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BWR lower head penetration failure test focusing on eutectic melting

山下 拓哉; 佐藤 拓未; 間所 寛; 永江 勇二

Annals of Nuclear Energy, 173, p.109129_1 - 109129_15, 2022/08

Decommissioning work occasioned by the Fukushima Daiichi Nuclear Power Station (1F) accident of March 2011 is in progress. Severe accident (SA) analysis, testing, and internal investigation are being used to grasp the 1F internal state. A PWR system that refers to the TMI-2 accident is typical for SA codes and testing, on the other hand, a BWR system like 1F is uncommon, understanding the 1F internal state is challenging. The present study conducted the ELSA-1 test, a test that focused on damage from eutectic melting of the liquid metal pool and control rod drive (CRD), to elucidate the lower head (LH) failure mechanism in the 1F accident. The results demonstrated that depending on the condition of the melt pool formed in the lower plenum, a factor of LH boundary failure was due to eutectic melting. In addition, the state related to the CRD structure of 1F unit 2 were estimated.


Numerical simulation of sodium mist behavior in turbulent Rayleigh-B$'e$nard convection using new developed mist models

大平 博昭*; 田中 正暁; 吉川 龍志; 江連 俊樹

Annals of Nuclear Energy, 172, p.109075_1 - 109075_10, 2022/07

ナトリウム冷却高速炉(SFR)のカバーガス領域におけるミスト挙動を高精度で評価するため、混合気体のレイリー・ベナール対流(RBC)に対する乱流モデルを選定するとともに、ミストに対するレイノルズ平均数密度とミストの運動量方程式を開発し、OpenFOAMコードに組み込んだ。最初に、単純な並列チャネルのRBCを、Favre平均k-$$omega$$SSTモデルを使用して計算した。その結果、平均温度と流量特性はDNS, LES、および実験の結果とよく一致した。次に、本乱流モデルと新しく開発したミストモデルを用いて、SFRのカバーガス領域を模擬した熱伝達試験装置を計算した。その結果、計算された高さ方向の平均温度分布とミスト質量濃度が試験結果とよく一致した。本研究により、SFRのカバーガス領域において乱流RBC環境でのミスト挙動を高精度にシミュレートできる手法を開発した。


Dynamic probabilistic risk assessment of nuclear power plants using multi-fidelity simulations

Zheng, X.; 玉置 等史; 杉山 智之; 丸山 結

Reliability Engineering & System Safety, 223, p.108503_1 - 108503_12, 2022/07

Dynamic probabilistic risk assessment (PRA) more explicitly treats timing issues and stochastic elements of risk models. It extensively resorts to iterative simulations of accident progressions for the quantification of risk triplets including accident scenarios, probabilities and consequences. Dynamic PRA leverages the level of detail for risk modeling while intricately increases computational complexities, which result in heavy computational cost. This paper proposes to apply multi-fidelity simulations for a cost- effective dynamic PRA. It applies and improves the multi-fidelity importance sampling (MFIS) algorithm to generate cost-effective samples of nuclear reactor accident sequences. Sampled accident sequences are paralleled simulated by using mechanistic codes, which is treated as a high-fidelity model. Adaptively trained by using the high-fidelity data, low-fidelity model is used to predicting simulation results. Interested predictions with reactor core damages are sorted out to build the density function of the biased distribution for importance sampling. After when collect enough number of high-fidelity data, risk triplets can be estimated. By solving a demonstration problem and a practical PRA problem by using MELCOR 2.2, the approach has been proven to be effective for risk assessment. Comparing with previous studies, the proposed multi-fidelity approach provides comparative estimation of risk triplets, while significantly reduces computational cost.


Temporal variability of $$^{137}$$Cs concentrations in coastal sediments off Fukushima

鈴木 翔太郎*; 天野 洋典*; 榎本 昌宏*; 松本 陽*; 守岡 良晃*; 佐久間 一幸; 鶴田 忠彦; 帰山 秀樹*; 三浦 輝*; 津旨 大輔*; et al.

Science of the Total Environment, 831, p.154670_1 - 154670_15, 2022/07

The monthly monitoring data (total 3647 samples) between May. 2011 and Mar. 2020 were analyzed to describe temporal variability of $$^{137}$$Cs concentration in coastal sediments off Fukushima. $$^{137}$$Cs concentration of sediment had decreasing trend, but non-linear model fitting suggested that this decreasing trend showed slower. Additionally, $$^{137}$$Cs concentration were up to 4.08 times greater in shallow sampling sites (7, 10, 20 m depth) following heavy rainfall events (before five months vs. after five months), such as typhoons. These were consistent with increasing particulate $$^{137}$$Cs (P-$$^{137}$$Cs) fluxes from river and increasing dissolved $$^{137}$$Cs (D-$$^{137}$$Cs) concentration in seawater. Finally, the numerical experiment was conducted and revealed that riverine $$^{137}$$Cs input could preserve $$^{137}$$Cs concentration in coastal sediment. These results indicate that riverine $$^{137}$$Cs input via heavy rainfall events is one of the main factors for preserving $$^{137}$$Cs concentration in coastal sediment off Fukushima.


Online solid-phase extraction-inductively coupled plasma-quadrupole mass spectrometric quantification of $$^{90}$$Sr using $$^{88}$$Sr/$$^{86}$$Sr isotope dilution method

柳澤 華代*; 小田島 瑞樹*; 松枝 誠; 古川 真*; 高貝 慶隆*

Talanta, 244, p.123442_1 - 123442_7, 2022/07



Phase-field mobility for crystal growth rates in undercooled silicates, SiO$$_2$$ and GeO$$_2$$ liquids

河口 宗道; 宇埜 正美*

Journal of Crystal Growth, 585, p.126590_1 - 126590_7, 2022/05

過冷却ケイ酸塩,SiO$$_2$$,GeO$$_2$$融液中の11種類の酸化物または混合酸化物の結晶化におけるフェーズフィールド易動度$$L$$と結晶成長速度をフェーズフィールドモデル(PFM)を用いて計算し、$$L$$の物質依存性を議論した。実験の結晶成長速度と$$L=1$$のPFMシミュレーションから得られた結晶成長速度の比は、両対数プロットで結晶成長における固液界面プロセスの$$frac{TDelta T}{eta}$$のべき乗に比例した。また$$L=A(frac{k_{B}TDelta T}{6pi^{2}lambda^{3}eta T_{m} })^{B}$$のパラメータ$$A$$$$B$$$$A=6.7times 10^{-6}-2.6$$m$$^4$$J$$^{-1}$$s$$^{-1}$$,$$B=0.65-1.3$$であり、材料に固有の値であることが分かった。決定された$$L$$を用いたPFMシミュレーションにより、実験の結晶成長速度を定量的に再現することができた。$$A$$$$T_{m}$$における単位酸素モル質量あたりの陽イオンモル質量の平均の拡散係数と両対数グラフで比例関係にある。$$B$$は化合物中の酸素モル質量あたりの陽イオンのモル質量の総和$$frac{Sigma_{i}M_{i}}{M_{O}}$$に依存する。$$frac{Sigma_{i}M_{i}}{M_{O}}leq 25$$では、陽イオンのモル質量が大きくなるにつれて$$B$$は小さくなる。陽イオンのモル質量は陽イオンの移動の慣性抵抗に比例するため、$$B$$は陽イオンのモル質量の逆数で減少する。$$frac{Sigma_{i}M_{i}}{M_{O}}geq 25$$の重い陽イオンのケイ酸塩の結晶化では、$$B$$は約$$0.67$$で飽和し、$$T_{p}approx 0.9T_{m}$$となる。


Chemical species of iodine during sorption by activated carbon; Effects of original chemical species and fulvic acids

加藤 友彰; 香西 直文; 田中 万也; Kaplan, D. I.*; 宇都宮 聡*; 大貫 敏彦

Journal of Nuclear Science and Technology, 59(5), p.580 - 589, 2022/05



Development of a laser-driven ultrasonic technology for characterizations of heated and aged concrete samples

山田 知典; 大道 博行*; 柴田 卓弥

Journal of Nuclear Science and Technology, 59(5), p.614 - 628, 2022/05

We have demonstrated a full noncontact laser technology to measure the velocity of ultrasonic waves and their spectra propagated through concrete samples exposed to specified high-temperature conditions with specified durations as models of concrete structures in a severe accident at the Fukushima Daiichi Nuclear Power Station. The velocities and spectra of the ultrasonic waves were strongly dependent on the exposed temperature, i.e., at a high-temperature condition of 400$$^{circ}$$C, the velocity was 3700 m/s, and at room temperature, the velocity was 5000 m/s. Experimental results are almost comparable to those obtained by the contact ultrasonic technique.


Simulation of the self-propagating hydrogen-air premixed flame in a closed-vessel by an open-source CFD code

Thwe, T. A.; 寺田 敦彦; 日野 竜太郎; 永石 隆二; 門脇 敏

Journal of Nuclear Science and Technology, 59(5), p.573 - 579, 2022/05



Migration processes of radioactive cesium in the Fukushima nearshore area; Impacts of riverine input and resuspension

御園生 敏治; 中西 貴宏; 鶴田 忠彦; 尻引 武彦; 眞田 幸尚

Marine Pollution Bulletin, 178, p.113597_1 - 113597_9, 2022/05



Deep groundwater physicochemical components affecting actinide migration

桐島 陽*; 寺崎 万里子*; 宮川 和也; 岡本 芳浩; 秋山 大輔*

Chemosphere, 289, p.133181_1 - 133181_12, 2022/04

令和2年度以降の幌延深地層研究計画において原子力機構が取り組んでいる課題の1つである「実際の地質環境における人工バリアの適用性確認」では、坑道周辺の掘削損傷領域において物質移行に関するデータの取得が必要である。これに資することが期待される基礎的知見として、深部地下水中のアクチニドの移行挙動をより良く理解するために、水質の異なる2種類の地下水試料にトレーサーを添加し、地下水中の溶存成分との相互作用を調べた。地下水試料は、幌延深地層研究センターの地下施設の250mおよび350m調査坑道のボーリング孔および、瑞浪超深地層研究所の地下施設の300mおよび500m坑道のボーリング孔から採取した。得られた地下水試料に対して、トレーサーとしてLa, Sm, Ho, Uを濃度10ppbまたは100ppbになるように添加した。その後、地下水試料を0.2$$mu$$mフィルターと10kDaフィルターで順次濾過し、ろ液中のトレーサー濃度をICP-MSで分析し、ろ紙に捕獲されたトレーサー濃度をTOF-SIMSで分析し、化学形態をXAFSにより分析した。その結果、幌延の地下水中では、ランタニドの移行はリン酸塩により支配されていることが分かった。このことから、高レベル放射性廃棄物から海成堆積層の地下水中に溶出するマイナーアクチニドの溶解度は、リン酸塩により規定されることが示唆された。一方、瑞浪の地下水のように塩濃度が低くリン酸イオン濃度の低い地下水では、マイナーアクチニドの一部は水酸化物もしくはヒドロオキシ炭酸塩を形成することが示唆された。


Sorption of Cs$$^{+}$$ and Eu$$^{3+}$$ ions onto sedimentary rock in the presence of gamma-irradiated humic acid

Zhao, Q.*; 齊藤 毅*; 宮川 和也; 笹本 広; 小林 大志*; 佐々木 隆之*

Journal of Hazardous Materials, 428, p.128211_1 - 128211_10, 2022/04



Volatilization of B$$_{4}$$C control rods in Fukushima Daiichi nuclear reactors during meltdown; B-Li isotopic signatures in cesium-rich microparticles

笛田 和希*; 高見 龍*; 蓑毛 健太*; 諸岡 和也*; 堀江 憲路*; 竹原 真美*; 山崎 信哉*; 斉藤 拓巳*; 塩津 弘之; 大貫 敏彦*; et al.

Journal of Hazardous Materials, 428, p.128214_1 - 128214_10, 2022/04

Boron carbide control rods remain in the fuel debris of the damaged reactors in the Fukushima Daiichi Nuclear Power Plant, potentially preventing re-criticality; however, the state and stability of the control rods remain unknown. Sensitive high-resolution ion microprobe analyses have revealed B-Li isotopic signatures in radioactive Cs-rich microparticles (CsMPs) that formed by volatilization and condensation of Si-oxides during the meltdowns. The CsMPs contain 1518-6733 mg kg$$^{-1}$$ of $$^{10+11}$$B and 11.99-1213 mg kg$$^{-1}$$ of Li. The $$^{11}$$B/$$^{10}$$B (4.15-4.21) and $$^{7}$$Li/$$^{6}$$Li (213-406) isotopic ratios are greater than natural abundances ($$sim$$4.05 and $$sim$$12.5, respectively), indicating that $$^{10}$$B(n,$$alpha$$)$$^{7}$$Li reactions occurred in B$$_{4}$$C prior to the meltdowns. The total amount of B released with CsMPs was estimated to be 0.024-62 g, suggesting that essentially all B remains in reactor Units 2 and/or 3 and is enough to prevent re-criticality; however, the heterogeneous distribution of B needs to be considered during decommissioning.


Post-test analyses of the CMMR-4 test

山下 拓哉; 間所 寛; 佐藤 一憲

Journal of Nuclear Engineering and Radiation Science, 8(2), p.021701_1 - 021701_13, 2022/04

Understanding the final distribution of core materials and their characteristics is important for decommissioning the Fukushima Daiichi Nuclear Power Station (1F). Such characteristics depend on the accident progression in each unit. However, boiling water reactor accident progression involves great uncertainty. This uncertainty, which was clarified by MAAP-MELCOR Crosswalk, cannot be resolved with existing knowledge and was thus addressed in this work through core material melting and relocation (CMMR) tests. For the test bundle, ZrO$$_{2}$$ pellets were installed instead of UO$$_{2}$$ pellets. A plasma heating system was used for the tests. In the CMMR-4 test, useful information was obtained on the core state just before slumping. The presence of macroscopic gas permeability of the core approaching ceramic fuel melting was confirmed, and the fuel columns remained standing, suggesting that the collapse of fuel columns, which is likely in the reactor condition, would not allow effective relocation of the hottest fuel away from the bottom of the core. This information will help us comprehend core degradation in boiling water reactors, similar to those in 1F. In addition, useful information on abrasive water suspension jet (AWSJ) cutting for debris-containing boride was obtained in the process of dismantling the test bundle. When the mixing debris that contains oxide, metal, and boride material is cut, AWSJ may be repelled by the boride in the debris, which may cut unexpected parts, thus generating a large amount of waste in cutting the boride part in the targeted debris. This information will help the decommissioning of 1F.


Depletion calculation of subcritical system with consideration of spontaneous fission reaction

Riyana, E. S.; 奥村 啓介; 坂本 雅洋; 松村 太伊知; 寺島 顕一

Journal of Nuclear Science and Technology, 59(4), p.424 - 430, 2022/04

Modification of the Monte Carlo depletion calculation code OpenMC was performed to enable the depletion calculation of the subcritical neutron multiplying system. With the modified code, it became possible to evaluate the quantity of short half-life fission products from spontaneous and induced fissions in the subcritical system. As a preliminary study, it was applied to the fuel debris storage canister filled with nuclear materials and spontaneous fission nuclides. It was confirmed that the code could successfully provide a quantity of short half-life FPs over time and provide the relationship between the activity ratio of Kr-88 to Xe-135 and effective neutron multiplication factor of the canister.


Distribution, dynamics, and fate of radiocesium derived from FDNPP accident in the ocean

乙坂 重嘉*; 上平 雄基; 池之上 翼; 川村 英之

Journal of Nuclear Science and Technology, 59(4), p.409 - 423, 2022/04



Estimated isotopic compositions of Yb in enriched $$^{176}$$Yb for producing $$^{177}$$Lu with high radionuclide purity by $$^{176}$$Yb($$d,x$$)$$^{177}$$Lu

永井 泰樹*; 川端 方子*; 橋本 慎太郎; 塚田 和明; 橋本 和幸*; 本石 章司*; 佐伯 秀也*; 本村 新*; 湊 太志; 伊藤 正俊*

Journal of the Physical Society of Japan, 91(4), p.044201_1 - 044201_10, 2022/04



Estimation of long-term ex-vessel debris cooling behavior in Fukushima Daiichi Nuclear Power Plant unit 3

佐藤 一憲; 山路 哲史*; Li, X.*; 間所 寛

Mechanical Engineering Journal (Internet), 9(2), p.21-00436_1 - 21-00436_17, 2022/04

Interpretation for the two-week long Unit 3 ex-vessel debris cooling behavior was conducted based on the Fukushima-Daiichi Nuclear Power Plant (1F) data and the site data such as pressure, temperature, gamma ray level and live camera pictures. It was estimated that the debris relocated to the pedestal was in partial contact with liquid water for about initial two days. With the reduction of the sea water injection flowrate, the debris, existed mainly in the pedestal region, became "dry", in which the debris was only weakly cooled by vapor and this condition lasted for about four days until the increase of the sea water injection. During this dry period, the pedestal debris was heated up and it took further days to re-flood the heated up debris.


Time-resolved 3D visualization of liquid jet breakup and impingement behavior in a shallow liquid pool

木村 郁仁*; 山村 聡太*; 藤原 広太*; 吉田 啓之; 齋藤 慎平*; 金子 暁子*; 阿部 豊*

Nuclear Engineering and Design, 389, p.111660_1 - 111660_11, 2022/04

A new three-dimensional laser-induced fluorescent (3D-LIF) technology to obtain the hydrodynamic behavior of liquid jets in a shallow pool were developed. In this technology, firstly, a refractive index matching was applied to acquire a clear cross-sectional image. Secondly, a series of cross-sectional images was obtained by using a high-speed galvanometer scanner. Finally, to evaluate the unsteady 3D interface shape of liquid jet, a method was developed to reconstruct 3D shapes from the series of cross-sectional images obtained using the 3D-LIF method. The spatial and temporal resolutions of measurement were 4.7 $$times$$ 4.7 $$times$$ 1.0 lines/mm and 25 $$mu$$s, respectively. The shape of a 3D liquid jet in a liquid pool and its impingement, spreading and atomization behavior were reconstructed using the proposed method, successfully. The behaviors of atomized particles detached from the jet were obtained by applying data processing techniques. Diameters distribution and position of atomized droplets after detachment were estimated from the results.


Status of the JAEA-ADS superconducting linac design

Yee-Rendon, B.; 近藤 恭弘; 田村 潤; 明午 伸一郎; 前川 藤夫

Proceedings of 64th ICFA Advanced Beam Dynamics Workshop on High Intensity and High Brightness Hadron Beams (ICFA-HB2021) (Internet), p.30 - 34, 2022/04


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