Large-eddy simulation on gas mixing induced by the high-buoyancy flow in the CIGMA facility

安部 諭; 柴本 泰照

Nuclear Engineering and Technology, 55(5), p.1742 - 1756, 2023/05

https://doi.org/10.1016/j.net.2023.01.019

The hydrogen behavior in a nuclear containment vessel is a significant issue when discussing the potential of hydrogen combustion during a severe accident. After the Fukushima-Daiichi accident in Japan, we have investigated in-depth the hydrogen transport mechanisms by utilizing experimental and numerical approaches. Computational fluid dynamics is a powerful tool for better understanding the transport behavior of gas mixtures, including hydrogen. This paper describes a large-eddy simulation of gas mixing driven by a high-buoyancy flow. We focused on the interaction behavior of heat and mass transfers driven by the horizontal high-buoyant flow during density stratification. For validation, the experimental data of the Containment InteGral effects Measurement Apparatus (CIGMA) facility were used. With a high-power heater for the gas-injection line in the CIGMA facility, a high temperature flow of approximately 390C was injected into the test vessel. By using the CIGMA facility, we can extend the experimental data to the high temperature region. The phenomenological discussion in this paper help understand the heat and mass transfer induced by the high-buoyancy flow in the containment vessel during a severe accident.

Numerical analysis of natural convection behavior in density stratification induced by external cooling of a containment vessel

石垣 将宏*; 安部 諭; Hamdani, A.; 廣瀬 意育

Annals of Nuclear Energy, 168, p.108867_1 - 108867_20, 2022/04

https://doi.org/10.1016/j.anucene.2021.108867

It is essential to improve computational fluid dynamics (CFD) analysis accuracy to estimate thermal flow in a containment vessel during a severe accident. Previous studies pointed out the importance of the influence of initial and boundary conditions on the CFD analysis. The purpose of this study is to evaluate the influence of initial and boundary conditions by numerical analysis of natural convection experiments in a large containment vessel test facility CIGMA(Containment InteGral effects Measurement Apparatus). A density stratification layer was initially formed in the vessel using helium and air, and external cooling of the vessel surface-induced natural convection. In this study, we carried out numerical simulations of the density stratification erosion driven by the natural convection using the RANS (Reynolds averaged Navier-Stokes) model. As a result, the temperature boundary condition of the small internal structure in the vessel had a significant influence on the fluid temperature distribution in the vessel. The erosion velocity of the density stratification layer changed depending on the initial gas concentration distribution. Then, appropriate settings of the temperature and gas concentration conditions are necessary for accurate analysis.

Density stratification breakup by a vertical jet; Experimental and numerical investigation on the effect of dynamic change of turbulent Schmidt number

安部 諭; Studer, E.*; 石垣 将宏; 柴本 泰照; 与能本 泰介

Nuclear Engineering and Design, 368, p.110785_1 - 110785_14, 2020/11

https://doi.org/10.1016/j.nucengdes.2020.110785

The hydrogen behavior in a nuclear containment vessel is one of the significant issues raised when discussing the potential of hydrogen combustion during a severe accident. Computational Fluid Dynamics (CFD) is a powerful tool for better understanding the turbulence transport behavior of a gas mixture, including hydrogen. Reynolds-averaged Navier-Stokes (RANS) is a practical-use approach for simulating the averaged gaseous behavior in a large and complicated geometry, such as a nuclear containment vessel; however, some improvements are required. We implemented the dynamic modeling for based on the previous studies into the OpenFOAM ver 2.3.1 package. The experimental data obtained by using a small scale test apparatus at Japan Atomic Energy Agency (JAEA) was used to validate the RANS methodology. Moreover, Large-Eddy Simulation (LES) was performed to phenomenologically discuss the interaction behavior. The comparison study indicated that the turbulence production ratio by shear stress and buoyancy force predicted by the RANS with the dynamic modeling for was a better agreement with the LES result, and the gradual decay of the turbulence fluctuation in the stratification was predicted accurately. The time transient of the helium molar fraction in the case with the dynamic modeling was very closed to the VIMES experimental data. The improvement on the RANS accuracy was produced by the accurate prediction of the turbulent mixing region, which was explained with the turbulent helium mass flux in the interaction region. Moreover, the parametric study on the jet velocity indicates the good performance of the RANS with the dynamic modeling for on the slower erosive process. This study concludes that the dynamic modeling for is a useful and practical approach to improve the prediction accuracy.

Influence of grating type obstacle on stratification breakup by a vertical jet

安部 諭; 石垣 将宏; 柴本 泰照; 与能本 泰介

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

At Japan Atomic Energy Agency (JAEA), small scale experiment, named VIMES (VIsualization and MEasurement system on stratification behavior) experiment, has been performed since 2014. In this paper, we introduce the influence of grating type obstacle to the VIMES experiment. Two types of grating obstacle were constructed based on the aperture area ratio. The obstacles were placed at the intermediate position between the jet nozzle exit and bottom of the initial stratification. Experimental results showed that the vertical jet was strongly affected by the grating obstacle. Due to the rectifying effect, the radial spreading was suppressed and the velocity magnitude on the jet center line became larger than that in case without the grating obstacle. Meanwhile, due to the resistance effect, the integral momentum flux of the vertical jet was decayed with decrease of the aperture area ratio. It means that in case with the grating obstacle the integral jet penetration strength was decayed, although the local jet penetration to the stratification was stronger than that in case without the grating obstacle. Also, the slower stratification breakup could be observed with decrease of the aperture area ratio, indicating that stratification breakup rate to be discussed in detail considering every possible effect of a jet penetration.

Experimental study on outer surface cooling of containment vessel by using CIGMA

柴本 泰照; 石垣 将宏; 安部 諭; 与能本 泰介

Proceedings of 17th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-17) (USB Flash Drive), 14 Pages, 2017/09

The present paper introduces the recent outcome from the CIGMA experiments regarding containment vessel cooling, in which an external side of a vessel upper head was flooded by water. The test vessel was initially pressurized by steam and noncondensable gas (air and/or helium), and was subsequently cooled by pouring water to the outside of the vessel top. Similar experiments were performed by authors using air-steam binary system in the previous study, which showed several characteristic phenomena such as inverse temperature stratification. The experimental conditions were extended systematically in this study to investigate the effects of initial gas composition and distribution in a vessel. The measurement results indicated that natural circulation was significantly affected by distributions of each gas species. In particular, it was enhanced when the gas density became heavier after condensation on the vessel inner wall, while it was suppressed when the gas density became lighter, creating density stratification with helium-rich gas in the upper region. The results are explained by the simplified model.

Outcome of first containment cooling experiments using CIGMA

柴本 泰照; 与能本 泰介; 石垣 将宏; 安部 諭

Proceedings of 11th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, Operation and Safety (NUTHOS-11) (USB Flash Drive), 10 Pages, 2016/10

The Japan Atomic Energy Agency (JAEA) initiated the ROSA-SA project in 2013 for the purpose of studying thermal hydraulics relevant to over-temperature containment damage, hydrogen risk, and fission product transport. For this purpose, the JAEA newly constructed the Containment InteGral Measurement Apparatus (CIGMA) in 2015 for the experiments addressing containment responses, separate effects, and accident managements. Recently, we successfully conducted first experiments using CIGMA to characterize the facility under typical experimental conditions. Among these experiments, the present paper focuses on the results of containment cooling tests, for which an upper part of the vessel outer surface was cooled by spray water. Several distinctive phenomena were observed in the tests, including inverse temperature stratification in the vessel due to the cooling in the upper region. The RELAP5 analysis result was also presented to roughly indicate the prediction capability of the best-estimate two-phase flow code in predicting the containment thermal hydraulics.

First experiments at the CIGMA facility for investigations of LWR containment thermal hydraulics

柴本 泰照; 安部 諭; 石垣 将宏; 与能本 泰介

Proceedings of 24th International Conference on Nuclear Engineering (ICONE-24) (DVD-ROM), 9 Pages, 2016/06

http://doi.org/10.1115/ICONE24-60515

There has been an extensive reorientation of the light water reactor research in Japan since the Fukushima Dai-ichi Nuclear Power Station accident, which focuses on severe accidents and accident managements. The Japan Atomic Energy Agency (JAEA) initiated the ROSA-SA project in 2013 for the purpose of studying thermal hydraulics relevant to over-temperature containment damage, hydrogen risk, and fission product transport. For this purpose, the JAEA newly constructed the Containment InteGral Measurement Apparatus (CIGMA) in 2015 for the experiments addressing containment responses, separate effects, and accident managements. Recently, we successfully conducted first experiments using CIGMA to characterize the facility under typical experimental conditions investigating basic phenomena such as buildup of pressure by steam injection, containment cooling and depressurization by internal or external cooling, and density stratified layer mixing by impinging jet. This paper provides an overview of the research programs, the brief description of the facility specification and the outcomes obtained from the first experiments.

Leak-tightness characteristics concerning the containment structures of the HTTR

坂場 成昭; 飯垣 和彦; 近藤 雅明; 江森 恒一

Nuclear Engineering and Design, 233(1-3), p.135 - 145, 2004/10

https://doi.org/10.1016/j.nucengdes.2004.08.023

HTTRの原子炉格納施設は、原子炉格納容器,サービスエリア及び非常用空気浄化設備で構成され、減圧事故等におけるFPの原子炉外への放出を抑制させるものである。原子炉格納容器は、減圧事故時の圧力及び温度挙動に耐え、漏えい率が規定されている。また、サービスエリアは、非常用空気浄化設備により負圧に保たれる。本論文では、原子炉格納施設の気密性能について、系統別総合機能試験等により評価した結果を示す。試験の結果、原子炉格納容器の漏えい率は、規定値0.1%/dを十分満たし、サービスエリアは、非常用空気浄化設備により規定の負圧が保たれること等が確認された。

HTTR原子炉格納施設に関する機能試験

坂場 成昭; 飯垣 和彦; 川路 さとし; 伊与久 達夫

JAERI-Tech 98-013, 152 Pages, 1998/03

JAERI-Tech-98-013.pdf:7.69MB

HTTRの原子炉格納施設は、主冷却設備、補助冷却設備等を配置する原子炉格納容器(CV)、1次ヘリウム純化設備、1次ヘリウムサンプリング設備等を配置するサービスエリア(SA)及び非常用空気浄化設備から構成し、1次冷却設備の二重管破断事故(減圧事故)時等に外部へ放出する放射性物質の量を低減する役目を担っている。このため、CVには漏洩率、SAには気密性、非常用空気浄化設備にはSAの負圧維持、ヨウ素及び微粒子の除去効率並びに起動時間を規定している。これら規定した事項を、原子炉格納施設の系統別機能試験として燃料装荷前に確認した。CVの漏洩率試験では、1次冷却材がヘリウムガスであるHTTRに適応するため、原子炉冷却材圧力バウンダリを閉鎖したまま試験を実施するという従来の軽水炉等とは異なる新しい試験方法を確立し、規定値を満たすことを確認した。また、SA及び非常用空気浄化設備の機能試験では、所定の性能を発揮することを確認した。原子炉格納施設の機能試験の結果、減圧事故時等に外部へ放出する放射性物質の量は所定値内に低減することができるといえる。

Shielding design of obtain compact marine reactor

山路 昭雄; 迫 淳

Journal of Nuclear Science and Technology, 31(6), p.510 - 520, 1994/06

https://doi.org/10.3327/jnst.31.510

舶用炉は船内の狭隘な場所に設置されること及び原子力船の経済上の観点から、軽量・小型でなければならない。現在の舶用炉では遮蔽体が原子炉プラント重量の大きな割合を占めている。例えば、原子力船「むつ」の遮蔽体は原子炉プラント重量の70%を越えている。また、遮蔽体の重量と大きさの大部分は二次遮蔽体によるものであり、「むつ」の場合では二次遮蔽体が全遮蔽重量の88%を占めている。改良舶用炉MRXは一体型PWRと水張り式格納容器を採用することによってこの問題をかなりの程度まで解決している。この概念では二次遮蔽体を必要としない設計が可能である。この結果、MRXは従来の舶用炉と比べて軽量・小型化されている。例えば、MRXの原子炉出力は「むつ」の2.8倍であるが、プラント重量は「むつ」の0.5倍、格納容器体積は「むつ」の0.7倍である。