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Journal Articles

JSME series in thermal and nuclear power generation Vol.3 (Sodium-cooled fast reactor development; R&Ds on thermal-hydraulics and safety assessment towards social implementation)

Tanaka, Masaaki; Uchibori, Akihiro; Okano, Yasushi; Yokoyama, Kenji; Uwaba, Tomoyuki; Enuma, Yasuhiro; Wakai, Takashi; Asayama, Tai

Dai-27-Kai Doryoku, Enerugi Gijutsu Shimpojiumu Koen Rombunshu (Internet), 5 Pages, 2023/09

The book, JSME Series in Thermal and Nuclear Power Generation Vol.3 Sodium-cooled Fast Reactor, was published as a 30th anniversary memorial project of Power & Energy Systems Division. This paper describes an introduction of the book on a part of key technologies regarding safety assessment, thermal-hydraulics, neutronics, and fuel and material development. This introductory paper also provides an overview of an integrated evaluation system named ARKADIA to offer the best possible solutions for challenges arising during the design process, safety assessment, and operation of a nuclear plant over its life cycle, in active use of the R&D efforts and knowledges on thermal-hydraulics and safety assessment with state-of-the-art numerical analysis technologies.

Journal Articles

The Development of a Multiphysics Coupled Solver for Studying the Effect of Dynamic Heterogeneous Configuration on Particulate Debris Bed Criticality and Cooling Characteristics

Li, C.-Y.; Wang, K.*; Uchibori, Akihiro; Okano, Yasushi; Pellegrini, M.*; Erkan, N.*; Takata, Takashi*; Okamoto, Koji*

Applied Sciences (Internet), 13(13), p.7705_1 - 7705_29, 2023/07

 Times Cited Count:0 Percentile:0

Journal Articles

Development of the ex-vessel modules for the integrated SFR safety analysis code SPECTRA

Aoyagi, Mitsuhiro; Makino, Toru*; Oki, Hiroshi*; Uchibori, Akihiro; Okano, Yasushi

Proceedings of 30th International Conference on Nuclear Engineering (ICONE30) (Internet), 7 Pages, 2023/05

Journal Articles

Journal Articles

Experimental study on the breakup of liquid jet discharged from a nozzle with sudden contraction

Sun, G.*; Okawa, Tomio*; Aoyagi, Mitsuhiro; Uchibori, Akihiro; Okano, Yasushi

Proceedings of 30th International Conference on Nuclear Engineering (ICONE30) (Internet), 8 Pages, 2023/05

When liquid sodium leaks as a liquid jet from piping in a sodium-cooled fast reactor, the jet impinges with structures to produce splashing droplets which can cause significant combustion. According to previous studies on circular nozzles, the amount of splash is affected by the state of the jet at the moment of impingement. In the present work, a nozzle with a sudden contraction in the cross-sectional area was designed to reproduce a supposed pipe leakage, and the breakup behavior of jet discharged from this nozzle was observed. The result shows that the breakup of jet was accelerated until the jet transformed into a particularly stable state when the jet velocity exceeded a certain value. Once the jet has transformed, it will not turn back unless turning down the flow rate to a very low value. The stable jet after the transformation has a longer breakup length than that before the transformation in the same flow rate.

Journal Articles

Study on safety characteristics of a sodium-cooled fast reactor with negative void reactivity during initiating phase in severe accident

Ishida, Shinya; Fukano, Yoshitaka; Tobita, Yoshiharu; Okano, Yasushi

Proceedings of 2023 International Congress on Advanced in Nuclear Power Plants (ICAPP 2023) (Internet), 8 Pages, 2023/04

JAEA Reports

In-vessel source term analysis code TRACER Version 2.4.1 (User's manual)

Ono, Masahiro*; Uchibori, Akihiro; Okano, Yasushi; Takata, Takashi*

JAEA-Testing 2022-004, 193 Pages, 2023/03

JAEA-Testing-2022-004.pdf:3.31MB

A computer code TRACER (Transport phenomena of Radionuclides for Accident Consequence Evaluation of Reactor) version 2.4.1 has been developed to evaluate species and quantities of fission products (FPs) released into cover gas due to a fuel pin failure in an LMFBR. The TRACER version 2.4.1 includes the models related to NUREG-0772 and also new or modified computational program codes in order to possess a new function shown below, and partial modify of coefficient of FP transition model between coolant and cover gas. This manual includes manual conventions for TRACER Version 2.3, addition of reference such as formula, improvement of explanation of input file creation method, addition of improvement of NUREG-0772 model added to TRACER code, modification of figure of sample analysis performed in appendix. It includes modifications and additions of sample analysis.

Journal Articles

Numerical study of initiating phase of core disruptive accident in small sodium-cooled fast reactors with negative void reactivity

Ishida, Shinya; Fukano, Yoshitaka; Tobita, Yoshiharu; Okano, Yasushi

Journal of Nuclear Science and Technology, 13 Pages, 2023/00

Journal Articles

Development of ARKADIA-Safety for severe accident evaluation of sodium-cooled fast reactors

Aoyagi, Mitsuhiro; Sonehara, Masateru; Ishida, Shinya; Uchibori, Akihiro; Kawada, Kenichi; Okano, Yasushi; Takata, Takashi

Proceedings of Technical Meeting on State-of-the-art Thermal Hydraulics of Fast Reactors (Internet), 3 Pages, 2022/09

Journal Articles

Experiment study on the effect of nozzle shape on liquid jet breakup

Sun, G.*; Zhan, Y.*; Okawa, Tomio*; Aoyagi, Mitsuhiro; Uchibori, Akihiro; Okano, Yasushi

Proceedings of 29th International Conference on Nuclear Engineering (ICONE 29) (Internet), 6 Pages, 2022/08

When a liquid sodium leakage accident occurs in a sodium-cooled fast reactor, the injected sodium collides with structures to produce splashing droplets, which can result in a violent combustion. According to previous studies on circular nozzles, the amount of splash is affected by the state of the jet at the moment of impact. However, the outlet shape of damaged area is hardly to be circular; and meanwhile it influences the flow pattern of jet a lot. Considering about this, in the present work, high-speed cameras were used to observe the jet discharged from oval nozzles vertically downward to investigate the falling process of the jet. The result shows that surface wave appears on the jet and within a certain range of flow velocity it can be observed obviously, meanwhile accelerate the breakup of jet.

Journal Articles

Development of dynamic PRA methodology for external hazards (Application of CMMC method to severe accident analysis code)

Li, C.-Y.; Watanabe, Akira*; Uchibori, Akihiro; Okano, Yasushi

Dai-26-Kai Doryoku, Enerugi Gijutsu Shimpojiumu Koen Rombunshu (Internet), 4 Pages, 2022/07

Identifying accident scenarios that could lead to severe accidents and evaluating their frequency of occurrence are essential issues. This study aims to establish the methodology of the dynamic Probabilistic Risk Assessment (PRA) for sodium-cooled fast reactors that can consider the time dependency and the interdependence of each event. Specifically, the Continuous Markov chain Monte Carlo (CMMC) method is newly applied to the SPECTRA code, which analyzes the severe accident conditions of nuclear reactors, to develop an evaluation methodology for typical external hazards. Currently, a fault-tree model of air coolers of decay heat removal system is implemented as the CMMC method, and a series of preliminary analysis of the plant's transient characteristics under the scenario of volcanic ashfall has been conducted.

Journal Articles

GIF risk and safety working group; Application of the ISAM methodology to Gen-IV nuclear systems

Okano, Yasushi; Ammirabile, L.*; Sofu, T.*

2018 GIF Symposium Proceedings (Internet), p.253 - 262, 2020/05

GIF ISAM (Integrated Safety Assessment Methodology) includes five analytical tools (i.e. QSR, PIRT, OPT, DPA, PSA) and it is intended that each tool be used to answer specific safety-related questions with different levels of detail during various design stages and the ISAM as a whole offers flexibility and a graded approach to analyse technical issues of complex system architectures. Although each tool can be selected for individual and exclusive use, the full value of the integrated methodology is derived from using all tools, in an iterative fashion and in combination with the others, throughout the design process. The paper describes what is ISAM and pilot examples of individual use of QSR, PIRT and OPT and also combination application of DPA-PSA.

Journal Articles

A Study of probabilistic risk assessment methodology of external hazard combinations; Identification of hazard combination impacts on air-cooling decay heat removal system

Okano, Yasushi; Nishino, Hiroyuki; Yamano, Hidemasa; Kurisaka, Kenichi

Proceedings of International Topical Meeting on Probabilistic Safety Assessment and Analysis (PSA 2019), p.274 - 281, 2019/04

A sodium-cooled fast reactor uses the ambient air as an ultimate heat sink to remove decay heat, thus meteorological phenomena can potentially pose risks to the reactor. If a rare and intense external hazard occurs concurrently with another external hazard, it would affect the systems (i.e. air cooler of decay heat removal system). In this study, a new scheme of screening of the external hazard combinations was proposed. The authors classified simultaneous or sequential combinational hazards, and identified associated potential effects in terms of hazard duration and sequential order. As a result, this study identified scenarios of the external hazard combinations of preceding rare and intense external hazard with an following additional external hazard.

Journal Articles

Development of safety design guideline of structures, systems and components of Generation-IV Sodium-cooled Fast Reactor

Okano, Yasushi

Nihon Genshiryoku Gakkai-Shi ATOMO$$Sigma$$, 60(12), p.764 - 769, 2018/12

JAEA has developed the second safety design guidelines report, "Safety Design Guidelines on Structures, Systems and Components" for Generation-IV SFR system, following the previously published SFR Safety Design Criteria and the first SFR Safety Design Guidelines report and with the reviews by a technical committee under Atomic Energy Society of Japan. This article explains about 14 key points on reactor core system, coolant system, and containment system and also current consistency of international SFR designs to the safety design guidelines.

Journal Articles

Level 1 PRA for external vessel storage tank of Japan sodium-cooled fast reactor in whole core refueling

Yamano, Hidemasa; Kurisaka, Kenichi; Nishino, Hiroyuki; Okano, Yasushi; Naruto, Kenichi*

Proceedings of 12th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation and Safety (NUTHOS-12) (USB Flash Drive), 15 Pages, 2018/10

Spent fuels are transferred from a reactor core to a spent fuel pool through an external vessel storage tank (EVST) filled with sodium in sodium-cooled fast reactors in Japan. This paper describes identification of dominant accident sequences leading to fuel failure, which was achieved through probabilistic risk assessment for the EVST designed for a next sodium-cooled fast reactor plant system in Japan to improve the EVST design. The safety strategy for the EVST involves whole core refueling (early transfer of all core fuel assemblies into the EVST) assuming a severe situation that results in sodium level reduction leading finally to the top of the reactor core fuel assemblies in a long time. This study introduces the success criteria mitigation along the decay heat decrease over time. Based on the design information, this study has carried out identification of initiating events, event and fault tree analyses, a probability analysis for human error, and quantification of accident sequences. The fuel damage frequency of the EVST was evaluated to be approx. 10$$^{-5}$$/year. The dominant accident sequence resulted from the static failure and human error for the switching from the stand-by to operation mode in the three stand-by cooling circuits after loss of one circuit for refueling heat removal operation as an initiating phase.

Journal Articles

Level 1 PRA for external vessel storage tank of Japan sodium-cooled fast reactor in scheduled refueling

Yamano, Hidemasa; Naruto, Kenichi*; Kurisaka, Kenichi; Nishino, Hiroyuki; Okano, Yasushi

Proceedings of 26th International Conference on Nuclear Engineering (ICONE-26) (Internet), 9 Pages, 2018/07

Spent fuels are transferred from a reactor core to a spent fuel pool through an external vessel storage tank (EVST) filled with sodium in sodium-cooled fast reactors in Japan. This paper describes identification of dominant accident sequences leading to fuel failure by conducting probabilistic risk assessment for EVST designed for a next sodium-cooled fast reactor plant system in Japan to improve the EVST design. Based on the design information, this study has carried out identification of initiating events, event and fault tree analyses, human error probability analysis, and quantification of accident sequences. Fuel damage frequency of the EVST was evaluated approx. 10$$^{-6}$$ /year in this paper. By considering the secondary sodium freezing, the fuel damage frequency was twice increased. The dominant accident sequence resulted from the common cause failure of the damper opening and/or the human error for the switching from the stand-by to the operation mode in the three stand-by cooling circuits. The importance analyses have indicated high risk contributions.

Journal Articles

Study on combination hazard curve of forest fire with lightning and strong wind

Okano, Yasushi; Yamano, Hidemasa

Proceedings of Asian Symposium on Risk Assessment and Management 2017 (ASRAM 2017) (USB Flash Drive), 3 Pages, 2017/11

Forest fire hazard assessment methodologies using a logic tree have been applied for the evaluation of combination hazard curves of a forest fire with lightning as an initiator of a forest fire and with a strong wind being independent from a forest fire. The complex shape of the combinational hazard curve of forest fire and lighting is due to that both lightning and high velocity wind tend to appear under unstable weather conditions, and there is correlation between two hazards. The evaluated combinational hazard curve of forest fire and strong wind for the instantaneous wind velocity over 80 m/s has extremely small frequency in the range below 10$$^{-14}$$/year.

Journal Articles

Level 1 PRA for external vessel storage tank of Japan sodium-cooled fast reactor in scheduled refueling

Yamano, Hidemasa; Naruto, Kenichi*; Kurisaka, Kenichi; Nishino, Hiroyuki; Okano, Yasushi

Proceedings of Asian Symposium on Risk Assessment and Management 2017 (ASRAM 2017) (USB Flash Drive), 3 Pages, 2017/11

Spent fuels are transferred from a reactor core to a spent fuel pool through an external vessel storage tank (EVST) filled with sodium in sodium-cooled fast reactors in Japan (JSFR). The objective of this study is to identify dominant accident sequences leading to fuel failure by conducting PRA for EVST. The EVST heat removal system in JSFR consists of four independent loops with for primary and secondary ones. Based on the JSFR design information, this study has identified initiating events, event and /fault tree analyses, human reliability analysis, and quantification of accident sequences. Fuel damage frequency of the EVST was evaluated approx. 10$$^{-6}$$ /year in this paper. The main contributor of the fuel damage frequency is the loss of heat removal function of the cooling system. The dominant initiating event was the loss of one circuit of normal heat removal operation.

Journal Articles

Hazard curve evaluation for forest fire smoke effects on air-cooling decay heat removal systems

Okano, Yasushi; Yamano, Hidemasa

Proceedings of International Topical Meeting on Probabilistic Safety Assessment and Analysis (PSA 2017) (USB Flash Drive), p.1334 - 1342, 2017/09

This study evaluates a hazard curve of smoke effects generated by a forest fire by applying a new method using a logic tree which consists of variable parameters on a forest fire, weather conditions, types of vegetation and topography, and simulation conditions. A response surface of the smoke spatial density was evaluated using two simulation codes: FARSITE for forest fire propagation and ALOFT-FT for smoke transportation. It is followed by a Monte Carlo simulation to evaluate the hazard curve representing the annual exceedance frequency of the total amount of the smoke captured on air filters. The evaluated hazard curve is about 1$$times$$10$$^{-2}$$ per year for 3.5 kg/m$$^{2}$$/(m/s).

Journal Articles

Sensitivity study on forest fire breakout and propagation conditions for forest fire hazard curve evaluations

Okano, Yasushi; Yamano, Hidemasa

Mechanical Engineering Journal (Internet), 4(3), p.16-00517_1 - 16-00517_10, 2017/06

A sensitivity study on forest fire hazard curves was performed. The probability fluctuation on forest fire breakout time affects the reaction intensity and the fireline intensity around 4% and 14% respectively. The probability fluctuation on forest fire breakout points affects the hazard curve frequency around +70% to -40%. The probability fluctuation due to forest firefighting operation only affects the frequency of the hazard curves, but not the intensity. The hazard curves without the effect of firefighting remarkably increase around 40 to 80 times in frequency in comparison with those with considering the forest firefighting operation effect outside the plant. This study indicated that the most significant factor in the forest fire hazard risk is whether the forest firefighting operation outside the plant is expected before the forest fire arrival at the plant.

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