Bayesian approach to model temperature dependence of Charpy absorbed energy and uncertainty evaluation of ductile-to-brittle transition temperature for reactor pressure vessel steel

Takamizawa, Hisashi; Nishiyama, Yutaka

Journal of Pressure Vessel Technology, 148(3), p.031501_1 - 031502_12, 2026/06

https://doi.org/10.1115/1.4070725

Embrittlement of reactor pressure vessel (RPV) steel caused by neutron irradiation has been evaluated using ductile-to-brittle transition temperature (DBTT) derived from surveillance tests (Charpy impact tests) during plant operation. For reliable structural integrity assessment of the RPV, incorporating adequate safety margins which take into account uncertainties inherent in surveillance Charpy impact tests is needed. In this study, a model to evaluate temperature dependence of Charpy absorbed energy variability using approximately 1,900 datasets of unirradiated and irradiated materials manufactured in Japan and United States was developed. Next, probability distribution of Charpy ductile-to-brittle transition temperature at a 41J energy level () was evaluated by estimating the probability distribution of Charpy test data using Monte Carlo sampling and Bayesian inference. From the detailed evaluation of the relationship between the number of specimens and uncertainty, uncertainty of was found to be almost the same in materials manufactured in Japan and U.S., and unchanged with neutron irradiation (no clear change in material inhomogeneity). Regarding product form on the other hand, uncertainty of for base metal and weld metal was almost the same, but the heat affected zone was shown to have large uncertainty.

Accurate measurement of the I neutron capture cross-section in the keV neutron region

Rovira Leveroni, G.; Kimura, Atsushi; Nakamura, Shoji; Endo, Shunsuke; Iwamoto, Osamu; Iwamoto, Nobuyuki; Katabuchi, Tatsuya*

Journal of Nuclear Science and Technology, 63(4), p.358 - 369, 2026/04

https://doi.org/10.1080/00223131.2025.2543579

Simple technique for the preparation of uranium-impregnated porous silica particles and their application as working standard particles for analysis of the safeguards environmental samples

Tomita, Jumpei; Tomita, Ryohei; Suzuki, Daisuke; Yasuda, Kenichiro; Miyamoto, Yutaka

Journal of Nuclear Science and Technology, 63(4), p.443 - 454, 2026/04

https://doi.org/10.1080/00223131.2025.2557376

Temperature effect on radiolytically generated hydrogen yield from a plutonium nitric acid aqueous solution

Toigawa, Tomohiro; Hotoku, Shinobu; Kumagai, Yuta; Abe, Yuma*; Oyama, Kanichi*; Fukaya, Hiroyuki; Ban, Yasutoshi; Kida, Takashi; Hasegawa, Satoshi*; Nakano, Masanao*; et al.

Journal of Nuclear Science and Technology, 63(3), p.322 - 327, 2026/03

https://doi.org/10.1080/00223131.2025.2541067

The effect of temperature on hydrogen production generated from radiolysis was investigated to determine the associated implications for nuclear fuel reprocessing safety. The hydrogen yield from radiolysis of plutonium nitric acid solution was measured at temperatures up to the boiling temperature of the solution. The results showed no notable temperature dependence even under boiling conditions. The impact of solution agitation on hydrogen production was also assessed, which revealed minor differences in the hydrogen yield between static and agitated conditions at room temperature. These findings suggest that high temperatures or boiling the solution do not considerably enhance hydrogen generation, and provide crucial information for accurately modeling hydrogen risks under severe accidents.

Feasibility study on the production of Th as a long-life Ac generator using the experimental fast reactor Joyo

Sasaki, Yuto; Maeda, Shigetaka; Fukasawa, Tetsuo*; Takaki, Naoyuki*

Journal of Nuclear Science and Technology, 63(2), p.154 - 165, 2026/02

https://doi.org/10.1080/00223131.2025.2558244

In recent years, targeted alpha therapy, which utilizes Ac combined with antibodies or peptides that selectively accumulate in cancer cells, has garnered attention in the field of nuclear medicine. To meet the resulting increasing demand for Ac, exploring alternative production methods is essential. While several researchers, including the authors, have explored production methods using Ra as a raw material, challenges remain, such as the limited availability of Ra, difficulties in handling it, and the requirement for regular irradiation. To address these challenges, the authors focused on developing a production strategy for a long-life Ac generator using Th as a raw material and the experimental fast reactor Joyo. A detailed investigation was conducted, encompassing chemical processing after irradiation, target availability, and production yields, including the most probable values and associated uncertainties. Results revealed that although enrichment of the raw material and long-term irradiation are required, Ac can be produced in quantities comparable to its current global supply. Furthermore, this research has shown that the THOREX method, which is already in practical use, be applied to effectively separate by-products such as fission products and radioactive materials from thorium during the chemical processing after irradiation, as revealed by a literature survey.

Sub-pin level distribution tallies and statistical error estimation with POD tallies in two-dimensional C5G7 benchmark

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

Journal of Nuclear Science and Technology, 63(2), p.142 - 153, 2026/02

https://doi.org/10.1080/00223131.2025.2554969

The flux distribution tallies using proper orthogonal decomposition, called POD tallies, have been developed to address issues of high-fidelity Monte Carlo simulations. The POD tallies can reduce both dimensionality and statistical error. The present study verifies the applicability of the POD tallies to sub-pin level flux distribution in the two-dimensional C5G7 benchmark. Statistical error estimation is also proposed by applying the circular block bootstrap method to the POD tallies to estimate the statistical error of the flux distribution in a single Monte Carlo calculation. In the verification, the dimensionality of the finely discretized distribution is reduced by more than 90% compared with conventional cell tallies. The statistical error is reduced by more than half as the average value of all tally regions. The proposed approach is confirmed to properly estimate the statistical error of flux distribution considering both the inter-cycle correlation and the correlation between the expansion coefficients of different POD orders.

Machine learning potentials for refractory high-entropy alloys applied to atomistic modeling of dislocation slip behavior

Lobzenko, I.; Mori, Hideki*; Tsuru, Tomohito

Journal of Materials Research and Technology, 40, p.3798 - 3805, 2026/01

https://doi.org/10.1016/j.jmrt.2025.12.203

no abstracts in English

Impact of nuclear data updates from JENDL-4.0 to JENDL-5 on burnup calculations of light-water reactor fuels

Watanabe, Tomoaki; Tada, Kenichi; Endo, Tomohiro*; Yamamoto, Akio*

Journal of Nuclear Science and Technology, 63(1), p.3 - 18, 2026/01

https://doi.org/10.1080/00223131.2025.2486798

This study investigated the impact of nuclear data updates from JENDL-4.0 (J4) to JENDL-5 (J5) on the light-water reactor fuel burnup calculations. Burnup calculations were conducted with J4 and J5 for PWR pin-cell and BWR fuel assembly geometries. The calculation results revealed significant burnup-dependent differences in the neutron multiplication factor (k). Across the burnup range of 0-50 GWd/t, k values of J5 were consistently smaller than those of J4 and the difference gradually increased as burnup progressed. Direct sensitivity calculations, in which each nuclide data was replaced from J4 to J5, indicated that updates to the cross-sections of U, U, and Pu and the thermal scattering law data of H in HO notably impacted the k differences. For the BWR assembly geometry containing Gd fuels, large k differences were observed in the burnup range of 10-15 GWd/t. This difference was primarily attributed to updates in the U, Gd, and Gd cross-sections, and thermal scattering law data of H in HO. Furthermore, we investigated how the nuclear data updates affected the k differences by examining nuclide number densities, the energy-dependent sensitivities, and the neutron spectra.

Generation of pressure pulse and water hammer triggered by high-burnup fuel failure under reactivity-initiated accident conditions

Mihara, Takeshi; Udagawa, Yutaka

Journal of Nuclear Science and Technology, 17 Pages, 2026/00

https://doi.org/10.1080/00223131.2025.2611410

Special issue on progressive reactor physics for current and future challenges

Tada, Kenichi; Aizawa, Naoto*; Fujita, Tatsuya*; Fukushima, Masahiro; Pyeon, C. H.*

Journal of Nuclear Science and Technology, 63(1), p.1 - 2, 2026/00

https://doi.org/10.1080/00223131.2026.2613783

This document is the preface to "Special Issue on Progressive Reactor Physics for Current and Future Challenges" published in the Journal of Nuclear Science and Technology.