Study on Tc separation/concentration technology from Mo by (n,) method, 4

Suematsu, Hisayuki*; Yang, Y.*; Ito, Akito*; Le, A. V.*; Su, Y.*; Kato, Suzuna*; Do, T. M. D.*; Suzuki, Tatsuya*; Osawa, Naoki*; Fujita, Yoshitaka; et al.

KURNS Progress Report 2025, P. 118, 2026/06

https://adm.rri.kyoto-u.ac.jp/pub/progressrep2/

no abstracts in English

Burnup calculation using POD-based neutron spectrum reconstruction

Watanabe, Tomoaki; Aizawa, Naoto*; Chiba, Go*; Tada, Kenichi; Fujita, Tatsuya*; Yamamoto, Akio*

Journal of Nuclear Science and Technology, 63(2), p.166 - 186, 2026/02

https://doi.org/10.1080/00223131.2025.2560559

A fast burnup calculation method based on neutron spectrum reconstruction is proposed. The method employs a reduced-order model (ROM), constructed using proper orthogonal decomposition (POD) and regression models, to estimate neutron spectra experienced by fuel during burnup. The ROM is built from snapshot data generated through detailed burnup and neutron transport simulations under various conditions. During burnup calculations, the ROM is used to rapidly reconstruct neutron spectra at each burnup step. These reconstructed spectra are then used to compute one-group cross sections from multi-group effective cross sections derived using background cross sections. The proposed method significantly reduces computational time by avoiding repeated neutron transport simulations. Its performance is demonstrated using a PWR UO fuel pin model. Results show that, with the 6th-order POD, the method predicts nuclide inventories with an average error within 5% compared to reference Monte Carlo calculations. Error analysis indicates that prediction accuracy is primarily limited by the regression models, rather than by the POD truncation or the multi-group cross section calculations.

Research plan on geosphere stability for long-term isolation of radioactive waste (Scientific program for fiscal year 2025)

Asamori, Koichi; Sueoka, Shigeru; Komatsu, Tetsuya; Ogata, Manabu; Uchida, Mao; Nishiyama, Nariaki; Tanaka, Kiriha; Kobayashi, Tomoharu; Mitsuguchi, Takehiro; Murakami, Osamu; et al.

JAEA-Review 2025-035, 29 Pages, 2025/10

JAEA-Review-2025-035.pdf:1.12MB

This report is a plan of research and development (R&D) on geosphere stability for long-term isolation of high-level radioactive waste (HLW) in Japan Atomic Energy Agency (JAEA), in fiscal year 2025. The objectives and contents of this research are described in detail based on the JAEA 4th Medium- and Long-term Plan (fiscal years 2022-2028). In addition, the background of this research is described from the necessity and the significance for site investigation and safety assessment, and the past progress. The plan framework is structured into the following categories: (1) Development and systematization of investigation techniques, (2) Development of models for long-term estimation and effective assessment, (3) Development of dating techniques.

Study on Tc separation/concentration technology from Mo by (n,) method, 3

Suematsu, Hisayuki*; Yang, Y.*; Kitagawa, Taiga*; Do, T. M. D.*; Suzuki, Tatsuya*; Fujita, Yoshitaka; Fujihara, Yasuyuki*; Yoshinaga, Hisao*; Hori, Junichi*

KURNS Progress Report 2024, P. 123, 2025/06

no abstracts in English

Verification of direct coupling code system using FRENDY version 2 and GENESIS for light water reactor lattices

Fujita, Tatsuya; Yamamoto, Akio*

Journal of Nuclear Science and Technology, 62(2), p.179 - 196, 2025/02

https://doi.org/10.1080/00223131.2024.2410918

This study newly established a direct coupling code system consisting of the nuclear data processing code FRENDY version 2, and the three-dimensional heterogeneous transport code GENESIS (FRENDY-V2/GENESIS) for easy implementation of the random-sampling-based uncertainty quantification considering the implicit effect due to nuclear cross-section (XS) perturbations. The multi-group macroscopic XSs prepared for GENESIS were generated by FRENDY version 2, where the Dancoff factor was calculated by the neutron current method. Then the background XSs were evaluated based on the Carlvik two-term rational approximation. The infinite multiplication factor (k-infinity) and the fission reaction rate distribution in UO and MOX lattice geometries were compared with MVP3 to verify the calculation accuracy of FRENDY-V2/GENESIS. The sensitivity analyses on the discretization conditions such as the ray tracing of the method of characteristics were also carried out. Through several comparisons between FRENDY-V2/GENESIS and MVP3, FRENDY-V2/GENESIS with the SHEM 361-group structure calculates the k-infinity within approximately 50 pcm and the fission reaction rate distribution within approximately 0.1% by the root mean square, respectively. Consequently, the applicability of FRENDY-V2/GENESIS was verified, and FRENDY-V2/GENESIS can be used to discuss the implicit effect due to multi-group XS perturbations.

Enhancement of random sampling by a combined approach of control variates and Latin hypercube sampling for uncertainty quantification in light water reactor lattice calculations

Fujita, Tatsuya

Journal of Nuclear Science and Technology, 62(5), p.470 - 479, 2025/01

https://doi.org/10.1080/00223131.2024.2448320

This study confirmed the efficiency of a combined approach of the control variates (CV) and the Latin hypercube sampling (LHS), which enhanced the random-sampling-based uncertainty quantification due to cross-section (XS) covariance data, by considering the effect of statistical variation and also performed the sensitivity analyses on the influence due to the selection of alternative parameter to apply CV. The convergence performance for the uncertainty of infinite multiplication factor (k-infinity) during the random sampling was compared between several efficient sampling techniques such as the antithetic sampling (AS), LHS, CV, and the combined approaches of them in the PWR-UO fuel assembly geometry. The k-infinity uncertainty was evaluated by statistically processing several times Serpent2 calculations using perturbed ACE-formatted XS files based on ENDF/B-VIII.0. CV+LHS was more efficient than AS, LHS, and CV+AS. In addition, sensitivity analyses were performed to select alternative parameters used in CV. The 33 mini fuel lattice calculation can improve the efficiency of CV+LHS. The reason was qualitatively considered that this calculation can capture the influence of XS covariance data for Gd isotopes. Consequently, the applicability of CV+LHS for the improvement of convergence performance to evaluate the k-infinity uncertainty during the random sampling was confirmed.

Study on Tc separation/concentration technology from Mo by (n, ) method, 2

Fujita, Yoshitaka; Hu, X.*; Yang, Y.*; Kitagawa, Taiga*; Fujihara, Yasuyuki*; Yoshinaga, Hisao*; Hori, Junichi*; Do, T. M. D.*; Suzuki, Tatsuya*; Suematsu, Hisayuki*; et al.

KURNS Progress Report 2023, P. 122, 2024/07

no abstracts in English

Water extraction of technetium-99m from neutron irradiated porous molybdenum dioxide pellet

Hu, X.*; Fujita, Yoshitaka; Tsuchiya, Kunihiko; Fukutani, Satoshi*; Hori, Junichi*; Suzuki, Tatsuya*

Journal of Radioanalytical and Nuclear Chemistry, 333(11), p.6057 - 6063, 2024/05

https://doi.org/10.1007/s10967-024-09529-z

no abstracts in English

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.

-MoO whiskers in Mo/Tc radioisotope production and Mo/Tc extraction using hot atoms

Ngo, M. C.*; Fujita, Yoshitaka; Suzuki, Tatsuya*; Do, T. M. D.*; Seki, Misaki; Nakayama, Tadachika*; Niihara, Koichi*; Suematsu, Hisayuki*

Inorganic Chemistry, 62(32), p.13140 - 13147, 2023/08

https://doi.org/10.1021/acs.inorgchem.3c02125

Technetium-99m (Tc) is one of the most important radioisotopes for diagnostic radio-imaging applications. Tc is a daughter product of the Mo isotope. There are two methods used to produce Mo/Tc: the nuclear fission (n,f) and the neutron capture (n,) methods. Between them, the (n,f) method is the main route, used for approximately 90% of the world's production. However, the (n,f) method faces numerous problems, including the use of highly enriched uranium, the release of highly radioactive waste, and nonproliferation problems. Therefore, the (n,) method is being developed as a future replacement for the (n,f) method. In this work, -MoO whiskers prepared by the thermal evaporation method and -MoO particles were irradiated in a nuclear reactor to produce Mo/Tc via neutron capture. The irradiated targets were dispersed into water to extract the Mo/Tc. As a result, -MoO whisker yielded higher Mo extraction rate than that from -MoO. In addition, by comparing the dissolved Mo concentrations in water, we clarified a prominent hot-atom of -MoO whiskers. This research is the first demonstration of -MoO being used as an irradiation target in the neutron capture method. On the basis of the results, -MoO is considered a promising irradiation target for producing Mo/Tc by neutron capture and using water for the radioisotope extraction process in the future.