PZR corresponded to three loops, and loop-B mounted with the break was equal to one loop. The nodalization schemes of the PWR components were referred to those of the LSTF components. Moreover, interpretations were added to the main input data for the PWR LBLOCA analysis, and further information such as the basis for determining the input data was provided. In addition, transient analysis was performed employing the prepared input data for the loss of ECCS recirculation functions event. The present transient analysis was confirmed to be appropriate generally by comparing with the calculation in the previous study using the RELAP5/MOD3.3 code. Furthermore, sensitivity analyses were executed exploiting the RELAP5/MOD3.3 code to clarify the effects of a discharge coefficient through the break and water injection flow rate of the alternative recirculation on the fuel rod cladding surface temperature. This report explains the results of the sensitivity analyses within the defined ranges, which complement some of the content of the previous study's calculation for the loss of ECCS recirculation functions event.

An Evaluation on Inelastic Thermal Neutron Scattering Cross-Section Data of Crystalline Graphite

Okita, Shoichiro; Abe, Yutaka*; Tasaki, Seiji*; Fukaya, Yuji

Radioisotopes, 73(3), p.233 - 240, 2024/11

https://doi.org/10.3769/radioisotopes.73.233

Analysis of the stress field around concealed active fault from minor faults-slip data collected by geological survey; An Example in the 1984 Western Nagano Earthquake region

Nishiyama, Nariaki; Nakajima, Toru; Goto, Akira*; Hakoiwa, Hiroaki; Nagata, Mitsuhiro; Shimada, Koji; Niwa, Masakazu

Earth and Space Science (Internet), 11(6), p.e2023EA003360_1 - e2023EA003360_15, 2024/06

https://doi.org/10.1029/2023EA003360

Earthquakes with magnitudes of 6-7 have been reported even in various active tectonic settings where fault deformation topography have not been detected. Therefore, delineating concealed active faults generating such earthquakes is necessary to reduce earthquake damage; however, few studies exist to provide its clues regarding such faults. The 1984 Western Nagano Earthquake in Japan was a main shock with a magnitude of Mj 6.8 and a depth of 2 km at the source. Solid bedrocks are well-exposed in the earthquake source region; however, no surface rupture have been identified, and the active fault is known to be concealed. In this study, we collected data on striations observed in fractures by geological survey around the source area of the 1984 Western Nagano Earthquake. Using the collected data, the multiple inverse method was used to estimate the stresses that affected the striation formation. Consequently, stresses similar to acting faults in this area were detected in minor faults around the known concealed active fault. This suggests that the minor faults might be part of the damage zone that has been developed around the concealed active fault. Some minor faults were recognized in Quaternary volcanic rocks, confirming that they experienced displacements recently. This study indicates the possibility of detecting concealed active faults in the bedrock by geological survey.

A Comparative study of efficient sampling techniques for uncertainty quantification due to cross-section covariance data

Fujita, Tatsuya

Proceedings of International Conference on Physics of Reactors (PHYSOR 2024) (Internet), p.718 - 727, 2024/04

https://doi.org/10.13182/PHYSOR24-43640

The convergence process of the k-infinity uncertainty during random-sampling-based uncertainty quantification was compared between several efficient sampling techniques. The k-infinity uncertainty was evaluated by statistically processing several times of SERPENT 2.2.1 calculations using perturbed ACE files based on JENDL-5 cross-section covariance data. The antithetic sampling (AS), the Latin hypercube sampling (LHS), the control variates (CV), and the combination approaches of them were focused on in the present paper. In PWR-UO fuel assembly geometry without the nuclide depletion, as discussed in past studies, AS and LHS showed higher efficient convergence than nominal sampling without any efficient sampling techniques. In terms of CV, though a stand-alone application did not have a large impact on the k-infinity uncertainty convergence, its performance was improved in combination with AS, as discussed in the past study. In addition, a new combined approach of LHS and CV (CV+LHS) was proposed in the present paper. CV+LHS improved the k-infinity uncertainty convergence and was more efficient than CV+AS. The main reason for this improvement was that the convergence for the mean value of alternative parameters in CV was enhanced by applying LHS. Consequently, this study proposed the new combined approach of CV+LHS and confirmed its efficiency performance for the random-sampling-based uncertainty quantification in the PWR-UO fuel assembly geometry. The applicability of CV+LHS for the nuclide-depletion calculations will be confirmed in future studies.

A Side event at the IAEA 67th General Conference "Providing the best nuclear data for tomorrow's nuclear solutions; Challenges and opportunities"; For "visualization" of nuclear data usage

Fukahori, Tokio

Kaku Deta Nyusu (Internet), (137), p.1 - 10, 2024/02

http://www.aesj.or.jp/~ndd/ndnews/pdf137/No137-01.pdf

At the request of the EC/Joint Research Center, the author attended on an EU-sponsored side event "Providing the best nuclear data for tomorrow's nuclear solutions: challenges and opportunities" held simultaneously at the IAEA 67th General Conference as a panelist. Presented were the prospects for nuclear data activities in Japan and discussed the sustainability and revitalization of nuclear data activities. In addition, based on the roundtable discussion at this side event, the Nuclear Data Section held a meeting consisting mainly of panelists to consider future responses. In this article, I would like to report on the side event and subsequent follow-up meetings and discuss the background of these meetings.