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論文

Chemical forms of uranium evaluated by thermodynamic calculation associated with distribution of core materials in the damaged reactor pressure vessel

池内 宏知; 矢野 公彦; 鷲谷 忠博

Journal of Nuclear Science and Technology, 57(6), p.704 - 718, 2020/06

 被引用回数:0 パーセンタイル:100(Nuclear Science & Technology)

福島第一原子力発電所から取り出された燃料デブリへの効果的な処置方策を提案する上では、燃料デブリ中でUがとりうる化学形についての詳細な調査が不可欠である。特に、アクセス性に乏しい圧力容器内に残留する燃料デブリに関する情報が重要である。本研究では、圧力容器内燃料デブリ中、特にマイナー相におけるUの化学形を評価することを目的とし、1F-2号機の事故進展での材料のリロケーション及び環境変化を考慮した熱力学計算を実施した。組成,温度,酸素量といった計算条件は、既存の事故進展解析の結果から設定した。計算の結果、Uの化学形はFeとOの量によって変化し、Feの少ない領域で$$alpha$$-(Zr,U)(O)、Feの多い領域でFe$$_{2}$$(Zr,U) (Laves相)の生成が顕著であった。還元性条件で生成するこれらの金属相中には数パーセントのUが移行しており、燃料デブリの処置において核物質の化学分離を考慮する場合はこれらの相の生成に留意すべきと考えられる。

論文

Effect of quenching on molten core-concrete interaction product

北垣 徹; 池内 宏知; 矢野 公彦; Brissonneau, L.*; Tormos, B.*; Domenger, R.*; Roger, J.*; 鷲谷 忠博

Journal of Nuclear Science and Technology, 56(9-10), p.902 - 914, 2019/09

 被引用回数:2 パーセンタイル:34.3(Nuclear Science & Technology)

Characterization of fuel debris is required to develop fuel debris removal tools. Especially, knowledge pertaining to the characteristics of molten core-concrete interaction (MCCI) product is needed because of the limited information available at present. The samples of a large-scale MCCI test performed under quenching conditions, VULCANO VW-U1, by CEA were analyzed to evaluate the characteristics of the surface of MCCI product generated just below the cooling water. As a result, the microstructure of the samples were found to be similar despite the different locations of the test sections. The Vickers hardness of each of the phases in these samples was higher than that of previously analyzed samples in another VULCANO test campaign, VBS-U4. From the comparison between analytical results of VULCANO MCCI test product, MCCI product generated under quenching condition is homogeneous and its hardness could be higher than that of the bulk MCCI product.

論文

R&D strategy on mid- and long-term behavior of fuel debris

矢野 公彦; 北垣 徹; 鷲谷 忠博; 宮本 泰明; 小川 徹

Progress in Nuclear Science and Technology (Internet), 5, p.225 - 228, 2018/11

福島第一原子力発電所の廃炉に向けたロードマップによると、燃料デブリ取り出しは2021年、すなわち燃料デブリ生成の10年後に開始される予定である。また燃料デブリは燃料取り出しの終了まで炉内に存在することになる。加えて、炉から取り出された燃料デブリに対して保管が必要になることは想像に難くない。このような事故後の燃料デブリに対する作業を検討するうえで、数十年間の燃料デブリの状態や特性を議論することは不可欠である、そこで原子力機構は燃料デブリの中長期的挙動に関する研究開発戦略を暫定するとともに、この課題に対して国内の大学や他の研究機関と協力し基礎研究を立ち上げている。

論文

Characterization of the VULCANO test products for fuel debris removal from the Fukushima Daiichi Nuclear Power Plant

北垣 徹; 池内 宏知; 矢野 公彦; 荻野 英樹; Haquet, J.-F.*; Brissonneau, L.*; Tormos, B.*; Piluso, P.*; 鷲谷 忠博

Progress in Nuclear Science and Technology (Internet), 5, p.217 - 220, 2018/11

Characterization of the fuel debris is required to develop fuel debris removal tools for the decommissioning of Fukushima Daiichi Nuclear Power Plant (1F). In this study, the VULCANO MCCI test, VBS-U4, was selected as 1F similar conditions and the characteristics of the samples were examined. In the molten pool sample, the round-edged corium-rich oxides region, with diameters of 1-10 mm, is surrounded by a concrete-rich oxide region. It shows convection of the molten pool. Other samples also show the features of the MCCI progression. The main chemical forms of the samples are SiO$$_{2}$$, (U,Zr)O$$_{2}$$, Fe and so on. The microstructure of the samples is heterogeneous structure composed of these phases. The difference in Vickers hardness between the metallic phases and the oxide phases is a distinctive characteristic. It can be noted that the heterogeneous distribution of metallic phases in 1F MCCI products interrupt with the removal operation such as by damaging the core-boring bit.

論文

Mechanical properties of cubic (U,Zr)O$$_{2}$$

北垣 徹; 星野 貴紀; 矢野 公彦; 岡村 信生; 小原 宏*; 深澤 哲生*; 小泉 健治

Journal of Nuclear Engineering and Radiation Science, 4(3), p.031011_1 - 031011_7, 2018/07

Evaluation of fuel debris properties is required to develop fuel debris removal tools for the decommissioning of Fukushima Daiichi Nuclear Power Plant (1F). In this research, the mechanical properties of cubic (U,Zr)O$$_{2}$$ samples containing 10-65% ZrO$$_{2}$$ are evaluated. In case of the (U,Zr)O$$_{2}$$ samples containing less than 50% ZrO$$_{2}$$, Vickers hardness and fracture toughness increased, and the elastic modulus decreased slightly with increasing ZrO$$_{2}$$ content. Moreover, all of those values of the (U,Zr)O$$_{2}$$ samples containing 65% ZrO$$_{2}$$ increased slightly compared to (U,Zr)O$$_{2}$$ samples containing 55% ZrO$$_{2}$$. However, higher Zr content (exceeding 50%) has little effect on the mechanical properties. This result indicates that the wear of core-boring bits in the 1F drilling operation will accelerate slightly compared to that in the TMI-2 drilling operation.

論文

Thermodynamic evaluation of the solidification phase of molten core-concrete under estimated Fukushima Daiichi Nuclear Power Plant accident conditions

北垣 徹; 矢野 公彦; 荻野 英樹; 鷲谷 忠博

Journal of Nuclear Materials, 486, p.206 - 215, 2017/04

AA2016-0278.pdf:0.74MB

 被引用回数:10 パーセンタイル:10.91(Materials Science, Multidisciplinary)

The solidification phases of molten core-concrete under the estimated molten core-concrete interaction (MCCI) conditions in the Fukushima Daiichi Nuclear Power Plant Unit 1 were predicted using the thermodynamic equilibrium calculation tool in order to contribute toward the 1F decommissioning work and to understand the accident progression via the analytical results for the 1F MCCI products. We showed that most of the U and Zr in the molten core-concrete forms (U,Zr)O$$_{2}$$ and (Zr,U)SiO$$_{4}$$, and the formation of other phases with these elements is limited. However, the formation of (Zr,U)SiO$$_{4}$$ requires a relatively long time. Therefore, the formation of (Zr,U)SiO$$_{4}$$ is limited under quenching conditions. The solidification phenomenon of the crust under quenching conditions and that of the molten pool under thermodynamic equilibrium conditions in the 1F MCCI progression are discussed.

論文

Purification of uranium products in crystallization system for nuclear fuel reprocessing

竹内 正行; 矢野 公彦; 柴田 淳広; 三本松 勇次*; 中村 和仁*; 近沢 孝弘*; 平沢 泉*

Journal of Nuclear Science and Technology, 53(4), p.521 - 528, 2016/04

 被引用回数:2 パーセンタイル:69.72(Nuclear Science & Technology)

Uranium crystallization system has been developed to establish an advanced aqueous reprocessing for fast breeder reactor (FBR) fuel cycle in JAEA. In the advanced process, most of uranium in dissolved solution of spent FBR-MOX fuels with high heavy metal concentration is separated as uranyl nitrate hexahydrate (UNH) crystals by a cooling operation. The technical targets on the crystallization system are decided from FBR cycle performance, and the U yield from dissolved solution of the spent fuel is 70% and the decontamination factor (DF) of impurities in the crystal products is more than 100. The DF is lowered by involving liquid and solid impurities on and in the UNH crystals during the crystallization. In order to achieve the DF target, we discussed the purification technology of UNH crystals using a Kureha crystal purifier. As results, the uranium more than 90% in the feed crystals could be recovered as the purified crystals in all test conditions, and the DFs of solid and liquid impurities on the purified crystals showed more than 100 under longer residence time of crystals. In conclusion, the both targets for the yield and DF could be achieved simultaneously by introducing the crystal purification technology.

論文

Mechanical properties of fuel debris for defueling toward decommissioning

星野 貴紀; 北垣 徹; 矢野 公彦; 岡村 信生; 小原 浩史*; 深澤 哲生*; 小泉 健治

Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 6 Pages, 2015/05

In the decommissioning of Fukushima Daiichi Nuclear Power Plant (1F), safe and steady defueling work is requested. Before the defueling in 1F, it is necessary to evaluate fuel debris for properties related to the defueling procedure and technology. It is speculated that uranium and zirconium oxide solid solution is one of the major materials of fuel debris in 1F, according to TMI-2 accident experience and the results of past severe accident studies. In this report, mechanical properties of uranium and zirconium oxide solid solution evaluated in the ZrO$$_{2}$$ content range from 10% to 65%.

論文

Study of treatment scenarios for fuel debris removed from Fukushima Daiichi NPS

鷲谷 忠博; 矢野 公彦; 鍛治 直也; 山田 誠也*; 紙谷 正仁

Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 7 Pages, 2015/05

福島第一原子力発電所の燃料デブリ取出し後の処置については、燃料デブリ取出し開始時までにデブリの処置の選択決定に係る一定の議論が必要になるものと想定し、それまでに各シナリオの比較評価に用いる情報や比較評価の進め方を決める必要がある。そのため、本検討では燃料デブリの取出し後の処置シナリオの検討に向けた技術的要件の整理として、各処置シナリオ案の得失評価を行った。評価の結果、総合すると技術課題は有するものの経済性、廃棄物発生量の面で有利なシナリオは長期保管及び直接処分と推定された。一方、安定化処理、湿式処理、乾式処理は経済性、廃棄物発生量の面で不利と推定された。

論文

Dissolution behavior of (U,Zr)O$$_{2}$$-based simulated fuel debris in nitric acid

池内 宏知; 石原 美穂; 矢野 公彦; 鍛治 直也; 中島 靖雄; 鷲谷 忠博

Journal of Nuclear Science and Technology, 51(7-8), p.996 - 1005, 2014/07

 被引用回数:5 パーセンタイル:51.92(Nuclear Science & Technology)

To explore the possibility of dissolving fuel debris as a potential pre-treatment for waste treatment, dissolution tests of U$$_{1-}$$$$_{x}$$Zr$$_{x}$$O$$_{2}$$ and (U,Pu)$$_{1-}$$$$_{x}$$Zr$$_{x}$$O$$_{2}$$ were carried out in 6 M HNO$$_{3}$$ at 353 K. While the U and Zr indicated congruent leaching from the simulated debris with U-rich compositions, a preferential leaching of U was observed with Zr-rich compositions. Taking into account these different dissolution phenomena, the dissolution rate analysis was carried out using surface-area model to calculate the instantaneous dissolution rate (IDR). From these findings, dissolution with HNO$$_{3}$$ is expected to be only applicable in U-rich compositions ($$x$$ $$<$$ 0.3) if the dissolution in 6 M HNO$$_{3}$$ at 353 K is assumed. Application of complexing acids such as mixture of HNO$$_{3}$$ and HF should be considered to increase the dissolution rate of the phases with Zr-rich compositions.

論文

Suggestion of typical phases of in-vessel fuel-debris by thermodynamic calculation for decommissioning technology of Fukushima-Daiichi Nuclear Power Station

池内 宏知; 近藤 賀計*; 野口 芳宏*; 矢野 公彦; 鍛治 直也; 鷲谷 忠博

Proceedings of International Nuclear Fuel Cycle Conference; Nuclear Energy at a Crossroads (GLOBAL 2013) (CD-ROM), p.1349 - 1356, 2013/09

For the decommissioning of Fukushima-Daiichi Nuclear Power Station (1F), characterization of fuel-debris in cores of Unit 1-3 is necessary. In this study, typical phases of fuel-debris generated in reactor pressure vessel were suggested by means of thermodynamic calculation using compositions of core materials and core temperatures. At low ogygen potential where metallic zirconium remains, (U,Zr)O$$_{2}$$, UO$$_{2}$$, and ZrO$$_{2}$$ were formed as oxides, and oxygen-dispersed Zr, Fe$$_{2}$$(Zr,U), and Fe$$_{3}$$UZr$$_{2}$$ were formed as metals. With an increase in zirconium oxidation, the mass of those metals, especially Fe$$_{3}$$UZr$$_{2}$$, were decreased, but the other phases of metals hardly changed qualitatively. Consequently, (U,Zr)O$$_{2}$$ is suggested as a typical phase of oxide, and Fe$$_{2}$$(Zr,U) is suggested as that of metal. This result can contribute to the characterization of debris in 1F, which will be also revised by considering the effect of iron content in RPV.

論文

Direction on characterization of fuel debris for defueling process in Fukushima Daiichi Nuclear Power Station

矢野 公彦; 北垣 徹; 池内 宏知; 涌井 遼平; 樋口 英俊; 鍛治 直也; 小泉 健治; 鷲谷 忠博

Proceedings of International Nuclear Fuel Cycle Conference; Nuclear Energy at a Crossroads (GLOBAL 2013) (CD-ROM), p.1554 - 1559, 2013/09

For the decommissioning of Fukushima Daiichi Nuclear Power Station (1F), defueling work for the fuel debris in the reactor core of Unit 1-3 is planned to be started within 10 years. Preferential items in the characterization of the fuel debris were identified for the defueling work at 1F, in which the procedure and handling tools were assumed from information of 1F and experience of Three Mile Island Unit 2 (TMI-2) accident. The candidates of defueling tools for 1F were selected from TMI-2 defueling tools. It was found out that they were categorized as 6 groups by their working principles. Important properties on the fuel debris for the defueling were picked up from considering influence of objective materials on their performance. The selected properties are shape, size, density, thermal conductivity, heat capacity, melting point, hardness, elastic modulus, and fracture toughness. In these properties, mechanical properties, i.e. hardness, elastic modulus, fracture toughness were identified as preferential items, because there are few data on that of fuel debris in the past severe accident studies.

論文

Fission product separation from seawater by electrocoagulation method

北垣 徹; 星野 貴紀; 三本松 勇二; 矢野 公彦; 竹内 正行; 五十嵐 武士*; 鈴木 達也*

Journal of Radioanalytical and Nuclear Chemistry, 296(2), p.975 - 979, 2013/05

 被引用回数:4 パーセンタイル:60.1(Chemistry, Analytical)

At the Fukushima Daiichi NPPs, a large amount of seawater containing high activity fission product was accumulated and its treatment has been serious problem. Electrocoagulation method is expected to be part of a useful separation system that can reduce the amount of waste and decrease processing time. In this study, powdered adsorbents, such as ferrocyanide and zeolite, added to seawater containing simulated fission products, and electrocoagulation effect were investigated. As a result, more than 99% of Cs and I were removed. Moreover, rapid solution reactivity with heat was not observed, so the thermal risk of aqueous processing of the aggregation would be low. In addition, thermal analyses showed that the electrocoagulation process did not lead to thermal decomposition. Therefore, in the case electrocoagulation method is applied to decontamination system, it has the potential to thermally stabilize and reduce waste.

論文

Nitric acid concentration dependence of dicesium plutonium(IV) nitrate formation during solution growth of uranyl nitrate hexahydrate

中原 将海; 鍛治 直也; 矢野 公彦; 柴田 淳広; 竹内 正行; 岡野 正紀; 久野 剛彦

Journal of Chemical Engineering of Japan, 46(1), p.56 - 62, 2013/01

 被引用回数:1 パーセンタイル:92.13(Engineering, Chemical)

U晶析工程においてCs$$_{2}$$Pu(NO$$_{3}$$)$$_{6}$$の生成挙動に及ぼすHNO$$_{3}$$濃度の依存性を調べた。硝酸ウラニル溶液に対するCs$$_{2}$$Pu(NO$$_{3}$$)$$_{6}$$の溶解度は、HNO$$_{3}$$濃度が高くなるほど低下する傾向を示した。照射済高速炉燃料溶解液を用いた晶析実験では母液のHNO$$_{3}$$濃度が6.5mol/dm$$^{3}$$の条件において、Cs$$_{2}$$Pu(NO$$_{3}$$)$$_{6}$$が析出し、硝酸ウラニル六水和物結晶に対するCsの除染係数は低下した。一方、母液のHNO$$_{3}$$濃度が4.0mol/dm$$^{3}$$のときは、Cs$$_{2}$$Pu(NO$$_{3}$$)$$_{6}$$が生成せず、硝酸ウラニル六水和物結晶とCsが良好に分離できることを示した。

論文

Characteristics of dicesium plutonium(IV) nitrate formation in separation system of uranyl nitrate hexahydrate crystal

中原 将海; 矢野 公彦; 柴田 淳広; 竹内 正行; 岡野 正紀; 久野 剛彦

Procedia Chemistry, 7, p.282 - 287, 2012/00

 被引用回数:1 パーセンタイル:36.8

Uの冷却晶析法において生成するCs$$_{2}$$Pu(NO$$_{3}$$)$$_{6}$$を除去するため、Cs$$_{2}$$Pu(NO$$_{3}$$)$$_{6}$$の硝酸ウラニル溶液に対する溶解度測定試験と照射済高速中性子炉燃料溶解液を用いた晶析試験を実施した。温度が低下するに従い、Cs$$_{2}$$Pu(NO$$_{3}$$)$$_{6}$$の溶解度は減少した。晶析試験では、原料液のCs濃度が高いほどCs$$_{2}$$Pu(NO$$_{3}$$)$$_{6}$$の生成が促進し、Cs及びPuの除染係数が低下する傾向を示した。晶析工程におけるCs$$_{2}$$Pu(NO$$_{3}$$)$$_{6}$$の生成挙動について基礎データを取得した。

論文

FaCT Phase I evaluation on the advanced aqueous reprocessing process, 5; Research and development of uranium crystallization system

柴田 淳広; 矢野 公彦; 三本松 勇二; 中原 将海; 竹内 正行; 鷲谷 忠博; 長田 正信*; 近沢 孝弘*

Proceedings of International Conference on Toward and Over the Fukushima Daiichi Accident (GLOBAL 2011) (CD-ROM), 6 Pages, 2011/12

FaCTプロジェクトの一環として、ウラン晶析技術開発を実施している。開発目標は、70%以上のU回収率,100以上のDF,晶析装置の性能確認などである。実溶解液を用いたビーカ規模試験により基礎データを取得した。U晶析率は供給液組成や冷却温度により制御可能である。大半のFPのDFは洗浄操作により改善する。しかしながら、Pu-Cs複塩の生成によりCsの低DFが生じている。円環型晶析装置及び結晶分離機の性能を確認するため、各種試験を実施し、良好な機械的性能を確認した。しかしながら、結晶分離機によるU結晶の洗浄は、固体不純物に対して効果が認められなかった。U結晶の純度を改善するため、結晶精製技術の導入を検討し、KCP(Kureha Crystal Purifier)を選定した。KCPにおける固体不純物の挙動把握のため、ベンチスケールのKCP装置を用いてU結晶精製試験を実施した。KCPは液体不純物のみならず、固体不純物についてもよい除染性能を示した。

論文

Continuous operation test at engineering scale uranium crystallizer

鷲谷 忠博; 田山 敏光; 中村 和仁*; 矢野 公彦; 柴田 淳広; 野村 和則; 近沢 孝弘*; 長田 正信*; 菊池 俊明*

Journal of Power and Energy Systems (Internet), 4(1), p.191 - 201, 2010/02

本件は、先進湿式再処理技術の革新技術である晶析技術における晶析装置開発に関するものである。本報では工学規模晶析試験装置を用いたウラン系での連続運転試験結果として、本晶析装置の定常及び非定常時における装置安定性,過渡的な応答性等に関する工学的な知見を中心に報告するものである。なお、本件は2009年7月ベルギーで開催されたICONE-17特集号への論文投稿である。

論文

先進湿式法再処理の晶析工程におけるCs挙動把握のための模擬溶解液を用いた基礎試験

柴田 淳広; 矢野 公彦; 紙谷 正仁; 中村 和仁; 鷲谷 忠博; 近沢 孝弘*; 菊池 俊明*

日本原子力学会和文論文誌, 8(3), p.245 - 253, 2009/09

U晶析工程におけるCsの挙動を調べるため、模擬溶解液を用いたU晶析バッチ試験及びU(IV)溶液を用いたCs複塩生成基礎試験を実施した。使用済燃料の溶解液中のCs濃度では、先進湿式法再処理のU晶析工程の条件においてCsNO$$_{3}$$やCs$$_{2}$$UO$$_{2}$$(NO$$_{3}$$)$$_{4}$$は生成せず、他のFP元素との相互作用によるCs塩も生成する可能性は小さいことを確認した。また、U(IV)溶液を用いたCs複塩生成基礎試験の結果から、酸濃度が5mol/dm$$^{3}$$以上の場合にはCsとPu(IV)の複塩が生成する可能性が示唆された。

論文

Research and development of crystal purification for product of uranium crystallization process

矢野 公彦; 中原 将海; 中村 雅弘; 柴田 淳広; 野村 和則; 中村 和仁*; 田山 敏光; 鷲谷 忠博; 近沢 孝弘*; 菊池 俊明*; et al.

Proceedings of International Conference on Advanced Nuclear Fuel Cycle; Sustainable Options & Industrial Perspectives (Global 2009) (CD-ROM), p.143 - 150, 2009/09

The behaviors of impurities and applicability of sweating and melting-filtration operations to the purification for UNH crystal were investigated experimentally on a beaker and an engineering scale. With regard to behaviors of impurities, the conditions of cesium and barium precipitation were surveyed and it was clarified that there were most impurities on the outside of UNH single crystal and that they make no eutectoid with UNH. On the other hand, it is confirmed that sweating and melting-filtration operations were effective in principle by the experiment with uranium and simulated FP system. After that, its effects verified by beaker scale experiments with the system including plutonium and irradiated fuel. Additionally, engineering scale tests were carried out with a Kureha Crystal Purifier (KCP) type testing device to evaluate that its performance was suitable for UNH purification. This work was supported by the Ministry of Education, Culture, Sports, Science and Technology of Japan (MEXT).

論文

Current status on research and development of uranium crystallization system in advanced aqueous reprocessing of FaCT project

柴田 淳広; 鍛治 直也; 中原 将海; 矢野 公彦; 田山 敏光; 中村 和仁; 鷲谷 忠博; 明珍 宗孝; 近沢 孝弘*; 菊池 俊明*

Proceedings of International Conference on Advanced Nuclear Fuel Cycle; Sustainable Options & Industrial Perspectives (Global 2009) (CD-ROM), p.151 - 157, 2009/09

原子力機構では、FBRサイクル実用化研究開発の一部として、三菱マテリアルと協力し、ウラン晶析プロセスの開発を実施している。このプロセスは、Uと他の元素の溶解度の差を利用しており、温度や酸濃度により制御可能である。溶解液中のUの大半は、溶解液の温度を下げることにより硝酸ウラニル結晶として回収される。本報では、U晶析プロセスと機器に関する研究開発状況について報告する。実溶解液を用いたビーカ規模の試験をCPFにて実施した。U晶析工程におけるFPの挙動について議論する予定である。また、工学規模の晶析装置を用いた、非定常事象評価試験を実施した。スクリュー回転数低下,結晶排出口閉塞及び母液排出口閉塞の各事象について、事象の進展及び事象検知手段を確認した。

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