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JAEA Reports

Review of research on advanced computational science in FY2019

Center for Computational Science & e-Systems

JAEA-Evaluation 2020-002, 37 Pages, 2020/12

JAEA-Evaluation-2020-002.pdf:1.59MB

Research on advanced computational science for nuclear applications, based on "the plan to achieve the mid and long term goal of the Japan Atomic Energy Agency", has been performed at Center for Computational Science & e-Systems (CCSE), Japan Atomic Energy Agency. CCSE established a committee consisting of outside experts and authorities which does research evaluation and advice for the assistance of the future research and development. This report summarizes the results of the R&D performed at CCSE in FY2019 (April 1st, 2019 - March 31st, 2020) and the evaluation by the committee on them.

Journal Articles

A Model intercomparison of atmospheric $$^{137}$$Cs concentrations from the Fukushima Daiichi Nuclear Power Plant accident, phase III; Simulation with an identical source term and meteorological field at 1-km resolution

Sato, Yosuke*; Sekiyama, Tsuyoshi*; Fang, S.*; Kajino, Mizuo*; Qu$'e$rel, A.*; Qu$'e$lo, D.*; Kondo, Hiroaki*; Terada, Hiroaki; Kadowaki, Masanao; Takigawa, Masayuki*; et al.

Atmospheric Environment; X (Internet), 7, p.100086_1 - 100086_12, 2020/10

The third model intercomparison project for investigating the atmospheric behavior of $$^{137}$$Cs emitted during the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident (FDNPP-MIP) was conducted. A finer horizontal grid spacing (1 km) was used than in the previous FDNPP-MIP. Nine of the models used in the previous FDNPP-MIP were also used, and all models used identical source terms and meteorological fields. Our analyses indicated that most of the observed high atmospheric $$^{137}$$Cs concentrations were well simulated, and the good performance of some models improved the performance of the multi-model ensemble. The analyses also confirmed that the use of a finer grid resolution resulted in the meteorological field near FDNPP being better reproduced. The good representation of the wind field resulted in the reasonable simulation of the narrow distribution of high deposition amount to the northwest of FDNPP and the reduction of the overestimation over the area to the south of FDNPP. In contrast, the performance of the models in simulating plumes observed over the Nakadori area, the northern part of Gunma, and the Tokyo metropolitan area was slightly worse.

Journal Articles

Intercomparison of numerical atmospheric dispersion prediction models for emergency response to emissions of radionuclides with limited source information in the Fukushima Dai-ichi Nuclear Power Plant accident

Iwasaki, Toshiki*; Sekiyama, Tsuyoshi*; Nakajima, Teruyuki*; Watanabe, Akira*; Suzuki, Yasushi*; Kondo, Hiroaki*; Morino, Yu*; Terada, Hiroaki; Nagai, Haruyasu; Takigawa, Masayuki*; et al.

Atmospheric Environment, 214, p.116830_1 - 116830_11, 2019/10

 Times Cited Count:1 Percentile:84.27(Environmental Sciences)

The utilization of numerical atmospheric dispersion prediction (NDP) models for accidental discharge of radioactive substances was recommended by a working group of the Meteorological Society of Japan. This paper is to validate the recommendation through NDP model intercomparison in the accidental release from the Fukushima Dai-ichi Nuclear Power Plant in 2011. Emission intensity is assumed to be constant during the whole forecast period for the worst-case scenario unless time sequence of emission is available. We expect to utilize forecasts of surface air contaminations for preventions of inhalations of radioactive substances, and column-integrated amounts for mitigation of radiation exposure associated with wet deposition. Although NDP forecasts have ensemble spread, they commonly figure out relative risk in space and time. They are of great benefit to disseminating effective warnings to public without failure. The multi-model ensemble technique may be effective to improve the reliability.

Journal Articles

Numerical study on effect of nucleation site density on behavior of bubble coalescence by using CMFD simulation code TPFIT

Ono, Ayako; Suzuki, Takayuki*; Yoshida, Hiroyuki

Proceedings of 12th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation and Safety (NUTHOS-12) (USB Flash Drive), 9 Pages, 2018/10

The mechanism of Critical Heat Flux (CHF) remains to be clarified, even though it is important to evaluate the CHF for super high heat flux components such as light water reactors (LWRs). Some theoretical models to predict the CHF is proposed so far. A macrolayer formation model which is proposed in order to predict the CHF based on the macrolayer dryout model. In this model, it is assumed that the liquid is captured inside vapor mass at coalescence. In this study, the verification of the assumption of a macrolayer formation model by the numerical simulation of CMFD code, TPFIT, from the view point of hydrodynamics.

Journal Articles

Atmospheric modeling of $$^{137}$$Cs plumes from the Fukushima Daiichi Nuclear Power Plant; Evaluation of the model intercomparison data of the Science Council of Japan

Kitayama, Kyo*; Morino, Yu*; Takigawa, Masayuki*; Nakajima, Teruyuki*; Hayami, Hiroshi*; Nagai, Haruyasu; Terada, Hiroaki; Saito, Kazuo*; Shimbori, Toshiki*; Kajino, Mizuo*; et al.

Journal of Geophysical Research; Atmospheres, 123(14), p.7754 - 7770, 2018/07

 Times Cited Count:12 Percentile:24.72(Meteorology & Atmospheric Sciences)

We compared seven atmospheric transport model results for $$^{137}$$Cs released during the Fukushima Daiichi Nuclear Power Plant accident. All the results had been submitted for a model intercomparison project of the Science Council of Japan in 2014. We assessed model performance by comparing model results with observed hourly atmospheric concentrations of $$^{137}$$Cs, focusing on nine plumes over the Tohoku and Kanto regions. The results showed that model performance for $$^{137}$$Cs concentrations was highly variable among models and plumes. We also assessed model performance for accumulated $$^{137}$$Cs deposition. Simulated areas of high deposition were consistent with the plume pathways, though the models that best simulated $$^{137}$$Cs concentrations were different from those that best simulated deposition. The ensemble mean of all models consistently reproduced $$^{137}$$Cs concentrations and deposition well, suggesting that use of a multimodel ensemble results in more effective and consistent model performance.

Journal Articles

Some characteristics of gas-liquid two-phase flow in vertical large-diameter channels

Shen, X.*; Schlegel, J. P.*; Hibiki, Takashi*; Nakamura, Hideo

Nuclear Engineering and Design, 333, p.87 - 98, 2018/07

 Times Cited Count:5 Percentile:65.38(Nuclear Science & Technology)

Journal Articles

Modeling approach to various time and spatial scale environmental issues in Fukushima; Related to radioactive cesium migration in aquatic systems

Kurikami, Hiroshi; Kitamura, Akihiro; Yamada, Susumu; Machida, Masahiko

Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 6 Pages, 2015/05

Several numerical models have been prepared to deal with various time- and spatial-scale issues related to radioactive cesium migration in environment in Fukushima area. This paper describes fragments of the JAEA's approaches of modeling to deal with the issues corresponding to radioactive cesium migration in environment with some case studies.

Journal Articles

Numerical simulations of short-term migration processes of dissolved Cesium-137 due to a hypothetical accident of a nuclear submarine in the Japan Sea

Kobayashi, Takuya; Chino, Masamichi; Togawa, Orihiko

Journal of Nuclear Science and Technology, 43(5), p.569 - 575, 2006/05

 Times Cited Count:3 Percentile:73.68(Nuclear Science & Technology)

A dissolved radionuclide migration code system that consists of a ocean circulation model, Princeton Ocean Model, and a particle random-walk model, SEA-GEARN, has been developed. The oceanic migration of $$^{137}$$Cs discharged from a nuclear submarine in a hypothetical accident at the Tsushima Strait was calculated in the southwestern area of the Japan Sea as a model application. The calculations for instantaneous releases every 10 days were carried out for one year to study the seasonal differences of migration process of the dissolved radionuclides. The migration tendencies of dissolved radionuclides were divided into two patterns. For the releases started from January to September, all of the high concentration areas migrated to the northeast along the coastline of the Main Island of Japan from the release point. As for the releases from October to December, some high concentrations areas migrated to the west from the release point and the concentrations of $$^{137}$$Cs along the coastline of the Main Island of Japan were comparatively low.

Journal Articles

Incorporation of CO$$_{2}$$ exchange processes into a multilayer atmosphere-soil-vegetation model

Nagai, Haruyasu

Journal of Applied Meteorology, 44(10), p.1574 - 1592, 2005/10

This paper describes the incorporation of CO$$_{2}$$ exchange processes into an atmosphere-soil-vegetation model SOLVEG and examination of its sensitivity and impact of its stomatal resistance calculation on the latent heat flux over a winter wheat field. The model framework for the heat and water exchanges between the atmosphere and ground surface was validated in the previous papers (Nagai 2002, 2003). In this study, CO$$_{2}$$ exchange processes are incorporated in the model and the performance is examined. In the test calculation, the model simulated the CO$$_{2}$$ flux at 2 m above the ground well as a whole. A sensitivity test to clarify uncertainties for the model settings and parameters showed that the CO$$_{2}$$ production in the soil is the most important factor for the CO$$_{2}$$ calculation. Also, the impact of the CO$$_{2}$$ processes on the latent heat flux is discussed. The results indicate that the new model is effective and preferable to study surface exchanges of heat and water as well as CO$$_{2}$$.

Journal Articles

Development of a long-range atmospheric transport model for nuclear emergency and its application to the Chernobyl nuclear accident

Terada, Hiroaki; Chino, Masamichi

Proceedings of 2nd International Conference on Radioactivity in the Environment, p.15 - 18, 2005/10

The previous version of Worldwide version of System for Prediction of Environmental Emergency Dose Information (WSPEEDI) has been composed of mass-consistent wind field model WSYNOP and particle dispersion model GEARN. Because WSYNOP has no capability to predict meteorological fields, its accuracy and resolution depends on meteorological input data, and it is impossible to treat physical processes realistically. To improve these problems, an atmospheric dynamic model MM5 is introduced and applied to the Chernobyl accident for the verification. Two calculation cases are conducted, CASE-1 a calculation for European region Domain-1, and CASE-2 a domain nesting calculation for Domain-1 and the region around Chernobyl Domain-2. The air concentration and surface deposition of $$^{137}$$Cs calculated by CASE-1 agree well with the measurements by statistical analysis and comparison for the horizontal distribution. In the result of CASE-2, the detailed distribution of surface $$^{137}$$Cs deposition around Chernobyl which was impossible to calculate in CASE-1 is predicted with high accuracy.

JAEA Reports

Verification of HTTR hydrogen production system analysis code using experimental data of mock-up model test facility with a full-scale reaction tube; Cooling system of the secondary helium gas using steam generator and radiator (Contract research)

Sato, Hiroyuki; Ohashi, Hirofumi; Inaba, Yoshitomo; Maeda, Yukimasa; Takeda, Tetsuaki; Nishihara, Tetsuo; Inagaki, Yoshiyuki

JAERI-Tech 2005-014, 89 Pages, 2005/03

JAERI-Tech-2005-014.pdf:7.25MB

In a hydrogen production system using HTTR, it is required to control a secondary helium gas temperature within an allowable value at an intermediate heat exchanger (IHX) inlet to prevent a reactor scram. To mitigate thermal disturbance of the secondary helium gas caused by the hydrogen production system, a cooling system of the secondary helium gas using a steam generator(SG) and a radiator will be installed at the downstream of the chemical reactor. In order to verify a numerical analysis code of the cooling system, numerical analysis has been conducted. The pressure controllability in SG is highly affected by the heat transfer characteristics of air which flows outside of the heat exchanger tube of the radiator. In order to verify a numerical analysis code of the cooling system, the heat transfer characteristics of air has been investigated with experimental results of a mock-up model test. It was confirmed that numerical analysis results were agreed well with experimental results, and the analysis code was successfully verified.

JAEA Reports

Physics and numerical methods of OPTMAN; A Coupled-channels method based on soft-rotator model for a description of collective nuclear structure and excitations

Soukhovitskij, E. Sh.*; Morogovskij, G. B.*; Chiba, Satoshi; Iwamoto, Osamu; Fukahori, Tokio

JAERI-Data/Code 2004-002, 32 Pages, 2004/03

JAERI-Data-Code-2004-002.pdf:1.43MB

This report gives a detailed description of the theory and computational algorithms of modernized coupled-channels optical model code OPTMAN based on the soft-rotator model for the collective nuclear structure and excitations. This work was performed under the Project Agreement B-521 with the International Science and Technology Center (Moscow), financing party of which is Japan. As a result of this work, the computational method of OPTMAN was totally updated, and an user-friendly interface was attached.

Journal Articles

Engineering aspects in modeling of high burnup LWR fuel behavior

Suzuki, Motoe

Proceedings of 2nd Japan-Korea-China (5th Japan-Korea) Seminar on Nuclear Reactor Fuel and Materials, p.4 - 10, 2004/03

In designing a fuel performance code which describes complicated interactions working in high burnup fuel, the code will inevitably become a complex structure of inter-dependent models. In normal operation conditions, PCMI occurs and the pellet-clad firm bonding layer makes the cladding to be subjected to a bi-axial stress state, i.e. under tough mechanical loading. In contrast, the bonding layer enhances thermal conductance, decreases the pellet temperature and keeps the pellet-clad contact, resulting in increased resistance against the Lift-Off. For pellet behaviors, the fission gas bubble growth is strongly dependent on temperature, so that a reliable prediction of fuel temperature is required by pellet radial meshing which can fully accommodate the burning analysis results and the rim structure growth. The presentation deals with modeling method in terms of specific aspects such as meshing.

Journal Articles

Numerical modelling and laboratory experiments of tritium transport in unsaturated soil

Koarashi, Jun*; Iida, Takao*; Atarashi-Andoh, Mariko; Yamazawa, Hiromi; Amano, Hikaru

Fusion Science and Technology, 41(3), p.464 - 469, 2002/05

no abstracts in English

Journal Articles

Validation and sensitivity analysis of a new atmosphere-soil-vegetation model

Nagai, Haruyasu

Journal of Applied Meteorology, 41(2), p.160 - 176, 2002/02

no abstracts in English

Journal Articles

Development of ocean pollution prediction system for Shimokita region; Model development and verification

Kobayashi, Takuya; Lee, S.; Chino, Masamichi

Journal of Nuclear Science and Technology, 39(2), p.171 - 179, 2002/02

 Times Cited Count:3 Percentile:75.36(Nuclear Science & Technology)

A three-dimensional model system was developed to predict oceanic dispersions of radionuclides released into the eastern area of Shimokita Peninsula. This system is a combination of the Princeton Ocean Model (POM) for predicting ocean currents and a particle random walk model for oceanic dispersion of radionuclides. The model was verified by using measured currents, temperature and salinity at the coastal area of Shimokita, Aomori-ken, Japan, where a nuclear fuel reprocessing plant is under construction. The results obtained from simulations area as follows; (1) Wind and the Tsugaru Warm Current entering into the objective region through the Tsugaru Strait significantly affect the structure of current over the region. (2) POM can represent seasonal variations of the Tsugaru Warm Current well with hypothetical oceanographic data. The calculation succeeded to reproduce the coastal mode from winter to spring and the gyre mode from summer to autumn.

Journal Articles

Trend of acid rain and neutralization by yellow sand in east Asia; A Numerical study

Terada, Hiroaki; Ueda, Hiromasa*; Wang, Z.*

Atmospheric Environment, 36(3), p.503 - 509, 2002/01

 Times Cited Count:42 Percentile:30.81(Environmental Sciences)

Acid rain and its neutralization by yellow-sand in East Asia was investigated numerically by an Air Quality Prediction Modeling System (AQPMS). AQPMS consists of advection, diffusion, dry and wet deposition, gas- and liquid-phase chemistry. A new deflation module of the yellow-sand was designed to provide explicit information on the dust loading, and linked to the AQPMS. For model validation, the predicted pH values and sulfate- and nitrate-ion levels of precipitation, together with the surface concentrations of gaseous pollutants, were compared with measured values at atmospheric monitoring stations, and a reasonable agreement was obtained. Firstly, trend of the acid rain in East Asia due to the rapid increase of Chinese pollutants emission was investigated, and a remarkably rapid increase of acid rain area was predicted in the period from 1985 to 1995. Secondly, the simulation results of April 1995 exhibited a strong neutralization of the precipitation by the yellow-sand.

Journal Articles

A One-dimensional dynamical soil-atmosphere tritiated water transport model

Yamazawa, Hiromi

Environmental Modelling & Software, 16(8), p.739 - 751, 2001/12

no abstracts in English

Journal Articles

Verification of models for bubble turbulent diffusion and bubble diameter in multi-dimensional two-fluid model

Onuki, Akira; Akimoto, Hajime

Proceedings of the 8th International Symposium on Flow Modeling and Turbulence Measurements (FMTM2001) (CD-ROM), 7 Pages, 2001/12

Multi-dimensional analyses have been expected with expanding computation resources for gas-liquid two-phase flow. We recently developed models for bubble turbulent diffusion and bubble diameter to predict the phase distribution by a multi-dimensional two-fluid model. This study was performed to verify our model. The verification was performed using databases under diameter; 9 mm to 155 mm, pressure; atmospheric to 4.9 MPa, flow rate; superficial gas velocity = 0.01 to 5.5 m/s and superficial liquid one = 0.0 to 4.3 m/s, fluid combination; air-water or steam-water. Through the assessments, our model was found to be applicable to the wide range of flow conditions including the effect of pipe diameter. The shape of phase distribution and the average void fraction are predicted well qualitatively and quantitatively. Since the model is established using the ratio of bubble diameter to eddy size as a key-parameter, the ratio is one of important parameters to develop the constitutive equations in the multi-dimensional two-fluid model.

Journal Articles

Comparative studies in the local circulations induced by land-use and by topography

Lee, S.; Kimura, Fujio*

Boundary-Layer Meteorology, 101(2), p.157 - 182, 2001/11

 Times Cited Count:49 Percentile:24.68(Meteorology & Atmospheric Sciences)

no abstracts in English

65 (Records 1-20 displayed on this page)