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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.*; 内堀 昭寛; 岡野 靖; Pellegrini, M.*; Erkan, N.*; 高田 孝*; 岡本 孝司*

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

 被引用回数:0 パーセンタイル:0

For a sodium-cooled fast reactor, the capability for stable cooling and avoiding re-criticality on the debris bed is essential for achieving in-vessel retention when severe accidents occur. However, an unexploited uncertainty still existed regarding the compound effect of the heterogeneous configuration and dynamic particle redistribution for the debris bed's criticality and cooling safety assessment. Therefore, this research aims to develop a numerical tool for investigating the effects of the different transformations of the heterogeneous configurations on the debris bed's criticality/cooling assessment. Based on the newly proposed methodology in this research, via integrating the Discrete Element Method (DEM) with Computational Fluid Dynamics (CFD) and Monte-Carlo-based Neutronics (MCN), the coupled CFD-DEM-MCN solver was constructed with the originally created interface to integrate two existing codes. The effects of the different bed configurations' transformations on the bed safety assessments were also quantitively confirmed, indicating that the effect of the particle-centralized fissile material had the dominant negative effect on the safety margin of avoiding re-criticality and particle re-melting accidents and had a more evident impact than the net bed-centralized effect. This coupled solver can serve to further assess the debris bed's safety via a multi-physics simulation approach, leading to safer SFR design concepts.


Data processing and visualization of X-ray computed tomography images of a JOYO MK-III fuel assembly

Tsai, T.-H.; 佐々木 新治; 前田 宏治

Journal of Nuclear Science and Technology, 60(6), p.715 - 723, 2023/06

 被引用回数:1 パーセンタイル:40.11(Nuclear Science & Technology)

A method for processing and visualizing X-ray computed tomography (CT) images of a fuel assembly is developed and applied to a JOYO MK-III fuel assembly. The method provides vertical-section-like images to observe the spatial distribution of CT values in fuel pins and also supplies images that show the relationship between the linear heat rate (LHR) and radial CT-value distribution. In addition, an attempt to analyze the radial cracks in the CT images is proposed, and the results demonstrate the correlation between LHR and the radial cracks.


Investigation of the core neutronics analysis conditions for evaluation of burn-up nuclear characteristics of the next-generation fast reactors

滝野 一夫; 大木 繁夫

JAEA-Data/Code 2023-003, 26 Pages, 2023/05




Effectiveness evaluation methodology of the measures for improving resilience of nuclear structures against excessive earthquake

栗坂 健一; 西野 裕之; 山野 秀将

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

本研究の目的は破損拡大抑制技術によって過大地震時の原子炉構造レジリエンス向上策の有効性評価手法を開発することである。安全上重要な機器・構造物のレジリエンス向上策によって耐震裕度が増すとみなす。同向上策の有効性を評価するため、炉心損傷頻度CDFを指標に選び、CDFの低減を 地震PRAによって定量化する。崩壊熱除去機能喪失に至る事故シーケンスがナトリウム冷却高速炉SFRの地震時CDFに有意な寄与を示す。また、同事故シーケンスは超高温を経て炉心損傷に至る。本研究では過大地震時の振動への対策のみならず超高温での対策も評価するよう手法を考案した。手法の適用性を検討するため、ループ型SFRを想定して試計算を実施した。仮定した範囲内では、レジリエンス向上策は設計地震動の数倍の地震までCDFを有意に低減する効果を示した。適用性検討を通じて、有効性評価手法が開発された。


Analysis by hazard plotting on steam generator tube leak in sodium-cooled fast reactors Phenix and BN600

栗坂 健一

Proceedings of 30th International Conference on Nuclear Engineering (ICONE30) (Internet), 10 Pages, 2023/05



Development of dynamic PRA methodology for external hazards in sodium-cooled fast reactor via applying Markov chain Monte Carlo method to severe accident analysis code; Assessment of accident management of assigning independent emergency diesel generators to each air cooler

Li, C.-Y.; 渡部 晃*; 内堀 昭寛; 岡野 靖

Proceedings of 30th International Conference on Nuclear Engineering (ICONE30) (Internet), 10 Pages, 2023/05

Quantitative assessment of the effect of accident management on the various external hazards is essential in the nuclear safety analysis. This study aims to establish the dynamic probabilistic risk assessment methodology for sodium-cooled fast reactors that can consider the transient plant status under continuous external hazards with corresponding countermeasures operating stochastically. Specifically, the Continuous Markov chain Monte Carlo (CMMC) and Deterministic and Stochastic Petri Nets (DSPN) methods are newly applied to the severe accident analysis code, SPECTRA, which can conduct dynamic plant evaluation in the different severe accident conditions of nuclear reactors, to develop an evaluation methodology for typical external hazards. In the DSPN-CMMC-SPECTRA coupled frame, the latest safety functions of the plant components/systems can be stochastically determined by the DSPN-CMMC grounded on the current plant states under continuous hazard and the interaction between the multi-state components/systems; then, SPECTRA can evaluate the following plant state determined by the latest safety function of the components/systems. Therefore, the advantage of this newly developed DSPN-CMMC-SPECTRA frame is having the capability to quantitatively and stochastically evaluate the transient accident progressions that potentially lead to the core damage under the continuous external hazard scenario. As for the preliminary exam on the DSPN-CMMC-SPECTRA frame, one of the typical external hazards of continuous volcanic ashfall is selected in this research. In addition, the numerical investigation of alternative accident management' effects has also been carried out and quantitatively confirmed in this research.


Development of adjusted nuclear data library for fast reactor application

横山 賢治

EPJ Web of Conferences, 281, p.00004_1 - 00004_10, 2023/03



Chapter 5, Sodium-cooled Fast Reactor (SFRs)/ Chapter 12, Generation-IV Sodium-cooled Fast Reactor (SFR) concepts in Japan

久保 重信; 近澤 佳隆; 大島 宏之; 上出 英樹

Handbook of Generation IV Nuclear Reactors, Second Edition, p.173 - 194, 2023/03



先進ループ型ナトリウム冷却高速炉の炉心出口部における高サイクル熱疲労の防止に関する実験研究; 炉上部構造下部における温度変動の特徴と温度変動緩和方策

小林 順; 相澤 康介; 江連 俊樹; 長澤 一嘉*; 栗原 成計; 田中 正暁

JAEA-Research 2022-009, 125 Pages, 2023/01




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

石田 真也; 深野 義隆; 飛田 吉春; 岡野 靖

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

To improve the safety of future SFRs, the development of SFRs with low void reactivity has been promoted. Small SFRs can have a negative void coefficient of reactivity, so the analysis of the CDA event sequence in small SFRs is valuable for the investigation of the reactor characteristics for the future research and development of SFRs. In this study, the typical initiating events of a CDA in small SFRs were evaluated with the computational code, SAS4A. The event progression of ULOF and UTOP in the low void reactivity reactor is found to be slow due to the effective operation of the negative reactivity feedback and the absence of significant positive reactivity insertion. No power excursion occurs in the initiating phase. In ULOF, the cladding melt and relocation behavior becomes more important for the evaluation of the event progression due to its positive reactivity.


A 3D particle-based simulation of heat and mass transfer behavior in the EAGLE ID1 in-pile test

Zhang, T.*; 守田 幸路*; Liu, X.*; Liu, W.*; 神山 健司

Annals of Nuclear Energy, 179, p.109389_1 - 109389_10, 2022/12

 被引用回数:1 パーセンタイル:40.11(Nuclear Science & Technology)

The ID1 test was the final target test of the EAGLE experimental framework program. It was used to verify that during a core disruptive accident, the molten fuel could be discharged via wall failure of an inner duct in FAIDUS, a design concept for the sodium-cooled fast reactor. The ID1 results revealed that the wall failure behavior owed to the large heat flow from the surrounding fuel/steel mixture. The present study numerically investigated the heat transfer mechanisms in the test using the finite volume particle method in the three-dimensional domain. The thermal hydraulic behaviors during wall failure were reproduced reasonably. The present three-dimensional simulation mitigated inherent defects of our previous two-dimensional calculation and clarified that the solid fuel and liquid steel close to the outer surface of the duct can expose the duct to high thermal loads, resulting in the wall failure.


Evaluation of fuel reactivity worth measurement in the prototype fast reactor Monju

大釜 和也; 竹越 淳*; 片桐 寛樹; 羽様 平

Nuclear Technology, 208(10), p.1619 - 1633, 2022/10

 被引用回数:3 パーセンタイル:77.29(Nuclear Science & Technology)

In the prototype fast breeder reactor Monju, fuel reactivity worth was measured at six positions as the reactivity corresponding to the differences of critical control rod positions between cores with and without a dummy fuel subassembly. In this paper, the measurements are evaluated in detail, and their reliability and usefulness as the validation data for fast reactor neutronics design methodologies are investigated through a comparison with calculations by using the latest methodology developed in Japan Atomic Energy Agency. Calculated-to-experiment values (C/Es) and their uncertainties of fuel reactivity worth were 0.97 to 1.02 and 4% to 6%. Through this study, the measurements and calculations were found consistent and reliable.


Investigation on natural circulation behavior for decay heat removal in reactor vessel of sodium-cooled fast reactor under severe accident condition, 1; Effect of decay-heat conditions on natural circulation behavior under dipped-type DHX operation conditions

辻 光世; 相澤 康介; 小林 順; 栗原 成計

Proceedings of 12th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS12) (Internet), 6 Pages, 2022/10

ナトリウム冷却高速炉(SFR)において、炉心溶融を含むシビアアクシデント時の安全性強化のため、炉内冷却機器の設計と運用を最適化することが重要である。SFRの原子炉容器を模擬した1/10縮尺の水試験装置を用いて、原子炉容器内部の自然循環現象を把握するための水試験を実施している。本報では、炉心燃料とコアキャッチャ上の燃料デブリの発熱割合が原子炉容器内部の自然循環挙動へ与える影響を調査するために、浸漬型DHXを運転した条件で実施した実験結果を示す。全体の発熱量を一定として、全体の発熱量に対するコアキャッチャ上の燃料デブリの発熱割合を20%, 80%とした2条件で原子炉容器内部の温度分布及び流速分布を計測した。炉心部とコアキャッチャ上の燃料デブリの発熱割合による炉容器内の自然循環挙動への影響を定量的に把握した。


Preliminary deformation analysis of the reactor vessel due to core debris accumulation onto the reactor vessel bottom for sodium-cooled fast reactor

小野田 雄一; 山野 秀将

Proceedings of 12th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS12) (Internet), 9 Pages, 2022/10

原子力機構におけるナトリウム冷却高速炉の設計では、シビアアクシデントが生じた場合に、さまざまな設計対策により損傷炉心物質を原子炉容器内で安定的に冷却する方針(炉容器内保持: IVR)をとっている。IVRに失敗する可能性は非常に低いものの、確率論的リスク評価の研究では、IVRの失敗を含むさまざまなシナリオの検討が必要となる。そこで本研究では、原子炉容器内におけるデブリの安定冷却に関わる事象スペクトルを幅広く検討するため、コアキャッチャーのスカート部にデブリが堆積する場合の原子炉容器の変形・破損挙動を、構造解析コードFNAS-STARを用いて数値的に解析した。原子炉容器の破損条件を調査する観点から、出力密度の異なる2ケースの解析を実施した。今回の想定条件下における高出力密度のケースでは、原子炉容器の温度が約1100$$^{circ}$$Cに達すると原子炉容器が大幅に変形し、その破損判断基準に到達した。


Development of safety design criteria and safety design guidelines for Generation IV sodium-cooled fast reactors

二神 敏; 久保 重信; Sofu, T.*; Ammirabile, L.*; Gauthe, P.*

Proceedings of International Conference on Topical Issues in Nuclear Installation Safety; Strengthening Safety of Evolutionary and Innovative Reactor Designs (TIC 2022) (Internet), 10 Pages, 2022/10

In the framework of the GIF, an effort to develop Safety Design Criteria (SDC) for SFR systems was initiated in 2011. For this purpose, an SDC task force (SDC-TF) was formulated in July 2011. The SDC-TF members consist of representatives of CIAE (China), CEA (France), JAEA (Japan), KAERI, KINS (Republic of Korea), IPPE (Russia), ANL, INL, ORNL (United States of America), EC and IAEA. This paper describes the outline of the SDC and SDGs contents and its development background as shown above. These SDC and SDGs refer related IAEA safety standards, such as SSR-2/1 Safety of Nuclear Power Plants: Design, SSG-52 Design of the Reactor Core for Nuclear Power Plants. This paper focuses on both technology neutral aspects, which are common parts between the SDC/SDG and IAEA standards, and SFR specific aspects.


Study on the discharge behavior of the molten-core materials through the control rod guide tube; Investigations of the effect of an internal structure in the control rod guide tube on the discharge behavior

加藤 慎也; 松場 賢一; 神山 健司; Akaev, A.*; Vurim, A.*; Baklanov, V.*

Proceedings of 13th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation and Safety (NUTHOS-13) (Internet), 12 Pages, 2022/09



Analysis on cooling behavior for simulated molten core material impinging to a horizontal plate in a sodium pool

松下 肇希*; 小林 蓮*; 堺 公明*; 加藤 慎也; 松場 賢一; 神山 健司

Proceedings of 13th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation and Safety (NUTHOS-13) (Internet), 9 Pages, 2022/09

ナトリウム冷却高速炉の炉心損傷事故では、溶融炉心物質が制御棒案内管などの流路を通って炉心領域下の炉心入口プレナムに流れ込む。溶融炉心物質は、ナトリウム冷却材中で入口プレナムの水平板に衝突しながら冷却・固化されると見込まれる。しかし、水平構造物に衝突した溶融炉心物質の固化・冷却挙動は、これまで十分に研究されていなかった。これはナトリウム冷却高速炉の安全性向上の観点から解明が必要な重要な現象である。そこで、カザフスタン共和国国立原子力センターの実験施設において、模擬溶融炉心物質(アルミナ: Al$$_{2}$$O$$_{3}$$)を水平構造物上のナトリウム冷却材中に放出する一連の実験が実施された。本研究では、高速炉安全性評価コードSIMMER-IIIを用いたナトリウム試験に関する解析を実施した。解析結果と実験データの比較により、解析手法の妥当性を確認した。また、ジェット衝突時の冷却・固化挙動を評価した。その結果、溶融炉心物質が水平板への衝突により破砕され、周辺部へ飛散することがわかった。さらに、模擬溶融炉心物質がナトリウムによって冷却され、その後、固化することを確認した。


Numerical simulation of annular dispersed flow in simplified subchannel of light water cooled fast reactor RBWR

吉田 啓之; 堀口 直樹; 小野 綾子; 古市 肇*; 上遠野 健一*

Proceedings of 29th International Conference on Nuclear Engineering (ICONE 29) (Internet), 7 Pages, 2022/08

About the boiling transition (BT) that determines the maximum thermal output of the BWR, it is considered that the spacers have significant effects on the occurrence of BT. And occurrence conditions of BT can be changed by devising the spacer shapes. In the light water cooled fast reactor: RBWR, thermal-hydraulics conditions are more severe than the current BWR. Then, the effect of the spacer on BT should be sufficiently utilized in the RBWR. In the thermal-hydraulics design for the current BWR, large-scale tests were carried out and used to evaluate BT conditions. The RBWR is still in the design stage, and there is room to be changed to many parameters. Then, it is not reasonable to determine the shape of the spacer by evaluation only for large-scale tests. On the other hand, by applying a two-phase CFD method with remarkable development in recent years, we can develop a model that can predict the effect of spacers mechanistically. This research used the detailed two-phase flow simulation code TPFIT developed by JAEA to simulate annular dispersed flow in RBWR subchannels. In the occurrence of BT, it is considered that the two-phase flow pattern is the annular dispersed flow, and we want to evaluate the effects of spacer shape on annular dispersed flow in RBWR subchannels. As the first step of this research, we performed numerical simulations of annular dispersed flow in the simplified subchannel of RBWR. We used a circular tube with the same hydraulic diameter as the RBWR subchannel to consider the basic effects of spacer on the annular dispersed flow. As a simulation parameter, we choose the existence of the spacer. The spacer used in the simulation has a simplified shape and the same blockage ratio as the RBWR. In this paper, we describe the result of numerical simulation. We evaluated droplets' size and velocity based on simulation results for the spacer's existence and non-existence cases.


Hydrogen release reaction from sodium hydride with different sample quantities

土井 大輔

Proceedings of 29th International Conference on Nuclear Engineering (ICONE 29) (Internet), 7 Pages, 2022/08

In sodium-cooled fast reactors (SFRs), hydrogen is a major nonmetallic impurity in the coolant during normal operation. A higher hydrogen concentration than the gas-liquid equilibrium had been transiently detected in the gas space of the actual SFR plant. However, the chemical reactions that caused hydrogen generation, which involve several sodium compounds, have not been identified. Furthermore, the thermal behavior of these hydrogen release reactions has not been thoroughly investigated. In this study, the hydrogen release behavior of sodium hydride, which could be involved in all of these reactions, was clarified by two experimental methods dealing with different sample quantities. In the thermal analysis with a semi-micro sample of about 1mmol, the hydrogen generation was demonstrated by mass spectrometry as the sample mass decreased, suggesting thermal decomposition. A monomodal hydrogen release curve similar to the thermal analysis result was obtained in the heating experiment with a macro amount sample of about 1mol. These experimental results showed consistent activation energies within the standard error. Therefore, it was elucidated that the ideal reaction behavior obtained by thermal analysis could be sufficiently extrapolated to the reaction behavior occurring in a larger amount of sample. These findings provide fundamental insights into the thermal decomposition of sodium hydride and are indispensable for analyzing hydrogen release behavior in other hydrogen release reactions involving sodium hydride.


Development of evaluation method of gas entrainment on the free surface in the reactor vessel in pool-type sodium-cooled fast reactors; Gas entrainment judgment based on three-dimensional evaluation of vortex center line and distribution of pressure decrease

松下 健太郎; 江連 俊樹; 今井 康友*; 藤崎 竜也*; 田中 正暁

Proceedings of 29th International Conference on Nuclear Engineering (ICONE 29) (Internet), 8 Pages, 2022/08


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