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Journal Articles

Case study on sampling techniques using machine learning and simplified physical model for simulation-based dynamic probabilistic risk assessment

Kubo, Kotaro; Zheng, X.; Ishikawa, Jun; Sugiyama, Tomoyuki; Jang, S.*; Takata, Takashi*; Yamaguchi, Akira*

Proceedings of Asian Symposium on Risk Assessment and Management 2020 (ASRAM 2020) (Internet), 11 Pages, 2020/11

Dynamic probabilistic risk assessment (PRA) enables a more realistic and detailed analysis than classical PRA. However, the trade-off for these improvements is the enormous computational cost associated with performing a large number of thermal-hydraulic (TH) analyses. In this study, based on machine learning (ML), we aim to reduce these costs by skipping the TH analysis. For the ML algorithm, we selected a support vector machine; we built it using a high-fidelity/high-cost detailed model and low-fidelity/low-cost simplified model. As a result, the computational costs could be reduced by approximately 80% without significantly decreasing the accuracy under the assumed conditions.

Journal Articles

The Analysis for Ex-Vessel debris coolability of BWR

Matsumoto, Toshinori; Iwasawa, Yuzuru; Ajima, Kohei*; Sugiyama, Tomoyuki

Proceedings of Asian Symposium on Risk Assessment and Management 2020 (ASRAM 2020) (Internet), 10 Pages, 2020/11

The probability of ex-vessel debris coolability under the wet cavity strategy is analyzed. The first step is the uncertainty analyses by severe accident analysis code MELCOR to obtain the melt condition. Five uncertain parameters which are relating with the core degradation and transfer process were chosen. Input parameter sets were generated by LHS. The analyses were conducted and the conditions of the melt were obtained. The second step is the analyses for the behavior of melt under the water by JASMINE code. The probabilistic distribution of parameters are determined from the results of MELCOR analyses. Fifty-nine parameter sets were generated by LHS. The depth of water pool is set to be 0.5, 1.0 and 2.0 m. Debris height were compared with the criterion to judge the debris coolability. As the result, the success probability of debris cooling was obtained through the sequence of calculations. The technical difficulties of this evaluation method are also discussed.

Journal Articles

A Comparative study of sampling techniques for dynamic probabilistic risk assessment of nuclear power plants

Kubo, Kotaro; Zheng, X.; Tanaka, Yoichi; Tamaki, Hitoshi; Sugiyama, Tomoyuki; Jang, S.*; Takata, Takashi*; Yamaguchi, Akira*

Proceedings of Joint International Conference on Supercomputing in Nuclear Applications + Monte Carlo 2020 (SNA + MC 2020), p.308 - 315, 2020/10

Dynamic probabilistic risk assessment (PRA) is a method for improving the realism and completeness of conventional PRA. However, enormous calculation costs are incurred by these improvements. One solution is to select an appropriate sampling method. In this paper, we applied the Monte Carlo, Latin hypercube, grid-point, and quasi-Monte Carlo sampling methods to the dynamic PRA of a simplified accident sequence and compared the results for each method. Quasi-Monte Carlo sampling was found to be the most effective method in this case.

Journal Articles

Consistent robin boundary enforcement of particle method for heat transfer problem with arbitrary geometry

Wang, Z.; Duan, G.*; Matsunaga, Takuya*; Sugiyama, Tomoyuki

International Journal of Heat and Mass Transfer, 157, p.119919_1 - 119919_20, 2020/08

 Times Cited Count:1 Percentile:28.34(Thermodynamics)

Journal Articles

Development of a multiphase particle method for melt-jet breakup behavior of molten core in severe accident

Wang, Z.; Iwasawa, Yuzuru; Sugiyama, Tomoyuki

Proceedings of 2020 International Conference on Nuclear Engineering (ICONE 2020) (Internet), 12 Pages, 2020/08

Journal Articles

Computational study on the spherical laminar flame speed of hydrogen-air mixtures

Trianti, N.; Motegi, Kosuke; Sugiyama, Tomoyuki; Maruyama, Yu

Proceedings of 2020 International Conference on Nuclear Engineering (ICONE 2020) (Internet), 9 Pages, 2020/08

Journal Articles

Experimental and analytical investigation of formation and cooling phenomena in high temperature debris bed

Hotta, Akitoshi*; Akiba, Miyuki*; Morita, Akinobu*; Konovalenko, A.*; Vilanueva, W.*; Bechta, S.*; Komlev, A.*; Thakre, S.*; Hoseyni, S. M.*; Sk$"o$ld, P.*; et al.

Journal of Nuclear Science and Technology, 57(4), p.353 - 369, 2020/04

 Times Cited Count:0 Percentile:100(Nuclear Science & Technology)

Journal Articles

Thresholds for failure of high-burnup LWR fuels by pellet cladding mechanical interaction under reactivity-initiated accident conditions

Udagawa, Yutaka; Sugiyama, Tomoyuki; Amaya, Masaki

Journal of Nuclear Science and Technology, 56(12), p.1063 - 1072, 2019/12

 Times Cited Count:2 Percentile:34.3(Nuclear Science & Technology)

no abstracts in English

Journal Articles

CFD analysis of hydrogen flame acceleration with burning velocity models

Motegi, Kosuke; Trianti, N.; Matsumoto, Toshinori; Sugiyama, Tomoyuki; Maruyama, Yu

Proceedings of 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18) (USB Flash Drive), p.4324 - 4335, 2019/08

Journal Articles

Analysis for the accident at unit 1 of the Fukushima Daiichi NPS with THALES2/KICHE code in BSAF2 project

Tamaki, Hitoshi; Ishikawa, Jun; Sugiyama, Tomoyuki; Maruyama, Yu

Proceedings of 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18) (USB Flash Drive), p.72 - 82, 2019/08

JAEA participated in the OECD/NEA BSAF2 project with our integrated severe accident analysis code, THALES2/KICHE, in order to analyze and discuss the accident progression and source term of the accident at the Fukushima Daiichi NPS. One of important characteristics of THALES2/KICHE code is that it has the capability of predicting iodine chemistry based on reaction kinetics in the aqueous phase. JAEA performed the three week analysis for the accident at unit 1 on the basis of the boundary conditions and assumptions proposed by the BSAF2 project and our own assumptions. In addition to the failure of the drywell, it was assumed in the present analysis that continuous leakage occurred through the containment venting line due to incomplete closing of valves in the line. The releases of fission products, especially for iodine and cesium, within three weeks after the earthquake were estimated to be approximately 6% and 1% of the initial inventory, respectively.

Journal Articles

Analysis for the accident at unit 2 of the Fukushima Daiichi NPS with THALES2/KICHE code in BSAF2 project

Tamaki, Hitoshi; Ishikawa, Jun; Sugiyama, Tomoyuki; Maruyama, Yu

Proceedings of 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18) (USB Flash Drive), p.100 - 111, 2019/08

JAEA participated in the OECD/NEA BSAF2 project with our integrated severe accident analysis code, THALES2/KICHE, in order to analyze and discuss the accident progression and source term of the accident at the Fukushima Daiichi NPS. One of important characteristics of THALES2/KICHE code is that it has the capability of predicting iodine chemistry based on reaction kinetics in the aqueous phase. JAEA performed the three week analysis for the accident at unit 2 on the basis of the boundary conditions and assumptions proposed by the BSAF2 project and our own assumptions. One of focusing points in the BSAF2 project was the trend of measured data of reactor vessel from 20:00 March 14 to 02:00 March 15. An assumption was made that the lower part of the suppression chamber failed to form a water leakage path. The released iodine and cesium within three weeks after the earthquake were predicted to be approximately 3% and 0.1% of the initial inventory, respectively.

Journal Articles

Analysis for the accident at Unit 3 of the Fukushima Daiichi NPS with THALES2/KICHE Code in BSAF2 project

Ishikawa, Jun; Tamaki, Hitoshi; Sugiyama, Tomoyuki; Maruyama, Yu

Proceedings of 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18) (USB Flash Drive), p.536 - 547, 2019/08

Journal Articles

Outline of the OECD/NEA/ARC-F Project

Nakatsuka, Toru; Maeda, Toshikatsu; Sugiyama, Tomoyuki; Maruyama, Yu

Proceedings of 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18) (USB Flash Drive), p.1650 - 1656, 2019/08

The OECD/NEA is launching a new project named "Analysis of Information from Reactor Buildings and Containment Vessels of Fukushima Daiichi Nuclear Power Station (ARC-F)" Project. This project will serve as the successor to the precedent NEA project, "Benchmark Study of the Accident at the Fukushima Daiichi Nuclear Power Station (BSAF) Phase II" which investigated the accident scenarios, associated fission products behavior in the damaged units and source term to the environment. The ARC-F project comprises three tasks: Task 1: Refinement of analysis for accident scenarios and associated fission product transportation and dispersion; Task 2: Compilation and management of data and information; and Task 3: Discussion for future long-term project. Japan Atomic Energy Agency is the operating agent, responsible to lead all the tasks. Duration of the project is from January 2019 to December 2021 and the final report is planned to be published in 2022.

Journal Articles

Formation of agglomerated debris in jet-breakup experiment using metallic melts

Iwasawa, Yuzuru; Sugiyama, Tomoyuki; Maruyama, Yu; Kaneko, Akiko*; Abe, Yutaka*

Proceedings of 27th International Conference on Nuclear Engineering (ICONE-27) (Internet), 6 Pages, 2019/05

Journal Articles

Analysis of transport behaviors of cesium and iodine in VERDON-2 experiment for chemical model validation

Shiotsu, Hiroyuki; Ito, Hiroto*; Ishikawa, Jun; Sugiyama, Tomoyuki; Maruyama, Yu

Proceedings of 11th Korea-Japan Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-11) (Internet), 6 Pages, 2018/11

Journal Articles

Computational fluid dynamics analysis for hydrogen deflagration tests at ENACCEF2 facility

Trianti, N.; Sato, Masatoshi*; Sugiyama, Tomoyuki; Maruyama, Yu

Proceedings of 11th Korea-Japan Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-11) (Internet), 7 Pages, 2018/11

JAEA Reports

CHEMKEq; Evaluation code for chemical composition based on partial mixed model with Chemical Equilibrium and Reaction Kinetics (Contract research)

Ito, Hiroto*; Shiotsu, Hiroyuki; Tanaka, Yoichi*; Nishihara, Satomichi*; Sugiyama, Tomoyuki; Maruyama, Yu

JAEA-Data/Code 2018-012, 42 Pages, 2018/10

JAEA-Data-Code-2018-012.pdf:4.93MB

Chemical composition of fission products transported in nuclear facilities in severe accidents is controlled by slower chemical reaction rates, therefore, it could be different from that evaluated on the chemical equilibrium assumption. Hence, it is necessary to evaluate the chemical composition with reaction kinetics. On the other hand, databases applicable to the analysis of nuclear facilities have not been constructed because knowledge of reaction rates of complex chemical reactions in severe accidents is currently limited. Accordingly, we have developed the CHEMKEq code based on a partial mixed model with chemical equilibrium and reaction kinetics to decrease uncertainties of the chemical composition caused by the reaction rate. The CHEMKEq code, under mass conservation law, firstly evaluates chemical species obeying the chemical equilibrium model, and then, relatively slow reactions are solved by the reaction kinetics model. Moreover, the CHEMKEq code has a multiplicity of use in evaluations of chemical composition because general chemical equilibrium and reaction kinetics models are also available and databases required to calculation are external file formats. This report is the user's guide of the CHEMKEq code, showing models, solution methods, structure of the code and calculation examples. And information to run the CHEMKEq code is summarized in appendixes.

Journal Articles

Sensitivity analysis of source term in the accident of Fukushima Dai-ichi Nuclear Power Station Unit 1 using THALES2/KICHE

Tamaki, Hitoshi; Ishikawa, Jun; Sugiyama, Tomoyuki; Maruyama, Yu

Proceedings of Asian Symposium on Risk Assessment and Management 2018 (ASRAM 2018) (USB Flash Drive), 6 Pages, 2018/10

In the accidents at Fukushima Dai-ichi Nuclear Power Station, Tsunami caused loss of electric power supply and this event led to core melt and failure of Containment vessel. Finally, fission products were released to the environment. Currently, the activities for understanding of accident progressions are carried out based on the measured data during the accident, accident progression analysis using integrated severe accident analysis codes and investigation of inside of reactor buildings and containment vessels. On the other hand, there are some research activities with combination of accident progression analysis and accident consequence analysis. In Japan Atomic Energy Agency (JAEA), the research project of combination of these analyses using the computational simulation codes has been started. The results obtained from the combination analysis are expected to have broad width of uncertainty because of many uncertainty factors in this combined analysis. In order to perform the analysis efficiently, sensitivity analysis for failure location on containment vessel and its failure size were carried out by THALES2/KICHE developed by JAEA at first. This analysis was performed on unit 1, since it was the first plant to release radioactive materials to the environment during the accident and its consequence had no effect from other plants. The authors focused on the failure of containment vessel head flange, penetration seal and vacuum breaker pipe, and possibility of partial open of vent valve based on the investigations of reactor building inside performed by TEPCO. This paper presents the results obtained from this sensitivity analysis.

Journal Articles

Evaluation of chemical speciation of iodine and cesium considering fission product chemistry in reactor coolant system

Ishikawa, Jun; Zheng, X.; Shiotsu, Hiroyuki; Sugiyama, Tomoyuki; Maruyama, Yu

Proceedings of Asian Symposium on Risk Assessment and Management 2018 (ASRAM 2018) (USB Flash Drive), 6 Pages, 2018/10

Journal Articles

Severe accident scenario uncertainty analysis using the dynamic event tree method

Zheng, X.; Tamaki, Hitoshi; Ishikawa, Jun; Sugiyama, Tomoyuki; Maruyama, Yu

Proceedings of 14th International Conference on Probabilistic Safety Assessment and Management (PSAM-14) (USB Flash Drive), 10 Pages, 2018/09

175 (Records 1-20 displayed on this page)