Applicability of instrumented indentation for assessing allowable flaw sizes of circumferentially flawed stainless steel piping

Ha, Yoosung; Negyesi, M.*; Hasegawa, Kunio; Lacroix, V.*

Journal of Nondestructive Evaluation, Diagnostics and Prognostics of Engineering Systems, 9(3), p.031001_1 - 031001_6, 2026/08

https://doi.org/10.1115/1.4071687

Cold sintering of whitlockite-based phosphate ceramics for ALPS carbonate slurry waste immobilization

Gubarevich, A.*; Kubo, Ryotaro*; Arisaka, Makoto; Osugi, Takeshi; Yoshida, Katsumi*; Takeshita, Kenji*

Journal of Nuclear Science and Technology, 63(6), p.667 - 676, 2026/06

https://doi.org/10.1080/00223131.2025.2592963

To immobilize and solidify carbonate-based Advanced Liquid Processing System (ALPS) sediment wastes, this study introduces a chemical transformation process that converts these wastes into calcium and magnesium phosphate phases, followed by densification using a novel cold sintering press (CSP) technique. Simulated calcium-magnesium carbonate slurries were treated with phosphoric acid to synthesize calcium and magnesium phosphates, which were then sintered at 300-500C using CSP. The effects of the calcium-to-magnesium ratio, strontium incorporation, and sodium chloride addition on phase composition and CSP densification were investigated. Dense bulk samples were successfully fabricated and characterized using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and the Archimedes method. The results showed that the chemical transformation process led to the formation of whitlockite and newberyite, with the calcium-to-magnesium ratio determining the relative proportions of these phases. Strontium was effectively incorporated into the whitlockite crystal structure, while newberyite enhanced densification through a dehydration-driven process. Sodium chloride had no effect on chemical transformation and was not found in the final solid product. These results show that direct conversion of calcium-magnesium carbonate slurries to whitlockite-based phosphate ceramics, followed by CSP, enables stable solidification, making this method promising for ALPS sediment waste management.

Measurements of neutron capture cross-sections for nuclides of interest in decommissioning (V); Zr(n, )Zr and Zr(n, )Zr reactions at JRR-3

Nakamura, Shoji; Kimura, Atsushi; Endo, Shunsuke; Rovira Leveroni, G.; Shibahara, Yuji*

Journal of Nuclear Science and Technology, 63(6), p.653 - 666, 2026/06

https://doi.org/10.1080/00223131.2025.2586632

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

Analysis of the effect of crack curvature in Mini-C(T) specimen on fracture toughness evaluation

Shimodaira, Masaki; Ha, Yoosung; Takamizawa, Hisashi; Katsuyama, Jinya; Onizawa, Kunio

Journal of Pressure Vessel Technology, 148(2), p.021504_1 - 021504_10, 2026/04

https://doi.org/10.1115/1.4070669

In the current structural integrity assessment of the reactor pressure vessel, the accurate reference temperature (T) based on the Master Curve method is necessary. The T can be estimated by using the Mini-C(T) fracture toughness specimen in accordance with ASTM E1921 and JEAC4216, which prescribe the crack straightness criteria. A requirement in ASTM E1921 has been revised in a decade to increase the accuracy and reasonability, and the applicable crack curvature has been varied by applied codes. The crack curvature of the Mini-C(T) specimen might have an impact on the T because of the variation of the plastic constraint. In this work, the effect of the crack curvature on the fracture toughness (K) evaluation using the Mini-C(T) specimen was quantitatively evaluated by using the finite element analysis (FEA) including the Weibull stress analysis, to discuss the difference in a requirement of the crack straightness in ASTM E1921 and JEAC4216. FEAs showed a possibility that the upper limit curvature would decrease the plastic constraint, and consequently obtain higher K in the Mini-C(T) specimen. Furthermore, if the upper limit curvature according to the ASTM E1921-21 was allowed, the T would be estimated as nonconservative based on the Weibull stress analysis. In contrast, the difference in (T) between the crack with upper limit curvature according to JEAC4216 and the ideal straight crack was not significant.

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.

Experimental measurements for the first series of the modified STACY critical assembly with simple core configurations and experimental analysis using simplified computational models

Gunji, Satoshi; Araki, Shohei; Yoshikawa, Tomoki

Journal of Nuclear Science and Technology, 63(2), p.207 - 215, 2026/02

https://doi.org/10.1080/00223131.2025.2592962

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.