Computer code analysis of irradiation performance of an annular mixed oxide fuel element

Yokoyama, Keisuke; Uwaba, Tomoyuki

Journal of Nuclear Science and Technology, 60(10), p.1219 - 1227, 2023/10

https://doi.org/10.1080/00223131.2023.2188272

no abstracts in English

Development of the evaluation method for the mobile radioactive contaminants for assessing public exposure risk in accidental events during decommissioning of nuclear power station

Sasagawa, Tsuyoshi; Shimada, Taro; Takeda, Seiji

Proceedings of 31st International Conference Nuclear Energy for New Europe (NENE2022) (USB Flash Drive), 8 Pages, 2022/12

In the risk assessment of the decommissioning phase, the inventory of radioactivity accumulated in filters and other materials changes with the progress of dismantling work under normal conditions, and a method that can evaluate the public exposure dose during an accident in which these changes are taken into account is required. The inventories (the mobile radioactive contaminants) include filters in which radioactive dust dispersed by equipment cutting work has accumulated and combustible waste generated by decontamination work. In this study, we developed a method to evaluate the accumulation of mobile contaminants in filters by calculating the amount of dust transferred into the air during equipment cutting operations using a model that evaluates the volume of the cutting kerf width and the dispersion ratio. Furthermore, the amount of the mobile contaminants that accumulates in local filters and building filters for each equipment was evaluated using this method, taking into account differences in cutting methods (underwater or in air) and work processes, and the equipment and work processes that should be focused on during regulatory inspections were studied preliminarily. It was suggested that some equipment cut in air generate the same amount of the mobile contaminants compared to reactor internals with high radioactivity that are cut in underwater. This indicates that the mobile contaminant is one of the important indicators in nuclear regulatory inspections that influence the selection of inspection targets.

Development and evaluation of XRF imaging instrument for moving objects

Fuchita, Tomoki*; Urata, Taisei*; Matsuyama, Tsugufumi*; Murakami, Masashi; Yoshida, Yukihiko; Ueda, Akihiko; Machida, Masahiko; Sasaki, Toshiki; Tsuji, Koichi*

Advances in X-Ray Chemical Analysis, Japan, 53, p.77 - 87, 2022/03

X-ray fluorescence (XRF) analysis is an analytical method to obtain elemental information by detecting fluorescence X-rays emitted from a sample irradiated with X-rays. It is possible to obtain two-dimensional elemental distribution images by scanning a sample with micro X-ray beam. In this study, we developed an XRF analytical instrument to rapidly obtain the elemental distributions for moving samples on a belt conveyor by applying the micro XRF technique. X-rays were widely irradiated to the belt conveyor. The elemental distributions were measured by scanning an X-ray detector, crossing above the belt conveyor. A collimator was attached to the top of the detector to limit the analyzing area. Both detection limit and spatial resolutions for moving directions of the detector and the belt conveyor were evaluated. Finally, it was demonstrated that the multi-elemental imaging was possible with the developed XRF instrument.

Evaluation of the mass transfer coefficients for the minor actinide separation; Evaluation by the single drop method

Sakamoto, Atsushi; Kibe, Satoshi*; Kawanobe, Kazunori*; Fujisaku, Kazuhiko*; Sano, Yuichi; Takeuchi, Masayuki; Suzuki, Hideya*; Tsubata, Yasuhiro; Ban, Yasutoshi; Matsumura, Tatsuro

JAEA-Research 2021-003, 30 Pages, 2021/06

JAEA-Research-2021-003.pdf:1.81MB

Japan Atomic Energy Agency has been developing a solvent extraction process called SELECT to recover minor actinides (MA) from spent nuclear fuel. In the SELECT process, TDdDGA, HONTA, and ADAAM are used as the extractants for MA + Ln corecovery, MA/Ln separation and Am/Cm separation, respectively. These extractants do not contain phosphorus (P), and consist of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N). In this study, in order to give beneficial information for designing flowsheet, the mass transfer coefficients of Ln between HNO solution and TDdDGA or HONTA / n-dodecane solvent were evaluated by the single drop technique. Prior to the evaluation of mass transfer coefficient, we had optimized the structure of the single drop apparatus to improve accuracy of the measurement. Based on the mass transfer coefficients obtained in HNO / TDdDGA-n-dodecane system, Ln behaviors in the counter-current extraction and back-extraction using mixer-settlers and centrifugal contactors were estimated by simple calculation, and they had a good agreement with our previous experimental results. We also confirmed the mass transfer coefficients of Ln in HNO / HONTA - n-dodecane system are under 10 m/s.

Molecular dynamics study of phosphorus migration in 5 grain boundary of -iron

Ebihara, Kenichi; Suzudo, Tomoaki

Proceedings of Joint International Conference on Supercomputing in Nuclear Applications + Monte Carlo 2020 (SNA + MC 2020), p.65 - 69, 2020/10

Phosphorus (P) is known as one of the elements which cause the grain boundary (GB) embrittlement in steels and its GB segregation is promoted by the increase of vacancies and self-interstitial atoms due to irradiation. Thus we have been developing the rate-theory model for estimating GB P segregation under several temperatures and irradiation conditions. Because the model does not include the trapping and de-trapping processes properly, however, the model cannot calculate GB P coverage which is measured by experiments. As for the de-trapping process, so far, we have considered the migration of a P atom in the GB region of 3 symmetrical tilt GB using molecular dynamics (MD). In the current study, we also simulated the P migration in 5 GB using MD and compared the result with that of 3. As a result, at 800K, it was found that a P atom cannot migrate in 5 without vacancies while a P atom can migrate between iron atoms in 3.

Evaluation and mitigation of reactive ion etching-induced damage in AlGaN/GaN MOS structures fabricated by low-power inductively coupled plasma

Nozaki, Mikito*; Terashima, Daiki*; Yoshigoe, Akitaka; Hosoi, Takuji*; Shimura, Takayoshi*; Watanabe, Heiji*

Japanese Journal of Applied Physics, 59(SM), p.SMMA07_1 - SMMA07_7, 2020/07

https://doi.org/10.35848/1347-4065/ab8f0e

AlGaN/GaN metal-oxide-semiconductor (MOS) structures were fabricated by low-power inductively coupled plasma reactive ion etching and chemical vapor deposition of SiO dielectrics on the etched surfaces, and they were systematically investigated by physical and electrical characterizations in an effort to develop a low-damage recessed gate process. The comprehensive research demonstrates the significant advantages of the proposed low-damage recessed gate process for fabricating next-generation AlGaN/GaN MOS-HFET devices.

Computer code analysis of irradiation performance of axially heterogeneous mixed oxide fuel elements attaining high burnup in a fast reactor

Uwaba, Tomoyuki; Yokoyama, Keisuke; Nemoto, Junichi*; Ishitani, Ikuo*; Ito, Masahiro*; Pelletier, M.*

Nuclear Engineering and Design, 359, p.110448_1 - 110448_7, 2020/04

https://doi.org/10.1016/j.nucengdes.2019.110448

Coupled computer code analyses of irradiation performance of axially heterogeneous mixed oxide (MOX) fuel elements with high burnup in a fast reactor were conducted. Post-irradiation experiments revealed local concentration of Cs near the interfaces between MOX fuel and blanket columns including the internal blanket of the fuel elements as well as an increase in their cladding diameters. The analyses indicated that the local Cs concentration occurred as a result of Cs axial migration from the MOX fuels toward the blanket pellets near the interfaces. Swelling of the blanket pellets induced by the formation of low-density Cs-U-O compound was not sufficient to cause pellet-to-cladding mechanical interaction (PCMI). The PCMI analyzed in the MOX fuel column regions was insignificant, and the cladding diameter increases were caused mainly by void swelling in cladding and irradiation creep due to fission gas pressure.

Study on chemisorption model of cesium hydroxide onto stainless steel type 304

Nakajima, Kunihisa; Nishioka, Shunichiro; Suzuki, Eriko; Osaka, Masahiko

Proceedings of 27th International Conference on Nuclear Engineering (ICONE-27) (Internet), 8 Pages, 2019/05

Cesium chemisorption models were developed for estimation of amount of cesium chemisorbed onto stainless steel type 304 (SS304) during light water reactor severe accident. However, existing chemisorption models cannot accurately reproduce experimental results. In this study, a modified cesium chemisorption model was constructed based on a penetration theory for gas-liquid mass transfer with chemical reaction and was able to adequately describe effects on concentration of cesium hydroxide in gaseous phase and silicon content in SS304. It was found that the modified model can more accurately reproduce the experimental data than the existing model.

Saturation behavior of thermal ratcheting strain due to long range travel of temperature distribution

Okajima, Satoshi; Wakai, Takashi

Nihon Kikai Gakkai 2017-Nendo Nenji Taikai Koen Rombunshu (DVD-ROM), 5 Pages, 2017/09

It was reported that the long distance travel of temperature distribution causes a new type of thermal ratcheting, even in the absence of primary stress. In this paper, based on the results of inelastic finite element analyses, we investigated saturation behavior of thermal ratcheting strain due to long range travel of temperature distribution. As a result, we revealed that the long distance travel of temperature distribution generates plastic strain distribution made maximum at the central part. Because of the shape of the generated strain distribution, the residual stress accumulates even at the central part of the region passed through the temperature distribution. In the case with excessive long traveling of temperature distribution, the region with plastic deformation extended to the surrounding region. Otherwise, sufficient magnitude of residual stress to cause shakedown behavior accumulated on entire region, and the accumulation of the plastic strain saturated.

Data acquisition of mass transport parameters

Iwasaki, Riyo*; Hama, Katsuhiro; Morikawa, Keita*; Hosoya, Shinichi*

JAEA-Technology 2016-037, 62 Pages, 2017/02

JAEA-Technology-2016-037.pdf:8.69MB

Mass transport study is mainly performed as part of Phase III in the Mizunami Underground Research Laboratory Project. In Phase III, the goal of mass transport study is to obtain a better understanding of mass transport phenomena in the geological environment as well as to develop technologies for measurement of the mass transport parameters, model construction, numerical analysis and validation of those technologies. This study was planned to understand the influence of the geological characteristics of fracture on the mass transport parameters.