Brittle-fracture simulations of curved cleavage cracks in -iron; A Molecular dynamics study

Suzudo, Tomoaki; Ebihara, Kenichi; Tsuru, Tomohito

AIP-Advances, 10(11), p.115209_1 - 115209_8, 2020/11

https://doi.org/10.1063/5.0026659

The mechanism of their brittle fracture of BCC metals is not fully understood. In this study, we conduct a series of three-dimensional molecular dynamics simulations of cleavage fracture of -iron. In particular, we focus on mode-I loading starting from curved crack fronts. In the simulations, brittle fractures are observed at cleavages on the {100} plane, while the initial cracks become blunted on other planes as a result of dislocation emissions. Our modeling results agreed with a common experimental observation, that is, {100} is the preferential cleavage plane in bcc transition metals.

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.

Assessment of nuclear simulation credibility

Tanaka, Masaaki; Nakada, Kotaro*; Kudo, Yoshiro*

Nippon Kikai Gakkai-Shi, 123(1222), p.26 - 29, 2020/09

In the nuclear engineering, simulations are used in radiation, thermal hydraulic, chemical reaction, and structural fields, and the integrated fields thereof, to be applied to the design, construction and operation of nuclear facilities. This article describes brief history of discussion in the AESJ to the publication and introductory explanation of the procedures in the five major elements described in the "Guideline for Credibility Assessment of Nuclear Simulations (AESJ-SC-A008: 2015)". And also, a practical experience of the V&V activity according to the fundamental concept indicated in the Guideline is introduced.

Numerical validation of AQUA-SF in SNL T3 sodium spray fire experiment

Sonehara, Masateru; Aoyagi, Mitsuhiro; Uchibori, Akihiro; Takata, Takashi; Ohshima, Hiroyuki; Clark, A. J.*; Louie, D. L. Y.*

Proceedings of 2020 International Conference on Nuclear Engineering (ICONE 2020) (Internet), 4 Pages, 2020/08

https://doi.org/10.1115/ICONE2020-16851

In order to investigate the multi-dimensional effects of sodium combustion, a benchmark analysis of the SNL Surtsey spray combustion experiment (SNL T3 experiments) using AQUA-SF and SPHINCS is conducted in JAEA. As a best estimate analysis, the spray burning duration is adjusted in the computation in order to take into account the temporary suppression of the spray combustion observed in the experiment. Furthermore, droplet size of SPHINCS and AQUA-SF are optimized to represent the T3 experimental results. The best estimate of AQUA-SF results in the droplet diameter of 2.5 mm, which agrees quite well with the spatial temperature measurements, and the sodium droplet diameter measurement with a high speed camera.

Molecular dynamics simulations of phosphorus migration in a grain boundary of -iron

Ebihara, Kenichi; Suzudo, Tomoaki

TMS 2020; 149th Annual Meeting & Exhibition Supplemental Proceedings, p.995 - 1002, 2020/02

https://doi.org/10.1007/978-3-030-36296-6_93

Phosphorus (P) is known as an element which causes grain boundary (GB) embrittlement in steels. In addition, GB P segregation is promoted by the increase of vacancies and self interstitial atoms due to irradiation. Thus, the diffusion rate theory model for estimating irradiation-induced GB P segregation has been developed based on the atomic processes. Since the present model does not include the trapping and de-trapping processes at GBs, however, it cannot calculate the value which is directly compared with experimental results. In this study, we simulated the migration of a P atom in the 3(111) symmetrical tilt GB. In addition, by tracking the migration of the P atom, the diffusion barrier energy was evaluated. As a result, the diffusion barrier energy was almost the same as the P segregation energy of an interstitial site in the GB, and it was found that P atoms migrate via interstitial sites in the GB.

Research and development behind a computation system for 3D distributions of air dose rates in the environment; Estimating environmental radiation doses using PHITS together with remote sensing data

Kim, M.; Malins, A.; Sakuma, Kazuyuki; Kitamura, Akihiro; Machida, Masahiko; Hasegawa, Yukihiro*; Yanagi, Hideaki*

Isotope News, (765), p.30 - 33, 2019/10

https://www.jrias.or.jp/books/cat3/2019/765.html

Here we outline a system for generating three dimensional models of urban and rural areas in Fukushima Prefecture. The Cs and Cs radioactivity distribution can be set flexibly across the different components of the model. The models incorporate realistic representations of local buildings, individual conifer and broadleaf trees, and the topography of the land surface. The system is demonstrated by modelling a suburban area 4 km from the Fukushima Daiichi Nuclear Power Plant that has yet to be decontaminated. Air dose rates calculated in PHITS were correlated with measurements taken across the site in a car-borne survey.

Exascale simulations of fusion plasmas

Idomura, Yasuhiro; Watanabe, Tomohiko*; Todo, Yasushi*

Shimyureshon, 38(2), p.79 - 86, 2019/06

We promote the research and development of exascale fusion plasma simulations on Post-K towards estimation and prediction of core plasma performance, and exploration of improved operation scenarios on the next generation fusion experimental reactor ITER. In this paper, we review developed exascale simulation technologies and outcomes from validation studies on existing experimental devices, and discuss perspectives on exascale fusion plasma simulations on Post-K.

Overview of computational mouse models

Mohammadi, A.*; Kinase, Sakae; Safavi-Naeini, M.*

Computational Anatomical Animal Models; Methodological Developments and Research Applications, p.3_1 - 3_27, 2018/12

https://doi.org/10.1088/2053-2563/aae1b4ch3

Review of the performance of a car-borne survey system, KURAMA-II, used to measure the dose rate after the Fukushima Dai-ichi Nuclear Power Plant accident

Tsuda, Shuichi; Tanigaki, Minoru*; Yoshida, Tadayoshi; Saito, Kimiaki

Hoshasen, 44(3), p.109 - 118, 2018/11

JAEA has started to perform dose rate monitoring using a car-borne survey system KURAMA to rapidly produce the dose rate mappings of the deposited radionuclides in the environment after the Fukushima Dai-ichi Nuclear Power Plant accident. KURAMA is a car-borne survey system developed by Kyoto University to perform dose rate monitoring in a wide area in detail with rapidity. By improving KURAMA with continuous dose rate monitoring, the 2nd generation of KURAMA (KURAMA-II) succeeded in downsizing, durability and automated transmission of data so that enable detailed dose rate mapping in wide area in shorter period of time. This paper reports the radiation characteristics and the simulation analysis of KURAMA-II on the special issue of Hoshasen, the journal of Ionization Radiation Division in the Japan society of applied physics.

Numerical simulation of thermal striping phenomena for fundamental validation and uncertainty quantification; Application of least square version GCI and area validation method to impinging jet in a T-Junction piping system

Tanaka, Masaaki

Proceedings of 12th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation and Safety (NUTHOS-12) (USB Flash Drive), 14 Pages, 2018/10

A numerical simulation code MUGTHES has been developed to estimate high cycle thermal fatigue in SFRs. In development of numerical simulation code, verification, validation, and uncertainty quantification (VVUQ) are indispensable. In this study, numerical simulation at impinging jet condition in the WATLON experiment which was the water experiment of a T-junction piping system was performed for the fundamental validation. Based on the previous studies, the simplified least square version GCI method and the area validation metrics were employed as reference methods to quantify uncertainty and to measure the degree of difference between the numerical and the experimental results, respectively. Through the examinations, the potential applicability of the MUGTHES to the thermal striping phenomena was indicated and requirements of modification in the simulation was suggested in accordance with the uncertainty values.