Utilization of gamma ray irradiation at the WASTEF Facility

Sano, Naruto; Yamashita, Naoki; Watanabe, Masaya; Tsukada, Manabu*; Hoshino, Kazutoyo*; Hirai, Koki; Ikegami, Yuta*; Tashiro, Shinsuke; Yoshida, Ryoichiro; Hatakeyama, Yuichi; et al.

JAEA-Technology 2023-029, 36 Pages, 2024/03

JAEA-Technology-2023-029.pdf:2.47MB

At the Waste Safety Testing Facility (WASTEF), the gamma ray irradiation device "Gamma Cell 220" was relocated from the 4th research building of the Nuclear Science Research Institute in FY2019, and the use of gamma ray irradiation has begun. Initially, Fuel Cycle Safety Research Group, Fuel Cycle Safety Research Division, Nuclear Safety Research Center, Sector of Nuclear Safety Research and Emergency Preparedness, the owner of this device, conducted the tests as the main user, but since 2022, other users, including those outside the organization, have started using it. The gamma ray irradiation device "Gamma Cell 220" is manufactured by Nordion International Inc. in Canada. Since it was purchased in 1989, the built-in 60Co radiation source has been updated once, and safety research related to nuclear fuel cycles, etc. It is still used for this purpose to this day. This report summarizes the equipment overview of the gamma ray irradiation device "Gamma Cell 220", its permits and licenses at WASTEF, usage status, maintenance and inspection, and future prospects.

Training using JMTR and related facilities in FY2021 and FY2022

Nakano, Hiroko; Fujinami, Kyoko; Yamaura, Takayuki; Kawakami, Jun; Hanakawa, Hiroki

JAEA-Review 2023-036, 33 Pages, 2024/03

JAEA-Review-2023-036.pdf:2.47MB

A practical training course using the JMTR (Japan Materials Testing Reactor) and other research infrastructures was held from November 29 to December 2 in 2021 for Asian young researchers and engineers. This course was adopted as International Youth Exchange Program in Science (SAKURA SCIENCE Exchange Program) which is the project of the Japan Science and Technology Agency, and this course aims to enlarge the number of high-level nuclear researchers/engineers in Asian countries which are planning to introduce a nuclear power plant, and to promote the use of facilities in future. In this year, from the viewpoint of preventing the spread of COVID-19 infection, it was decided to hold the event online. 53 young researchers and engineers joined the course from 6 countries. In FY2022, training programs with invitations were held due to the easing of restrictions on entry into Japan from overseas. 7 young researchers and engineers from4 Asian countries participated in the training from February 1 to 10, 2023.The common curriculum in the training course of FY2021 and FY2022 included lectures on nuclear energy, irradiation testing, safety management, JMTR decommissioning plan, etc. In the online session, conducted in FY2021, information exchange on the energy situation in each country was conducted. On-site training conducted in FY2022, included practical training on operation using simulations, environmental monitoring, etc. and facility tours of the JMTR, etc. Many participants could join the online training course, they created a diversity of expertise and made lively discussions during the information exchange. On-site training, while limited in number of participants, provided a good opportunity for personnel exchange through practical training and face-face communication. It is desirable to hold on-site training as long as circumstances permit. This report summarizes the training conducted in FY2021 and FY2022.

Latent ion tracks were finally observed in diamond

Amekura, Hiroshi*; Chettah, A.*; Narumi, Kazumasa*; Chiba, Atsuya*; Hirano, Yoshimi*; Yamada, Keisuke*; Yamamoto, Shunya*; Leino, A. A.*; Djurabekova, F.*; Nordlund, K.*; et al.

Nature Communications (Internet), 15, p.1786_1 - 1786_10, 2024/02

https://doi.org/10.1038/s41467-024-45934-4

Injecting high-energy heavy ions in the electronic stopping regime into solids can create cylindrical damage zones called latent ion tracks. Although these tracks form in many materials, none have ever been observed in diamond, even when irradiated with high-energy GeV uranium ions. Here we report the first observation of ion track formation in diamond irradiated with 2-9 MeV C fullerene ions. Depending on the ion energy, the mean track length (diameter) changed from 17 (3.2) nm to 52 (7.1) nm. High resolution scanning transmission electron microscopy (HR-STEM) indicated the amorphization in the tracks, in which -bonding signal from graphite was detected by the electron energy loss spectroscopy (EELS).

Meso-timescale atomistic simulations on coalescence process of He bubbles in Fe by SEAKMC method

Yamamoto, Yojiro*; Hayakawa, Sho*; Okita, Taira*; Itakura, Mitsuhiro

Computational Materials Science, 229, p.112389_1 - 112389_9, 2023/10

https://doi.org/10.1016/j.commatsci.2023.112389

He bubbles are characteristic microstructures under fusion reactor conditions. They approach and coalesce through their own migration, which significantly impacts the microstructure and material properties. However, these processes, which involve multiple migrations of metal atoms, cannot be treated by molecular dynamics (MD) due to its timescale limitation. In this study, self-evolving atomistic kinetic Monte Carlo (SEAKMC) was used to expand the timescale and reproduce bubble coalescences in Fe. To enhance selections of events that led to the process by avoiding trivial events with an extremely low activation energy such as tiny vibrations of a He atom or short-range displacements of the Fe atom, we introduced two algorithms into SEAKMC, a two-step saddle point search for the former measure and setting a threshold for a displacement distance of the Fe atom for the latter. Furthermore, by adding another algorithm to set an upper bound for the activation energy to prevent selections of events with an impractically high activation energy, we succeeded to reproduce the change in the configuration from dumbbell to elliptical up to a simulated time of s, 8 orders longer than MD timescales. The developed method is effective for analyzing microstructures of metallic materials containing light elements and is the only method that can reach timescales comparable to those of experiments.

Validation of fuel behavior analysis code FEMAXI-8 using fast reactor MOX fuel irradiation tests

Ikusawa, Yoshihisa; Nagayama, Masahiro*

JAEA-Data/Code 2023-006, 24 Pages, 2023/07

JAEA-Data-Code-2023-006.pdf:1.42MB

Core fuels with stainless steel cladding and high plutonium content mixed oxide (MOX) fuel in a water-cooled environment, such as supercritical water-cooled reactors (SCWR) and reduced-moderation water reactors (RMWR), have been studied. In order to contribute to the research and development of such a core fuel concept, the fuel performance code "FEMAXI-8" was verified based on the results of post irradiation examinations of MOX fuel irradiated in the experimental fast reactor "JOYO". FEMAXI-8 is the latest version of the behavior analysis code developed by JAEA to analyze the behavior of light water reactor fuels under normal operation and transient conditions. This latest code has been improved and developed to allow the selection of stainless steel cladding property models to analyze improved fuels such as accident tolerant fuels. The purpose of this report is to confirm the prediction accuracy of FEMAXI-8 for the irradiation behavior of the new type of core fuel that is currently being developed. As a result of the verification, it was confirmed that FEMAXI-8 has sufficient analysis accuracy for the irradiation behavior of sodium-cooled fast reactor MOX fuel with stainless steel cladding, which exceeds the plutonium content and irradiation conditions of light water reactors. In the future, the analysis accuracy of FEMAXI-8 could be improved by adopting the O/M ratio dependence of MOX fuel thermal conductivity and the irradiation behavior evaluation model at high temperature.

Mechanical properties of pure tungsten and tantalum irradiated by protons and neutrons at the Swiss spallation-neutron source

Saito, Shigeru; Suzuki, Kazuhiro; Obata, Hiroki; Dai, Y.*

Nuclear Materials and Energy (Internet), 34, p.101338_1 - 101338_9, 2023/03

https://doi.org/10.1016/j.nme.2022.101338

In this study, a post-irradiation examination of pure tungsten (W) and tantalum (Ta) specimens irradiated at the Swiss Spallation-Neutron Source is conducted. W is used as a potential candidate for a solid spallation-target material owing to its favorable properties. However, W also suffers from several disadvantages such as poor corrosion resistance to water coolant and irradiation embrittlement. To improve these properties, cladding technologies using Ta for W alloys have been developed. In the present study, we investigated the irradiation effects on two tungsten materials, poly-crystal W (W-Poly) and single-crystal W (W-Sin), along with pure polycrystalline Ta. The tensile-test results revealed that W-Poly exhibited almost no ductility after irradiation of 10.2-35.0 dpa. W-Sin was irradiated up to 10.2 dpa and demonstrated 6% of total elongation (TE). With regard to Ta, TE decreased based on the increase in irradiation, reaching almost zero at doses of more than 10.3 dpa.

Long-timescale transformations of self-interstitial atom clusters of Cu using the SEAKMC method; The Effect of setting an activation energy threshold for saddle point searches

Hayakawa, Sho*; Yamamoto, Yojiro*; Okita, Taira*; Itakura, Mitsuhiro; Suzuki, Katsuyuki*

Computational Materials Science, 218, p.111987_1 - 111987_10, 2023/02

https://doi.org/10.1016/j.commatsci.2022.111987

Tensile properties of modified 316 stainless steel (PNC316) after neutron irradiation over 100 dpa

Yano, Yasuhide; Uwaba, Tomoyuki; Tanno, Takashi; Yoshitake, Tsunemitsu; Otsuka, Satoshi; Kaito, Takeji

Journal of Nuclear Science and Technology, 9 Pages, 2023/00

https://doi.org/10.1080/00223131.2023.2243943

The effects of fast neutron irradiation on tensile properties of modified 316 stainless steel (PNC316) claddings and wrappers for fast reactors were investigated. PNC316 claddings and wrappers were irradiated in the experimental fast reactor Joyo at irradiation temperatures between 400 and 735 C to fast neutron doses ranging from 21 to 125 dpa. The post-irradiation tensile tests were carried out at room and irradiation temperatures. Elongations of PNC316 measured by the tensile tests were maintained at an engineering level, although the material incurred significant irradiation hardening and softening. The maximum swelling of PNC316 wrappers was about 2.5 vol.% at irradiation temperature between 400 and 500C up to 110 dpa. Japanese 20% cold-worked austenitic steels, PNC316 and 15Cr-20Ni, had sufficient ductility and work-hardenability even after above 10 vol.% swelling, while they had very weak plastic instabilities.

Structure and magnetic properties of Fe nanoparticles in amorphous silica implanted with Fe ions and effect of subsequent energetic heavy ion irradiation

Iwase, Akihiro*; Fukuda, Kengo*; Saito, Yuichi*; Okamoto, Yoshihiro; Semboshi, Satoshi*; Amekura, Hiroshi*; Matsui, Toshiyuki*

Journal of Applied Physics, 132(16), p.163902_1 - 163902_10, 2022/10

https://doi.org/10.1063/5.0102438

Amorphous SiO samples were implanted with 380 keV Fe ions at room temperature. After implantation, some of the samples were irradiated with 16 MeV Au ions. magnetic properties were investigated using a SQUID magnetometer, and the morphology of the Fe-implanted SiO samples was examined using transmission electron microscopy and X-ray absorption spectroscopy (EXAFS and XANES), which showed that the size of Fe nanoparticles was increasing The size of Fe nanoparticles increased with increasing Fe implantation amount; some of the Fe nanoparticles consisted of Fe oxides, and the valence and structure of Fe atoms became closer to that of metallic -Fe with increasing Fe injection amount. The magnetization-field curve of the sample implanted with a small amount of Fe was reproduced by Langevin's equation, suggesting that the Fe nanoparticles behave in a superparamagnetic manner. In addition, when a large amount of Fe was implanted, the magnetization-magnetic field curve shows a ferromagnetic state. These magnetic property results are consistent with the X-ray absorption results. Subsequent 16 MeV Au irradiation crushed the Fe nanoparticles, resulting in a decrease in magnetization.

The Damage analysis for irradiation tolerant spin-driven thermoelectric device based on single-crystalline YFeO/Pt heterostructures

Ieda, Junichi; Okayasu, Satoru; Harii, Kazuya*; Kobata, Masaaki; Yoshii, Kenji; Fukuda, Tatsuo; Ishida, Masahiko*; Saito, Eiji

IEEE Transactions on Magnetics, 58(8), p.1301106_1 - 1301106_6, 2022/08

https://doi.org/10.1109/TMAG.2022.3145888

The combination of spin-driven thermoelectric (STE) devices based on spin Seebeck effect (SSE), and radioactive isotopes as heat sources, has potential as a next-generation method of power generation in applications such as power supplies for space probes. However, there has been very limited knowledge available indicating the irradiation tolerance of spin thermoelectric devices. Through analysis using a heavy ion-beam accelerator and the hard X-ray photoemission spectroscopy (HAXPES) measurements, we show that a prototypical STE device based on YFeO/Pt heterostructures has tolerance to irradiation of high-energy heavy-ion beams. We used 320 MeV gold ion beams modeling cumulative damages due to fission products emitted from the surface of spent nuclear fuels. By varying the dose level, we confirmed that the thermoelectric and magnetic properties of the SSE elements are not affected by the ion-irradiation dose up to ions/cm fluence and that the SSE signal is extinguished around ions/cm, in which the ion tracks almost fully cover the sample surface. In addition, the HAXPES measurements were performed to understand the effects at the interface of YFeO/Pt. The HAXPES measurements suggest that the chemical reaction that diminishes the SSE signals is enhanced with the increase of the irradiation dose. We share the current understandings of the damage analysis in YFeO/Pt for developing better STE devices applicable to harsh environmental usages.